the mpm_get_child_pid hook is unnecessary, as was the per-MPM MPM_CHILD_PID() macro...

[apache] / server / mpm / event / event.c

/* Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/**
 * This MPM tries to fix the 'keep alive problem' in HTTP.
 *
 * After a client completes the first request, the client can keep the
 * connection open to send more requests with the same socket.  This can save
 * signifigant overhead in creating TCP connections.  However, the major
 * disadvantage is that Apache traditionally keeps an entire child
 * process/thread waiting for data from the client.  To solve this problem,
 * this MPM has a dedicated thread for handling both the Listenting sockets,
 * and all sockets that are in a Keep Alive status.
 *
 * The MPM assumes the underlying apr_pollset implmentation is somewhat
 * threadsafe.  This currently is only compatible with KQueue and EPoll.  This
 * enables the MPM to avoid extra high level locking or having to wake up the
 * listener thread when a keep-alive socket needs to be sent to it.
 *
 * This MPM not preform well on older platforms that do not have very good
 * threading, like Linux with a 2.4 kernel, but this does not matter, since we
 * require EPoll or KQueue.
 *
 * For FreeBSD, use 5.3.  It is possible to run this MPM on FreeBSD 5.2.1, if
 * you use libkse (see `man libmap.conf`).
 *
 * For NetBSD, use at least 2.0.
 *
 * For Linux, you should use a 2.6 kernel, and make sure your glibc has epoll
 * support compiled in.
 *
 */

#include "apr.h"
#include "apr_portable.h"
#include "apr_strings.h"
#include "apr_file_io.h"
#include "apr_thread_proc.h"
#include "apr_signal.h"
#include "apr_thread_mutex.h"
#include "apr_proc_mutex.h"
#include "apr_poll.h"
#include "apr_ring.h"
#include "apr_queue.h"
#define APR_WANT_STRFUNC
#include "apr_want.h"

#if APR_HAVE_UNISTD_H
#include <unistd.h>
#endif
#if APR_HAVE_SYS_SOCKET_H
#include <sys/socket.h>
#endif
#if APR_HAVE_SYS_WAIT_H
#include <sys/wait.h>
#endif
#ifdef HAVE_SYS_PROCESSOR_H
#include <sys/processor.h>      /* for bindprocessor() */
#endif

#if !APR_HAS_THREADS
#error The Event MPM requires APR threads, but they are unavailable.
#endif

#include "ap_config.h"
#include "httpd.h"
#include "http_main.h"
#include "http_log.h"
#include "http_config.h"        /* for read_config */
#include "http_core.h"          /* for get_remote_host */
#include "http_connection.h"
#include "ap_mpm.h"
#include "pod.h"
#include "mpm_common.h"
#include "ap_listen.h"
#include "scoreboard.h"
#include "fdqueue.h"
#include "mpm_default.h"
#include "http_vhost.h"
#include "unixd.h"

#include <signal.h>
#include <limits.h>             /* for INT_MAX */

#include "mod_serf.h"

#if AP_HAS_SERF
#include "serf.h"
#endif

/* Limit on the total --- clients will be locked out if more servers than
 * this are needed.  It is intended solely to keep the server from crashing
 * when things get out of hand.
 *
 * We keep a hard maximum number of servers, for two reasons --- first off,
 * in case something goes seriously wrong, we want to stop the fork bomb
 * short of actually crashing the machine we're running on by filling some
 * kernel table.  Secondly, it keeps the size of the scoreboard file small
 * enough that we can read the whole thing without worrying too much about
 * the overhead.
 */
#ifndef DEFAULT_SERVER_LIMIT
#define DEFAULT_SERVER_LIMIT 16
#endif

/* Admin can't tune ServerLimit beyond MAX_SERVER_LIMIT.  We want
 * some sort of compile-time limit to help catch typos.
 */
#ifndef MAX_SERVER_LIMIT
#define MAX_SERVER_LIMIT 20000
#endif

/* Limit on the threads per process.  Clients will be locked out if more than
 * this are needed.
 *
 * We keep this for one reason it keeps the size of the scoreboard file small
 * enough that we can read the whole thing without worrying too much about
 * the overhead.
 */
#ifndef DEFAULT_THREAD_LIMIT
#define DEFAULT_THREAD_LIMIT 64
#endif

/* Admin can't tune ThreadLimit beyond MAX_THREAD_LIMIT.  We want
 * some sort of compile-time limit to help catch typos.
 */
#ifndef MAX_THREAD_LIMIT
#define MAX_THREAD_LIMIT 100000
#endif

#define MPM_CHILD_PID(i) (ap_scoreboard_image->parent[i].pid)

/*
 * Actual definitions of config globals
 */

static int threads_per_child = 0;   /* Worker threads per child */
static int ap_daemons_to_start = 0;
static int min_spare_threads = 0;
static int max_spare_threads = 0;
static int ap_daemons_limit = 0;
static int max_clients = 0;
static int server_limit = 0;
static int thread_limit = 0;
static int dying = 0;
static int workers_may_exit = 0;
static int start_thread_may_exit = 0;
static int listener_may_exit = 0;
static int requests_this_child;
static int num_listensocks = 0;
static int resource_shortage = 0;
static fd_queue_t *worker_queue;
static fd_queue_info_t *worker_queue_info;
static int mpm_state = AP_MPMQ_STARTING;
static int sick_child_detected;
static ap_generation_t volatile my_generation = 0;

static apr_thread_mutex_t *timeout_mutex;
APR_RING_HEAD(timeout_head_t, conn_state_t);
static struct timeout_head_t timeout_head, keepalive_timeout_head;

static apr_pollset_t *event_pollset;

#if AP_HAS_SERF
typedef struct {
    apr_pollset_t *pollset;
    apr_pool_t *pool;
} s_baton_t;

static serf_context_t *g_serf;
#endif

/* The structure used to pass unique initialization info to each thread */
typedef struct
{
    int pid;
    int tid;
    int sd;
} proc_info;

/* Structure used to pass information to the thread responsible for
 * creating the rest of the threads.
 */
typedef struct
{
    apr_thread_t **threads;
    apr_thread_t *listener;
    int child_num_arg;
    apr_threadattr_t *threadattr;
} thread_starter;

typedef enum
{
    PT_CSD,
    PT_ACCEPT
#if AP_HAS_SERF
    , PT_SERF
#endif
} poll_type_e;

typedef struct
{
    poll_type_e type;
    int bypass_push;
    void *baton;
} listener_poll_type;

/* data retained by event across load/unload of the module
 * allocated on first call to pre-config hook; located on
 * subsequent calls to pre-config hook
 */
typedef struct event_retained_data {
    int first_server_limit;
    int first_thread_limit;
    int module_loads;
} event_retained_data;
static event_retained_data *retained;

#define ID_FROM_CHILD_THREAD(c, t)    ((c * thread_limit) + t)

/*
 * The max child slot ever assigned, preserved across restarts.  Necessary
 * to deal with MaxClients changes across AP_SIG_GRACEFUL restarts.  We
 * use this value to optimize routines that have to scan the entire
 * scoreboard.
 */
static int max_daemons_limit = -1;

static ap_event_pod_t *pod;

/* The event MPM respects a couple of runtime flags that can aid
 * in debugging. Setting the -DNO_DETACH flag will prevent the root process
 * from detaching from its controlling terminal. Additionally, setting
 * the -DONE_PROCESS flag (which implies -DNO_DETACH) will get you the
 * child_main loop running in the process which originally started up.
 * This gives you a pretty nice debugging environment.  (You'll get a SIGHUP
 * early in standalone_main; just continue through.  This is the server
 * trying to kill off any child processes which it might have lying
 * around --- Apache doesn't keep track of their pids, it just sends
 * SIGHUP to the process group, ignoring it in the root process.
 * Continue through and you'll be fine.).
 */

static int one_process = 0;

#ifdef DEBUG_SIGSTOP
int raise_sigstop_flags;
#endif

static apr_pool_t *pconf;       /* Pool for config stuff */
static apr_pool_t *pchild;      /* Pool for httpd child stuff */

static pid_t ap_my_pid;         /* Linux getpid() doesn't work except in main
                                   thread. Use this instead */
static pid_t parent_pid;
static apr_os_thread_t *listener_os_thread;

/* The LISTENER_SIGNAL signal will be sent from the main thread to the
 * listener thread to wake it up for graceful termination (what a child
 * process from an old generation does when the admin does "apachectl
 * graceful").  This signal will be blocked in all threads of a child
 * process except for the listener thread.
 */
#define LISTENER_SIGNAL     SIGHUP

/* An array of socket descriptors in use by each thread used to
 * perform a non-graceful (forced) shutdown of the server.
 */
static apr_socket_t **worker_sockets;

static void close_worker_sockets(void)
{
    int i;
    for (i = 0; i < threads_per_child; i++) {
        if (worker_sockets[i]) {
            apr_socket_close(worker_sockets[i]);
            worker_sockets[i] = NULL;
        }
    }
}

static void wakeup_listener(void)
{
    listener_may_exit = 1;
    if (!listener_os_thread) {
        /* XXX there is an obscure path that this doesn't handle perfectly:
         *     right after listener thread is created but before
         *     listener_os_thread is set, the first worker thread hits an
         *     error and starts graceful termination
         */
        return;
    }

    /* unblock the listener if it's waiting for a worker */
    ap_queue_info_term(worker_queue_info); 

    /*
     * we should just be able to "kill(ap_my_pid, LISTENER_SIGNAL)" on all
     * platforms and wake up the listener thread since it is the only thread
     * with SIGHUP unblocked, but that doesn't work on Linux
     */
#ifdef HAVE_PTHREAD_KILL
    pthread_kill(*listener_os_thread, LISTENER_SIGNAL);
#else
    kill(ap_my_pid, LISTENER_SIGNAL);
#endif
}

#define ST_INIT              0
#define ST_GRACEFUL          1
#define ST_UNGRACEFUL        2

static int terminate_mode = ST_INIT;

static void signal_threads(int mode)
{
    if (terminate_mode == mode) {
        return;
    }
    terminate_mode = mode;
    mpm_state = AP_MPMQ_STOPPING;

    /* in case we weren't called from the listener thread, wake up the
     * listener thread
     */
    wakeup_listener();

    /* for ungraceful termination, let the workers exit now;
     * for graceful termination, the listener thread will notify the
     * workers to exit once it has stopped accepting new connections
     */
    if (mode == ST_UNGRACEFUL) {
        workers_may_exit = 1;
        ap_queue_interrupt_all(worker_queue);
        close_worker_sockets(); /* forcefully kill all current connections */
    }
}

static apr_status_t event_query(int query_code, int *result)
{
    switch (query_code) {
    case AP_MPMQ_MAX_DAEMON_USED:
        *result = max_daemons_limit;
        return APR_SUCCESS;
    case AP_MPMQ_IS_THREADED:
        *result = AP_MPMQ_STATIC;
        return APR_SUCCESS;
    case AP_MPMQ_IS_FORKED:
        *result = AP_MPMQ_DYNAMIC;
        return APR_SUCCESS;
    case AP_MPMQ_IS_ASYNC:
        *result = 1;
        return APR_SUCCESS;
    case AP_MPMQ_HAS_SERF:
        *result = 1;
        return APR_SUCCESS;
    case AP_MPMQ_HARD_LIMIT_DAEMONS:
        *result = server_limit;
        return APR_SUCCESS;
    case AP_MPMQ_HARD_LIMIT_THREADS:
        *result = thread_limit;
        return APR_SUCCESS;
    case AP_MPMQ_MAX_THREADS:
        *result = threads_per_child;
        return APR_SUCCESS;
    case AP_MPMQ_MIN_SPARE_DAEMONS:
        *result = 0;
        return APR_SUCCESS;
    case AP_MPMQ_MIN_SPARE_THREADS:
        *result = min_spare_threads;
        return APR_SUCCESS;
    case AP_MPMQ_MAX_SPARE_DAEMONS:
        *result = 0;
        return APR_SUCCESS;
    case AP_MPMQ_MAX_SPARE_THREADS:
        *result = max_spare_threads;
        return APR_SUCCESS;
    case AP_MPMQ_MAX_REQUESTS_DAEMON:
        *result = ap_max_requests_per_child;
        return APR_SUCCESS;
    case AP_MPMQ_MAX_DAEMONS:
        *result = ap_daemons_limit;
        return APR_SUCCESS;
    case AP_MPMQ_MPM_STATE:
        *result = mpm_state;
        return APR_SUCCESS;
    case AP_MPMQ_GENERATION:
        *result = my_generation;
        return APR_SUCCESS;
    }
    return APR_ENOTIMPL;
}

static apr_status_t event_note_child_killed(int childnum)
{
    ap_scoreboard_image->parent[childnum].pid = 0;
    return APR_SUCCESS;
}

static const char *event_get_name(void)
{
    return "event";
}

/* a clean exit from a child with proper cleanup */
static void clean_child_exit(int code) __attribute__ ((noreturn));
static void clean_child_exit(int code)
{
    mpm_state = AP_MPMQ_STOPPING;
    if (pchild) {
        apr_pool_destroy(pchild);
    }
    exit(code);
}

static void just_die(int sig)
{
    clean_child_exit(0);
}

/*****************************************************************
 * Connection structures and accounting...
 */

