Adding upstream version 2.4.63.
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
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356
modules/examples/mod_example_ipc.c
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356
modules/examples/mod_example_ipc.c
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/* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership.
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* The ASF licenses this file to You under the Apache License, Version 2.0
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* (the "License"); you may not use this file except in compliance with
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* the License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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/*
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* mod_example_ipc -- Apache sample module
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*
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* This module illustrates the use in an Apache 2.x module of the Interprocess
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* Communications routines that come with APR. It is example code, and not meant
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* to be used in a production server.
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*
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* To play with this sample module first compile it into a DSO file and install
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* it into Apache's modules directory by running:
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*
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* $ /path/to/apache2/bin/apxs -c -i mod_example_ipc.c
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*
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* Then activate it in Apache's httpd.conf file for instance for the URL
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* /example_ipc in as follows:
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*
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* # httpd.conf
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* LoadModule example_ipc_module modules/mod_example_ipc.so
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* <Location /example_ipc>
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* SetHandler example_ipc
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* </Location>
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*
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* Then restart Apache via
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*
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* $ /path/to/apache2/bin/apachectl restart
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*
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* The module allocates a counter in shared memory, which is incremented by the
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* request handler under a mutex. After installation, activate the handler by
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* hitting the URL configured above with ab at various concurrency levels to see
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* how mutex contention affects server performance.
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*/
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#include "apr.h"
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#include "apr_strings.h"
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#include "httpd.h"
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#include "http_config.h"
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#include "http_core.h"
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#include "http_log.h"
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#include "http_protocol.h"
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#include "util_mutex.h"
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#include "ap_config.h"
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#if APR_HAVE_SYS_TYPES_H
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#include <sys/types.h>
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#endif
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#if APR_HAVE_UNISTD_H
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#include <unistd.h>
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#endif
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#define HTML_HEADER "<html>\n<head>\n<title>Mod_example_IPC Status Page " \
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"</title>\n</head>\n<body>\n<h1>Mod_example_IPC Status</h1>\n"
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#define HTML_FOOTER "</body>\n</html>\n"
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/* Number of microseconds to camp out on the mutex */
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#define CAMPOUT 10
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/* Maximum number of times we camp out before giving up */
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#define MAXCAMP 10
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/* Number of microseconds the handler sits on the lock once acquired. */
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#define SLEEPYTIME 1000
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apr_shm_t *exipc_shm; /* Pointer to shared memory block */
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char *shmfilename; /* Shared memory file name, used on some systems */
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apr_global_mutex_t *exipc_mutex; /* Lock around shared memory segment access */
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static const char *exipc_mutex_type = "example-ipc-shm";
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/* Data structure for shared memory block */
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typedef struct exipc_data {
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apr_uint64_t counter;
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/* More fields if necessary */
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} exipc_data;
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/*
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* Clean up the shared memory block. This function is registered as
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* cleanup function for the configuration pool, which gets called
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* on restarts. It assures that the new children will not talk to a stale
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* shared memory segment.
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*/
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static apr_status_t shm_cleanup_wrapper(void *unused)
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{
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if (exipc_shm)
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return apr_shm_destroy(exipc_shm);
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return OK;
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}
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/*
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* This routine is called in the parent; we must register our
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* mutex type before the config is processed so that users can
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* adjust the mutex settings using the Mutex directive.
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*/
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static int exipc_pre_config(apr_pool_t *pconf, apr_pool_t *plog,
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apr_pool_t *ptemp)
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{
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ap_mutex_register(pconf, exipc_mutex_type, NULL, APR_LOCK_DEFAULT, 0);
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return OK;
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}
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/*
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* This routine is called in the parent, so we'll set up the shared
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* memory segment and mutex here.
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*/
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static int exipc_post_config(apr_pool_t *pconf, apr_pool_t *plog,
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apr_pool_t *ptemp, server_rec *s)
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{
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apr_status_t rs;
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exipc_data *base;
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const char *tempdir;
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/*
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* Do nothing if we are not creating the final configuration.
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* The parent process gets initialized a couple of times as the
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* server starts up, and we don't want to create any more mutexes
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* and shared memory segments than we're actually going to use.
