ARTEMIS-6179 Fix deleteReference/depage deadlock - #6607
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Removes synchronized from QueueImpl#deleteReference(). It calls iterQueue(), which acquires depageLock internally, while depage() acquires depageLock first and then enters a synchronized(this) block. The reversed lock order deadlocks QueueControl#removeMessage() against the paging executor whenever they race on an actively paging queue. This mirrors the fix already applied to copyReference() in ARTEMIS-5376: iterQueue() already provides its own synchronization via depageLock, so the outer synchronized on deleteReference() is redundant and unsafe. Verified with testRemoveMessageWhilstPagingAndConsuming, which reliably deadlocks without this change and passes cleanly with it.
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https://issues.apache.org/jira/browse/ARTEMIS-6179
QueueImpl#deleteReference()issynchronizedand callsiterQueue(), which blocks ondepageLock.lock().depage()does the reverse: it takesdepageLockfirst (viatryLock()), then needs to entersynchronized(this). Two threads acquiring the same two locks in opposite order deadlock as soon as they interleave: aremoveMessage()call holds the object monitor and blocks ondepageLock, whiledepage()holdsdepageLockand blocks on the monitor. Neither ever releases.This is the same bug class already fixed for
copyReference()in ARTEMIS-5376 (30c8fc7).deleteReference()wasn't touched by that fix because it didn't call `it