On 18/03/2020 4:39 pm, Schmelter, Ralf wrote:
Hi David,
However I'm not clear how this solves the problem of destroying
the monitor while it can still be being accessed - is the dumping
occurring at a safepoint in the WorkGang threads?
Because when the run_task() method returns, I can be sure none
of the work gang threads still use the mutex. They have to exit the
thread_loop() method to finish the task. And by exiting the method
they have released the mutex.
All of which is happening via VM_HeapDumper::doit().
Got it.
Thanks,
David
Best regards,
Ralf
From: David Holmes <david.hol...@oracle.com>
Sent: Wednesday, March 18, 2020 6:11 AM
To: Schmelter, Ralf <ralf.schmel...@sap.com>; Ioi Lam <ioi....@oracle.com>; Langer, Christoph
<christoph.lan...@sap.com>; Yasumasa Suenaga <suen...@oss.nttdata.com>;
serguei.spit...@oracle.com <serguei.spit...@oracle.com>; hotspot-runtime-...@openjdk.java.net
runtime <hotspot-runtime-...@openjdk.java.net>
Cc: serviceability-dev@openjdk.java.net <serviceability-dev@openjdk.java.net>
Subject: Re: RFR(L) 8237354: Add option to jcmd to write a gzipped heap dump
Hi Ralf,
On 13/03/2020 9:43 pm, Schmelter, Ralf wrote:
Hi,
I have updated the webrev:
http://cr.openjdk.java.net/~rschmelter/webrevs/8237354/webrev.1/
It has the following significant changes:
- The jcmd now uses two separate flags. The -gz flag is now a boolean flag
which toggles the compression on/off. And the new -gz-level flag can be used
to change the compression level. If tried to change the jlong flag coding to
allow the old behavior (only
one flag, which acts both as a boolean flag and a jlong flag), but decided
against it, since it changes the semantic of a jlong flag. And I don't expect
the -gz-level flag to be used all that much.
- I no longer use my own threads. Instead I use the WorkGang returned from
CollectedHeap:: get_safepoint_workers(). This works fine, apart from Shenandoah
GC, which runs into assertions when calling the CollectedHeap::object_iterate()
method from a worker
thread. I'm not sure if the assertion is too strong, but since the GC is
currently experimental, I switch back to single threading in this case (as
would be the case for serial GC or epsilon GC). Using the worker threads
removes the problems the original code
had regarding destruction of the monitor used.
I'm glad to see you are no longer using your own threads, and I
apologise that I have not yet been able to look further into the thread
lifecycle issues you encountered. However I'm not clear how this solves
the problem of destroying the monitor while it can still be being
accessed - is the dumping occurring at a safepoint in the WorkGang threads?
Thanks,
David
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