/* volatile just in case */
static int volatile shutdown_pending;
static int volatile restart_pending;
static int volatile is_graceful;
static volatile int child_fatal;

/*
 * ap_start_shutdown() and ap_start_restart(), below, are a first stab at
 * functions to initiate shutdown or restart without relying on signals.
 * Previously this was initiated in sig_term() and restart() signal handlers,
 * but we want to be able to start a shutdown/restart from other sources --
 * e.g. on Win32, from the service manager. Now the service manager can
 * call ap_start_shutdown() or ap_start_restart() as appropiate.  Note that
 * these functions can also be called by the child processes, since global
 * variables are no longer used to pass on the required action to the parent.
 *
 * These should only be called from the parent process itself, since the
 * parent process will use the shutdown_pending and restart_pending variables
 * to determine whether to shutdown or restart. The child process should
 * call signal_parent() directly to tell the parent to die -- this will
 * cause neither of those variable to be set, which the parent will
 * assume means something serious is wrong (which it will be, for the
 * child to force an exit) and so do an exit anyway.
 */

static void ap_start_shutdown(int graceful)
{
    mpm_state = AP_MPMQ_STOPPING;
    if (shutdown_pending == 1) {
        /* Um, is this _probably_ not an error, if the user has
         * tried to do a shutdown twice quickly, so we won't
         * worry about reporting it.
         */
        return;
    }
    shutdown_pending = 1;
    is_graceful = graceful;
}

/* do a graceful restart if graceful == 1 */
static void ap_start_restart(int graceful)
{
    mpm_state = AP_MPMQ_STOPPING;
    if (restart_pending == 1) {
        /* Probably not an error - don't bother reporting it */
        return;
    }
    restart_pending = 1;
    is_graceful = graceful;
}

static void sig_term(int sig)
{
    ap_start_shutdown(sig == AP_SIG_GRACEFUL_STOP);
}

static void restart(int sig)
{
    ap_start_restart(sig == AP_SIG_GRACEFUL);
}

static void set_signals(void)
{
#ifndef NO_USE_SIGACTION
    struct sigaction sa;
#endif

    if (!one_process) {
        ap_fatal_signal_setup(ap_server_conf, pconf);
    }

#ifndef NO_USE_SIGACTION
    sigemptyset(&sa.sa_mask);
    sa.sa_flags = 0;

    sa.sa_handler = sig_term;
    if (sigaction(SIGTERM, &sa, NULL) < 0)
        ap_log_error(APLOG_MARK, APLOG_WARNING, errno, ap_server_conf,
                     "sigaction(SIGTERM)");
#ifdef AP_SIG_GRACEFUL_STOP
    if (sigaction(AP_SIG_GRACEFUL_STOP, &sa, NULL) < 0)
        ap_log_error(APLOG_MARK, APLOG_WARNING, errno, ap_server_conf,
                     "sigaction(" AP_SIG_GRACEFUL_STOP_STRING ")");
#endif
#ifdef SIGINT
    if (sigaction(SIGINT, &sa, NULL) < 0)
        ap_log_error(APLOG_MARK, APLOG_WARNING, errno, ap_server_conf,
                     "sigaction(SIGINT)");
#endif
#ifdef SIGXCPU
    sa.sa_handler = SIG_DFL;
    if (sigaction(SIGXCPU, &sa, NULL) < 0)
        ap_log_error(APLOG_MARK, APLOG_WARNING, errno, ap_server_conf,
                     "sigaction(SIGXCPU)");
#endif
#ifdef SIGXFSZ
    sa.sa_handler = SIG_DFL;
    if (sigaction(SIGXFSZ, &sa, NULL) < 0)
        ap_log_error(APLOG_MARK, APLOG_WARNING, errno, ap_server_conf,
                     "sigaction(SIGXFSZ)");
#endif
#ifdef SIGPIPE
    sa.sa_handler = SIG_IGN;
    if (sigaction(SIGPIPE, &sa, NULL) < 0)
        ap_log_error(APLOG_MARK, APLOG_WARNING, errno, ap_server_conf,
                     "sigaction(SIGPIPE)");
#endif

    /* we want to ignore HUPs and AP_SIG_GRACEFUL while we're busy
     * processing one */
    sigaddset(&sa.sa_mask, SIGHUP);
    sigaddset(&sa.sa_mask, AP_SIG_GRACEFUL);
    sa.sa_handler = restart;
    if (sigaction(SIGHUP, &sa, NULL) < 0)
        ap_log_error(APLOG_MARK, APLOG_WARNING, errno, ap_server_conf,
                     "sigaction(SIGHUP)");
    if (sigaction(AP_SIG_GRACEFUL, &sa, NULL) < 0)
        ap_log_error(APLOG_MARK, APLOG_WARNING, errno, ap_server_conf,
                     "sigaction(" AP_SIG_GRACEFUL_STRING ")");
#else
    if (!one_process) {
#ifdef SIGXCPU
        apr_signal(SIGXCPU, SIG_DFL);
#endif /* SIGXCPU */
#ifdef SIGXFSZ
        apr_signal(SIGXFSZ, SIG_DFL);
#endif /* SIGXFSZ */
    }

    apr_signal(SIGTERM, sig_term);
#ifdef SIGHUP
    apr_signal(SIGHUP, restart);
#endif /* SIGHUP */
#ifdef AP_SIG_GRACEFUL
    apr_signal(AP_SIG_GRACEFUL, restart);
#endif /* AP_SIG_GRACEFUL */
#ifdef AP_SIG_GRACEFUL_STOP
     apr_signal(AP_SIG_GRACEFUL_STOP, sig_term);
#endif /* AP_SIG_GRACEFUL_STOP */
#ifdef SIGPIPE
    apr_signal(SIGPIPE, SIG_IGN);
#endif /* SIGPIPE */

#endif
}

/*****************************************************************
 * Child process main loop.
 */

static int process_socket(apr_thread_t *thd, apr_pool_t * p, apr_socket_t * sock,
                          conn_state_t * cs, int my_child_num,
                          int my_thread_num)
{
    conn_rec *c;
    listener_poll_type *pt;
    long conn_id = ID_FROM_CHILD_THREAD(my_child_num, my_thread_num);
    int rc;
    ap_sb_handle_t *sbh;

    ap_create_sb_handle(&sbh, p, my_child_num, my_thread_num);

    if (cs == NULL) {           /* This is a new connection */

        cs = apr_pcalloc(p, sizeof(conn_state_t));

        pt = apr_pcalloc(p, sizeof(*pt));

        cs->bucket_alloc = apr_bucket_alloc_create(p);
        c = ap_run_create_connection(p, ap_server_conf, sock,
                                     conn_id, sbh, cs->bucket_alloc);
        c->current_thread = thd;
        cs->c = c;
        c->cs = cs;
        cs->p = p;
        cs->pfd.desc_type = APR_POLL_SOCKET;
        cs->pfd.reqevents = APR_POLLIN;
        cs->pfd.desc.s = sock;
        pt->type = PT_CSD;
        pt->bypass_push = 1;
        pt->baton = cs;
        cs->pfd.client_data = pt;
        APR_RING_ELEM_INIT(cs, timeout_list);

        ap_update_vhost_given_ip(c);

        rc = ap_run_pre_connection(c, sock);
        if (rc != OK && rc != DONE) {
            ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, ap_server_conf,
                         "process_socket: connection aborted");
            c->aborted = 1;
        }

        /**
         * XXX If the platform does not have a usable way of bundling
         * accept() with a socket readability check, like Win32,
         * and there are measurable delays before the
         * socket is readable due to the first data packet arriving,
         * it might be better to create the cs on the listener thread
         * with the state set to CONN_STATE_CHECK_REQUEST_LINE_READABLE
         *
         * FreeBSD users will want to enable the HTTP accept filter
         * module in their kernel for the highest performance
         * When the accept filter is active, sockets are kept in the
         * kernel until a HTTP request is received.
         */
        cs->state = CONN_STATE_READ_REQUEST_LINE;

    }
    else {
        c = cs->c;
        c->sbh = sbh;
        pt = cs->pfd.client_data;
        c->current_thread = thd;
    }

    if (c->clogging_input_filters && !c->aborted) {
        /* Since we have an input filter which 'cloggs' the input stream,
         * like mod_ssl, lets just do the normal read from input filters,
         * like the Worker MPM does.
         */
        ap_run_process_connection(c);
        if (cs->state != CONN_STATE_SUSPENDED) {
            cs->state = CONN_STATE_LINGER;
        }
    }

read_request:
    if (cs->state == CONN_STATE_READ_REQUEST_LINE) {
        if (!c->aborted) {
            ap_run_process_connection(c);

            /* state will be updated upon return
             * fall thru to either wait for readability/timeout or
             * do lingering close
             */
        }
        else {
            cs->state = CONN_STATE_LINGER;
        }
    }

    if (cs->state == CONN_STATE_WRITE_COMPLETION) {
        ap_filter_t *output_filter = c->output_filters;
        apr_status_t rv;
        while (output_filter->next != NULL) {
            output_filter = output_filter->next;
        }
        rv = output_filter->frec->filter_func.out_func(output_filter, NULL);
        if (rv != APR_SUCCESS) {
            ap_log_error(APLOG_MARK, APLOG_WARNING, rv, ap_server_conf,
                     "network write failure in core output filter");
            cs->state = CONN_STATE_LINGER;
        }
        else if (c->data_in_output_filters) {
            /* Still in WRITE_COMPLETION_STATE:
             * Set a write timeout for this connection, and let the
             * event thread poll for writeability.
             */
            cs->expiration_time = ap_server_conf->timeout + apr_time_now();
            apr_thread_mutex_lock(timeout_mutex);
            APR_RING_INSERT_TAIL(&timeout_head, cs, conn_state_t, timeout_list);
            apr_thread_mutex_unlock(timeout_mutex);
            pt->bypass_push = 0;
            cs->pfd.reqevents = APR_POLLOUT | APR_POLLHUP | APR_POLLERR;
            rc = apr_pollset_add(event_pollset, &cs->pfd);
            return 1;
        }
        else if (c->keepalive != AP_CONN_KEEPALIVE || c->aborted ||
            listener_may_exit) {
            c->cs->state = CONN_STATE_LINGER;
        }
        else if (c->data_in_input_filters) {
            cs->state = CONN_STATE_READ_REQUEST_LINE;
            goto read_request;
        }
        else {
            cs->state = CONN_STATE_CHECK_REQUEST_LINE_READABLE;
        }
    }

    if (cs->state == CONN_STATE_LINGER) {
        ap_lingering_close(c);
        apr_pool_clear(p);
        ap_push_pool(worker_queue_info, p);
        return 0;
    }
    else if (cs->state == CONN_STATE_CHECK_REQUEST_LINE_READABLE) {
        apr_status_t rc;
        listener_poll_type *pt = (listener_poll_type *) cs->pfd.client_data;

        /* It greatly simplifies the logic to use a single timeout value here
         * because the new element can just be added to the end of the list and
         * it will stay sorted in expiration time sequence.  If brand new
         * sockets are sent to the event thread for a readability check, this
         * will be a slight behavior change - they use the non-keepalive
         * timeout today.  With a normal client, the socket will be readable in
         * a few milliseconds anyway.
         */
        cs->expiration_time = ap_server_conf->keep_alive_timeout +
                              apr_time_now();
        apr_thread_mutex_lock(timeout_mutex);
        APR_RING_INSERT_TAIL(&keepalive_timeout_head, cs, conn_state_t, timeout_list);
        apr_thread_mutex_unlock(timeout_mutex);

        pt->bypass_push = 0;
        /* Add work to pollset. */
        cs->pfd.reqevents = APR_POLLIN;
        rc = apr_pollset_add(event_pollset, &cs->pfd);

        if (rc != APR_SUCCESS) {
            ap_log_error(APLOG_MARK, APLOG_ERR, rc, ap_server_conf,
                         "process_socket: apr_pollset_add failure");
            AP_DEBUG_ASSERT(rc == APR_SUCCESS);
        }
    }
    return 1;
}

