#! /bin/sh /usr/share/dpatch/dpatch-run
## ast_channel_trylock_safe.dpatch by Philipp Berndt <philipp.berndt@smeet.de>
##
## All lines beginning with `## DP:' are a description of the patch.
## DP: Add thread safe alternative to ast_mutex_lock(&chan->lock)
## DP: in case that chan might have gone away.
## DP: 
## DP: In some occasions ast_mutex_lock(&chan->lock) is used where chan could
## DP: already have been freed. This is of course not thread-safe.
## DP: 
## DP: In this case the only thread-safe way to atomically check for and lock a
## DP: channel would be to use channel_find_locked(). However this method has three
## DP: disadvantages in the described context:
## DP: 
## DP: - It is somewhat slow because it needs to do string comparison.
## DP: - You need some other information (besides the channel pointer) by which to
## DP:   search.
## DP: - By trying to lock 10 times the semantics of channel_find_lock is something
## DP:   like a compromise between lock and trylock.
## DP:   (This is not what you want because if you can't lock chan->lock you
## DP:   will probably want to release locks on mutexes outside of
## DP:   channel_find_locked(), too before you try again.)

@DPATCH@
diff -urNad asterisk-1.2.13~dfsg~/channel.c asterisk-1.2.13~dfsg/channel.c
--- asterisk-1.2.13~dfsg~/channel.c	2006-09-27 18:54:30.000000000 +0200
+++ asterisk-1.2.13~dfsg/channel.c	2008-02-08 17:38:31.000000000 +0100
@@ -821,5 +821,22 @@
 }
 
+/*--- ast_channel_trylock_safe: Search for channel in list and try to lock it */
+int ast_channel_trylock_safe(struct ast_channel *ptr)
+{
+	int res = EINVAL;
+	struct ast_channel *c;
+
+	ast_mutex_lock(&chlock);
+	for (c = channels; c; c = c->next) {
+		if (c == ptr) {
+			res = ast_mutex_trylock( &c->lock );
+			break;
+		}
+	}
+	ast_mutex_unlock(&chlock);
+	return res;
+}
+
 /*--- ast_safe_sleep_conditional: Wait, look for hangups and condition arg */
 int ast_safe_sleep_conditional(	struct ast_channel *chan, int ms,
 	int (*cond)(void*), void *data )
--- asterisk-1.2.13~dfsg~/include/asterisk/channel.h	2006-09-26 22:38:06.000000000 +0200
+++ asterisk-1.2.13~dfsg/include/asterisk/channel.h	2008-02-08 17:37:34.000000000 +0100
@@ -842,4 +842,7 @@
 
+/*! ast_channel_trylock_safe: Search for channel in list and try to lock it */
+int ast_channel_trylock_safe(struct ast_channel *ptr);
+
 /*! Waits for a digit */
 /*! 
  * \param c channel to wait for a digit on