1 /* Licensed to the Apache Software Foundation (ASF) under one or more
2 * contributor license agreements. See the NOTICE file distributed with
3 * this work for additional information regarding copyright ownership.
4 * The ASF licenses this file to You under the Apache License, Version 2.0
5 * (the "License"); you may not use this file except in compliance with
6 * the License. You may obtain a copy of the License at
8 * http://www.apache.org/licenses/LICENSE-2.0
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
18 * mod_example_ipc -- Apache sample module
20 * This module illustrates the use in an Apache 2.x module of the Interprocess
21 * Communications routines that come with APR. It is example code, and not meant
22 * to be used in a production server.
24 * To play with this sample module first compile it into a DSO file and install
25 * it into Apache's modules directory by running:
27 * $ /path/to/apache2/bin/apxs -c -i mod_example_ipc.c
29 * Then activate it in Apache's httpd.conf file for instance for the URL
30 * /example_ipc in as follows:
33 * LoadModule example_ipc_module modules/mod_example_ipc.so
34 * <Location /example_ipc>
35 * SetHandler example_ipc
38 * Then restart Apache via
40 * $ /path/to/apache2/bin/apachectl restart
42 * The module allocates a counter in shared memory, which is incremented by the
43 * request handler under a mutex. After installation, activate the handler by
44 * hitting the URL configured above with ab at various concurrency levels to see
45 * how mutex contention affects server performance.
49 #include "apr_strings.h"
52 #include "http_config.h"
54 #include "http_protocol.h"
55 #include "util_mutex.h"
56 #include "ap_config.h"
58 #if APR_HAVE_SYS_TYPES_H
59 #include <sys/types.h>
65 #define HTML_HEADER "<html>\n<head>\n<title>Mod_example_IPC Status Page " \
66 "</title>\n</head>\n<body>\n<h1>Mod_example_IPC Status</h1>\n"
67 #define HTML_FOOTER "</body>\n</html>\n"
69 /* Number of microseconds to camp out on the mutex */
71 /* Maximum number of times we camp out before giving up */
73 /* Number of microseconds the handler sits on the lock once acquired. */
74 #define SLEEPYTIME 1000
76 apr_shm_t *exipc_shm; /* Pointer to shared memory block */
77 char *shmfilename; /* Shared memory file name, used on some systems */
78 apr_global_mutex_t *exipc_mutex; /* Lock around shared memory segment access */
79 static const char *exipc_mutex_type = "example-ipc-shm";
81 /* Data structure for shared memory block */
82 typedef struct exipc_data {
84 /* More fields if necessary */
88 * Clean up the shared memory block. This function is registered as
89 * cleanup function for the configuration pool, which gets called
90 * on restarts. It assures that the new children will not talk to a stale
91 * shared memory segment.
93 static apr_status_t shm_cleanup_wrapper(void *unused) {
95 return apr_shm_destroy(exipc_shm);
100 * This routine is called in the parent; we must register our
101 * mutex type before the config is processed so that users can
102 * adjust the mutex settings using the Mutex directive.
105 static int exipc_pre_config(apr_pool_t *pconf, apr_pool_t *plog,
108 ap_mutex_register(pconf, exipc_mutex_type, NULL, APR_LOCK_DEFAULT, 0);
113 * This routine is called in the parent, so we'll set up the shared
114 * memory segment and mutex here.
117 static int exipc_post_config(apr_pool_t *pconf, apr_pool_t *plog,
118 apr_pool_t *ptemp, server_rec *s)
120 void *data; /* These two help ensure that we only init once. */
121 const char *userdata_key;
128 * The following checks if this routine has been called before.
129 * This is necessary because the parent process gets initialized
130 * a couple of times as the server starts up, and we don't want
131 * to create any more mutexes and shared memory segments than
132 * we're actually going to use.
134 * The key needs to be unique for the entire web server, so put
135 * the module name in it.
137 userdata_key = "example_ipc_init_module";
138 apr_pool_userdata_get(&data, userdata_key, s->process->pool);
141 * If no data was found for our key, this must be the first
142 * time the module is initialized. Put some data under that
145 apr_pool_userdata_set((const void *) 1, userdata_key,
146 apr_pool_cleanup_null, s->process->pool);
148 } /* Kilroy was here */
151 * The shared memory allocation routines take a file name.
152 * Depending on system-specific implementation of these
153 * routines, that file may or may not actually be created. We'd
154 * like to store those files in the operating system's designated
155 * temporary directory, which APR can point us to.
157 rs = apr_temp_dir_get(&tempdir, pconf);
158 if (APR_SUCCESS != rs) {
159 ap_log_error(APLOG_MARK, APLOG_ERR, rs, s,
160 "Failed to find temporary directory");
161 return HTTP_INTERNAL_SERVER_ERROR;
164 /* Create the shared memory segment */
167 * Create a unique filename using our pid. This information is
168 * stashed in the global variable so the children inherit it.
170 shmfilename = apr_psprintf(pconf, "%s/httpd_shm.%ld", tempdir,
173 /* Now create that segment */
174 rs = apr_shm_create(&exipc_shm, sizeof(exipc_data),
175 (const char *) shmfilename, pconf);
176 if (APR_SUCCESS != rs) {
177 ap_log_error(APLOG_MARK, APLOG_ERR, rs, s,
178 "Failed to create shared memory segment on file %s",
180 return HTTP_INTERNAL_SERVER_ERROR;
183 /* Created it, now let's zero it out */
184 base = (exipc_data *)apr_shm_baseaddr_get(exipc_shm);
187 /* Create global mutex */
189 rs = ap_global_mutex_create(&exipc_mutex, NULL, exipc_mutex_type, NULL,
191 if (APR_SUCCESS != rs) {
192 return HTTP_INTERNAL_SERVER_ERROR;
196 * Destroy the shm segment when the configuration pool gets destroyed. This
197 * happens on server restarts. The parent will then (above) allocate a new
198 * shm segment that the new children will bind to.