/* requests_this_child has gone to zero or below.  See if the admin coded
   "MaxRequestsPerChild 0", and keep going in that case.  Doing it this way
   simplifies the hot path in worker_thread */
static void check_infinite_requests(void)
{
    if (ap_max_requests_per_child) {
        signal_threads(ST_GRACEFUL);
    }
    else {
        /* wow! if you're executing this code, you may have set a record.
         * either this child process has served over 2 billion requests, or
         * you're running a threaded 2.0 on a 16 bit machine.
         *
         * I'll buy pizza and beers at Apachecon for the first person to do
         * the former without cheating (dorking with INT_MAX, or running with
         * uncommitted performance patches, for example).
         *
         * for the latter case, you probably deserve a beer too.   Greg Ames
         */

        requests_this_child = INT_MAX;  /* keep going */
    }
}

static void unblock_signal(int sig)
{
    sigset_t sig_mask;

    sigemptyset(&sig_mask);
    sigaddset(&sig_mask, sig);
#if defined(SIGPROCMASK_SETS_THREAD_MASK)
    sigprocmask(SIG_UNBLOCK, &sig_mask, NULL);
#else
    pthread_sigmask(SIG_UNBLOCK, &sig_mask, NULL);
#endif
}

static void dummy_signal_handler(int sig)
{
    /* XXX If specifying SIG_IGN is guaranteed to unblock a syscall,
     *     then we don't need this goofy function.
     */
}


#if AP_HAS_SERF
static apr_status_t s_socket_add(void *user_baton,
                                 apr_pollfd_t *pfd,
                                 void *serf_baton)
{
    s_baton_t *s = (s_baton_t*)user_baton;
    /* XXXXX: recycle listener_poll_types */
    listener_poll_type *pt = malloc(sizeof(*pt));
    pt->type = PT_SERF;
    pt->baton = serf_baton;
    pfd->client_data = pt;
    return apr_pollset_add(s->pollset, pfd);
}

static apr_status_t s_socket_remove(void *user_baton,
                                    apr_pollfd_t *pfd,
                                    void *serf_baton)
{
    s_baton_t *s = (s_baton_t*)user_baton;
    listener_poll_type *pt = pfd->client_data;
    free(pt);
    return apr_pollset_remove(s->pollset, pfd);
}
#endif

static apr_status_t init_pollset(apr_pool_t *p)
{
#if AP_HAS_SERF
    s_baton_t *baton = NULL;
#endif
    apr_status_t rv;
    ap_listen_rec *lr;
    listener_poll_type *pt;

    rv = apr_thread_mutex_create(&timeout_mutex, APR_THREAD_MUTEX_DEFAULT, p);
    if (rv != APR_SUCCESS) {
        ap_log_error(APLOG_MARK, APLOG_ERR, rv, ap_server_conf,
                     "creation of the timeout mutex failed.");
        return rv;
    }

    APR_RING_INIT(&timeout_head, conn_state_t, timeout_list);
    APR_RING_INIT(&keepalive_timeout_head, conn_state_t, timeout_list);

    /* Create the main pollset */
    rv = apr_pollset_create(&event_pollset,
                            threads_per_child,
                            p, APR_POLLSET_THREADSAFE | APR_POLLSET_NOCOPY);
    if (rv != APR_SUCCESS) {
        ap_log_error(APLOG_MARK, APLOG_ERR, rv, ap_server_conf,
                     "apr_pollset_create with Thread Safety failed.");
        return rv;
    }

    for (lr = ap_listeners; lr != NULL; lr = lr->next) {
        apr_pollfd_t *pfd = apr_palloc(p, sizeof(*pfd));
        pt = apr_pcalloc(p, sizeof(*pt));
        pfd->desc_type = APR_POLL_SOCKET;
        pfd->desc.s = lr->sd;
        pfd->reqevents = APR_POLLIN;

        pt->type = PT_ACCEPT;
        pt->baton = lr;

        pfd->client_data = pt;

        apr_socket_opt_set(pfd->desc.s, APR_SO_NONBLOCK, 1);
        apr_pollset_add(event_pollset, pfd);

        lr->accept_func = ap_unixd_accept;
    }

#if AP_HAS_SERF
    baton = apr_pcalloc(p, sizeof(*baton));
    baton->pollset = event_pollset;
    /* TODO: subpools, threads, reuse, etc.  -- currently use malloc() inside :( */
    baton->pool = p;

    g_serf = serf_context_create_ex(baton,
                                    s_socket_add,
                                    s_socket_remove, p);

    ap_register_provider(p, "mpm_serf",
                         "instance", "0", g_serf);

#endif

    return APR_SUCCESS;
}

static apr_status_t push_timer2worker(timer_event_t* te)
{
    return ap_queue_push_timer(worker_queue, te);
}

static apr_status_t push2worker(const apr_pollfd_t * pfd,
                                apr_pollset_t * pollset)
{
    listener_poll_type *pt = (listener_poll_type *) pfd->client_data;
    conn_state_t *cs = (conn_state_t *) pt->baton;
    apr_status_t rc;

    if (pt->bypass_push) {
        return APR_SUCCESS;
    }

    pt->bypass_push = 1;

    rc = apr_pollset_remove(pollset, pfd);

    /*
     * Some of the pollset backends, like KQueue or Epoll
     * automagically remove the FD if the socket is closed,
     * therefore, we can accept _SUCCESS or _NOTFOUND,
     * and we still want to keep going
     */
    if (rc != APR_SUCCESS && !APR_STATUS_IS_NOTFOUND(rc)) {
        cs->state = CONN_STATE_LINGER;
    }

    rc = ap_queue_push(worker_queue, cs->pfd.desc.s, cs, cs->p);
    if (rc != APR_SUCCESS) {
        /* trash the connection; we couldn't queue the connected
         * socket to a worker
         */
        apr_bucket_alloc_destroy(cs->bucket_alloc);
        apr_socket_close(cs->pfd.desc.s);
        ap_log_error(APLOG_MARK, APLOG_CRIT, rc,
                     ap_server_conf, "push2worker: ap_queue_push failed");
        apr_pool_clear(cs->p);
        ap_push_pool(worker_queue_info, cs->p);
    }

    return rc;
}

/* get_worker:
 *     reserve a worker thread, block if all are currently busy.
 *     this prevents the worker queue from overflowing and lets
 *     other processes accept new connections in the mean time.
 */
static int get_worker(int *have_idle_worker_p)
{
    apr_status_t rc;

    if (!*have_idle_worker_p) {
        rc = ap_queue_info_wait_for_idler(worker_queue_info);

        if (rc == APR_SUCCESS) {
            *have_idle_worker_p = 1;
            return 1;
        }
        else {
            if (!APR_STATUS_IS_EOF(rc)) {
                ap_log_error(APLOG_MARK, APLOG_ERR, rc, ap_server_conf,
                             "ap_queue_info_wait_for_idler failed.  "
                             "Attempting to shutdown process gracefully");
                signal_threads(ST_GRACEFUL);
            }
            return 0;
        }
    }
    else {
        /* already reserved a worker thread - must have hit a
         * transient error on a previous pass
         */
        return 1;
    }
}

/* XXXXXX: Convert to skiplist or other better data structure 
 * (yes, this is VERY VERY VERY VERY BAD)
 */

/* Structures to reuse */
static APR_RING_HEAD(timer_free_ring_t, timer_event_t) timer_free_ring;
/* Active timers */
static APR_RING_HEAD(timer_ring_t, timer_event_t) timer_ring;

static apr_thread_mutex_t *g_timer_ring_mtx;

static apr_status_t event_register_timed_callback(apr_time_t t,
                                                  ap_mpm_callback_fn_t *cbfn,
                                                  void *baton)
{
    int inserted = 0;
    timer_event_t *ep;
    timer_event_t *te;
    /* oh yeah, and make locking smarter/fine grained. */
    apr_thread_mutex_lock(g_timer_ring_mtx);

    if (!APR_RING_EMPTY(&timer_free_ring, timer_event_t, link)) {
        te = APR_RING_FIRST(&timer_free_ring);
        APR_RING_REMOVE(te, link);
    }
    else {
        /* XXXXX: lol, pool allocation without a context from any thread.Yeah. Right. MPMs Suck. */
        te = malloc(sizeof(timer_event_t));
        APR_RING_ELEM_INIT(te, link);
    }

    te->cbfunc = cbfn;
    te->baton = baton;
    /* XXXXX: optimize */
    te->when = t + apr_time_now();

    /* Okay, insert sorted by when.. */
    for (ep = APR_RING_FIRST(&timer_ring);
         ep != APR_RING_SENTINEL(&timer_ring,
                                 timer_event_t, link);
         ep = APR_RING_NEXT(ep, link))
    {
        if (ep->when > te->when) {
            inserted = 1;
            APR_RING_INSERT_BEFORE(ep, te, link);
            break;
        }
    }
    
    if (!inserted) {
        APR_RING_INSERT_TAIL(&timer_ring, te, timer_event_t, link);
    }

    apr_thread_mutex_unlock(g_timer_ring_mtx);

    return APR_SUCCESS;
}

#ifndef apr_time_from_msec
#define apr_time_from_msec(x) (x * 1000)
#endif

static void * APR_THREAD_FUNC listener_thread(apr_thread_t * thd, void *dummy)
{
    timer_event_t *ep;
    timer_event_t *te;
    apr_status_t rc;
    proc_info *ti = dummy;
    int process_slot = ti->pid;
    apr_pool_t *tpool = apr_thread_pool_get(thd);
    void *csd = NULL;
    apr_pool_t *ptrans;         /* Pool for per-transaction stuff */
    ap_listen_rec *lr;
    int have_idle_worker = 0;
    conn_state_t *cs;
    const apr_pollfd_t *out_pfd;
    apr_int32_t num = 0;
    apr_time_t time_now = 0;
    apr_interval_time_t timeout_interval;
    apr_time_t timeout_time;
    listener_poll_type *pt;

    free(ti);

    /* the following times out events that are really close in the future
     *   to prevent extra poll calls
     *
     * current value is .1 second
     */
#define TIMEOUT_FUDGE_FACTOR 100000
#define EVENT_FUDGE_FACTOR 10000

    rc = init_pollset(tpool);
    if (rc != APR_SUCCESS) {
        ap_log_error(APLOG_MARK, APLOG_ERR, rc, ap_server_conf,
                     "failed to initialize pollset, "
                     "attempting to shutdown process gracefully");
        signal_threads(ST_GRACEFUL);
        return NULL;
    }

    /* Unblock the signal used to wake this thread up, and set a handler for
     * it.
     */
    unblock_signal(LISTENER_SIGNAL);
    apr_signal(LISTENER_SIGNAL, dummy_signal_handler);

    while (!listener_may_exit) {

        if (requests_this_child <= 0) {
            check_infinite_requests();
        }


        {
            apr_time_t now = apr_time_now();
            apr_thread_mutex_lock(g_timer_ring_mtx);

            if (!APR_RING_EMPTY(&timer_ring, timer_event_t, link)) {
                te = APR_RING_FIRST(&timer_ring);
                if (te->when > now) {
                    timeout_interval = te->when - now;
                }
                else {
                    timeout_interval = 1;
                }
            }
            else {
                timeout_interval = apr_time_from_msec(100);
            }
            apr_thread_mutex_unlock(g_timer_ring_mtx);
        }

#if AP_HAS_SERF
        rc = serf_context_prerun(g_serf);
        if (rc != APR_SUCCESS) {
            /* TOOD: what should do here? ugh. */
        }
        
#endif
        rc = apr_pollset_poll(event_pollset, timeout_interval, &num,
                              &out_pfd);

        if (rc != APR_SUCCESS) {
            if (APR_STATUS_IS_EINTR(rc)) {
                continue;
            }
            if (!APR_STATUS_IS_TIMEUP(rc)) {
                ap_log_error(APLOG_MARK, APLOG_ERR, rc, ap_server_conf,
                             "apr_pollset_poll failed.  Attempting to "
                             "shutdown process gracefully");
                signal_threads(ST_GRACEFUL);
            }
        }

        if (listener_may_exit)
            break;

