| /* 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. |
| */ |
| |
| /* |
| * mod_example_ipc -- Apache sample module |
| * |
| * This module illustrates the use in an Apache 2.x module of the Interprocess |
| * Communications routines that come with APR. It is example code, and not meant |
| * to be used in a production server. |
| * |
| * To play with this sample module first compile it into a DSO file and install |
| * it into Apache's modules directory by running: |
| * |
| * $ /path/to/apache2/bin/apxs -c -i mod_example_ipc.c |
| * |
| * Then activate it in Apache's httpd.conf file for instance for the URL |
| * /example_ipc in as follows: |
| * |
| * # httpd.conf |
| * LoadModule example_ipc_module modules/mod_example_ipc.so |
| * <Location /example_ipc> |
| * SetHandler example_ipc |
| * </Location> |
| * |
| * Then restart Apache via |
| * |
| * $ /path/to/apache2/bin/apachectl restart |
| * |
| * The module allocates a counter in shared memory, which is incremented by the |
| * request handler under a mutex. After installation, activate the handler by |
| * hitting the URL configured above with ab at various concurrency levels to see |
| * how mutex contention affects server performance. |
| */ |
| |
| #include "apr.h" |
| #include "apr_strings.h" |
| |
| #include "httpd.h" |
| #include "http_config.h" |
| #include "http_core.h" |
| #include "http_log.h" |
| #include "http_protocol.h" |
| #include "util_mutex.h" |
| #include "ap_config.h" |
| |
| #if APR_HAVE_SYS_TYPES_H |
| #include <sys/types.h> |
| #endif |
| #if APR_HAVE_UNISTD_H |
| #include <unistd.h> |
| #endif |
| |
| #define HTML_HEADER "<html>\n<head>\n<title>Mod_example_IPC Status Page " \ |
| "</title>\n</head>\n<body>\n<h1>Mod_example_IPC Status</h1>\n" |
| #define HTML_FOOTER "</body>\n</html>\n" |
| |
| /* Number of microseconds to camp out on the mutex */ |
| #define CAMPOUT 10 |
| /* Maximum number of times we camp out before giving up */ |
| #define MAXCAMP 10 |
| /* Number of microseconds the handler sits on the lock once acquired. */ |
| #define SLEEPYTIME 1000 |
| |
| apr_shm_t *exipc_shm; /* Pointer to shared memory block */ |
| char *shmfilename; /* Shared memory file name, used on some systems */ |
| apr_global_mutex_t *exipc_mutex; /* Lock around shared memory segment access */ |
| static const char *exipc_mutex_type = "example-ipc-shm"; |
| |
| /* Data structure for shared memory block */ |
| typedef struct exipc_data { |
| apr_uint64_t counter; |
| /* More fields if necessary */ |
| } exipc_data; |
| |
| /* |
| * Clean up the shared memory block. This function is registered as |
| * cleanup function for the configuration pool, which gets called |
| * on restarts. It assures that the new children will not talk to a stale |
| * shared memory segment. |
| */ |
| static apr_status_t shm_cleanup_wrapper(void *unused) |
| { |
| if (exipc_shm) |
| return apr_shm_destroy(exipc_shm); |
| return OK; |
| } |
| |
| /* |
| * This routine is called in the parent; we must register our |
| * mutex type before the config is processed so that users can |
| * adjust the mutex settings using the Mutex directive. |
| */ |
| |
| static int exipc_pre_config(apr_pool_t *pconf, apr_pool_t *plog, |
| apr_pool_t *ptemp) |
| { |
| ap_mutex_register(pconf, exipc_mutex_type, NULL, APR_LOCK_DEFAULT, 0); |
| return OK; |
| } |
| |
| /* |
| * This routine is called in the parent, so we'll set up the shared |
| * memory segment and mutex here. |
| */ |
| |
| static int exipc_post_config(apr_pool_t *pconf, apr_pool_t *plog, |
| apr_pool_t *ptemp, server_rec *s) |
| { |
| apr_status_t rs; |
| exipc_data *base; |
| const char *tempdir; |
| |
| |
| /* |
| * Do nothing if we are not creating the final configuration. |
