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From "Tim Armstrong (Code Review)" <ger...@cloudera.org>
Subject [Impala-ASF-CR] IMPALA-4946: fix hang in BufferPool
Date Thu, 02 Mar 2017 17:19:33 GMT
Tim Armstrong has uploaded a new change for review.

  http://gerrit.cloudera.org:8080/6224

Change subject: IMPALA-4946: fix hang in BufferPool
......................................................................

IMPALA-4946: fix hang in BufferPool

Once the write is removed from the "in flight" list,
both the Client and Page may be destroyed by a different
thread. The fix is to signal condition variables before
inside the critical section that removes the write from
the in flight list.

Also fix a potential pitfall with DiskIoMgr::CancelContext()
where concurrent calls to the method, which can be called
asynchronously with other methods, could result in a hang in
DiskIoMgr::CancelContext(). I do not believe any Impala code
calls it concurrently from multiple threads, so the bug was
only latent.

Testing:
I was able to reproduce reliably by inserting a 1s sleep before
the NotifyAll() calls. After the fix, the hang didn't reproduce
with sleeps inside or outside the critical section.

I could not come up with a unit test that had a higher reproduction
rate than the current tests - the window for the race is very small.
I considered adding a debug stress option to insert these delays,
but with all the code moved into the critical section it wouldn't
be useful.

Change-Id: I13fc95b5a664544dee789c4107fccf81d2077347
---
M be/src/runtime/bufferpool/buffer-pool.cc
M be/src/runtime/disk-io-mgr-internal.h
2 files changed, 5 insertions(+), 3 deletions(-)


  git pull ssh://gerrit.cloudera.org:29418/Impala-ASF refs/changes/24/6224/1
-- 
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Gerrit-MessageType: newchange
Gerrit-Change-Id: I13fc95b5a664544dee789c4107fccf81d2077347
Gerrit-PatchSet: 1
Gerrit-Project: Impala-ASF
Gerrit-Branch: master
Gerrit-Owner: Tim Armstrong <tarmstrong@cloudera.com>

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