diff options
| -rw-r--r-- | funcs/func_lock.c | 166 |
1 files changed, 130 insertions, 36 deletions
diff --git a/funcs/func_lock.c b/funcs/func_lock.c index e9ac0651b..e950aef57 100644 --- a/funcs/func_lock.c +++ b/funcs/func_lock.c @@ -57,24 +57,49 @@ static struct ast_datastore_info lock_info = { 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) { - struct lock_frame *frame = data; - if (!frame) - return; - frame->channel = NULL; - ast_mutex_unlock(&frame->mutex); + 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; - int res; + struct channel_lock_frame *clframe, *save_clframe; + 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); @@ -83,17 +108,21 @@ static int get_lock(struct ast_channel *chan, char *lockname, int try) ast_log(LOG_ERROR, "Unable to allocate new datastore. No locks will be obtained.\n"); return -1; } - ast_channel_datastore_add(chan, lock_store); - } - /* If the channel already has a lock, then free the existing lock */ - if (lock_store->data) { - struct lock_frame *old = lock_store->data; - old->channel = NULL; - ast_mutex_unlock(&old->mutex); - } + 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 already exist? */ + 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) { @@ -119,21 +148,70 @@ static int get_lock(struct ast_channel *chan, char *lockname, int try) 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) { + /* If we fail after a certain number of attempts, assume a possible deadlock and bail. */ + int x; + for (x = 0; x < 30; x++) { + if ((res = ast_mutex_trylock(¤t->mutex)) == 0) + break; + 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); + } - res = try ? ast_mutex_trylock(¤t->mutex) : ast_mutex_lock(¤t->mutex); if (res == 0) { - lock_store->data = current; + current->count++; current->channel = chan; } - AST_LIST_UNLOCK(&locklist); 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 lock_frame *current; + 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"); @@ -141,15 +219,37 @@ static int unlock_read(struct ast_channel *chan, const char *cmd, char *data, ch return 0; } - current = lock_store->data; + if (!(list = lock_store->data)) { + ast_debug(1, "This should NEVER happen\n"); + ast_copy_string(buf, "0", len); + return 0; + } - if (!current) { + /* 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; } - current->channel = NULL; - ast_mutex_unlock(¤t->mutex); + /* 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; } @@ -170,13 +270,11 @@ 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\n" -"from obtaining the same lock. LOCK will wait for the lock to become\n" -"available. Returns 1 if the lock was obtained or 0 on error.\n\n" +"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" -"grab a single lock. If you have a lock already and you attempt to lock\n" -"another name, LOCK will unlock the first name before attempting to lock\n" -"the second name.\n", +"obtain the lock for 3 seconds if the channel already has another lock.\n", .syntax = "LOCK(<lockname>)", .read = lock_read, }; @@ -187,11 +285,7 @@ static struct ast_custom_function trylock_function = { .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\n" -"Note: to avoid the possibility of a deadlock, TRYLOCK will only attempt to\n" -"grab a single lock. If you have a lock already and you attempt to lock\n" -"another name, TRYLOCK will unlock the first name before attempting to lock\n" -"the second name.\n", +"otherwise.\n", .syntax = "TRYLOCK(<lockname>)", .read = trylock_read, }; @@ -201,9 +295,9 @@ static struct ast_custom_function unlock_function = { .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 lock held is automatically freed when the\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()", + .syntax = "UNLOCK(<lockname>)", .read = unlock_read, }; |