| * The parent process gets initialized a couple of times as the |
| * server starts up, and we don't want to create any more mutexes |
| * and shared memory segments than we're actually going to use. |
| */ |
| if (ap_state_query(AP_SQ_MAIN_STATE) == AP_SQ_MS_CREATE_PRE_CONFIG) |
| return OK; |
| |
| /* |
| * The shared memory allocation routines take a file name. |
| * Depending on system-specific implementation of these |
| * routines, that file may or may not actually be created. We'd |
| * like to store those files in the operating system's designated |
| * temporary directory, which APR can point us to. |
| */ |
| rs = apr_temp_dir_get(&tempdir, pconf); |
| if (APR_SUCCESS != rs) { |
| ap_log_error(APLOG_MARK, APLOG_ERR, rs, s, APLOGNO(02992) |
| "Failed to find temporary directory"); |
| return HTTP_INTERNAL_SERVER_ERROR; |
| } |
| |
| /* Create the shared memory segment */ |
| |
| /* |
| * Create a unique filename using our pid. This information is |
| * stashed in the global variable so the children inherit it. |
| */ |
| shmfilename = apr_psprintf(pconf, "%s/httpd_shm.%ld", tempdir, |
| (long int)getpid()); |
| |
| /* Now create that segment */ |
| rs = apr_shm_create(&exipc_shm, sizeof(exipc_data), |
| (const char *) shmfilename, pconf); |
| if (APR_SUCCESS != rs) { |
| ap_log_error(APLOG_MARK, APLOG_ERR, rs, s, APLOGNO(02993) |
| "Failed to create shared memory segment on file %s", |
| shmfilename); |
| return HTTP_INTERNAL_SERVER_ERROR; |
| } |
| |
| /* Created it, now let's zero it out */ |
| base = (exipc_data *)apr_shm_baseaddr_get(exipc_shm); |
| base->counter = 0; |
| |
| /* Create global mutex */ |
| |
| rs = ap_global_mutex_create(&exipc_mutex, NULL, exipc_mutex_type, NULL, |
| s, pconf, 0); |
| if (APR_SUCCESS != rs) { |
| return HTTP_INTERNAL_SERVER_ERROR; |
| } |
| |
| /* |
| * Destroy the shm segment when the configuration pool gets destroyed. This |
| * happens on server restarts. The parent will then (above) allocate a new |
| * shm segment that the new children will bind to. |
| */ |
| apr_pool_cleanup_register(pconf, NULL, shm_cleanup_wrapper, |
| apr_pool_cleanup_null); |
| return OK; |
| } |
| |
| /* |
| * This routine gets called when a child inits. We use it to attach |
| * to the shared memory segment, and reinitialize the mutex. |
| */ |
| |
| static void exipc_child_init(apr_pool_t *p, server_rec *s) |
| { |
| apr_status_t rs; |
| |
| /* |
| * Re-open the mutex for the child. Note we're reusing |
| * the mutex pointer global here. |
| */ |
| rs = apr_global_mutex_child_init(&exipc_mutex, |
| apr_global_mutex_lockfile(exipc_mutex), |
| p); |
| if (APR_SUCCESS != rs) { |
| ap_log_error(APLOG_MARK, APLOG_CRIT, rs, s, APLOGNO(02994) |
| "Failed to reopen mutex %s in child", |
| exipc_mutex_type); |
| /* There's really nothing else we can do here, since This |
| * routine doesn't return a status. If this ever goes wrong, |
| * it will turn Apache into a fork bomb. Let's hope it never |
| * will. |
| */ |
| exit(1); /* Ugly, but what else? */ |
| } |
| } |
| |
| /* The sample content handler */ |
| static int exipc_handler(request_rec *r) |
| { |
| int gotlock = 0; |
| int camped; |
| apr_time_t startcamp; |
| apr_int64_t timecamped; |
| apr_status_t rs; |
| exipc_data *base; |
| |
| if (strcmp(r->handler, "example_ipc")) { |
| return DECLINED; |
| } |
| |
| /* |
| * The main function of the handler, aside from sending the |
| * status page to the client, is to increment the counter in |
| * the shared memory segment. This action needs to be mutexed |
| * out using the global mutex. |
| */ |
| |
| /* |
| * First, acquire the lock. This code is a lot more involved than |
| * it usually needs to be, because the process based trylock |
| * routine is not implemented on unix platforms. I left it in to |