        {
            apr_time_t now = apr_time_now();
            apr_thread_mutex_lock(g_timer_ring_mtx);
            for (ep = APR_RING_FIRST(&timer_ring);
                 ep != APR_RING_SENTINEL(&timer_ring,
                                         timer_event_t, link);
                 ep = APR_RING_FIRST(&timer_ring))
            {
                if (ep->when < now + EVENT_FUDGE_FACTOR) {
                    APR_RING_REMOVE(ep, link);
                    push_timer2worker(ep);
                }
                else {
                    break;
                }
            }
            apr_thread_mutex_unlock(g_timer_ring_mtx);
        }

        while (num && get_worker(&have_idle_worker)) {
            pt = (listener_poll_type *) out_pfd->client_data;
            if (pt->type == PT_CSD) {
                /* one of the sockets is readable */
                cs = (conn_state_t *) pt->baton;
                switch (cs->state) {
                case CONN_STATE_CHECK_REQUEST_LINE_READABLE:
                    cs->state = CONN_STATE_READ_REQUEST_LINE;
                    break;
                case CONN_STATE_WRITE_COMPLETION:
                    break;
                default:
                    ap_log_error(APLOG_MARK, APLOG_ERR, rc,
                                 ap_server_conf,
                                 "event_loop: unexpected state %d",
                                 cs->state);
                    AP_DEBUG_ASSERT(0);
                }

                apr_thread_mutex_lock(timeout_mutex);
                APR_RING_REMOVE(cs, timeout_list);
                apr_thread_mutex_unlock(timeout_mutex);
                APR_RING_ELEM_INIT(cs, timeout_list);

                rc = push2worker(out_pfd, event_pollset);
                if (rc != APR_SUCCESS) {
                    ap_log_error(APLOG_MARK, APLOG_CRIT, rc,
                                 ap_server_conf, "push2worker failed");
                }
                else {
                    have_idle_worker = 0;
                }
            }
            else if (pt->type == PT_ACCEPT) {
                /* A Listener Socket is ready for an accept() */

                lr = (ap_listen_rec *) pt->baton;

                ap_pop_pool(&ptrans, worker_queue_info);

                if (ptrans == NULL) {
                    /* create a new transaction pool for each accepted socket */
                    apr_allocator_t *allocator;

                    apr_allocator_create(&allocator);
                    apr_allocator_max_free_set(allocator,
                                               ap_max_mem_free);
                    apr_pool_create_ex(&ptrans, pconf, NULL, allocator);
                    apr_allocator_owner_set(allocator, ptrans);
                    if (ptrans == NULL) {
                        ap_log_error(APLOG_MARK, APLOG_CRIT, rc,
                                     ap_server_conf,
                                     "Failed to create transaction pool");
                        signal_threads(ST_GRACEFUL);
                        return NULL;
                    }
                }
                apr_pool_tag(ptrans, "transaction");

                rc = lr->accept_func(&csd, lr, ptrans);

                /* later we trash rv and rely on csd to indicate
                 * success/failure
                 */
                AP_DEBUG_ASSERT(rc == APR_SUCCESS || !csd);

                if (rc == APR_EGENERAL) {
                    /* E[NM]FILE, ENOMEM, etc */
                    resource_shortage = 1;
                    signal_threads(ST_GRACEFUL);
                }

                if (csd != NULL) {
                    rc = ap_queue_push(worker_queue, csd, NULL, ptrans);
                    if (rc != APR_SUCCESS) {
                        /* trash the connection; we couldn't queue the connected
                         * socket to a worker
                         */
                        apr_socket_close(csd);
                        ap_log_error(APLOG_MARK, APLOG_CRIT, rc,
                                     ap_server_conf,
                                     "ap_queue_push failed");
                        apr_pool_clear(ptrans);
                        ap_push_pool(worker_queue_info, ptrans);
                    }
                    else {
                        have_idle_worker = 0;
                    }
                }
                else {
                    apr_pool_clear(ptrans);
                    ap_push_pool(worker_queue_info, ptrans);
                }
            }               /* if:else on pt->type */
#if AP_HAS_SERF
            else if (pt->type == PT_SERF) {
                /* send socket to serf. */
                /* XXXX: this doesn't require get_worker(&have_idle_worker) */
                serf_event_trigger(g_serf, pt->baton, out_pfd);
            }
#endif
            out_pfd++;
            num--;
        }                   /* while for processing poll */

        /* XXX possible optimization: stash the current time for use as
         * r->request_time for new requests
         */
        time_now = apr_time_now();

        /* handle timed out sockets */
        apr_thread_mutex_lock(timeout_mutex);

        /* Step 1: keepalive timeouts */
        cs = APR_RING_FIRST(&keepalive_timeout_head);
        timeout_time = time_now + TIMEOUT_FUDGE_FACTOR;
        while (!APR_RING_EMPTY(&keepalive_timeout_head, conn_state_t, timeout_list)
               && cs->expiration_time < timeout_time) {

            cs->state = CONN_STATE_LINGER;

            APR_RING_REMOVE(cs, timeout_list);
            apr_thread_mutex_unlock(timeout_mutex);

            if (!get_worker(&have_idle_worker)) {
                apr_thread_mutex_lock(timeout_mutex);
                APR_RING_INSERT_HEAD(&keepalive_timeout_head, cs,
                                     conn_state_t, timeout_list);
                break;
            }

            rc = push2worker(&cs->pfd, event_pollset);

            if (rc != APR_SUCCESS) {
                return NULL;
                /* XXX return NULL looks wrong - not an init failure
                 * that bypasses all the cleanup outside the main loop
                 * break seems more like it
                 * need to evaluate seriousness of push2worker failures
                 */
            }
            have_idle_worker = 0;
            apr_thread_mutex_lock(timeout_mutex);
            cs = APR_RING_FIRST(&keepalive_timeout_head);
        }

        /* Step 2: write completion timeouts */
        cs = APR_RING_FIRST(&timeout_head);
        while (!APR_RING_EMPTY(&timeout_head, conn_state_t, timeout_list)
               && cs->expiration_time < timeout_time) {

            cs->state = CONN_STATE_LINGER;
            APR_RING_REMOVE(cs, timeout_list);
            apr_thread_mutex_unlock(timeout_mutex);

            if (!get_worker(&have_idle_worker)) {
                apr_thread_mutex_lock(timeout_mutex);
                APR_RING_INSERT_HEAD(&timeout_head, cs,
                                     conn_state_t, timeout_list);
                break;
            }

            rc = push2worker(&cs->pfd, event_pollset);
            if (rc != APR_SUCCESS) {
                return NULL;
            }
            have_idle_worker = 0;
            apr_thread_mutex_lock(timeout_mutex);
            cs = APR_RING_FIRST(&timeout_head);
        }

        apr_thread_mutex_unlock(timeout_mutex);

    }     /* listener main loop */

    ap_close_listeners();
    ap_queue_term(worker_queue);
    dying = 1;
    ap_scoreboard_image->parent[process_slot].quiescing = 1;

    /* wake up the main thread */
    kill(ap_my_pid, SIGTERM);

    apr_thread_exit(thd, APR_SUCCESS);
    return NULL;
}

/* XXX For ungraceful termination/restart, we definitely don't want to
 *     wait for active connections to finish but we may want to wait
 *     for idle workers to get out of the queue code and release mutexes,
 *     since those mutexes are cleaned up pretty soon and some systems
 *     may not react favorably (i.e., segfault) if operations are attempted
 *     on cleaned-up mutexes.
 */
static void *APR_THREAD_FUNC worker_thread(apr_thread_t * thd, void *dummy)
{
    proc_info *ti = dummy;
    int process_slot = ti->pid;
    int thread_slot = ti->tid;
    apr_socket_t *csd = NULL;
    conn_state_t *cs;
    apr_pool_t *ptrans;         /* Pool for per-transaction stuff */
    apr_status_t rv;
    int is_idle = 0;
    timer_event_t *te = NULL;
    
    free(ti);

    ap_scoreboard_image->servers[process_slot][thread_slot].pid = ap_my_pid;
    ap_scoreboard_image->servers[process_slot][thread_slot].tid = apr_os_thread_current();
    ap_scoreboard_image->servers[process_slot][thread_slot].generation = my_generation;
    ap_update_child_status_from_indexes(process_slot, thread_slot,
                                        SERVER_STARTING, NULL);

    while (!workers_may_exit) {
        if (!is_idle) {
            rv = ap_queue_info_set_idle(worker_queue_info, NULL);
            if (rv != APR_SUCCESS) {
                ap_log_error(APLOG_MARK, APLOG_EMERG, rv, ap_server_conf,
                             "ap_queue_info_set_idle failed. Attempting to "
                             "shutdown process gracefully.");
                signal_threads(ST_GRACEFUL);
                break;
            }
            is_idle = 1;
        }

        ap_update_child_status_from_indexes(process_slot, thread_slot,
                                            SERVER_READY, NULL);
      worker_pop:
        if (workers_may_exit) {
            break;
        }

        te = NULL;
        
        rv = ap_queue_pop_something(worker_queue, &csd, &cs, &ptrans, &te);

        if (rv != APR_SUCCESS) {
            /* We get APR_EOF during a graceful shutdown once all the
             * connections accepted by this server process have been handled.
             */
            if (APR_STATUS_IS_EOF(rv)) {
                break;
            }
            /* We get APR_EINTR whenever ap_queue_pop() has been interrupted
             * from an explicit call to ap_queue_interrupt_all(). This allows
             * us to unblock threads stuck in ap_queue_pop() when a shutdown
             * is pending.
             *
             * If workers_may_exit is set and this is ungraceful termination/
             * restart, we are bound to get an error on some systems (e.g.,
             * AIX, which sanity-checks mutex operations) since the queue
             * may have already been cleaned up.  Don't log the "error" if
             * workers_may_exit is set.
             */
            else if (APR_STATUS_IS_EINTR(rv)) {
                goto worker_pop;
            }
            /* We got some other error. */
            else if (!workers_may_exit) {
                ap_log_error(APLOG_MARK, APLOG_CRIT, rv, ap_server_conf,
                             "ap_queue_pop failed");
            }
            continue;
        }
        if (te != NULL) {
            
            te->cbfunc(te->baton);

            {
                apr_thread_mutex_lock(g_timer_ring_mtx);
                APR_RING_INSERT_TAIL(&timer_free_ring, te, timer_event_t, link);
                apr_thread_mutex_unlock(g_timer_ring_mtx);
            }
        }
        else {
            is_idle = 0;
            worker_sockets[thread_slot] = csd;
            rv = process_socket(thd, ptrans, csd, cs, process_slot, thread_slot);
            if (!rv) {
                requests_this_child--;
            }
            worker_sockets[thread_slot] = NULL;
        }
    }

    ap_update_child_status_from_indexes(process_slot, thread_slot,
                                        (dying) ? SERVER_DEAD :
                                        SERVER_GRACEFUL,
                                        (request_rec *) NULL);

    apr_thread_exit(thd, APR_SUCCESS);
    return NULL;
}

static int check_signal(int signum)
{
    switch (signum) {
    case SIGTERM:
    case SIGINT:
        return 1;
    }
    return 0;
}



static void create_listener_thread(thread_starter * ts)
{
    int my_child_num = ts->child_num_arg;
    apr_threadattr_t *thread_attr = ts->threadattr;
    proc_info *my_info;
    apr_status_t rv;

    my_info = (proc_info *) malloc(sizeof(proc_info));
    my_info->pid = my_child_num;
    my_info->tid = -1;          /* listener thread doesn't have a thread slot */
    my_info->sd = 0;
    rv = apr_thread_create(&ts->listener, thread_attr, listener_thread,
                           my_info, pchild);
    if (rv != APR_SUCCESS) {
        ap_log_error(APLOG_MARK, APLOG_ALERT, rv, ap_server_conf,
                     "apr_thread_create: unable to create listener thread");
        /* let the parent decide how bad this really is */
        clean_child_exit(APEXIT_CHILDSICK);
    }
    apr_os_thread_get(&listener_os_thread, ts->listener);
}

