Ryan McMahon created GEODE-5653:
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Summary: Race between put of parallel WAN sender event and
distributed clear causes off-heap orphan
Key: GEODE-5653
URL: https://issues.apache.org/jira/browse/GEODE-5653
Project: Geode
Issue Type: Bug
Components: offheap, regions, wan
Reporter: Ryan McMahon
A race resulting in an off-heap orphan can occur with Parallel WAN when
off-heap is enabled on the cache and user's data region. It is the result of
the put occurring in two distinct steps without proper synchronization. The
initial value of the region entry is Token.REMOVED_PHASE_1 (step 1) then later
is replaced with actual GatewaySenderEvent (step 2). If a distributed clear is
processed between these two steps, it can result in an orphan. More details on
the race are described below.
The race is between:
*Thread 1*. A put of a {{GatewaySenderEvent}} containing an off-heap value to
one of the WAN "shadow" region's {{BucketRegionQueue}}
and
*Thread 2*. A distributed clear on the {{BucketRegionQueue}} containing that
value
The race occurs as follows:
*Thread 1 (Put)*: Put results in a new region entry where the value is
{{Token.REMOVED_PHASE1}} and put it into the {{CustomEntryConcurrentHashMap}}
owned by the {{AbstractRegionMap}}.
*Thread 2 (Clear)*: Iterates through bucket region's segments and clears the
entries. At this time the value is still {{Token.REMOVED_PHASE_1}}.
*Thread 1 (Put)*: The {{Token.REMOVED_PHASE_1}} is replaced with the actual
{{GatewaySenderEvent}} in the region entry. However, the entry was removed via
the clear above. When the entry is removed from the region, its off-heap is
orphaned because it is no longer in the {{CustomEntryConcurrentHashMap}}.
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