Avoid potential deadlocks in channel_walk_locked, and detect serious failures

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@3340 65c4cc65-6c06-0410-ace0-fbb531ad65f3

diff --git a/channel.c b/channel.c
index 8738777057a303a5a4a646fdf3237cd7c10fe689..510e0c0d12862ec177e8ded1f67369e120bbebb6 100755 (executable)
--- a/channel.c
+++ b/channel.c
@@ -452,6 +452,8 @@ struct ast_channel *ast_channel_walk_locked(struct ast_channel *prev)
 {
        /* Returns next channel (locked) */
        struct ast_channel *l, *ret=NULL;
+       int retries = 0;        
+retry:
        ast_mutex_lock(&chlock);
        l = channels;
        if (!prev) {
@@ -465,8 +467,21 @@ struct ast_channel *ast_channel_walk_locked(struct ast_channel *prev)
                        ret = l->next;
                l = l->next;
        }
-       if (ret)
-               ast_mutex_lock(&ret->lock);
+       if (ret) {
+               if (ast_mutex_trylock(&ret->lock)) {
+                       if (retries < 10)
+                               ast_log(LOG_DEBUG, "Avoiding deadlock for '%s'\n", ret->name);
+                       else
+                               ast_log(LOG_WARNING, "Avoided deadlock for '%s', %d retries!\n", ret->name, retries);
+                       ast_mutex_unlock(&chlock);
+                       if (retries < 10) {
+                               usleep(1);
+                               retries++;
+                               goto retry;
+                       } else
+                               return NULL;
+               }
+       }
        ast_mutex_unlock(&chlock);
        return ret;