diff options
Diffstat (limited to 'trunk/funcs/func_lock.c')
-rw-r--r-- | trunk/funcs/func_lock.c | 350 |
1 files changed, 350 insertions, 0 deletions
diff --git a/trunk/funcs/func_lock.c b/trunk/funcs/func_lock.c new file mode 100644 index 000000000..53b05a3e8 --- /dev/null +++ b/trunk/funcs/func_lock.c @@ -0,0 +1,350 @@ +/* + * Asterisk -- An open source telephony toolkit. + * + * Copyright (C) 2007, Tilghman Lesher + * + * Tilghman Lesher <func_lock_2007@the-tilghman.com> + * + * See http://www.asterisk.org for more information about + * the Asterisk project. Please do not directly contact + * any of the maintainers of this project for assistance; + * the project provides a web site, mailing lists and IRC + * channels for your use. + * + * This program is free software, distributed under the terms of + * the GNU General Public License Version 2. See the LICENSE file + * at the top of the source tree. + */ + +/*! \file + * + * \brief Dialplan mutexes + * + * \author Tilghman Lesher <func_lock_2007@the-tilghman.com> + * + * \ingroup functions + * + */ + +#include "asterisk.h" + +ASTERISK_FILE_VERSION(__FILE__, "$Revision$") + +#include "asterisk/lock.h" +#include "asterisk/file.h" +#include "asterisk/channel.h" +#include "asterisk/pbx.h" +#include "asterisk/module.h" +#include "asterisk/linkedlists.h" + +AST_LIST_HEAD_STATIC(locklist, lock_frame); + +static void lock_free(void *data); +static int unloading = 0; + +static struct ast_datastore_info lock_info = { + .type = "MUTEX", + .destroy = lock_free, +}; + +struct lock_frame { + AST_LIST_ENTRY(lock_frame) entries; + ast_mutex_t mutex; + /*! count is needed so if a recursive mutex exits early, we know how many times to unlock it. */ + unsigned int count; + /*! who owns us */ + struct ast_channel *channel; + /*! name of the lock */ + char name[0]; +}; + +struct channel_lock_frame { + AST_LIST_ENTRY(channel_lock_frame) list; + /*! Need to save channel pointer here, because during destruction, we won't have it. */ + struct ast_channel *channel; + struct lock_frame *lock_frame; +}; + +static void lock_free(void *data) +{ + AST_LIST_HEAD(, channel_lock_frame) *oldlist = data; + struct channel_lock_frame *clframe; + AST_LIST_LOCK(oldlist); + while ((clframe = AST_LIST_REMOVE_HEAD(oldlist, list))) { + /* Only unlock if we own the lock */ + if (clframe->channel == clframe->lock_frame->channel) { + clframe->lock_frame->channel = NULL; + while (clframe->lock_frame->count > 0) { + clframe->lock_frame->count--; + ast_mutex_unlock(&clframe->lock_frame->mutex); + } + } + ast_free(clframe); + } + AST_LIST_UNLOCK(oldlist); + AST_LIST_HEAD_DESTROY(oldlist); + ast_free(oldlist); +} + +static int get_lock(struct ast_channel *chan, char *lockname, int try) +{ + struct ast_datastore *lock_store = ast_channel_datastore_find(chan, &lock_info, NULL); + struct lock_frame *current; + struct channel_lock_frame *clframe = NULL, *save_clframe = NULL; + AST_LIST_HEAD(, channel_lock_frame) *list; + int res, count_channel_locks = 0; + + if (!lock_store) { + ast_debug(1, "Channel %s has no lock datastore, so we're allocating one.\n", chan->name); + lock_store = ast_channel_datastore_alloc(&lock_info, NULL); + if (!lock_store) { + ast_log(LOG_ERROR, "Unable to allocate new datastore. No locks will be obtained.\n"); + return -1; + } + + list = ast_calloc(1, sizeof(*list)); + if (!list) { + ast_log(LOG_ERROR, "Unable to allocate datastore list head. %sLOCK will fail.