/* XXX under some circumstances not understood, children can get stuck
 *     in start_threads forever trying to take over slots which will
 *     never be cleaned up; for now there is an APLOG_DEBUG message issued
 *     every so often when this condition occurs
 */
static void *APR_THREAD_FUNC start_threads(apr_thread_t * thd, void *dummy)
{
    thread_starter *ts = dummy;
    apr_thread_t **threads = ts->threads;
    apr_threadattr_t *thread_attr = ts->threadattr;
    int child_num_arg = ts->child_num_arg;
    int my_child_num = child_num_arg;
    proc_info *my_info;
    apr_status_t rv;
    int i;
    int threads_created = 0;
    int listener_started = 0;
    int loops;
    int prev_threads_created;

    /* We must create the fd queues before we start up the listener
     * and worker threads. */
    worker_queue = apr_pcalloc(pchild, sizeof(*worker_queue));
    rv = ap_queue_init(worker_queue, threads_per_child, pchild);
    if (rv != APR_SUCCESS) {
        ap_log_error(APLOG_MARK, APLOG_ALERT, rv, ap_server_conf,
                     "ap_queue_init() failed");
        clean_child_exit(APEXIT_CHILDFATAL);
    }

    rv = ap_queue_info_create(&worker_queue_info, pchild,
                              threads_per_child);
    if (rv != APR_SUCCESS) {
        ap_log_error(APLOG_MARK, APLOG_ALERT, rv, ap_server_conf,
                     "ap_queue_info_create() failed");
        clean_child_exit(APEXIT_CHILDFATAL);
    }

    worker_sockets = apr_pcalloc(pchild, threads_per_child
                                 * sizeof(apr_socket_t *));

    loops = prev_threads_created = 0;
    while (1) {
        /* threads_per_child does not include the listener thread */
        for (i = 0; i < threads_per_child; i++) {
            int status =
                ap_scoreboard_image->servers[child_num_arg][i].status;

            if (status != SERVER_GRACEFUL && status != SERVER_DEAD) {
                continue;
            }

            my_info = (proc_info *) malloc(sizeof(proc_info));
            if (my_info == NULL) {
                ap_log_error(APLOG_MARK, APLOG_ALERT, errno, ap_server_conf,
                             "malloc: out of memory");
                clean_child_exit(APEXIT_CHILDFATAL);
            }
            my_info->pid = my_child_num;
            my_info->tid = i;
            my_info->sd = 0;

            /* We are creating threads right now */
            ap_update_child_status_from_indexes(my_child_num, i,
                                                SERVER_STARTING, NULL);
            /* We let each thread update its own scoreboard entry.  This is
             * done because it lets us deal with tid better.
             */
            rv = apr_thread_create(&threads[i], thread_attr,
                                   worker_thread, my_info, pchild);
            if (rv != APR_SUCCESS) {
                ap_log_error(APLOG_MARK, APLOG_ALERT, rv, ap_server_conf,
                             "apr_thread_create: unable to create worker thread");
                /* let the parent decide how bad this really is */
                clean_child_exit(APEXIT_CHILDSICK);
            }
            threads_created++;
        }

        /* Start the listener only when there are workers available */
        if (!listener_started && threads_created) {
            create_listener_thread(ts);
            listener_started = 1;
        }


        if (start_thread_may_exit || threads_created == threads_per_child) {
            break;
        }
        /* wait for previous generation to clean up an entry */
        apr_sleep(apr_time_from_sec(1));
        ++loops;
        if (loops % 120 == 0) { /* every couple of minutes */
            if (prev_threads_created == threads_created) {
                ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, ap_server_conf,
                             "child %" APR_PID_T_FMT " isn't taking over "
                             "slots very quickly (%d of %d)",
                             ap_my_pid, threads_created,
                             threads_per_child);
            }
            prev_threads_created = threads_created;
        }
    }

    /* What state should this child_main process be listed as in the
     * scoreboard...?
     *  ap_update_child_status_from_indexes(my_child_num, i, SERVER_STARTING,
     *                                      (request_rec *) NULL);
     *
     *  This state should be listed separately in the scoreboard, in some kind
     *  of process_status, not mixed in with the worker threads' status.
     *  "life_status" is almost right, but it's in the worker's structure, and
     *  the name could be clearer.   gla
     */
    apr_thread_exit(thd, APR_SUCCESS);
    return NULL;
}

static void join_workers(apr_thread_t * listener, apr_thread_t ** threads)
{
    int i;
    apr_status_t rv, thread_rv;

    if (listener) {
        int iter;

        /* deal with a rare timing window which affects waking up the
         * listener thread...  if the signal sent to the listener thread
         * is delivered between the time it verifies that the
         * listener_may_exit flag is clear and the time it enters a
         * blocking syscall, the signal didn't do any good...  work around
         * that by sleeping briefly and sending it again
         */

        iter = 0;
        while (iter < 10 &&
#ifdef HAVE_PTHREAD_KILL
               pthread_kill(*listener_os_thread, 0)
#else
               kill(ap_my_pid, 0)
#endif
               == 0) {
            /* listener not dead yet */
            apr_sleep(apr_time_make(0, 500000));
            wakeup_listener();
            ++iter;
        }
        if (iter >= 10) {
            ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, ap_server_conf,
                         "the listener thread didn't exit");
        }
        else {
            rv = apr_thread_join(&thread_rv, listener);
            if (rv != APR_SUCCESS) {
                ap_log_error(APLOG_MARK, APLOG_CRIT, rv, ap_server_conf,
                             "apr_thread_join: unable to join listener thread");
            }
        }
    }

    for (i = 0; i < threads_per_child; i++) {
        if (threads[i]) {       /* if we ever created this thread */
            rv = apr_thread_join(&thread_rv, threads[i]);
            if (rv != APR_SUCCESS) {
                ap_log_error(APLOG_MARK, APLOG_CRIT, rv, ap_server_conf,
                             "apr_thread_join: unable to join worker "
                             "thread %d", i);
            }
        }
    }
}

static void join_start_thread(apr_thread_t * start_thread_id)
{
    apr_status_t rv, thread_rv;

    start_thread_may_exit = 1;  /* tell it to give up in case it is still
                                 * trying to take over slots from a
                                 * previous generation
                                 */
    rv = apr_thread_join(&thread_rv, start_thread_id);
    if (rv != APR_SUCCESS) {
        ap_log_error(APLOG_MARK, APLOG_CRIT, rv, ap_server_conf,
                     "apr_thread_join: unable to join the start " "thread");
    }
}

static void child_main(int child_num_arg)
{
    apr_thread_t **threads;
    apr_status_t rv;
    thread_starter *ts;
    apr_threadattr_t *thread_attr;
    apr_thread_t *start_thread_id;

    mpm_state = AP_MPMQ_STARTING;       /* for benefit of any hooks that run as this
                                         * child initializes
                                         */
    ap_my_pid = getpid();
    ap_fatal_signal_child_setup(ap_server_conf);
    apr_pool_create(&pchild, pconf);

    /*stuff to do before we switch id's, so we have permissions. */
    ap_reopen_scoreboard(pchild, NULL, 0);

    if (ap_run_drop_privileges(pchild, ap_server_conf)) {
        clean_child_exit(APEXIT_CHILDFATAL);
    }

    apr_thread_mutex_create(&g_timer_ring_mtx, APR_THREAD_MUTEX_DEFAULT, pchild);
    APR_RING_INIT(&timer_free_ring, timer_event_t, link);
    APR_RING_INIT(&timer_ring, timer_event_t, link);
    
    ap_run_child_init(pchild, ap_server_conf);

    /* done with init critical section */

    /* Just use the standard apr_setup_signal_thread to block all signals
     * from being received.  The child processes no longer use signals for
     * any communication with the parent process.
     */
    rv = apr_setup_signal_thread();
    if (rv != APR_SUCCESS) {
        ap_log_error(APLOG_MARK, APLOG_EMERG, rv, ap_server_conf,
                     "Couldn't initialize signal thread");
        clean_child_exit(APEXIT_CHILDFATAL);
    }

    if (ap_max_requests_per_child) {
        requests_this_child = ap_max_requests_per_child;
    }
    else {
        /* coding a value of zero means infinity */
        requests_this_child = INT_MAX;
    }

    /* Setup worker threads */

    /* clear the storage; we may not create all our threads immediately,
     * and we want a 0 entry to indicate a thread which was not created
     */
    threads = (apr_thread_t **) calloc(1,
                                       sizeof(apr_thread_t *) *
                                       threads_per_child);
    if (threads == NULL) {
        ap_log_error(APLOG_MARK, APLOG_ALERT, errno, ap_server_conf,
                     "malloc: out of memory");
        clean_child_exit(APEXIT_CHILDFATAL);
    }

    ts = (thread_starter *) apr_palloc(pchild, sizeof(*ts));

    apr_threadattr_create(&thread_attr, pchild);
    /* 0 means PTHREAD_CREATE_JOINABLE */
    apr_threadattr_detach_set(thread_attr, 0);

    if (ap_thread_stacksize != 0) {
        apr_threadattr_stacksize_set(thread_attr, ap_thread_stacksize);
    }

    ts->threads = threads;
    ts->listener = NULL;
    ts->child_num_arg = child_num_arg;
    ts->threadattr = thread_attr;

    rv = apr_thread_create(&start_thread_id, thread_attr, start_threads,
                           ts, pchild);
    if (rv != APR_SUCCESS) {
        ap_log_error(APLOG_MARK, APLOG_ALERT, rv, ap_server_conf,
                     "apr_thread_create: unable to create worker thread");
        /* let the parent decide how bad this really is */
        clean_child_exit(APEXIT_CHILDSICK);
    }

    mpm_state = AP_MPMQ_RUNNING;

    /* If we are only running in one_process mode, we will want to
     * still handle signals. */
    if (one_process) {
        /* Block until we get a terminating signal. */
        apr_signal_thread(check_signal);
        /* make sure the start thread has finished; signal_threads()
         * and join_workers() depend on that
         */
        /* XXX join_start_thread() won't be awakened if one of our
         *     threads encounters a critical error and attempts to
         *     shutdown this child
         */
        join_start_thread(start_thread_id);

        /* helps us terminate a little more quickly than the dispatch of the
         * signal thread; beats the Pipe of Death and the browsers
         */
        signal_threads(ST_UNGRACEFUL);

        /* A terminating signal was received. Now join each of the
         * workers to clean them up.
         *   If the worker already exited, then the join frees
         *   their resources and returns.
         *   If the worker hasn't exited, then this blocks until
         *   they have (then cleans up).
         */
        join_workers(ts->listener, threads);
    }
    else {                      /* !one_process */
        /* remove SIGTERM from the set of blocked signals...  if one of
         * the other threads in the process needs to take us down
         * (e.g., for MaxRequestsPerChild) it will send us SIGTERM
         */
        unblock_signal(SIGTERM);
        apr_signal(SIGTERM, dummy_signal_handler);
        /* Watch for any messages from the parent over the POD */
        while (1) {
            rv = ap_event_pod_check(pod);
            if (rv == AP_NORESTART) {
                /* see if termination was triggered while we slept */
                switch (terminate_mode) {
                case ST_GRACEFUL:
                    rv = AP_GRACEFUL;
                    break;
                case ST_UNGRACEFUL:
                    rv = AP_RESTART;
                    break;
                }
            }
            if (rv == AP_GRACEFUL || rv == AP_RESTART) {
                /* make sure the start thread has finished;
                 * signal_threads() and join_workers depend on that
                 */
                join_start_thread(start_thread_id);
                signal_threads(rv ==
                               AP_GRACEFUL ? ST_GRACEFUL : ST_UNGRACEFUL);
                break;
            }
        }

        /* A terminating signal was received. Now join each of the
         * workers to clean them up.
         *   If the worker already exited, then the join frees
         *   their resources and returns.
         *   If the worker hasn't exited, then this blocks until
         *   they have (then cleans up).
         */
        join_workers(ts->listener, threads);
    }

    free(threads);

    clean_child_exit(resource_shortage ? APEXIT_CHILDSICK : 0);
}

static int make_child(server_rec * s, int slot)
{
    int pid;

    if (slot + 1 > max_daemons_limit) {
        max_daemons_limit = slot + 1;
    }

    if (one_process) {
        set_signals();
        ap_scoreboard_image->parent[slot].pid = getpid();
        child_main(slot);
    }

    if ((pid = fork()) == -1) {
        ap_log_error(APLOG_MARK, APLOG_ERR, errno, s,
                     "fork: Unable to fork new process");

        /* fork didn't succeed.  There's no need to touch the scoreboard;
         * if we were trying to replace a failed child process, then
         * server_main_loop() marked its workers SERVER_DEAD, and if
         * we were trying to replace a child process that exited normally,
         * its worker_thread()s left SERVER_DEAD or SERVER_GRACEFUL behind.
         */

