Revise dialplan locks to permit multiple locks per channel, but with deadlock avoidance
git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@79813 65c4cc65-6c06-0410-ace0-fbb531ad65f3
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@ -57,24 +57,49 @@ static struct ast_datastore_info lock_info = {
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struct lock_frame {
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AST_LIST_ENTRY(lock_frame) entries;
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ast_mutex_t mutex;
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/*! count is needed so if a recursive mutex exits early, we know how many times to unlock it. */
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unsigned int count;
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/*! who owns us */
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struct ast_channel *channel;
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/*! name of the lock */
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char name[0];
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};
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struct channel_lock_frame {
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AST_LIST_ENTRY(channel_lock_frame) list;
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/*! Need to save channel pointer here, because during destruction, we won't have it. */
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struct ast_channel *channel;
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struct lock_frame *lock_frame;
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};
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static void lock_free(void *data)
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{
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struct lock_frame *frame = data;
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if (!frame)
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return;
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frame->channel = NULL;
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ast_mutex_unlock(&frame->mutex);
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AST_LIST_HEAD(, channel_lock_frame) *oldlist = data;
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struct channel_lock_frame *clframe;
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AST_LIST_LOCK(oldlist);
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while ((clframe = AST_LIST_REMOVE_HEAD(oldlist, list))) {
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/* Only unlock if we own the lock */
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if (clframe->channel == clframe->lock_frame->channel) {
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clframe->lock_frame->channel = NULL;
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while (clframe->lock_frame->count > 0) {
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clframe->lock_frame->count--;
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ast_mutex_unlock(&clframe->lock_frame->mutex);
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}
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}
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ast_free(clframe);
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}
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AST_LIST_UNLOCK(oldlist);
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AST_LIST_HEAD_DESTROY(oldlist);
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ast_free(oldlist);
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}
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static int get_lock(struct ast_channel *chan, char *lockname, int try)
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{
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struct ast_datastore *lock_store = ast_channel_datastore_find(chan, &lock_info, NULL);
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struct lock_frame *current;
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int res;
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struct channel_lock_frame *clframe, *save_clframe;
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AST_LIST_HEAD(, channel_lock_frame) *list;
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int res, count_channel_locks = 0;
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if (!lock_store) {
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ast_debug(1, "Channel %s has no lock datastore, so we're allocating one.\n", chan->name);
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@ -83,17 +108,21 @@ static int get_lock(struct ast_channel *chan, char *lockname, int try)
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ast_log(LOG_ERROR, "Unable to allocate new datastore. No locks will be obtained.\n");
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return -1;
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}
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list = ast_calloc(1, sizeof(*list));
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if (!list) {
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ast_log(LOG_ERROR, "Unable to allocate datastore list head. %sLOCK will fail.\n", try ? "TRY" : "");
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ast_channel_datastore_free(lock_store);
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return -1;
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}
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lock_store->data = list;
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AST_LIST_HEAD_INIT(list);
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ast_channel_datastore_add(chan, lock_store);
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}
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} else
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list = lock_store->data;
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/* If the channel already has a lock, then free the existing lock */
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if (lock_store->data) {
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struct lock_frame *old = lock_store->data;
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old->channel = NULL;
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ast_mutex_unlock(&old->mutex);
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}
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/* Lock already exist? */
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/* Lock already exists? */
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AST_LIST_LOCK(&locklist);
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AST_LIST_TRAVERSE(&locklist, current, entries) {
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if (strcmp(current->name, lockname) == 0) {
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@ -119,21 +148,70 @@ static int get_lock(struct ast_channel *chan, char *lockname, int try)
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ast_mutex_init(¤t->mutex);
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AST_LIST_INSERT_TAIL(&locklist, current, entries);
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}
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AST_LIST_UNLOCK(&locklist);
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/* Found lock or created one - now find or create the corresponding link in the channel */
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AST_LIST_LOCK(list);
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AST_LIST_TRAVERSE(list, clframe, list) {
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if (clframe->lock_frame == current)
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save_clframe = clframe;
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/* Only count mutexes that we currently hold */
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if (clframe->lock_frame->channel == chan)
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count_channel_locks++;
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}
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if (save_clframe) {
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clframe = save_clframe;
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} else {
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if (unloading) {
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/* Don't bother */
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AST_LIST_UNLOCK(list);
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return -1;
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}
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clframe = ast_calloc(1, sizeof(*clframe));
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if (!clframe) {
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ast_log(LOG_ERROR, "Unable to allocate channel lock frame. %sLOCK will fail.\n", try ? "TRY" : "");
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AST_LIST_UNLOCK(list);
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return -1;
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}
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clframe->lock_frame = current;
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clframe->channel = chan;
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/* Count the lock just created */
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count_channel_locks++;
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AST_LIST_INSERT_TAIL(list, clframe, list);
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}
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AST_LIST_UNLOCK(list);
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/* Okay, we have both frames, so now we need to try to lock the mutex. */
