Incorrect state transfer in high contention scenarios ----------------------------------------------------- Key: JGRP-425 URL: http://jira.jboss.com/jira/browse/JGRP-425 Project: JGroups Issue Type: Bug Affects Versions: 2.4 Reporter: Bela Ban Assigned To: Bela Ban Fix For: 2.5 State transfer (with digests) works as follows: - State is requested from a provider - Provider (1) gets the digest from NAKACK (below) and then (2) the application state from the channel (above) - Between (1) and (2), some multicast message received can alter the state, as follows: - Multicast message M is received - At the same time, a state request is received - To handle the state request, we ask NAKACK for the digest - The digest contains M - Now - before M is passed up - the digest is returned to STATE_TRANSFER and we fetch the state *WITHOUT* M ! When the state requester gets the state&digest, it will reject a resent M because it thinks it is in its state (because it is in its digest), however M is not part of the state ! Other issue: - M is received after the digest has been retrieved by STATE_TRANSFER, but then M passes the state transfer and is received by the channel and applied to the state *before* the state request can fetch the state. Now M is *not* part of the digest, but it *is* part of the state ! SOLUTION: - When getting the digest, set a flag (in NAKACK) such that all subsequent multicast up-messages are blocked (or add them into a bounded FIFO list) - Fetch the state from the channel (the application) - Unblock NAKACK (send down an UNBLOCK event) - Return the state&digest to the state requester -- 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