Changes between Version 1 and Version 2 of PJSUA_Locks

Timestamp:

Feb 13, 2008 7:51:30 PM (16 years ago)

Author:

bennylp

Comment:

--

PJSUA_Locks

@@ -34 +34 @@
 
 
+== Soft Deadlock ==
 
+Although hard deadlock (where application just freezes) should never happen when the above guidelines are used, there may be cases when application gets a ''soft deadlock'' state. When this happens, application will not freeze permanently, but rather it will freeze for few seconds while PJSUA-LIB is trying to acquire the locks, and these message may appear in the log:
+
+  ''Timed-out trying to acquire PJSUA mutex (possibly system has deadlocked) in pjsua_xxx''
+
+This could happen for example in the following scenario:
+ 1. application callback is called
+ 1. application posts a job to a worker thread, and blocks until it gets result from the worker thread
+ 1. the worker thread calls some PJSUA-LIB call API
+ 1. when PJSUA-LIB tries to acquire locks with {{{acquire_call()}}} on behalf of the worker thread, it will fail to get them because the locks are currently being held by the callback thread (in step no 1 above). In this case, rather than ''deadlocking'' permanently, PJSUA-LIB will timeout after it retries acquiring the locks for few seconds, and returns PJ_ETIMEDOUT error to {{{acquire_call()}}} caller.
+
+This problem is not caused by PJSUA-LIB, and in fact PJSUA-LIB has helped us not to deadlock permanently.
+
+As for the solution, quoting the famous saying, I'll leave that as an exercise for the reader. ;-)
+