        /* In case system resources are maxxed out, we don't want
           Apache running away with the CPU trying to fork over and
           over and over again. */
        apr_sleep(apr_time_from_sec(10));

        return -1;
    }

    if (!pid) {
#ifdef HAVE_BINDPROCESSOR
        /* By default, AIX binds to a single processor.  This bit unbinds
         * children which will then bind to another CPU.
         */
        int status = bindprocessor(BINDPROCESS, (int) getpid(),
                                   PROCESSOR_CLASS_ANY);
        if (status != OK)
            ap_log_error(APLOG_MARK, APLOG_WARNING, errno,
                         ap_server_conf,
                         "processor unbind failed %d", status);
#endif
        RAISE_SIGSTOP(MAKE_CHILD);

        apr_signal(SIGTERM, just_die);
        child_main(slot);

        clean_child_exit(0);
    }
    /* else */
    if (ap_scoreboard_image->parent[slot].pid != 0) {
        /* This new child process is squatting on the scoreboard
         * entry owned by an exiting child process, which cannot
         * exit until all active requests complete.
         * Don't forget about this exiting child process, or we
         * won't be able to kill it if it doesn't exit by the
         * time the server is shut down.
         */
        ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, ap_server_conf,
                     "taking over scoreboard slot from %" APR_PID_T_FMT "%s",
                     ap_scoreboard_image->parent[slot].pid,
                     ap_scoreboard_image->parent[slot].quiescing ?
                         " (quiescing)" : "");
        ap_register_extra_mpm_process(ap_scoreboard_image->parent[slot].pid);
    }
    ap_scoreboard_image->parent[slot].quiescing = 0;
    ap_scoreboard_image->parent[slot].pid = pid;
    return 0;
}

/* start up a bunch of children */
static void startup_children(int number_to_start)
{
    int i;

    for (i = 0; number_to_start && i < ap_daemons_limit; ++i) {
        if (ap_scoreboard_image->parent[i].pid != 0) {
            continue;
        }
        if (make_child(ap_server_conf, i) < 0) {
            break;
        }
        --number_to_start;
    }
}


/*
 * idle_spawn_rate is the number of children that will be spawned on the
 * next maintenance cycle if there aren't enough idle servers.  It is
 * doubled up to MAX_SPAWN_RATE, and reset only when a cycle goes by
 * without the need to spawn.
 */
static int idle_spawn_rate = 1;
#ifndef MAX_SPAWN_RATE
#define MAX_SPAWN_RATE        (32)
#endif
static int hold_off_on_exponential_spawning;

static void perform_idle_server_maintenance(void)
{
    int i, j;
    int idle_thread_count;
    worker_score *ws;
    process_score *ps;
    int free_length;
    int totally_free_length = 0;
    int free_slots[MAX_SPAWN_RATE];
    int last_non_dead;
    int total_non_dead;
    int active_thread_count = 0;

    /* initialize the free_list */
    free_length = 0;

    idle_thread_count = 0;
    last_non_dead = -1;
    total_non_dead = 0;

    for (i = 0; i < ap_daemons_limit; ++i) {
        /* Initialization to satisfy the compiler. It doesn't know
         * that threads_per_child is always > 0 */
        int status = SERVER_DEAD;
        int any_dying_threads = 0;
        int any_dead_threads = 0;
        int all_dead_threads = 1;

        if (i >= max_daemons_limit
            && totally_free_length == idle_spawn_rate)
            /* short cut if all active processes have been examined and
             * enough empty scoreboard slots have been found
             */
        
            break;
        ps = &ap_scoreboard_image->parent[i];
        for (j = 0; j < threads_per_child; j++) {
            ws = &ap_scoreboard_image->servers[i][j];
            status = ws->status;

            /* XXX any_dying_threads is probably no longer needed    GLA */
            any_dying_threads = any_dying_threads ||
                (status == SERVER_GRACEFUL);
            any_dead_threads = any_dead_threads || (status == SERVER_DEAD);
            all_dead_threads = all_dead_threads &&
                (status == SERVER_DEAD || status == SERVER_GRACEFUL);

            /* We consider a starting server as idle because we started it
             * at least a cycle ago, and if it still hasn't finished starting
             * then we're just going to swamp things worse by forking more.
             * So we hopefully won't need to fork more if we count it.
             * This depends on the ordering of SERVER_READY and SERVER_STARTING.
             */
            if (ps->pid != 0) { /* XXX just set all_dead_threads in outer
                                   for loop if no pid?  not much else matters */
                if (status <= SERVER_READY &&
                        !ps->quiescing && ps->generation == my_generation) {
                    ++idle_thread_count;
                }
                if (status >= SERVER_READY && status < SERVER_GRACEFUL) {
                    ++active_thread_count;
                }
            }
        }
        if (any_dead_threads
            && totally_free_length < idle_spawn_rate
            && free_length < MAX_SPAWN_RATE
            && (!ps->pid      /* no process in the slot */
                  || ps->quiescing)) {  /* or at least one is going away */
            if (all_dead_threads) {
                /* great! we prefer these, because the new process can
                 * start more threads sooner.  So prioritize this slot
                 * by putting it ahead of any slots with active threads.
                 *
                 * first, make room by moving a slot that's potentially still
                 * in use to the end of the array
                 */
                free_slots[free_length] = free_slots[totally_free_length];
                free_slots[totally_free_length++] = i;
            }
            else {
                /* slot is still in use - back of the bus
                 */
                free_slots[free_length] = i;
            }
            ++free_length;
        }
        /* XXX if (!ps->quiescing)     is probably more reliable  GLA */
        if (!any_dying_threads) {
            last_non_dead = i;
            ++total_non_dead;
        }
    }

    if (sick_child_detected) {
        if (active_thread_count > 0) {
            /* some child processes appear to be working.  don't kill the
             * whole server.
             */
            sick_child_detected = 0;
        }
        else {
            /* looks like a basket case.  give up.
             */
            shutdown_pending = 1;
            child_fatal = 1;
            ap_log_error(APLOG_MARK, APLOG_ALERT, 0,
                         ap_server_conf,
                         "No active workers found..."
                         " Apache is exiting!");
            /* the child already logged the failure details */
            return;
        }
    }

    max_daemons_limit = last_non_dead + 1;

    if (idle_thread_count > max_spare_threads) {
        /* Kill off one child */
        ap_event_pod_signal(pod, TRUE);
        idle_spawn_rate = 1;
    }
    else if (idle_thread_count < min_spare_threads) {
        /* terminate the free list */
        if (free_length == 0) { /* scoreboard is full, can't fork */

            if (active_thread_count >= ap_daemons_limit * threads_per_child) {
                static int reported = 0;
                if (!reported) {
                    /* only report this condition once */
                    ap_log_error(APLOG_MARK, APLOG_ERR, 0,
                                 ap_server_conf,
                                 "server reached MaxClients setting, consider"
                                 " raising the MaxClients setting");
                    reported = 1;
                }
            }
            else {
                ap_log_error(APLOG_MARK, APLOG_ERR, 0,
                             ap_server_conf,
                             "scoreboard is full, not at MaxClients");
            }
            idle_spawn_rate = 1;
        }
        else {
            if (free_length > idle_spawn_rate) {
                free_length = idle_spawn_rate;
            }
            if (idle_spawn_rate >= 8) {
                ap_log_error(APLOG_MARK, APLOG_INFO, 0,
                             ap_server_conf,
                             "server seems busy, (you may need "
                             "to increase StartServers, ThreadsPerChild "
                             "or Min/MaxSpareThreads), "
                             "spawning %d children, there are around %d idle "
                             "threads, and %d total children", free_length,
                             idle_thread_count, total_non_dead);
            }
            for (i = 0; i < free_length; ++i) {
                make_child(ap_server_conf, free_slots[i]);
            }
            /* the next time around we want to spawn twice as many if this
             * wasn't good enough, but not if we've just done a graceful
             */
            if (hold_off_on_exponential_spawning) {
                --hold_off_on_exponential_spawning;
            }
            else if (idle_spawn_rate < MAX_SPAWN_RATE) {
                idle_spawn_rate *= 2;
            }
        }
    }
    else {
        idle_spawn_rate = 1;
    }
}

static void server_main_loop(int remaining_children_to_start)
{
    int child_slot;
    apr_exit_why_e exitwhy;
    int status, processed_status;
    apr_proc_t pid;
    int i;

    while (!restart_pending && !shutdown_pending) {
        ap_wait_or_timeout(&exitwhy, &status, &pid, pconf);

        if (pid.pid != -1) {
            processed_status = ap_process_child_status(&pid, exitwhy, status);
            if (processed_status == APEXIT_CHILDFATAL) {
                shutdown_pending = 1;
                child_fatal = 1;
                return;
            }
            else if (processed_status == APEXIT_CHILDSICK) {
                /* tell perform_idle_server_maintenance to check into this
                 * on the next timer pop
                 */
                sick_child_detected = 1;
            }
            /* non-fatal death... note that it's gone in the scoreboard. */
            child_slot = ap_find_child_by_pid(&pid);
            if (child_slot >= 0) {
                for (i = 0; i < threads_per_child; i++)
                    ap_update_child_status_from_indexes(child_slot, i,
                                                        SERVER_DEAD,
                                                        (request_rec *) NULL);

                ap_scoreboard_image->parent[child_slot].pid = 0;
                ap_scoreboard_image->parent[child_slot].quiescing = 0;
                if (processed_status == APEXIT_CHILDSICK) {
                    /* resource shortage, minimize the fork rate */
                    idle_spawn_rate = 1;
                }
                else if (remaining_children_to_start
                         && child_slot < ap_daemons_limit) {
                    /* we're still doing a 1-for-1 replacement of dead
                     * children with new children
                     */
                    make_child(ap_server_conf, child_slot);
                    --remaining_children_to_start;
                }
            }
            else if (ap_unregister_extra_mpm_process(pid.pid) == 1) {
                /* handled */
#if APR_HAS_OTHER_CHILD
            }
            else if (apr_proc_other_child_alert(&pid, APR_OC_REASON_DEATH,
                                                status) == 0) {
                /* handled */
#endif
            }
            else if (is_graceful) {
                /* Great, we've probably just lost a slot in the
                 * scoreboard.  Somehow we don't know about this child.
                 */
                ap_log_error(APLOG_MARK, APLOG_WARNING, 0,
                             ap_server_conf,
                             "long lost child came home! (pid %ld)",
                             (long) pid.pid);
            }
            /* Don't perform idle maintenance when a child dies,
             * only do it when there's a timeout.  Remember only a
             * finite number of children can die, and it's pretty
             * pathological for a lot to die suddenly.
             */
            continue;
        }
        else if (remaining_children_to_start) {
            /* we hit a 1 second timeout in which none of the previous
             * generation of children needed to be reaped... so assume
             * they're all done, and pick up the slack if any is left.
             */
            startup_children(remaining_children_to_start);
            remaining_children_to_start = 0;
            /* In any event we really shouldn't do the code below because
             * few of the servers we just started are in the IDLE state
             * yet, so we'd mistakenly create an extra server.
             */
            continue;
        }

        perform_idle_server_maintenance();
    }
}

static int event_run(apr_pool_t * _pconf, apr_pool_t * plog, server_rec * s)
{
    int remaining_children_to_start;

    ap_log_pid(pconf, ap_pid_fname);

    if (!is_graceful) {
        if (ap_run_pre_mpm(s->process->pool, SB_SHARED) != OK) {
            mpm_state = AP_MPMQ_STOPPING;
            return 1;
        }
        /* fix the generation number in the global score; we just got a new,
         * cleared scoreboard
         */
        ap_scoreboard_image->global->running_generation = my_generation;
    }

    set_signals();
    /* Don't thrash... */
    if (max_spare_threads < min_spare_threads + threads_per_child)
        max_spare_threads = min_spare_threads + threads_per_child;

