Update copyright for 2016

[postgresql] / src / backend / storage / ipc / ipc.c

/*-------------------------------------------------------------------------
 *
 * ipc.c
 *        POSTGRES inter-process communication definitions.
 *
 * This file is misnamed, as it no longer has much of anything directly
 * to do with IPC.  The functionality here is concerned with managing
 * exit-time cleanup for either a postmaster or a backend.
 *
 *
 * Portions Copyright (c) 1996-2016, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *        src/backend/storage/ipc/ipc.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include <signal.h>
#include <unistd.h>
#include <sys/stat.h>

#include "miscadmin.h"
#ifdef PROFILE_PID_DIR
#include "postmaster/autovacuum.h"
#endif
#include "storage/dsm.h"
#include "storage/ipc.h"
#include "tcop/tcopprot.h"


/*
 * This flag is set during proc_exit() to change ereport()'s behavior,
 * so that an ereport() from an on_proc_exit routine cannot get us out
 * of the exit procedure.  We do NOT want to go back to the idle loop...
 */
bool            proc_exit_inprogress = false;

/*
 * This flag tracks whether we've called atexit() in the current process
 * (or in the parent postmaster).
 */
static bool atexit_callback_setup = false;

/* local functions */
static void proc_exit_prepare(int code);


/* ----------------------------------------------------------------
 *                                              exit() handling stuff
 *
 * These functions are in generally the same spirit as atexit(),
 * but provide some additional features we need --- in particular,
 * we want to register callbacks to invoke when we are disconnecting
 * from a broken shared-memory context but not exiting the postmaster.
 *
 * Callback functions can take zero, one, or two args: the first passed
 * arg is the integer exitcode, the second is the Datum supplied when
 * the callback was registered.
 * ----------------------------------------------------------------
 */

#define MAX_ON_EXITS 20

struct ONEXIT
{
        pg_on_exit_callback function;
        Datum           arg;
};

static struct ONEXIT on_proc_exit_list[MAX_ON_EXITS];
static struct ONEXIT on_shmem_exit_list[MAX_ON_EXITS];
static struct ONEXIT before_shmem_exit_list[MAX_ON_EXITS];

static int      on_proc_exit_index,
                        on_shmem_exit_index,
                        before_shmem_exit_index;


/* ----------------------------------------------------------------
 *              proc_exit
 *
 *              this function calls all the callbacks registered
 *              for it (to free resources) and then calls exit.
 *
 *              This should be the only function to call exit().
 *              -cim 2/6/90
 *
 *              Unfortunately, we can't really guarantee that add-on code
 *              obeys the rule of not calling exit() directly.  So, while
 *              this is the preferred way out of the system, we also register
 *              an atexit callback that will make sure cleanup happens.
 * ----------------------------------------------------------------
 */
void
proc_exit(int code)
{
        /* Clean up everything that must be cleaned up */
        proc_exit_prepare(code);

#ifdef PROFILE_PID_DIR
        {
                /*
                 * If we are profiling ourself then gprof's mcleanup() is about to
                 * write out a profile to ./gmon.out.  Since mcleanup() always uses a
                 * fixed file name, each backend will overwrite earlier profiles. To
                 * fix that, we create a separate subdirectory for each backend
                 * (./gprof/pid) and 'cd' to that subdirectory before we exit() - that
                 * forces mcleanup() to write each profile into its own directory.  We
                 * end up with something like: $PGDATA/gprof/8829/gmon.out
                 * $PGDATA/gprof/8845/gmon.out ...
                 *
                 * To avoid undesirable disk space bloat, autovacuum workers are
                 * discriminated against: all their gmon.out files go into the same
                 * subdirectory.  Without this, an installation that is "just sitting
                 * there" nonetheless eats megabytes of disk space every few seconds.
                 *
                 * Note that we do this here instead of in an on_proc_exit() callback
                 * because we want to ensure that this code executes last - we don't
                 * want to interfere with any other on_proc_exit() callback.  For the
                 * same reason, we do not include it in proc_exit_prepare ... so if
                 * you are exiting in the "wrong way" you won't drop your profile in a
                 * nice place.
                 */
                char            gprofDirName[32];

                if (IsAutoVacuumWorkerProcess())
                        snprintf(gprofDirName, 32, "gprof/avworker");
                else
                        snprintf(gprofDirName, 32, "gprof/%d", (int) getpid());

                mkdir("gprof", S_IRWXU | S_IRWXG | S_IRWXO);
                mkdir(gprofDirName, S_IRWXU | S_IRWXG | S_IRWXO);
                chdir(gprofDirName);
        }
#endif

        elog(DEBUG3, "exit(%d)", code);

        exit(code);
}

/*
 * Code shared between proc_exit and the atexit handler.  Note that in
 * normal exit through proc_exit, this will actually be called twice ...
 * but the second call will have nothing to do.
 */
static void
proc_exit_prepare(int code)
{
        /*
         * Once we set this flag, we are committed to exit.  Any ereport() will
         * NOT send control back to the main loop, but right back here.
         */
        proc_exit_inprogress = true;

