On 11/27/2013 10:41 AM, Jaroslav Bachorik wrote:
Hi,
I've uploaded the patch with the minimal changes that should resolve
this particular problem.
http://cr.openjdk.java.net/~jbachorik/6987597/webrev.04
Looks good. I'm happy to see this simple change resolves the issue. It
would be useful to add a comment before you push to explain why
-XX:+ExplicitGCInvokesConcurrent flag is used for simplicity even though
this flag is ignored by non-concurrent GC.
Mandy
-JB-
On 22.11.2013 14:57, Jaroslav Bachorik wrote:
On 21.11.2013 17:51, Mandy Chung wrote:
Hi Jaroslav,
On 11/19/2013 6:23 AM, Jaroslav Bachorik wrote:
Please, review this test fix.
Issue : https://bugs.openjdk.java.net/browse/JDK-6987597
Webrev: http://cr.openjdk.java.net/~jbachorik/6987597/webrev.03
The fix moves the execution of the test routine to the
GarbageCollectorMXBean notification handler - at that moment it's
certain that GC has already happened and it is safe to assert the data
provided by the MBean.
This patch may have a potential issue when GC happens during the
process
of adding the notification handlers such as the number of increments is
greater than the number of registered handlers. By the time the main
thread reaches p.arriveAndAwaitAdvance, the phaser has advanced to the
next phase with few arrived parties and will wait forever (until the
next GC happens). This should rarely happen though. Note that
p.arriveAndAwaitAdvance continue to run even if the thread is
interrupted and what happens if jtreg attempts to time out the test?
Thanks for catching this. It seems that using a Semaphore with adding
permissions when a GC notification arrives would be more stable.
Does this issue only happen to CMS with background GC thread? The
proposed patch seems a little overkill. I wonder if the test should
skip if running in CMS background mode. Does
-XX:+ExplicitGCInvokesConcurrent flag will get System.gc() to run in
foreground mode in CMS (I think that may get the GC to complete before
System.gc() returns?)
Yes, currently only CMS. It seems that the semantics of System.gc()
("When control returns from the method call, the Java Virtual Machine
has made a best effort to reclaim space from all discarded objects.")
doesn't apply to the CMS collector.
Adding "-XX:-ExplicitGCInvokesConcurrent" should force System.gc() to
wait till the GC has been performed. This could help resolve this
particular problem.
-JB-
Mandy
