Review Request 19174: Fixed a race condition in Latch which could lead to incorrect return value for Latch::await().

[Jiang Yan Xu]

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https://reviews.apache.org/r/19174/
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Review request for mesos, Benjamin Hindman, Ben Mahler, and Vinod Kone.


Bugs: MESOS-1088
    https://issues.apache.org/jira/browse/MESOS-1088


Repository: mesos-git


Description
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See https://issues.apache.org/jira/browse/MESOS-1088

The symptom was that the 'Future::await(Duration)' returns 'false' even though 
the future is set before it times out.


Diffs
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  3rdparty/libprocess/src/latch.cpp a6f1256ff8860e9a624c0f200ea53912048fd6e3 

Diff: https://reviews.apache.org/r/19174/diff/


Testing
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Ran 
ZooKeeperMasterContenderDetectorTest.MasterDetectorExpireSlaveZKSessionNewMaster
 1000 iterations.
make check 10 iterations.


Thanks,

Jiang Yan Xu