        /*
         * Forget any pending cancel or die requests; we're doing our best to
         * close up shop already.  Note that the signal handlers will not set
         * these flags again, now that proc_exit_inprogress is set.
         */
        InterruptPending = false;
        ProcDiePending = false;
        QueryCancelPending = false;
        InterruptHoldoffCount = 1;
        CritSectionCount = 0;

        /*
         * Also clear the error context stack, to prevent error callbacks from
         * being invoked by any elog/ereport calls made during proc_exit. Whatever
         * context they might want to offer is probably not relevant, and in any
         * case they are likely to fail outright after we've done things like
         * aborting any open transaction.  (In normal exit scenarios the context
         * stack should be empty anyway, but it might not be in the case of
         * elog(FATAL) for example.)
         */
        error_context_stack = NULL;
        /* For the same reason, reset debug_query_string before it's clobbered */
        debug_query_string = NULL;

        /* do our shared memory exits first */
        shmem_exit(code);

        elog(DEBUG3, "proc_exit(%d): %d callbacks to make",
                 code, on_proc_exit_index);

        /*
         * call all the registered callbacks.
         *
         * Note that since we decrement on_proc_exit_index each time, if a
         * callback calls ereport(ERROR) or ereport(FATAL) then it won't be
         * invoked again when control comes back here (nor will the
         * previously-completed callbacks).  So, an infinite loop should not be
         * possible.
         */
        while (--on_proc_exit_index >= 0)
                (*on_proc_exit_list[on_proc_exit_index].function) (code,
                                                                  on_proc_exit_list[on_proc_exit_index].arg);

        on_proc_exit_index = 0;
}

/* ------------------
 * Run all of the on_shmem_exit routines --- but don't actually exit.
 * This is used by the postmaster to re-initialize shared memory and
 * semaphores after a backend dies horribly.  As with proc_exit(), we
 * remove each callback from the list before calling it, to avoid
 * infinite loop in case of error.
 * ------------------
 */
void
shmem_exit(int code)
{
        /*
         * Call before_shmem_exit callbacks.
         *
         * These should be things that need most of the system to still be up and
         * working, such as cleanup of temp relations, which requires catalog
         * access; or things that need to be completed because later cleanup steps
         * depend on them, such as releasing lwlocks.
         */
        elog(DEBUG3, "shmem_exit(%d): %d before_shmem_exit callbacks to make",
                 code, before_shmem_exit_index);
        while (--before_shmem_exit_index >= 0)
                (*before_shmem_exit_list[before_shmem_exit_index].function) (code,
                                                before_shmem_exit_list[before_shmem_exit_index].arg);
        before_shmem_exit_index = 0;

        /*
         * Call dynamic shared memory callbacks.
         *
         * These serve the same purpose as late callbacks, but for dynamic shared
         * memory segments rather than the main shared memory segment.
         * dsm_backend_shutdown() has the same kind of progressive logic we use
         * for the main shared memory segment; namely, it unregisters each
         * callback before invoking it, so that we don't get stuck in an infinite
         * loop if one of those callbacks itself throws an ERROR or FATAL.
         *
         * Note that explicitly calling this function here is quite different from
         * registering it as an on_shmem_exit callback for precisely this reason:
         * if one dynamic shared memory callback errors out, the remaining
         * callbacks will still be invoked.  Thus, hard-coding this call puts it
         * equal footing with callbacks for the main shared memory segment.
         */
        dsm_backend_shutdown();

        /*
         * Call on_shmem_exit callbacks.
         *
         * These are generally releasing low-level shared memory resources.  In
         * some cases, this is a backstop against the possibility that the early
         * callbacks might themselves fail, leading to re-entry to this routine;
         * in other cases, it's cleanup that only happens at process exit.
         */
        elog(DEBUG3, "shmem_exit(%d): %d on_shmem_exit callbacks to make",
                 code, on_shmem_exit_index);
        while (--on_shmem_exit_index >= 0)
                (*on_shmem_exit_list[on_shmem_exit_index].function) (code,
                                                                on_shmem_exit_list[on_shmem_exit_index].arg);
        on_shmem_exit_index = 0;
}

