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

[Christian Tornqvist]

Hi Staffan/David,

I looked at how the other platforms deal with it, they throw an
IllegalArgumentException when they fail to open the file. I think it makes
sense for Windows to do the same, please see the updated webrev with IAE
instead of a NPE:

http://cr.openjdk.java.net/~ctornqvi/webrev/8159799/webrev.01/

Thanks,
Christian 

-----Original Message-----
From: Staffan Larsen [mailto:staffan.larsen at oracle.com] 
Sent: Friday, October 14, 2016 2:19 AM
To: Christian Tornqvist <christian.tornqvist at oracle.com>
Cc: hotspot-runtime-dev at openjdk.java.net
Subject: Re: RFR(XS): 8159799 - Tests using jcmd fails intermittently with
Could not open PerfMemory on Windows

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
> 
> 
> 
> 
>