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From keith-turner <...@git.apache.org>
Subject [GitHub] accumulo pull request: ACCUMULO-3509: Allow cleanup state to be ke...
Date Mon, 04 Jan 2016 16:59:31 GMT
Github user keith-turner commented on a diff in the pull request:

    https://github.com/apache/accumulo/pull/60#discussion_r48752641
  
    --- Diff: server/tserver/src/main/java/org/apache/accumulo/tserver/tablet/Scanner.java
---
    @@ -38,100 +40,126 @@
       private ScanDataSource isolatedDataSource;
       private boolean sawException = false;
       private boolean scanClosed = false;
    +  protected Semaphore scannerSemaphore;
     
       Scanner(Tablet tablet, Range range, ScanOptions options) {
         this.tablet = tablet;
         this.range = range;
         this.options = options;
    +    scannerSemaphore = new Semaphore(1, true);
    --- End diff --
    
    This semaphore replaces a synchronized block with a fair semaphore.  AFAICT from searching
around on the web, synchronized blocks are not fair.   Do we need fairness here?  The javadocs
say its more expensive.   If its not needed, not sure should set it.
    
    I was trying to determine the difference between the semaphore and a lock for this case.
 It seems like the only difference is re-entrance, which it does not seem is needed in this
case.


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