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From: wjsl <git@git.apache.org>
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Subject: [GitHub] accumulo pull request: ACCUMULO-4229 BatchWriter Locator
 cache out...
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Message-Id: <20160424155514.0CCD5DFE60@git1-us-west.apache.org>
Date: Sun, 24 Apr 2016 15:55:14 +0000 (UTC)

Github user wjsl commented on a diff in the pull request:

    https://github.com/apache/accumulo/pull/96#discussion_r60846778
  
    --- Diff: core/src/main/java/org/apache/accumulo/core/client/impl/TabletServerBatchReaderIterator.java ---
    @@ -329,6 +331,8 @@ private void processFailures(Map<KeyExtent,List<Range>> failures, ResultReceiver
     
         // since the first call to binRanges clipped the ranges to within a tablet, we should not get only
         // bin to the set of failed tablets
    +    if (!locator.isValid())
    +      locator = new TimeoutTabletLocator(TabletLocator.getLocator(instance, new Text(table)), timeout);
    --- End diff --
    
    Since TabletServerBatchReaderIterator#lookup is synchronized, the reassignment is thread-safe for other accesses that respect the instance's lock. This reassignment, in processFailures, only ever occurs though a branch from a QueryTask, which doesn't do the reassignment in a synchronized block (it does use a semaphore inside of the QueryTask, but that's separate from the TSBI instance lock). 
    
    So, where I'm going with this: is it safe to do these re-assignments outside of a synchronized block? It's implied to me that these updates can happen in different threads, since the QueryTasks are executed via an ExecutorService.


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