java.nio.BufferPoolMXBean getObjectName() occasionally returns null

[Alan Bateman]

(cc'ing serviceability-dev)

Thanks Steve, looks like this crept as part of some refactoring work 
[1]. Looks like PlatformLoggingMXBean has the same issue. I've created 
the following bug to track it:

7068328: BufferPoolMXBean and PlatformLoggingMXBean getObjectName may 
return null

If no one take it in the next few days then I can take it and get it 
push to jdk8 (listing you are contributer). The test will need a bit of 
clean-up, re-formatting, and throwing an exception rather than calling 
System.exit for example.

-Alan

[1] http://hg.openjdk.java.net/jdk7/jdk7/jdk/rev/77dd50ba670b



-------- Original Message --------
Subject: 	java.nio.BufferPoolMXBean getObjectName() occasionally returns 
null
Date: 	Mon, 18 Jul 2011 22:54:35 +0100
From: 	Steve Poole <spoole at linux.vnet.ibm.com>
To: 	nio-dev at openjdk.java.net



Hi all,  a small fix to a race condition that occurs under extreme and 
probably unrepresentative loading...

sun.management.ManagementFactoryHelper provides the default 
implementation of java.nio.BufferPoolMXBean. The  getObjectName() method 
uses a volatile field to store the object name. The name is filled in 
using a lazy sync method. Under high load a timing window is exposed in 
which the lazy sync succeeds but a caller still recieves null.

The failing code is question is in 
src/share/classes/sun/management/ManagementFactoryHelper.java

The diff and testcase are attached.

I don't know if the testcase is the right form - it creates a bunch of 
threads that drive the method to expose the problem and is fairly 
quick.   I can show it happening on Ubuntu with JDK7 and with my local 
build of JDK8.

Cheers

Steve



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