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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
This commit is contained in:
Tilghman Lesher 2007-08-16 23:31:14 +00:00
parent 782c22ccb4
commit d6eb859bc2
1 changed files with 131 additions and 37 deletions
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168
funcs/func_lock.c
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@ -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;
}
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;
/* 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);
}
/* Lock already exist? */
/* 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(&current->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(&current->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(&current->mutex) : ast_mutex_lock(&current->mutex);
}
res = try ? ast_mutex_trylock(&current->mutex) : ast_mutex_lock(&current->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 (!current) {
if (!(list = lock_store->data)) {
ast_debug(1, "This should NEVER happen\n");
ast_copy_string(buf, "0", len);
return 0;
}
current->channel = NULL;
ast_mutex_unlock(&current->mutex);
/* 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;
}
@ -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,
};