#endif
#define HTML_HEADER "\n\nMod_example_IPC Status Page " \
"\n\n\nMod_example_IPC Status
\n"
#define HTML_FOOTER "\n\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
apr_shm_t *exipc_shm;
char *shmfilename;
apr_global_mutex_t *exipc_mutex;
char *mutexfilename;
typedef struct exipc_data {
apr_uint64_t counter;
/* More fields if necessary */
} exipc_data;
/*
* 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)
{
void *data; /* These two help ensure that we only init once. */
const char *userdata_key = "example_ipc_init_module";
apr_status_t rs;
exipc_data *base;
/*
* The following checks if this routine has been called before.
* This is necessary because 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.
*/
apr_pool_userdata_get(&data, userdata_key, s->process->pool);
if (!data) {
apr_pool_userdata_set((const void *) 1, userdata_key,
apr_pool_cleanup_null, s->process->pool);
return OK;
} /* Kilroy was here */
/* 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.
* TODO get the location from the environment $TMPDIR or somesuch.
*/
shmfilename = apr_psprintf(pconf, "/tmp/httpd_shm.%ld", (long int)getpid());
/* Now create that segment */
rs = apr_shm_create(&exipc_shm, sizeof(exipc_data),
(const char *) shmfilename, pconf);
if (rs != APR_SUCCESS) {
ap_log_error(APLOG_MARK, APLOG_ERR, rs, s,
"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 */
/*
* Create another unique filename to lock upon. Note that
* depending on OS and locking mechanism of choice, the file
* may or may not be actually created.
*/
mutexfilename = apr_psprintf(pconf, "/tmp/httpd_mutex.%ld",
(long int) getpid());
rs = apr_global_mutex_create(&exipc_mutex, (const char *) mutexfilename,
APR_LOCK_DEFAULT, pconf);
if (rs != APR_SUCCESS) {
ap_log_error(APLOG_MARK, APLOG_ERR, rs, s,
"Failed to create mutex on file %s",
mutexfilename);
return HTTP_INTERNAL_SERVER_ERROR;
}
#ifdef MOD_EXIPC_SET_MUTEX_PERMS
rs = unixd_set_global_mutex_perms(exipc_mutex);
if (!APR_STATUS_IS_SUCCESS(rs)) {
ap_log_error(APLOG_MARK, APLOG_CRIT, rs, s,
"Parent could not set permissions on Example IPC "
"mutex: check User and Group directives");
return HTTP_INTERNAL_SERVER_ERROR;
}
#endif /* MOD_EXIPC_SET_MUTEX_PERMS */
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,
(const char *) mutexfilename,
p);
if (rs != APR_SUCCESS) {
ap_log_error(APLOG_MARK, APLOG_CRIT, rs, s,
"Failed to reopen mutex on file %s",
shmfilename);
/* There's really nothing else we can do here, since
* This routine doesn't return a status. */
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 */
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_STATUS_IS_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_STATUS_IS_SUCCESS(rs)) {
gotlock = 1;
break;
} else {
/* Some error, log and bail */
ap_log_error(APLOG_MARK, APLOG_ERR, rs, r->server,
"Child %ld failed to acquire lock",
(long int)getpid());
return HTTP_INTERNAL_SERVER_ERROR;
}
} else {
/* Some other error, log and bail */
ap_log_error(APLOG_MARK, APLOG_ERR, rs, r->server,
"Child %ld failed to try and acquire lock",
(long int)getpid());
return HTTP_INTERNAL_SERVER_ERROR;
}
timecamped += CAMPOUT;
ap_log_error(APLOG_MARK, APLOG_NOERRNO | APLOG_NOTICE,
0, r->server, "Child %ld camping out on mutex for %d microseconds",
(long int) getpid(), camped * CAMPOUT);
}
/* Sleep for a millisecond to make it a little harder for
* httpd children to acquire the lock.
*/
apr_sleep(1000);
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, "Lock acquired after camping out for %ld microseoncds.
\n",
(long int) timecamped);
ap_rputs("\n", r);
ap_rprintf(r, "| Child pid: | %d |
\n",
(int) getpid());
ap_rprintf(r, "| Counter: | %u |
\n",
(unsigned int)base->counter);
ap_rputs("
\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, "Child %d failed to acquire lock "
"after camping out for %d microseconds.
\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_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 */
module AP_MODULE_DECLARE_DATA example_ipc_module = {
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 */
};