/* ----------------------------------------------------------------
 *              atexit_callback
 *
 *              Backstop to ensure that direct calls of exit() don't mess us up.
 *
 * Somebody who was being really uncooperative could call _exit(),
 * but for that case we have a "dead man switch" that will make the
 * postmaster treat it as a crash --- see pmsignal.c.
 * ----------------------------------------------------------------
 */
static void
atexit_callback(void)
{
        /* Clean up everything that must be cleaned up */
        /* ... too bad we don't know the real exit code ... */
        proc_exit_prepare(-1);
}

/* ----------------------------------------------------------------
 *              on_proc_exit
 *
 *              this function adds a callback function to the list of
 *              functions invoked by proc_exit().   -cim 2/6/90
 * ----------------------------------------------------------------
 */
void
on_proc_exit(pg_on_exit_callback function, Datum arg)
{
        if (on_proc_exit_index >= MAX_ON_EXITS)
                ereport(FATAL,
                                (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
                                 errmsg_internal("out of on_proc_exit slots")));

        on_proc_exit_list[on_proc_exit_index].function = function;
        on_proc_exit_list[on_proc_exit_index].arg = arg;

        ++on_proc_exit_index;

        if (!atexit_callback_setup)
        {
                atexit(atexit_callback);
                atexit_callback_setup = true;
        }
}

/* ----------------------------------------------------------------
 *              before_shmem_exit
 *
 *              Register early callback to perform user-level cleanup,
 *              e.g. transaction abort, before we begin shutting down
 *              low-level subsystems.
 * ----------------------------------------------------------------
 */
void
before_shmem_exit(pg_on_exit_callback function, Datum arg)
{
        if (before_shmem_exit_index >= MAX_ON_EXITS)
                ereport(FATAL,
                                (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
                                 errmsg_internal("out of before_shmem_exit slots")));

        before_shmem_exit_list[before_shmem_exit_index].function = function;
        before_shmem_exit_list[before_shmem_exit_index].arg = arg;

        ++before_shmem_exit_index;

        if (!atexit_callback_setup)
        {
                atexit(atexit_callback);
                atexit_callback_setup = true;
        }
}

/* ----------------------------------------------------------------
 *              on_shmem_exit
 *
 *              Register ordinary callback to perform low-level shutdown
 *              (e.g. releasing our PGPROC); run after before_shmem_exit
 *              callbacks and before on_proc_exit callbacks.
 * ----------------------------------------------------------------
 */
void
on_shmem_exit(pg_on_exit_callback function, Datum arg)
{
        if (on_shmem_exit_index >= MAX_ON_EXITS)
                ereport(FATAL,
                                (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
                                 errmsg_internal("out of on_shmem_exit slots")));

        on_shmem_exit_list[on_shmem_exit_index].function = function;
        on_shmem_exit_list[on_shmem_exit_index].arg = arg;

        ++on_shmem_exit_index;

        if (!atexit_callback_setup)
        {
                atexit(atexit_callback);
                atexit_callback_setup = true;
        }
}

/* ----------------------------------------------------------------
 *              cancel_before_shmem_exit
 *
 *              this function removes a previously-registed before_shmem_exit
 *              callback.  For simplicity, only the latest entry can be
 *              removed.  (We could work harder but there is no need for
 *              current uses.)
 * ----------------------------------------------------------------
 */
void
cancel_before_shmem_exit(pg_on_exit_callback function, Datum arg)
{
        if (before_shmem_exit_index > 0 &&
                before_shmem_exit_list[before_shmem_exit_index - 1].function
                == function &&
                before_shmem_exit_list[before_shmem_exit_index - 1].arg == arg)
                --before_shmem_exit_index;
}

/* ----------------------------------------------------------------
 *              on_exit_reset
 *
 *              this function clears all on_proc_exit() and on_shmem_exit()
 *              registered functions.  This is used just after forking a backend,
 *              so that the backend doesn't believe it should call the postmaster's
 *              on-exit routines when it exits...
 * ----------------------------------------------------------------
 */
void
on_exit_reset(void)
{
        before_shmem_exit_index = 0;
        on_shmem_exit_index = 0;
        on_proc_exit_index = 0;
        reset_on_dsm_detach();
}