RFR(XS): 8159799 - Tests using jcmd fails intermittently with Could not open PerfMemory on Windows

[Staffan Larsen]

Thanks for getting to the bottom of this!

The fix looks good. Perhaps, as David points out, FileNotFoundException is a better choice but that requires more changes as FileNotFoundException is not used anywhere else in the JVM. 

Thanks,
/Staffan
 
> On 13 Oct 2016, at 20:09, Christian Tornqvist <christian.tornqvist at oracle.com> wrote:
> 
> Hi everyone,
> 
> 
> 
> Please review this small fix for an intermittent issue we've seen when
> running tests concurrently that use jcmd/jstack. 
> 
> When running jcmd, we enumerate the perfdata files and then open them one by
> one to read things like main class names etc. If the perfdata file
> disappears (because the Java process exited) before we get to it, we end up
> with different exceptions depending on where in the code we are.
> 
> 
> 
> The code at:
> 
> http://hg.openjdk.java.net/jdk9/hs/jdk/file/3d3f338b5aea/src/jdk.jcmd/share/
> classes/sun/tools/common/ProcessArgumentMatcher.java#l88
> 
> 
> 
> handles this, the problem is that if we get all the way to
> open_sharedmem_object() in the JVM, we'll throw a java.lang.Exception which
> isn't caught by this. The fix is to throw a NPE instead of Exception and let
> the existing code handle this. 
> 
> 
> 
> Fix has been tested locally and with 30 JPRT runs (with concurrency patch
> applied), also managed to reproduce and verify this fix locally using a
> debugger to trigger the race.
> 
> 
> 
> Webrev:
> 
> http://cr.openjdk.java.net/~ctornqvi/webrev/8159799/webrev.00/
> 
> 
> 
> Bug (unfortunately not visible):
> 
> https://bugs.openjdk.java.net/browse/JDK-8159799
> 
> 
> 
> Thanks,
> 
> Christian
> 
> 
> 
> 
>