200 apr_pool_cleanup_register(pconf, NULL, shm_cleanup_wrapper,
201 apr_pool_cleanup_null);
206 * This routine gets called when a child inits. We use it to attach
207 * to the shared memory segment, and reinitialize the mutex.
210 static void exipc_child_init(apr_pool_t *p, server_rec *s)
215 * Re-open the mutex for the child. Note we're reusing
216 * the mutex pointer global here.
218 rs = apr_global_mutex_child_init(&exipc_mutex,
219 apr_global_mutex_lockfile(exipc_mutex),
221 if (APR_SUCCESS != rs) {
222 ap_log_error(APLOG_MARK, APLOG_CRIT, rs, s,
223 "Failed to reopen mutex %s in child",
225 /* There's really nothing else we can do here, since This
226 * routine doesn't return a status. If this ever goes wrong,
227 * it will turn Apache into a fork bomb. Let's hope it never
230 exit(1); /* Ugly, but what else? */
234 /* The sample content handler */
235 static int exipc_handler(request_rec *r)
239 apr_time_t startcamp;
240 apr_int64_t timecamped;
244 if (strcmp(r->handler, "example_ipc")) {
249 * The main function of the handler, aside from sending the
250 * status page to the client, is to increment the counter in
251 * the shared memory segment. This action needs to be mutexed
252 * out using the global mutex.
256 * First, acquire the lock. This code is a lot more involved than
257 * it usually needs to be, because the process based trylock
258 * routine is not implemented on unix platforms. I left it in to
259 * show how it would work if trylock worked, and for situations
260 * and platforms where trylock works.
262 for (camped = 0, timecamped = 0; camped < MAXCAMP; camped++) {
263 rs = apr_global_mutex_trylock(exipc_mutex);
264 if (APR_STATUS_IS_EBUSY(rs)) {
266 } else if (APR_SUCCESS == rs) {
268 break; /* Get out of the loop */
269 } else if (APR_STATUS_IS_ENOTIMPL(rs)) {
270 /* If it's not implemented, just hang in the mutex. */
271 startcamp = apr_time_now();
272 rs = apr_global_mutex_lock(exipc_mutex);
273 timecamped = (apr_int64_t) (apr_time_now() - startcamp);
274 if (APR_SUCCESS == rs) {
276 break; /* Out of the loop */
278 /* Some error, log and bail */
279 ap_log_error(APLOG_MARK, APLOG_ERR, rs, r->server,
280 "Child %ld failed to acquire lock",
282 break; /* Out of the loop without having the lock */
285 /* Some other error, log and bail */
286 ap_log_error(APLOG_MARK, APLOG_ERR, rs, r->server,
287 "Child %ld failed to try and acquire lock",
289 break; /* Out of the loop without having the lock */
293 * The only way to get to this point is if the trylock worked
294 * and returned BUSY. So, bump the time and try again
296 timecamped += CAMPOUT;
297 ap_log_error(APLOG_MARK, APLOG_NOERRNO | APLOG_NOTICE,
298 0, r->server, "Child %ld camping out on mutex for %" APR_INT64_T_FMT
300 (long int) getpid(), timecamped);
301 } /* Lock acquisition loop */
303 /* Sleep for a millisecond to make it a little harder for
304 * httpd children to acquire the lock.
306 apr_sleep(SLEEPYTIME);
308 r->content_type = "text/html";
310 if (!r->header_only) {
311 ap_rputs(HTML_HEADER, r);
313 /* Increment the counter */
314 base = (exipc_data *)apr_shm_baseaddr_get(exipc_shm);
316 /* Send a page with our pid and the new value of the counter. */
317 ap_rprintf(r, "<p>Lock acquired after %ld microseoncds.</p>\n",
318 (long int) timecamped);
319 ap_rputs("<table border=\"1\">\n", r);
320 ap_rprintf(r, "<tr><td>Child pid:</td><td>%d</td></tr>\n",
322 ap_rprintf(r, "<tr><td>Counter:</td><td>%u</td></tr>\n",
323 (unsigned int)base->counter);
324 ap_rputs("</table>\n", r);
327 * Send a page saying that we couldn't get the lock. Don't say
328 * what the counter is, because without the lock the value could
331 ap_rprintf(r, "<p>Child %d failed to acquire lock "
332 "after camping out for %d microseconds.</p>\n",
333 (int) getpid(), (int) timecamped);
335 ap_rputs(HTML_FOOTER, r);
336 } /* r->header_only */
338 /* Release the lock */
340 rs = apr_global_mutex_unlock(exipc_mutex);
341 /* Swallowing the result because what are we going to do with it at
348 static void exipc_register_hooks(apr_pool_t *p)
350 ap_hook_pre_config(exipc_pre_config, NULL, NULL, APR_HOOK_MIDDLE);
351 ap_hook_post_config(exipc_post_config, NULL, NULL, APR_HOOK_MIDDLE);
352 ap_hook_child_init(exipc_child_init, NULL, NULL, APR_HOOK_MIDDLE);
353 ap_hook_handler(exipc_handler, NULL, NULL, APR_HOOK_MIDDLE);
356 /* Dispatch list for API hooks */
357 AP_DECLARE_MODULE(example_ipc) = {
358 STANDARD20_MODULE_STUFF,
359 NULL, /* create per-dir config structures */
360 NULL, /* merge per-dir config structures */
361 NULL, /* create per-server config structures */
362 NULL, /* merge per-server config structures */
363 NULL, /* table of config file commands */
364 exipc_register_hooks /* register hooks */