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*/
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if (ap_state_query(AP_SQ_MAIN_STATE) == AP_SQ_MS_CREATE_PRE_CONFIG)
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return OK;
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/*
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* The shared memory allocation routines take a file name.
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* Depending on system-specific implementation of these
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* routines, that file may or may not actually be created. We'd
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* like to store those files in the operating system's designated
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* temporary directory, which APR can point us to.
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*/
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rs = apr_temp_dir_get(&tempdir, pconf);
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if (APR_SUCCESS != rs) {
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ap_log_error(APLOG_MARK, APLOG_ERR, rs, s, APLOGNO(02992)
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"Failed to find temporary directory");
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return HTTP_INTERNAL_SERVER_ERROR;
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}
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/* Create the shared memory segment */
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/*
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* Create a unique filename using our pid. This information is
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* stashed in the global variable so the children inherit it.
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*/
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shmfilename = apr_psprintf(pconf, "%s/httpd_shm.%ld", tempdir,
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(long int)getpid());
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/* Now create that segment */
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rs = apr_shm_create(&exipc_shm, sizeof(exipc_data),
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(const char *) shmfilename, pconf);
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if (APR_SUCCESS != rs) {
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ap_log_error(APLOG_MARK, APLOG_ERR, rs, s, APLOGNO(02993)
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"Failed to create shared memory segment on file %s",
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shmfilename);
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return HTTP_INTERNAL_SERVER_ERROR;
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}
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/* Created it, now let's zero it out */
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base = (exipc_data *)apr_shm_baseaddr_get(exipc_shm);
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base->counter = 0;
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/* Create global mutex */
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rs = ap_global_mutex_create(&exipc_mutex, NULL, exipc_mutex_type, NULL,
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s, pconf, 0);
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if (APR_SUCCESS != rs) {
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return HTTP_INTERNAL_SERVER_ERROR;
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}
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/*
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* Destroy the shm segment when the configuration pool gets destroyed. This
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* happens on server restarts. The parent will then (above) allocate a new
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* shm segment that the new children will bind to.
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*/
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apr_pool_cleanup_register(pconf, NULL, shm_cleanup_wrapper,
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apr_pool_cleanup_null);
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return OK;
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}
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/*
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* This routine gets called when a child inits. We use it to attach
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* to the shared memory segment, and reinitialize the mutex.
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*/
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static void exipc_child_init(apr_pool_t *p, server_rec *s)
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{
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apr_status_t rs;
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/*
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* Re-open the mutex for the child. Note we're reusing
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* the mutex pointer global here.
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*/
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rs = apr_global_mutex_child_init(&exipc_mutex,
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apr_global_mutex_lockfile(exipc_mutex),
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p);
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if (APR_SUCCESS != rs) {
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ap_log_error(APLOG_MARK, APLOG_CRIT, rs, s, APLOGNO(02994)
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"Failed to reopen mutex %s in child",
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exipc_mutex_type);
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/* There's really nothing else we can do here, since This
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* routine doesn't return a status. If this ever goes wrong,
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* it will turn Apache into a fork bomb. Let's hope it never
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* will.
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*/
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exit(1); /* Ugly, but what else? */
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}
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}
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/* The sample content handler */
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static int exipc_handler(request_rec *r)
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{
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int gotlock = 0;
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int camped;
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apr_time_t startcamp;
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apr_int64_t timecamped;
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apr_status_t rs;
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exipc_data *base;
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if (strcmp(r->handler, "example_ipc")) {
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return DECLINED;
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}
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/*
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* The main function of the handler, aside from sending the
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* status page to the client, is to increment the counter in
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* the shared memory segment. This action needs to be mutexed
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* out using the global mutex.
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*/
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/*
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* First, acquire the lock. This code is a lot more involved than
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* it usually needs to be, because the process based trylock
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* routine is not implemented on unix platforms. I left it in to
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* show how it would work if trylock worked, and for situations
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* and platforms where trylock works.
