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https://issues.apache.org/jira/browse/ACCUMULO-3509?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15081330#comment-15081330
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ASF GitHub Bot commented on ACCUMULO-3509:
------------------------------------------
Github user keith-turner commented on a diff in the pull request:
https://github.com/apache/accumulo/pull/60#discussion_r48749879
--- 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);
}
- public synchronized ScanBatch read() throws IOException,
TabletClosedException {
-
- if (sawException)
- throw new IllegalStateException("Tried to use scanner after
exception occurred.");
+ public ScanBatch read() throws IOException, TabletClosedException {
if (scanClosed)
--- End diff --
Below is from the semaphore javadoc. Reading that is sounds like there is
no guarantee of seeing a change to `scanClosed` until after `acquire()`.
```
Memory consistency effects: Actions in a thread prior to calling a
"release" method such as release() happen-before actions following a successful
"acquire" method such as acquire() in another thread.
```
> Scanner lock cause Tablet lock, hence preventing idle scans from being swept,
> hence blocking SimpleTimer thread
> ----------------------------------------------------------------------------------------------------------------
>
> Key: ACCUMULO-3509
> URL: https://issues.apache.org/jira/browse/ACCUMULO-3509
> Project: Accumulo
> Issue Type: Bug
> Components: tserver
> Affects Versions: 1.6.0
> Reporter: marco polo
> Assignee: marco polo
> Fix For: 1.6.5, 1.7.1, 1.8.0
>
>
> Synchronization with Tablet$Scanner via a read() will block close() being
> called via the sweep method in TabletServer. As a result, the SimpleTimer
> thread does not continue, and idle threads grow until the scan completes.
> My patch, which is forthcoming, converts synchronized methods to use a fair
> lock. If the lock is held by a read call, the close call will attempt to
> obtain it, time out, and return indicating a close was not successful. The
> sweep will continue, and the SimpleTimer thread will respawn later,
> attempting closure on those Tablets at a later time.
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