[jboss-jira] [JBoss JIRA] Created: (JGRP-614) FC: deadlock with synchronous RPCs and exhausted credits

FC: deadlock with synchronous RPCs and exhausted credits -------------------------------------------------------- Key: JGRP-614 URL: http://jira.jboss.com/jira/browse/JGRP-614 Project: JGroups Issue Type: Feature Request Reporter: Bela Ban Assigned To: Bela Ban Fix For: 2.4.1 SP5 # Members A and B # A makes a *synchronous* clustered RPC # B handles the RPC by placing the message into a queue where it is processed by the one and only incoming handler thread. # The handler thread dequeues the message and passes it up the stack # In NAKACK, a lock(A) is acquired and the message is passed up # The app receives the message, invokes the method and - since it is synchronous - passes the response down # In FC.down(), we happen to run out of credits and block # FC.down() periodically requests credits from A. # A receives B's credit request and sends new credits to B # B receives the credits and places them into the incoming handler's queue # HOWEVER, B will never get the credits because its incoming handler thread is still stuck in FC.down() and never has a chance to process that message We currently suggest not to use FC with synchronous RPCs on JGroups 2.4.1 (note that 2.5 and higher doesn't have this issue). However, I think a lot of customers don't know this and will run into this issue. I mean, if you think about it, just one time you don't get credits sent to you by the receiver(s), and block in FC.down() and you will block forever ! Solution: introduce a 'minimal' OOB flag into messages, and when an OOB message is received, use a separate thread to pass it up the stack. Since we don't have many OOB messages, there shouldn't be too many threads spawned. -- This message is automatically generated by JIRA. - If you think it was sent incorrectly contact one of the administrators: http://jira.jboss.com/jira/secure/Administrators.jspa - For more information on JIRA, see: http://www.atlassian.com/software/jira