    /* If we're doing a graceful_restart then we're going to see a lot
     * of children exiting immediately when we get into the main loop
     * below (because we just sent them AP_SIG_GRACEFUL).  This happens pretty
     * rapidly... and for each one that exits we may start a new one, until
     * there are at least min_spare_threads idle threads, counting across
     * all children.  But we may be permitted to start more children than
     * that, so we'll just keep track of how many we're
     * supposed to start up without the 1 second penalty between each fork.
     */
    remaining_children_to_start = ap_daemons_to_start;
    if (remaining_children_to_start > ap_daemons_limit) {
        remaining_children_to_start = ap_daemons_limit;
    }
    if (!is_graceful) {
        startup_children(remaining_children_to_start);
        remaining_children_to_start = 0;
    }
    else {
        /* give the system some time to recover before kicking into
         * exponential mode */
        hold_off_on_exponential_spawning = 10;
    }

    ap_log_error(APLOG_MARK, APLOG_NOTICE, 0, ap_server_conf,
                 "%s configured -- resuming normal operations",
                 ap_get_server_description());
    ap_log_error(APLOG_MARK, APLOG_INFO, 0, ap_server_conf,
                 "Server built: %s", ap_get_server_built());

    restart_pending = shutdown_pending = 0;
    mpm_state = AP_MPMQ_RUNNING;

    server_main_loop(remaining_children_to_start);
    mpm_state = AP_MPMQ_STOPPING;

    if (shutdown_pending && !is_graceful) {
        /* Time to shut down:
         * Kill child processes, tell them to call child_exit, etc...
         */
        ap_event_pod_killpg(pod, ap_daemons_limit, FALSE);
        ap_reclaim_child_processes(1);  /* Start with SIGTERM */

        if (!child_fatal) {
            /* cleanup pid file on normal shutdown */
            const char *pidfile = NULL;
            pidfile = ap_server_root_relative(pconf, ap_pid_fname);
            if (pidfile != NULL && unlink(pidfile) == 0)
                ap_log_error(APLOG_MARK, APLOG_INFO, 0,
                             ap_server_conf,
                             "removed PID file %s (pid=%ld)",
                             pidfile, (long) getpid());

            ap_log_error(APLOG_MARK, APLOG_NOTICE, 0,
                         ap_server_conf, "caught SIGTERM, shutting down");
        }
        return 1;
    } else if (shutdown_pending) {
        /* Time to gracefully shut down:
         * Kill child processes, tell them to call child_exit, etc...
         */
        int active_children;
        int index;
        apr_time_t cutoff = 0;

        /* Close our listeners, and then ask our children to do same */
        ap_close_listeners();
        ap_event_pod_killpg(pod, ap_daemons_limit, TRUE);
        ap_relieve_child_processes();

        if (!child_fatal) {
            /* cleanup pid file on normal shutdown */
            const char *pidfile = NULL;
            pidfile = ap_server_root_relative (pconf, ap_pid_fname);
            if ( pidfile != NULL && unlink(pidfile) == 0)
                ap_log_error(APLOG_MARK, APLOG_INFO, 0,
                             ap_server_conf,
                             "removed PID file %s (pid=%ld)",
                             pidfile, (long)getpid());

            ap_log_error(APLOG_MARK, APLOG_NOTICE, 0, ap_server_conf,
                         "caught " AP_SIG_GRACEFUL_STOP_STRING
                         ", shutting down gracefully");
        }

        if (ap_graceful_shutdown_timeout) {
            cutoff = apr_time_now() +
                     apr_time_from_sec(ap_graceful_shutdown_timeout);
        }

        /* Don't really exit until each child has finished */
        shutdown_pending = 0;
        do {
            /* Pause for a second */
            apr_sleep(apr_time_from_sec(1));

            /* Relieve any children which have now exited */
            ap_relieve_child_processes();

            active_children = 0;
            for (index = 0; index < ap_daemons_limit; ++index) {
                if (ap_mpm_safe_kill(MPM_CHILD_PID(index), 0) == APR_SUCCESS) {
                    active_children = 1;
                    /* Having just one child is enough to stay around */
                    break;
                }
            }
        } while (!shutdown_pending && active_children &&
                 (!ap_graceful_shutdown_timeout || apr_time_now() < cutoff));

        /* We might be here because we received SIGTERM, either
         * way, try and make sure that all of our processes are
         * really dead.
         */
        ap_event_pod_killpg(pod, ap_daemons_limit, FALSE);
        ap_reclaim_child_processes(1);

        return 1;
    }

    /* we've been told to restart */
    apr_signal(SIGHUP, SIG_IGN);

    if (one_process) {
        /* not worth thinking about */
        return 1;
    }

    /* advance to the next generation */
    /* XXX: we really need to make sure this new generation number isn't in
     * use by any of the children.
     */
    ++my_generation;
    ap_scoreboard_image->global->running_generation = my_generation;

    if (is_graceful) {
        ap_log_error(APLOG_MARK, APLOG_NOTICE, 0, ap_server_conf,
                     AP_SIG_GRACEFUL_STRING
                     " received.  Doing graceful restart");
        /* wake up the children...time to die.  But we'll have more soon */
        ap_event_pod_killpg(pod, ap_daemons_limit, TRUE);


        /* This is mostly for debugging... so that we know what is still
         * gracefully dealing with existing request.
         */

    }
    else {
        /* Kill 'em all.  Since the child acts the same on the parents SIGTERM
         * and a SIGHUP, we may as well use the same signal, because some user
         * pthreads are stealing signals from us left and right.
         */
        ap_event_pod_killpg(pod, ap_daemons_limit, FALSE);

        ap_reclaim_child_processes(1);  /* Start with SIGTERM */
        ap_log_error(APLOG_MARK, APLOG_NOTICE, 0, ap_server_conf,
                     "SIGHUP received.  Attempting to restart");
    }

    return 0;
}

/* This really should be a post_config hook, but the error log is already
 * redirected by that point, so we need to do this in the open_logs phase.
 */
static int event_open_logs(apr_pool_t * p, apr_pool_t * plog,
                           apr_pool_t * ptemp, server_rec * s)
{
    int startup = 0;
    int level_flags = 0;
    apr_status_t rv;

    pconf = p;

    /* the reverse of pre_config, we want this only the first time around */
    if (retained->module_loads == 1) {
        startup = 1;
        level_flags |= APLOG_STARTUP;
    }

    if ((num_listensocks = ap_setup_listeners(ap_server_conf)) < 1) {
        ap_log_error(APLOG_MARK, APLOG_ALERT | level_flags, 0,
                     (startup ? NULL : s),
                     "no listening sockets available, shutting down");
        return DONE;
    }

    if (!one_process) {
        if ((rv = ap_event_pod_open(pconf, &pod))) {
            ap_log_error(APLOG_MARK, APLOG_CRIT | level_flags, rv,
                         (startup ? NULL : s),
                         "could not open pipe-of-death");
            return DONE;
        }
    }
    return OK;
}

static int event_pre_config(apr_pool_t * pconf, apr_pool_t * plog,
                            apr_pool_t * ptemp)
{
    int no_detach, debug, foreground;
    apr_status_t rv;
    const char *userdata_key = "mpm_event_module";

    mpm_state = AP_MPMQ_STARTING;

    debug = ap_exists_config_define("DEBUG");

    if (debug) {
        foreground = one_process = 1;
        no_detach = 0;
    }
    else {
        one_process = ap_exists_config_define("ONE_PROCESS");
        no_detach = ap_exists_config_define("NO_DETACH");
        foreground = ap_exists_config_define("FOREGROUND");
    }

    /* sigh, want this only the second time around */
    retained = ap_get_retained_data(userdata_key);
    if (!retained) {
        retained = ap_set_retained_data(userdata_key, sizeof(*retained));
    }
    ++retained->module_loads;
    if (retained->module_loads == 2) {
        is_graceful = 0;
        rv = apr_pollset_create(&event_pollset, 1, plog,
                                APR_POLLSET_THREADSAFE | APR_POLLSET_NOCOPY);
        if (rv != APR_SUCCESS) {
            ap_log_error(APLOG_MARK, APLOG_CRIT, rv, NULL,
                         "Couldn't create a Thread Safe Pollset. "
                         "Is it supported on your platform?");
            return HTTP_INTERNAL_SERVER_ERROR;
        }
        apr_pollset_destroy(event_pollset);

        if (!one_process && !foreground) {
            rv = apr_proc_detach(no_detach ? APR_PROC_DETACH_FOREGROUND
                                 : APR_PROC_DETACH_DAEMONIZE);
            if (rv != APR_SUCCESS) {
                ap_log_error(APLOG_MARK, APLOG_CRIT, rv, NULL,
                             "apr_proc_detach failed");
                return HTTP_INTERNAL_SERVER_ERROR;
            }
        }
        parent_pid = ap_my_pid = getpid();
    }

    ap_listen_pre_config();
    ap_daemons_to_start = DEFAULT_START_DAEMON;
    min_spare_threads = DEFAULT_MIN_FREE_DAEMON * DEFAULT_THREADS_PER_CHILD;
    max_spare_threads = DEFAULT_MAX_FREE_DAEMON * DEFAULT_THREADS_PER_CHILD;
    server_limit = DEFAULT_SERVER_LIMIT;
    thread_limit = DEFAULT_THREAD_LIMIT;
    ap_daemons_limit = server_limit;
    threads_per_child = DEFAULT_THREADS_PER_CHILD;
    max_clients = ap_daemons_limit * threads_per_child;
    ap_pid_fname = DEFAULT_PIDLOG;
    ap_lock_fname = DEFAULT_LOCKFILE;
    ap_max_requests_per_child = DEFAULT_MAX_REQUESTS_PER_CHILD;
    ap_extended_status = 0;
    ap_max_mem_free = APR_ALLOCATOR_MAX_FREE_UNLIMITED;

    apr_cpystrn(ap_coredump_dir, ap_server_root, sizeof(ap_coredump_dir));

    return OK;
}

static int event_check_config(apr_pool_t *p, apr_pool_t *plog,
                              apr_pool_t *ptemp, server_rec *s)
{
    int startup = 0;

    /* the reverse of pre_config, we want this only the first time around */
    if (retained->module_loads == 1) {
        startup = 1;
    }

    if (server_limit > MAX_SERVER_LIMIT) {
        if (startup) {
            ap_log_error(APLOG_MARK, APLOG_WARNING | APLOG_STARTUP, 0, NULL,
                         "WARNING: ServerLimit of %d exceeds compile-time "
                         "limit of", server_limit);
            ap_log_error(APLOG_MARK, APLOG_WARNING | APLOG_STARTUP, 0, NULL,
                         " %d servers, decreasing to %d.",
                         MAX_SERVER_LIMIT, MAX_SERVER_LIMIT);
        } else {
            ap_log_error(APLOG_MARK, APLOG_WARNING, 0, s,
                         "ServerLimit of %d exceeds compile-time limit "
                         "of %d, decreasing to match",
                         server_limit, MAX_SERVER_LIMIT);
        }
        server_limit = MAX_SERVER_LIMIT;
    }
    else if (server_limit < 1) {
        if (startup) {
            ap_log_error(APLOG_MARK, APLOG_WARNING | APLOG_STARTUP, 0, NULL,
                         "WARNING: ServerLimit of %d not allowed, "
                         "increasing to 1.", server_limit);
        } else {
            ap_log_error(APLOG_MARK, APLOG_WARNING, 0, s,
                         "ServerLimit of %d not allowed, increasing to 1",
                         server_limit);
        }
        server_limit = 1;
    }

    /* you cannot change ServerLimit across a restart; ignore
     * any such attempts
     */
    if (!retained->first_server_limit) {
        retained->first_server_limit = server_limit;
    }
    else if (server_limit != retained->first_server_limit) {
        /* don't need a startup console version here */
        ap_log_error(APLOG_MARK, APLOG_WARNING, 0, s,
                     "changing ServerLimit to %d from original value of %d "
                     "not allowed during restart",
                     server_limit, retained->first_server_limit);
        server_limit = retained->first_server_limit;
    }

    if (thread_limit > MAX_THREAD_LIMIT) {
        if (startup) {
            ap_log_error(APLOG_MARK, APLOG_WARNING | APLOG_STARTUP, 0, NULL,
                         "WARNING: ThreadLimit of %d exceeds compile-time "
                         "limit of", thread_limit);
            ap_log_error(APLOG_MARK, APLOG_WARNING | APLOG_STARTUP, 0, NULL,
                         " %d threads, decreasing to %d.",
                         MAX_THREAD_LIMIT, MAX_THREAD_LIMIT);
        } else {
            ap_log_error(APLOG_MARK, APLOG_WARNING, 0, s,
                         "ThreadLimit of %d exceeds compile-time limit "
                         "of %d, decreasing to match",
                         thread_limit, MAX_THREAD_LIMIT);
        }
        thread_limit = MAX_THREAD_LIMIT;
    }
    else if (thread_limit < 1) {
        if (startup) {
            ap_log_error(APLOG_MARK, APLOG_WARNING | APLOG_STARTUP, 0, NULL,
                         "WARNING: ThreadLimit of %d not allowed, "
                         "increasing to 1.", thread_limit);
        } else {
            ap_log_error(APLOG_MARK, APLOG_WARNING, 0, s,
                         "ThreadLimit of %d not allowed, increasing to 1",
                         thread_limit);
        }
        thread_limit = 1;
    }

