Review Request: Change coarse-grain lock to fine-grain lock by pre-populating the message map so that each entry for a vertex can be locked individually and the hazard condition is also avoided.

[Bo Wang]

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https://reviews.apache.org/r/4840/
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Review request for giraph.


Summary
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Improve concurrency of putMsg / putMsgList.


This addresses bug GIRAPH-185.
    https://issues.apache.org/jira/browse/GIRAPH-185


Diffs
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http://svn.apache.org/repos/asf/incubator/giraph/trunk/src/main/java/org/apache/giraph/comm/BasicRPCCommunications.java
 1328747 
  
http://svn.apache.org/repos/asf/incubator/giraph/trunk/src/main/java/org/apache/giraph/comm/WorkerCommunications.java
 1328747 
  
http://svn.apache.org/repos/asf/incubator/giraph/trunk/src/main/java/org/apache/giraph/graph/BspServiceWorker.java
 1328747 

Diff: https://reviews.apache.org/r/4840/diff


Testing
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All test passed. Wait for review. Thanks.


Thanks,

Bo