\n", try ? "TRY" : ""); + ast_channel_datastore_free(lock_store); + return -1; + } + + lock_store->data = list; + AST_LIST_HEAD_INIT(list); + ast_channel_datastore_add(chan, lock_store); + } else + list = lock_store->data; + + /* Lock already exists? */ + AST_LIST_LOCK(&locklist); + AST_LIST_TRAVERSE(&locklist, current, entries) { + if (strcmp(current->name, lockname) == 0) { + break; + } + } + + if (!current) { + if (unloading) { + /* Don't bother */ + AST_LIST_UNLOCK(&locklist); + return -1; + } + + /* Create new lock entry */ + current = ast_calloc(1, sizeof(*current) + strlen(lockname) + 1); + if (!current) { + AST_LIST_UNLOCK(&locklist); + return -1; + } + + strcpy((char *)current + sizeof(*current), lockname); + ast_mutex_init(¤t->mutex); + AST_LIST_INSERT_TAIL(&locklist, current, entries); + } + AST_LIST_UNLOCK(&locklist); + + /* Found lock or created one - now find or create the corresponding link in the channel */ + AST_LIST_LOCK(list); + AST_LIST_TRAVERSE(list, clframe, list) { + if (clframe->lock_frame == current) + save_clframe = clframe; + + /* Only count mutexes that we currently hold */ + if (clframe->lock_frame->channel == chan) + count_channel_locks++; + } + + if (save_clframe) { + clframe = save_clframe; + } else { + if (unloading) { + /* Don't bother */ + AST_LIST_UNLOCK(list); + return -1; + } + + clframe = ast_calloc(1, sizeof(*clframe)); + if (!clframe) { + ast_log(LOG_ERROR, "Unable to allocate channel lock frame. %sLOCK will fail.\n", try ? "TRY" : ""); + AST_LIST_UNLOCK(list); + return -1; + } + + clframe->lock_frame = current; + clframe->channel = chan; + /* Count the lock just created */ + count_channel_locks++; + AST_LIST_INSERT_TAIL(list, clframe, list); + } + AST_LIST_UNLOCK(list); + + /* Okay, we have both frames, so now we need to try to lock the mutex. */ + if (count_channel_locks > 1) { + struct timeval start = ast_tvnow(); + for (;;) { + if ((res = ast_mutex_trylock(¤t->mutex)) == 0) + break; + if (ast_tvdiff_ms(ast_tvnow(), start) > 3000) + break; /* bail after 3 seconds of waiting */ + usleep(1); + } + } else { + /* If the channel doesn't have any locks so far, then there's no possible deadlock. */ + res = try ? ast_mutex_trylock(¤t->mutex) : ast_mutex_lock(¤t->mutex); + } + + if (res == 0) { + current->count++; + current->channel = chan; + } + + return res; +} + +static int unlock_read(struct ast_channel *chan, const char *cmd, char *data, char *buf, size_t len) +{ + struct ast_datastore *lock_store = ast_channel_datastore_find(chan, &lock_info, NULL); + struct channel_lock_frame *clframe; + AST_LIST_HEAD(, channel_lock_frame) *list; + + if (!lock_store) { + ast_log(LOG_WARNING, "No datastore for dialplan locks. Nothing was ever locked!\n"); + ast_copy_string(buf, "0", len); + return 0; + } + + if (!(list = lock_store->data)) { + ast_debug(1, "This should NEVER happen\n"); + ast_copy_string(buf, "0", len); + return 0; + } + + /* Find item in the channel list */ + AST_LIST_LOCK(list); + AST_LIST_TRAVERSE(list, clframe, list) { + if (clframe->lock_frame && clframe->lock_frame->channel == chan && strcmp(clframe->lock_frame->name, data) == 0) { + break; + } + } + /* We never destroy anything until channel destruction, which will never + * happen while this routine is executing, so we don't need to hold the + * lock beyond this point. */ + AST_LIST_UNLOCK(list); + + if (!clframe) { + /* We didn't have this lock