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if (count_channel_locks > 1) {
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/* If we fail after a certain number of attempts, assume a possible deadlock and bail. */
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int x;
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for (x = 0; x < 30; x++) {
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if ((res = ast_mutex_trylock(¤t->mutex)) == 0)
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break;
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usleep(1);
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}
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} else {
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/* If the channel doesn't have any locks so far, then there's no possible deadlock. */
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res = try ? ast_mutex_trylock(¤t->mutex) : ast_mutex_lock(¤t->mutex);
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}
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if (res == 0) {
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lock_store->data = current;
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current->count++;
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current->channel = chan;
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}
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AST_LIST_UNLOCK(&locklist);
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return res;
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}
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static int unlock_read(struct ast_channel *chan, const char *cmd, char *data, char *buf, size_t len)
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{
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struct ast_datastore *lock_store = ast_channel_datastore_find(chan, &lock_info, NULL);
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struct lock_frame *current;
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struct channel_lock_frame *clframe;
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AST_LIST_HEAD(, channel_lock_frame) *list;
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if (!lock_store) {
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ast_log(LOG_WARNING, "No datastore for dialplan locks. Nothing was ever locked!\n");
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@ -141,15 +219,37 @@ static int unlock_read(struct ast_channel *chan, const char *cmd, char *data, ch
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return 0;
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}
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current = lock_store->data;
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if (!current) {
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if (!(list = lock_store->data)) {
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ast_debug(1, "This should NEVER happen\n");
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ast_copy_string(buf, "0", len);
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return 0;
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}
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current->channel = NULL;
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ast_mutex_unlock(¤t->mutex);
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/* Find item in the channel list */
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AST_LIST_LOCK(list);
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AST_LIST_TRAVERSE(list, clframe, list) {
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if (clframe->lock_frame && clframe->lock_frame->channel == chan && strcmp(clframe->lock_frame->name, data) == 0) {
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break;
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}
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}
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/* We never destroy anything until channel destruction, which will never
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* happen while this routine is executing, so we don't need to hold the
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* lock beyond this point. */
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AST_LIST_UNLOCK(list);
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if (!clframe) {
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/* We didn't have this lock in the first place */
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ast_copy_string(buf, "0", len);
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return 0;
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}
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/* Decrement before we release, because if a channel is waiting on the
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* mutex, there's otherwise a race to alter count. */
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clframe->lock_frame->count--;
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/* If we get another lock, this one shouldn't count against us for deadlock avoidance. */
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clframe->lock_frame->channel = NULL;
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ast_mutex_unlock(&clframe->lock_frame->mutex);
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ast_copy_string(buf, "1", len);
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return 0;
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}
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@ -170,13 +270,11 @@ static struct ast_custom_function lock_function = {
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.name = "LOCK",
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.synopsis = "Attempt to obtain a named mutex",
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.desc =
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"Attempts to grab a named lock exclusively, and prevents other channels\n"
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"from obtaining the same lock. LOCK will wait for the lock to become\n"
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"available. Returns 1 if the lock was obtained or 0 on error.\n\n"
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"Attempts to grab a named lock exclusively, and prevents other channels from\n"
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"obtaining the same lock. LOCK will wait for the lock to become available.\n"
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"Returns 1 if the lock was obtained or 0 on error.\n\n"
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"Note: to avoid the possibility of a deadlock, LOCK will only attempt to\n"
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"grab a single lock. If you have a lock already and you attempt to lock\n"
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"another name, LOCK will unlock the first name before attempting to lock\n"
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"the second name.\n",
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"obtain the lock for 3 seconds if the channel already has another lock.\n",
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.syntax = "LOCK(<lockname>)",
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.read = lock_read,
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};
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@ -187,11 +285,7 @@ static struct ast_custom_function trylock_function = {
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.desc =
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"Attempts to grab a named lock exclusively, and prevents other channels\n"
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"from obtaining the same lock. Returns 1 if the lock was available or 0\n"
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"otherwise.\n\n"
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"Note: to avoid the possibility of a deadlock, TRYLOCK will only attempt to\n"
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"grab a single lock. If you have a lock already and you attempt to lock\n"
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"another name, TRYLOCK will unlock the first name before attempting to lock\n"
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"the second name.\n",
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"otherwise.\n",
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.syntax = "TRYLOCK(<lockname>)",
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.read = trylock_read,
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};
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@ -201,9 +295,9 @@ static struct ast_custom_function unlock_function = {
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.synopsis = "Unlocks a named mutex",
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.desc =
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"Unlocks a previously locked mutex. Note that it is generally unnecessary to\n"
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"unlock in a hangup routine, as any lock held is automatically freed when the\n"
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"unlock in a hangup routine, as any locks held are automatically freed when the\n"
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"channel is destroyed. Returns 1 if the channel had a lock or 0 otherwise.\n",
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.syntax = "UNLOCK()",
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.syntax = "UNLOCK(<lockname>)",
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.read = unlock_read,
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};
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