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"
53 #include "http_core.h"
55 #include "http_protocol.h"
56 #include "util_mutex.h"
57 #include "ap_config.h"
59 #if APR_HAVE_SYS_TYPES_H
60 #include <sys/types.h>
66 #define HTML_HEADER "<html>\n<head>\n<title>Mod_example_IPC Status Page " \
67 "</title>\n</head>\n<body>\n<h1>Mod_example_IPC Status</h1>\n"
68 #define HTML_FOOTER "</body>\n</html>\n"
70 /* Number of microseconds to camp out on the mutex */
72 /* Maximum number of times we camp out before giving up */
74 /* Number of microseconds the handler sits on the lock once acquired. */
75 #define SLEEPYTIME 1000
77 apr_shm_t *exipc_shm; /* Pointer to shared memory block */
78 char *shmfilename; /* Shared memory file name, used on some systems */
79 apr_global_mutex_t *exipc_mutex; /* Lock around shared memory segment access */
80 static const char *exipc_mutex_type = "example-ipc-shm";
82 /* Data structure for shared memory block */
83 typedef struct exipc_data {
85 /* More fields if necessary */
89 * Clean up the shared memory block. This function is registered as
90 * cleanup function for the configuration pool, which gets called
91 * on restarts. It assures that the new children will not talk to a stale
92 * shared memory segment.
94 static apr_status_t shm_cleanup_wrapper(void *unused) {
96 return apr_shm_destroy(exipc_shm);
101 * This routine is called in the parent; we must register our
102 * mutex type before the config is processed so that users can
103 * adjust the mutex settings using the Mutex directive.
106 static int exipc_pre_config(apr_pool_t *pconf, apr_pool_t *plog,
109 ap_mutex_register(pconf, exipc_mutex_type, NULL, APR_LOCK_DEFAULT, 0);
114 * This routine is called in the parent, so we'll set up the shared
115 * memory segment and mutex here.
118 static int exipc_post_config(apr_pool_t *pconf, apr_pool_t *plog,
119 apr_pool_t *ptemp, server_rec *s)
127 * Do nothing if we are not creating the final configuration.
128 * The parent process gets initialized a couple of times as the
129 * server starts up, and we don't want to create any more mutexes
130 * and shared memory segments than we're actually going to use.
132 if (ap_state_query(AP_SQ_MAIN_STATE) == AP_SQ_MS_CREATE_PRE_CONFIG)
136 * The shared memory allocation routines take a file name.
137 * Depending on system-specific implementation of these
138 * routines, that file may or may not actually be created. We'd
139 * like to store those files in the operating system's designated
140 * temporary directory, which APR can point us to.
142 rs = apr_temp_dir_get(&tempdir, pconf);
143 if (APR_SUCCESS != rs) {
144 ap_log_error(APLOG_MARK, APLOG_ERR, rs, s,
145 "Failed to find temporary directory");
146 return HTTP_INTERNAL_SERVER_ERROR;
149 /* Create the shared memory segment */
152 * Create a unique filename using our pid. This information is
153 * stashed in the global variable so the children inherit it.
155 shmfilename = apr_psprintf(pconf, "%s/httpd_shm.%ld", tempdir,
158 /* Now create that segment */
159 rs = apr_shm_create(&exipc_shm, sizeof(exipc_data),
160 (const char *) shmfilename, pconf);
161 if (APR_SUCCESS != rs) {
162 ap_log_error(APLOG_MARK, APLOG_ERR, rs, s,
163 "Failed to create shared memory segment on file %s",
165 return HTTP_INTERNAL_SERVER_ERROR;
168 /* Created it, now let's zero it out */
169 base = (exipc_data *)apr_shm_baseaddr_get(exipc_shm);
172 /* Create global mutex */
174 rs = ap_global_mutex_create(&exipc_mutex, NULL, exipc_mutex_type, NULL,
176 if (APR_SUCCESS != rs) {
177 return HTTP_INTERNAL_SERVER_ERROR;
181 * Destroy the shm segment when the configuration pool gets destroyed. This
182 * happens on server restarts. The parent will then (above) allocate a new
183 * shm segment that the new children will bind to.
185 apr_pool_cleanup_register(pconf, NULL, shm_cleanup_wrapper,
186 apr_pool_cleanup_null);
191 * This routine gets called when a child inits. We use it to attach
192 * to the shared memory segment, and reinitialize the mutex.
195 static void exipc_child_init(apr_pool_t *p, server_rec *s)
200 * Re-open the mutex for the child. Note we're reusing
201 * the mutex pointer global here.
