java.nio.BufferPoolMXBean getObjectName() occasionally returns null

[Steve Poole]

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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