| * show how it would work if trylock worked, and for situations |
| * and platforms where trylock works. |
| */ |
| for (camped = 0, timecamped = 0; camped < MAXCAMP; camped++) { |
| rs = apr_global_mutex_trylock(exipc_mutex); |
| if (APR_STATUS_IS_EBUSY(rs)) { |
| apr_sleep(CAMPOUT); |
| } |
| else if (APR_SUCCESS == rs) { |
| gotlock = 1; |
| break; /* Get out of the loop */ |
| } |
| else if (APR_STATUS_IS_ENOTIMPL(rs)) { |
| /* If it's not implemented, just hang in the mutex. */ |
| startcamp = apr_time_now(); |
| rs = apr_global_mutex_lock(exipc_mutex); |
| timecamped = (apr_int64_t) (apr_time_now() - startcamp); |
| if (APR_SUCCESS == rs) { |
| gotlock = 1; |
| break; /* Out of the loop */ |
| } |
| else { |
| /* Some error, log and bail */ |
| ap_log_error(APLOG_MARK, APLOG_ERR, rs, r->server, APLOGNO(02995) |
| "Child %ld failed to acquire lock", |
| (long int)getpid()); |
| break; /* Out of the loop without having the lock */ |
| } |
| } |
| else { |
| /* Some other error, log and bail */ |
| ap_log_error(APLOG_MARK, APLOG_ERR, rs, r->server, APLOGNO(02996) |
| "Child %ld failed to try and acquire lock", |
| (long int)getpid()); |
| break; /* Out of the loop without having the lock */ |
| } |
| |
| /* |
| * The only way to get to this point is if the trylock worked |
| * and returned BUSY. So, bump the time and try again |
| */ |
| timecamped += CAMPOUT; |
| ap_log_error(APLOG_MARK, APLOG_NOTICE, 0, r->server, APLOGNO(03187) |
| "Child %ld camping out on mutex for %" APR_INT64_T_FMT |
| " microseconds", |
| (long int) getpid(), timecamped); |
| } /* Lock acquisition loop */ |
| |
| /* Sleep for a millisecond to make it a little harder for |
| * httpd children to acquire the lock. |
| */ |
| apr_sleep(SLEEPYTIME); |
| |
| r->content_type = "text/html"; |
| |
| if (!r->header_only) { |
| ap_rputs(HTML_HEADER, r); |
| if (gotlock) { |
| /* Increment the counter */ |
| base = (exipc_data *)apr_shm_baseaddr_get(exipc_shm); |
| base->counter++; |
| /* Send a page with our pid and the new value of the counter. */ |
| ap_rprintf(r, "<p>Lock acquired after %ld microseoncds.</p>\n", |
| (long int) timecamped); |
| ap_rputs("<table border=\"1\">\n", r); |
| ap_rprintf(r, "<tr><td>Child pid:</td><td>%d</td></tr>\n", |
| (int) getpid()); |
| ap_rprintf(r, "<tr><td>Counter:</td><td>%u</td></tr>\n", |
| (unsigned int)base->counter); |
| ap_rputs("</table>\n", r); |
| } |
| else { |
| /* |
| * Send a page saying that we couldn't get the lock. Don't say |
| * what the counter is, because without the lock the value could |
| * race. |
| */ |
| ap_rprintf(r, "<p>Child %d failed to acquire lock " |
| "after camping out for %d microseconds.</p>\n", |
| (int) getpid(), (int) timecamped); |
| } |
| ap_rputs(HTML_FOOTER, r); |
| } /* r->header_only */ |
| |
| /* Release the lock */ |
| if (gotlock) |
| rs = apr_global_mutex_unlock(exipc_mutex); |
| /* Swallowing the result because what are we going to do with it at |
| * this stage? |
| */ |
| |
| return OK; |
| } |
| |
| static void exipc_register_hooks(apr_pool_t *p) |
| { |
| ap_hook_pre_config(exipc_pre_config, NULL, NULL, APR_HOOK_MIDDLE); |
| ap_hook_post_config(exipc_post_config, NULL, NULL, APR_HOOK_MIDDLE); |
| ap_hook_child_init(exipc_child_init, NULL, NULL, APR_HOOK_MIDDLE); |
| ap_hook_handler(exipc_handler, NULL, NULL, APR_HOOK_MIDDLE); |
| } |
| |
| /* Dispatch list for API hooks */ |
| AP_DECLARE_MODULE(example_ipc) = { |
| STANDARD20_MODULE_STUFF, |
| NULL, /* create per-dir config structures */ |
| NULL, /* merge per-dir config structures */ |
| NULL, /* create per-server config structures */ |
| NULL, /* merge per-server config structures */ |
| NULL, /* table of config file commands */ |
| exipc_register_hooks /* register hooks */ |
| }; |