203 rs = apr_global_mutex_child_init(&exipc_mutex,
204 apr_global_mutex_lockfile(exipc_mutex),
206 if (APR_SUCCESS != rs) {
207 ap_log_error(APLOG_MARK, APLOG_CRIT, rs, s,
208 "Failed to reopen mutex %s in child",
210 /* There's really nothing else we can do here, since This
211 * routine doesn't return a status. If this ever goes wrong,
212 * it will turn Apache into a fork bomb. Let's hope it never
215 exit(1); /* Ugly, but what else? */
219 /* The sample content handler */
220 static int exipc_handler(request_rec *r)
224 apr_time_t startcamp;
225 apr_int64_t timecamped;
229 if (strcmp(r->handler, "example_ipc")) {
234 * The main function of the handler, aside from sending the
235 * status page to the client, is to increment the counter in
236 * the shared memory segment. This action needs to be mutexed
237 * out using the global mutex.
241 * First, acquire the lock. This code is a lot more involved than
242 * it usually needs to be, because the process based trylock
243 * routine is not implemented on unix platforms. I left it in to
244 * show how it would work if trylock worked, and for situations
245 * and platforms where trylock works.
247 for (camped = 0, timecamped = 0; camped < MAXCAMP; camped++) {
248 rs = apr_global_mutex_trylock(exipc_mutex);
249 if (APR_STATUS_IS_EBUSY(rs)) {
251 } else if (APR_SUCCESS == rs) {
253 break; /* Get out of the loop */
254 } else if (APR_STATUS_IS_ENOTIMPL(rs)) {
255 /* If it's not implemented, just hang in the mutex. */
256 startcamp = apr_time_now();
257 rs = apr_global_mutex_lock(exipc_mutex);
258 timecamped = (apr_int64_t) (apr_time_now() - startcamp);
259 if (APR_SUCCESS == rs) {
261 break; /* Out of the loop */
263 /* Some error, log and bail */
264 ap_log_error(APLOG_MARK, APLOG_ERR, rs, r->server,
265 "Child %ld failed to acquire lock",
267 break; /* Out of the loop without having the lock */
270 /* Some other error, log and bail */
271 ap_log_error(APLOG_MARK, APLOG_ERR, rs, r->server,
272 "Child %ld failed to try and acquire lock",
274 break; /* Out of the loop without having the lock */
278 * The only way to get to this point is if the trylock worked
279 * and returned BUSY. So, bump the time and try again
281 timecamped += CAMPOUT;
282 ap_log_error(APLOG_MARK, APLOG_NOTICE, 0, r->server,
283 "Child %ld camping out on mutex for %" APR_INT64_T_FMT
285 (long int) getpid(), timecamped);
286 } /* Lock acquisition loop */
288 /* Sleep for a millisecond to make it a little harder for
289 * httpd children to acquire the lock.
291 apr_sleep(SLEEPYTIME);
293 r->content_type = "text/html";
295 if (!r->header_only) {
296 ap_rputs(HTML_HEADER, r);
298 /* Increment the counter */
299 base = (exipc_data *)apr_shm_baseaddr_get(exipc_shm);
301 /* Send a page with our pid and the new value of the counter. */
302 ap_rprintf(r, "<p>Lock acquired after %ld microseoncds.</p>\n",
303 (long int) timecamped);
304 ap_rputs("<table border=\"1\">\n", r);
305 ap_rprintf(r, "<tr><td>Child pid:</td><td>%d</td></tr>\n",
307 ap_rprintf(r, "<tr><td>Counter:</td><td>%u</td></tr>\n",
308 (unsigned int)base->counter);
309 ap_rputs("</table>\n", r);
312 * Send a page saying that we couldn't get the lock. Don't say
313 * what the counter is, because without the lock the value could
316 ap_rprintf(r, "<p>Child %d failed to acquire lock "
317 "after camping out for %d microseconds.</p>\n",
318 (int) getpid(), (int) timecamped);
320 ap_rputs(HTML_FOOTER, r);
321 } /* r->header_only */
323 /* Release the lock */
325 rs = apr_global_mutex_unlock(exipc_mutex);
326 /* Swallowing the result because what are we going to do with it at
333 static void exipc_register_hooks(apr_pool_t *p)
335 ap_hook_pre_config(exipc_pre_config, NULL, NULL, APR_HOOK_MIDDLE);
336 ap_hook_post_config(exipc_post_config, NULL, NULL, APR_HOOK_MIDDLE);
337 ap_hook_child_init(exipc_child_init, NULL, NULL, APR_HOOK_MIDDLE);
338 ap_hook_handler(exipc_handler, NULL, NULL, APR_HOOK_MIDDLE);
341 /* Dispatch list for API hooks */
342 AP_DECLARE_MODULE(example_ipc) = {
343 STANDARD20_MODULE_STUFF,
344 NULL, /* create per-dir config structures */
345 NULL, /* merge per-dir config structures */
346 NULL, /* create per-server config structures */
347 NULL, /* merge per-server config structures */
348 NULL, /* table of config file commands */
349 exipc_register_hooks /* register hooks */