    /* you cannot change ThreadLimit across a restart; ignore
     * any such attempts
     */
    if (!retained->first_thread_limit) {
        retained->first_thread_limit = thread_limit;
    }
    else if (thread_limit != retained->first_thread_limit) {
        /* don't need a startup console version here */
        ap_log_error(APLOG_MARK, APLOG_WARNING, 0, s,
                     "changing ThreadLimit to %d from original value of %d "
                     "not allowed during restart",
                     thread_limit, retained->first_thread_limit);
        thread_limit = retained->first_thread_limit;
    }

    if (threads_per_child > thread_limit) {
        if (startup) {
            ap_log_error(APLOG_MARK, APLOG_WARNING | APLOG_STARTUP, 0, NULL,
                         "WARNING: ThreadsPerChild of %d exceeds ThreadLimit "
                         "of", threads_per_child);
            ap_log_error(APLOG_MARK, APLOG_WARNING | APLOG_STARTUP, 0, NULL,
                         " %d threads, decreasing to %d.",
                         thread_limit, thread_limit);
            ap_log_error(APLOG_MARK, APLOG_WARNING | APLOG_STARTUP, 0, NULL,
                         " To increase, please see the ThreadLimit "
                         "directive.");
        } else {
            ap_log_error(APLOG_MARK, APLOG_WARNING, 0, s,
                         "ThreadsPerChild of %d exceeds ThreadLimit "
                         "of %d, decreasing to match",
                         threads_per_child, thread_limit);
        }
        threads_per_child = thread_limit;
    }
    else if (threads_per_child < 1) {
        if (startup) {
            ap_log_error(APLOG_MARK, APLOG_WARNING | APLOG_STARTUP, 0, NULL,
                         "WARNING: ThreadsPerChild of %d not allowed, "
                         "increasing to 1.", threads_per_child);
        } else {
            ap_log_error(APLOG_MARK, APLOG_WARNING, 0, s,
                         "ThreadsPerChild of %d not allowed, increasing to 1",
                         threads_per_child);
        }
        threads_per_child = 1;
    }

    if (max_clients < threads_per_child) {
        if (startup) {
            ap_log_error(APLOG_MARK, APLOG_WARNING | APLOG_STARTUP, 0, NULL,
                         "WARNING: MaxClients of %d is less than "
                         "ThreadsPerChild of", max_clients);
            ap_log_error(APLOG_MARK, APLOG_WARNING | APLOG_STARTUP, 0, NULL,
                         " %d, increasing to %d.  MaxClients must be at "
                         "least as large",
                         threads_per_child, threads_per_child);
            ap_log_error(APLOG_MARK, APLOG_WARNING | APLOG_STARTUP, 0, NULL,
                         " as the number of threads in a single server.");
        } else {
            ap_log_error(APLOG_MARK, APLOG_WARNING, 0, s,
                         "MaxClients of %d is less than ThreadsPerChild "
                         "of %d, increasing to match",
                         max_clients, threads_per_child);
        }
        max_clients = threads_per_child;
    }

    ap_daemons_limit = max_clients / threads_per_child;

    if (max_clients % threads_per_child) {
        int tmp_max_clients = ap_daemons_limit * threads_per_child;

        if (startup) {
            ap_log_error(APLOG_MARK, APLOG_WARNING | APLOG_STARTUP, 0, NULL,
                         "WARNING: MaxClients of %d is not an integer "
                         "multiple of", max_clients);
            ap_log_error(APLOG_MARK, APLOG_WARNING | APLOG_STARTUP, 0, NULL,
                         " ThreadsPerChild of %d, decreasing to nearest "
                         "multiple %d,", threads_per_child,
                         tmp_max_clients);
            ap_log_error(APLOG_MARK, APLOG_WARNING | APLOG_STARTUP, 0, NULL,
                         " for a maximum of %d servers.",
                         ap_daemons_limit);
        } else {
            ap_log_error(APLOG_MARK, APLOG_WARNING, 0, s,
                         "MaxClients of %d is not an integer multiple of "
                         "ThreadsPerChild of %d, decreasing to nearest "
                         "multiple %d", max_clients, threads_per_child,
                         tmp_max_clients);
        }
        max_clients = tmp_max_clients;
    }

    if (ap_daemons_limit > server_limit) {
        if (startup) {
            ap_log_error(APLOG_MARK, APLOG_WARNING | APLOG_STARTUP, 0, NULL,
                         "WARNING: MaxClients of %d would require %d "
                         "servers and ", max_clients, ap_daemons_limit);
            ap_log_error(APLOG_MARK, APLOG_WARNING | APLOG_STARTUP, 0, NULL,
                         " would exceed ServerLimit of %d, decreasing to %d.",
                         server_limit, server_limit * threads_per_child);
            ap_log_error(APLOG_MARK, APLOG_WARNING | APLOG_STARTUP, 0, NULL,
                         " To increase, please see the ServerLimit "
                         "directive.");
        } else {
            ap_log_error(APLOG_MARK, APLOG_WARNING, 0, s,
                         "MaxClients of %d would require %d servers and "
                         "exceed ServerLimit of %d, decreasing to %d",
                         max_clients, ap_daemons_limit, server_limit,
                         server_limit * threads_per_child);
        }
        ap_daemons_limit = server_limit;
    }

    /* ap_daemons_to_start > ap_daemons_limit checked in ap_mpm_run() */
    if (ap_daemons_to_start < 0) {
        if (startup) {
            ap_log_error(APLOG_MARK, APLOG_WARNING | APLOG_STARTUP, 0, NULL,
                         "WARNING: StartServers of %d not allowed, "
                         "increasing to 1.", ap_daemons_to_start);
        } else {
            ap_log_error(APLOG_MARK, APLOG_WARNING, 0, s,
                         "StartServers of %d not allowed, increasing to 1",
                         ap_daemons_to_start);
        }
        ap_daemons_to_start = 1;
    }

    if (min_spare_threads < 1) {
        if (startup) {
            ap_log_error(APLOG_MARK, APLOG_WARNING | APLOG_STARTUP, 0, NULL,
                         "WARNING: MinSpareThreads of %d not allowed, "
                         "increasing to 1", min_spare_threads);
            ap_log_error(APLOG_MARK, APLOG_WARNING | APLOG_STARTUP, 0, NULL,
                         " to avoid almost certain server failure.");
            ap_log_error(APLOG_MARK, APLOG_WARNING | APLOG_STARTUP, 0, NULL,
                         " Please read the documentation.");
        } else {
            ap_log_error(APLOG_MARK, APLOG_WARNING, 0, s,
                         "MinSpareThreads of %d not allowed, increasing to 1",
                         min_spare_threads);
        }
        min_spare_threads = 1;
    }

    /* max_spare_threads < min_spare_threads + threads_per_child
     * checked in ap_mpm_run()
     */

    return OK;
}

static void event_hooks(apr_pool_t * p)
{
    /* Our open_logs hook function must run before the core's, or stderr
     * will be redirected to a file, and the messages won't print to the
     * console.
     */
    static const char *const aszSucc[] = { "core.c", NULL };
    one_process = 0;

    ap_hook_open_logs(event_open_logs, NULL, aszSucc, APR_HOOK_REALLY_FIRST);
    /* we need to set the MPM state before other pre-config hooks use MPM query
     * to retrieve it, so register as REALLY_FIRST
     */
    ap_hook_pre_config(event_pre_config, NULL, NULL, APR_HOOK_REALLY_FIRST);
    ap_hook_check_config(event_check_config, NULL, NULL, APR_HOOK_MIDDLE);
    ap_hook_mpm(event_run, NULL, NULL, APR_HOOK_MIDDLE);
    ap_hook_mpm_query(event_query, NULL, NULL, APR_HOOK_MIDDLE);
    ap_hook_mpm_note_child_killed(event_note_child_killed, NULL, NULL, APR_HOOK_MIDDLE);
    ap_hook_mpm_register_timed_callback(event_register_timed_callback, NULL, NULL,
                                        APR_HOOK_MIDDLE);
    ap_hook_mpm_get_name(event_get_name, NULL, NULL, APR_HOOK_MIDDLE);
}

static const char *set_daemons_to_start(cmd_parms *cmd, void *dummy,
                                        const char *arg)
{
    const char *err = ap_check_cmd_context(cmd, GLOBAL_ONLY);
    if (err != NULL) {
        return err;
    }

    ap_daemons_to_start = atoi(arg);
    return NULL;
}

static const char *set_min_spare_threads(cmd_parms * cmd, void *dummy,
                                         const char *arg)
{
    const char *err = ap_check_cmd_context(cmd, GLOBAL_ONLY);
    if (err != NULL) {
        return err;
    }

    min_spare_threads = atoi(arg);
    return NULL;
}

static const char *set_max_spare_threads(cmd_parms * cmd, void *dummy,
                                         const char *arg)
{
    const char *err = ap_check_cmd_context(cmd, GLOBAL_ONLY);
    if (err != NULL) {
        return err;
    }

    max_spare_threads = atoi(arg);
    return NULL;
}

static const char *set_max_clients(cmd_parms * cmd, void *dummy,
                                   const char *arg)
{
    const char *err = ap_check_cmd_context(cmd, GLOBAL_ONLY);
    if (err != NULL) {
        return err;
    }

    max_clients = atoi(arg);
    return NULL;
}

static const char *set_threads_per_child(cmd_parms * cmd, void *dummy,
                                         const char *arg)
{
    const char *err = ap_check_cmd_context(cmd, GLOBAL_ONLY);
    if (err != NULL) {
        return err;
    }

    threads_per_child = atoi(arg);
    return NULL;
}
static const char *set_server_limit (cmd_parms *cmd, void *dummy, const char *arg)
{
    const char *err = ap_check_cmd_context(cmd, GLOBAL_ONLY);
    if (err != NULL) {
        return err;
    }

    server_limit = atoi(arg);
    return NULL;
}

static const char *set_thread_limit(cmd_parms * cmd, void *dummy,
                                    const char *arg)
{
    const char *err = ap_check_cmd_context(cmd, GLOBAL_ONLY);
    if (err != NULL) {
        return err;
    }

    thread_limit = atoi(arg);
    return NULL;
}

static const command_rec event_cmds[] = {
    LISTEN_COMMANDS,
    AP_INIT_TAKE1("StartServers", set_daemons_to_start, NULL, RSRC_CONF,
                  "Number of child processes launched at server startup"),
    AP_INIT_TAKE1("ServerLimit", set_server_limit, NULL, RSRC_CONF,
                  "Maximum number of child processes for this run of Apache"),
    AP_INIT_TAKE1("MinSpareThreads", set_min_spare_threads, NULL, RSRC_CONF,
                  "Minimum number of idle threads, to handle request spikes"),
    AP_INIT_TAKE1("MaxSpareThreads", set_max_spare_threads, NULL, RSRC_CONF,
                  "Maximum number of idle threads"),
    AP_INIT_TAKE1("MaxClients", set_max_clients, NULL, RSRC_CONF,
                  "Maximum number of threads alive at the same time"),
    AP_INIT_TAKE1("ThreadsPerChild", set_threads_per_child, NULL, RSRC_CONF,
                  "Number of threads each child creates"),
    AP_INIT_TAKE1("ThreadLimit", set_thread_limit, NULL, RSRC_CONF,
                  "Maximum number of worker threads per child process for this "
                  "run of Apache - Upper limit for ThreadsPerChild"),
    AP_GRACEFUL_SHUTDOWN_TIMEOUT_COMMAND,
    {NULL}
};

module AP_MODULE_DECLARE_DATA mpm_event_module = {
    MPM20_MODULE_STUFF,
    NULL,                       /* hook to run before apache parses args */
    NULL,                       /* create per-directory config structure */
    NULL,                       /* merge per-directory config structures */
    NULL,                       /* create per-server config structure */
    NULL,                       /* merge per-server config structures */
    event_cmds,                 /* command apr_table_t */
    event_hooks                 /* register_hooks */
};