[jdk17] RFR: 8260684: vmTestbase/gc/gctests/PhantomReference/phantom002/TestDescription.java timed out

Kim Barrett kbarrett at openjdk.java.net
Sun Jun 20 21:50:25 UTC 2021


On Sun, 20 Jun 2021 18:43:33 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

> Please review this fix of
> vmTestbase/gc/gctests/PhantomReference/phantom001/phantom001.java
> to eliminate a race that can lead to the test very occasionally hanging and
> eventually timing out.
> 
> When the referent being tested by a particular iteration is a finalizable
> class, the test invoked eatMemory() repeatedly until the referent's
> finalize() function set a flag, then called eatMemory() once more to cause
> the reference to be cleared and notified.  The problem with this is that
> eatMemory() might trigger its GCs before the finalization thread has dropped
> the referent, so the referent is still live and the reference has not been
> cleared and notified afterward.
> 
> The testing thread then proceeds to wait for the reference to be notified.
> This usually doesn't cause a problem because other threads will trigger
> further GCs, and the finalization thread will eventually drop the object.
> However, if the test is nearing completion and this situation arises in the
> last thread running, it will wait forever for the notification that isn't
> coming.
> 
> While investigating this issue I did a bunch of code cleanup (for example,
> there was some really badly formatted code), refactoring, and commenting.
> As a result, a large fraction of the test has changed, though mostly in ways
> that don't affect it's function.  The first of the two commits in the PR is
> a whitespace-only cleanup.  Excluding it may make reviewing easier.
> 
> Testing:
> Ran the phantom002 test a couple thousand times.
> 
> Using a modified version of the test, verified that the described problem
> case actually occurs; that is, one eatMemory call is sometimes insufficient
> to cause clearing of the reference because the referent is still live on the
> finalization thread.

Oops, I messed up the last change, and testing didn't find it.  Withdrawing this change.

-------------

PR: https://git.openjdk.java.net/jdk17/pull/106


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