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*/
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for (camped = 0, timecamped = 0; camped < MAXCAMP; camped++) {
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rs = apr_global_mutex_trylock(exipc_mutex);
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if (APR_STATUS_IS_EBUSY(rs)) {
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apr_sleep(CAMPOUT);
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}
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else if (APR_SUCCESS == rs) {
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gotlock = 1;
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break; /* Get out of the loop */
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}
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else if (APR_STATUS_IS_ENOTIMPL(rs)) {
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/* If it's not implemented, just hang in the mutex. */
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startcamp = apr_time_now();
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rs = apr_global_mutex_lock(exipc_mutex);
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timecamped = (apr_int64_t) (apr_time_now() - startcamp);
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if (APR_SUCCESS == rs) {
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gotlock = 1;
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break; /* Out of the loop */
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}
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else {
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/* Some error, log and bail */
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ap_log_error(APLOG_MARK, APLOG_ERR, rs, r->server, APLOGNO(02995)
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"Child %ld failed to acquire lock",
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(long int)getpid());
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break; /* Out of the loop without having the lock */
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}
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}
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else {
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/* Some other error, log and bail */
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ap_log_error(APLOG_MARK, APLOG_ERR, rs, r->server, APLOGNO(02996)
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"Child %ld failed to try and acquire lock",
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(long int)getpid());
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break; /* Out of the loop without having the lock */
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}
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/*
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* The only way to get to this point is if the trylock worked
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* and returned BUSY. So, bump the time and try again
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*/
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timecamped += CAMPOUT;
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ap_log_error(APLOG_MARK, APLOG_NOTICE, 0, r->server, APLOGNO(03187)
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"Child %ld camping out on mutex for %" APR_INT64_T_FMT
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" microseconds",
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(long int) getpid(), timecamped);
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} /* Lock acquisition loop */
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/* Sleep for a millisecond to make it a little harder for
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* httpd children to acquire the lock.
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*/
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apr_sleep(SLEEPYTIME);
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r->content_type = "text/html";
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if (!r->header_only) {
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ap_rputs(HTML_HEADER, r);
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if (gotlock) {
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/* Increment the counter */
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base = (exipc_data *)apr_shm_baseaddr_get(exipc_shm);
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base->counter++;
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/* Send a page with our pid and the new value of the counter. */
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ap_rprintf(r, "<p>Lock acquired after %ld microseoncds.</p>\n",
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(long int) timecamped);
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ap_rputs("<table border=\"1\">\n", r);
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ap_rprintf(r, "<tr><td>Child pid:</td><td>%d</td></tr>\n",
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(int) getpid());
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ap_rprintf(r, "<tr><td>Counter:</td><td>%u</td></tr>\n",
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(unsigned int)base->counter);
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ap_rputs("</table>\n", r);
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}
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else {
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/*
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* Send a page saying that we couldn't get the lock. Don't say
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* what the counter is, because without the lock the value could
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* race.
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*/
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ap_rprintf(r, "<p>Child %d failed to acquire lock "
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"after camping out for %d microseconds.</p>\n",
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(int) getpid(), (int) timecamped);
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}
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ap_rputs(HTML_FOOTER, r);
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} /* r->header_only */
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/* Release the lock */
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if (gotlock)
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rs = apr_global_mutex_unlock(exipc_mutex);
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/* Swallowing the result because what are we going to do with it at
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* this stage?
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*/
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return OK;
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}
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static void exipc_register_hooks(apr_pool_t *p)
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{
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ap_hook_pre_config(exipc_pre_config, NULL, NULL, APR_HOOK_MIDDLE);
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ap_hook_post_config(exipc_post_config, NULL, NULL, APR_HOOK_MIDDLE);
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ap_hook_child_init(exipc_child_init, NULL, NULL, APR_HOOK_MIDDLE);
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ap_hook_handler(exipc_handler, NULL, NULL, APR_HOOK_MIDDLE);
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}
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/* Dispatch list for API hooks */
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AP_DECLARE_MODULE(example_ipc) = {
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STANDARD20_MODULE_STUFF,
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NULL, /* create per-dir config structures */
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NULL, /* merge per-dir config structures */
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NULL, /* create per-server config structures */
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NULL, /* merge per-server config structures */
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NULL, /* table of config file commands */
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exipc_register_hooks /* register hooks */
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};
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