in the first place */ + ast_copy_string(buf, "0", len); + return 0; + } + + /* Decrement before we release, because if a channel is waiting on the + * mutex, there's otherwise a race to alter count. */ + clframe->lock_frame->count--; + /* If we get another lock, this one shouldn't count against us for deadlock avoidance. */ + clframe->lock_frame->channel = NULL; + ast_mutex_unlock(&clframe->lock_frame->mutex); + + ast_copy_string(buf, "1", len); + return 0; +} + +static int lock_read(struct ast_channel *chan, const char *cmd, char *data, char *buf, size_t len) +{ + if (chan) + ast_autoservice_start(chan); + + ast_copy_string(buf, get_lock(chan, data, 0) ? "0" : "1", len); + + if (chan) + ast_autoservice_stop(chan); + + return 0; +} + +static int trylock_read(struct ast_channel *chan, const char *cmd, char *data, char *buf, size_t len) +{ + if (chan) + ast_autoservice_start(chan); + + ast_copy_string(buf, get_lock(chan, data, 1) ? "0" : "1", len); + + if (chan) + ast_autoservice_stop(chan); + + return 0; +} + +static struct ast_custom_function lock_function = { + .name = "LOCK", + .synopsis = "Attempt to obtain a named mutex", + .desc = +"Attempts to grab a named lock exclusively, and prevents other channels from\n" +"obtaining the same lock. LOCK will wait for the lock to become available.\n" +"Returns 1 if the lock was obtained or 0 on error.\n\n" +"Note: to avoid the possibility of a deadlock, LOCK will only attempt to\n" +"obtain the lock for 3 seconds if the channel already has another lock.\n", + .syntax = "LOCK(<lockname>)", + .read = lock_read, +}; + +static struct ast_custom_function trylock_function = { + .name = "TRYLOCK", + .synopsis = "Attempt to obtain a named mutex", + .desc = +"Attempts to grab a named lock exclusively, and prevents other channels\n" +"from obtaining the same lock. Returns 1 if the lock was available or 0\n" +"otherwise.\n", + .syntax = "TRYLOCK(<lockname>)", + .read = trylock_read, +}; + +static struct ast_custom_function unlock_function = { + .name = "UNLOCK", + .synopsis = "Unlocks a named mutex", + .desc = +"Unlocks a previously locked mutex. Note that it is generally unnecessary to\n" +"unlock in a hangup routine, as any locks held are automatically freed when the\n" +"channel is destroyed. Returns 1 if the channel had a lock or 0 otherwise.\n", + .syntax = "UNLOCK(<lockname>)", + .read = unlock_read, +}; + +static int unload_module(void) +{ + struct lock_frame *current; + + /* Module flag */ + unloading = 1; + + AST_LIST_LOCK(&locklist); + while ((current = AST_LIST_REMOVE_HEAD(&locklist, entries))) { + /* If any locks are currently in use, then we cannot unload this module */ + if (current->channel) { + /* Put it back */ + AST_LIST_INSERT_HEAD(&locklist, current, entries); + AST_LIST_UNLOCK(&locklist); + unloading = 0; + return -1; + } + ast_mutex_destroy(¤t->mutex); + ast_free(current); + } + + /* No locks left, unregister functions */ + ast_custom_function_unregister(&lock_function); + ast_custom_function_unregister(&trylock_function); + ast_custom_function_unregister(&unlock_function); + + AST_LIST_UNLOCK(&locklist); + return 0; +} + +static int load_module(void) +{ + int res = ast_custom_function_register(&lock_function); + res |= ast_custom_function_register(&trylock_function); + res |= ast_custom_function_register(&unlock_function); + return res; +} + +AST_MODULE_INFO_STANDARD(ASTERISK_GPL_KEY, "Dialplan mutexes"); |