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https://issues.apache.org/jira/browse/HBASE-7377?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Gregory Chanan updated HBASE-7377:
----------------------------------
Resolution: Fixed
Status: Resolved (was: Patch Available)
Thanks for the review, Jimmy.
Committed to 0.94 and 0.96.
> Clean up TestHBase7051
> ----------------------
>
> Key: HBASE-7377
> URL: https://issues.apache.org/jira/browse/HBASE-7377
> Project: HBase
> Issue Type: Improvement
> Affects Versions: 0.94.3, 0.96.0
> Reporter: Gregory Chanan
> Assignee: Gregory Chanan
> Priority: Minor
> Fix For: 0.96.0, 0.94.4
>
> Attachments: HBASE-7377-94.patch, HBASE-7377-trunk.patch
>
>
> TestHBase7051 tests a race condition between checkAndPuts and puts, but is
> hard to follow and verify correctness on for a few reasons:
> - there are no comments and the steps of the test are numbers
> - there are variables that are read/written on different threads with no
> synchronization/volatile (e.g. checkAndPutCompleted). This may be okay
> depending on the other synchronization, but hard to verify.
> - the worker threads are not checked for exceptions. This may also be okay
> if it is not possible for the test to succeed if exceptions are thrown, but
> hard to verify.
> - The test seems to work, but I'm not sure if it's for the reasons expected.
> HBASE-7051 is recreated if the following steps occur:
> 1) Put releases row lock (where we are now)
> 2) CheckAndPut grabs row lock and reads the value prior to the put (10)
> because the MVCC has not advanced
> 3) Put advances MVCC
> On Step 1 the test does the following:
> {code}
> latch.await();
> {code}
> which waits for the checkAndPut to grab the row lock:
> {code}
> latch.countDown();
> return super.getLock(lockid, row, waitForLock);
> {code}
> But now we haven't really done anything to guarantee the race we want: the
> put will try to advance the MVCC and the checkAndPut will try to read and
> either could win, when we really want the checkAndPut read to win.
> Luckily, the put actually waits before advancing its MVCC, but only because
> it happens to fall through to the next case in the if:
> {code}
> if (count == 2) {
> try {
> putCompleted = true;
> super.releaseRowLock(lockId);
> latch.await();
> } catch (InterruptedException e) {
> // TODO Auto-generated catch block
> e.printStackTrace();
> }
> }
> if (count == 3) {
> super.releaseRowLock(lockId);
> try {
> Thread.sleep(1000);
> } catch (InterruptedException e) {
> // TODO Auto-generated catch block
> e.printStackTrace();
> }
> latch.countDown();
> }
> {code}
> which happens to sleep. I doubt this is intentional. Also, there are
> multiple latch.countDown calls even though the latch is initialized to 1.
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