RFR (S) 8024517: runtime/CDSCompressedKPtrs/XShareAuto.java failed with RuntimeException

[David Holmes]

On 17/09/2013 12:53 AM, harold seigel wrote:
> Hi David,
>
> Thanks for the review.

Only "attempted review" at that stage :)

> My proposed fix maintains the current behavior for the client VM, which
> is that CDS is off by default if running on a server class machine.
> (Fwiw: the test for server class machine (os::is_server_class_machine())
> usually returns FALSE for c1 because NeverActAsServerClassMachine
> defaults to TRUE for c1 for arm, x86, ppc, and Sparc.)
>
> The fix only changes the behavior for -server.  Previously, CDS was off
> by default for -server only if the JVM was running on a server class
> machine.  With this change, CDS will always be off by default when
> -server is specified.  The fix implements this change by no longer
> checking for a  server class machine when running the server VM.

Okay I think I have it now. This all seems rather convoluted - not sure 
why we care about server-class-machine to make a CDS choice?

That aside what do we document about the CDS behaviour? Does this change 
need CCC request and/or updates to docs?

> The test failure reported in the bug occurred because the test was run
> with -server on a non server class machine and CDS was not disabled as
> expected.

Ok. Not sure why the test is 64-bit only though and why does it refer to 
ObjectAlignmentInBytes? Is this a copy/n/paste error when the test was 
created? I see this under the "compressed Kptrs" which is presumably 
64-bit only, but the tests doesn't see 64-bit related ??

Thanks,
David

> Thanks, Harold
>
> On 9/14/2013 3:41 AM, David Holmes wrote:
>> Hi Harold,
>>
>> Sorry I am a bit confused about the problem and solution. CDS should
>> be off when using the server VM - right? But this code:
>>
>> ! #ifndef COMPILER2
>> !   if (is_server_class_mach)
>> ! #endif
>>
>> only affects the client VM, so you seem to be saying that CDS should
>> be off on a client VM when running on a server class machine ???
>>
>> David
>>
>> On 14/09/2013 5:05 AM, harold seigel wrote:
>>> Hi,
>>>
>>> Please review this small fix for bug 8024517.  This test failed when run
>>> on a small system because CDS was not disabled by default. Although the
>>> test was run with '-server', CDS was not disabled because function
>>> os::is_server_class_machine() returned FALSE.  This fix disables CDS by
>>> default if either os::is_server_class_machine() returns TRUE or the
>>> server compiler is running.
>>>
>>> Also, the '-server' option was added to the test's '-Xshare:dump'
>>> command to ensure that the CDS region gets created by the same JVM that
>>> tries to read it.
>>>
>>> The change was tested with the XShareAuto.java test, by hand using the
>>> NeverActAsServerClassMachine and AlwaysActAsServerClassMachine options,
>>> the UTE vm quicktests, and JPRT.
>>>
>>> Open webrev at: http://cr.openjdk.java.net/~hseigel/bug_8024517/
>>> <http://cr.openjdk.java.net/%7Ehseigel/bug_8024517/>
>>> Bug: https://bugs.openjdk.java.net/browse/JDK-8024517
>>>
>>> Thanks! Harold
>