A serious concurrent bug can cause deadlock when Pool exhausted and borrowed
objects are invalid
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Key: POOL-149
URL: https://issues.apache.org/jira/browse/POOL-149
Project: Commons Pool
Issue Type: Bug
Reporter: shuyang.zhou
Priority: Critical
This bug will happen when the pool is in exhausted state and the borrowed
object are invalid.
Let's go through a simple scenario:
1)A GenericObjectPool with _maxActive==1,
whenExhaustedAction==WHEN_EXHAUSTED_BLOCK
2)Two threads using that pool, called thread1 and thread2
Here is error path:
1)thread1 calls pool.borrowObject() to get the object out of the pool
//now the pool is exhausted
2)thread2 calls pool.borrowObject(), adds a new latch to the _allocationQueue,
but before it enters the synchronized block for
WHEN_EXHAUSTED_BLOCK(GenericObjectPool line 1099 revision 806215),
context-switch happens
3)thread1 checks the object from pool, and decides to invalidate it. So it
calls pool.invalidateObject(), which calls allocate(), then calls
latch.notify(), but currently no thread is waiting on this latch.(thread2 has
not enter the wait synchronized block yet).
4)Then thread2 will wait there for ever.(it just missed the notify)
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