RFR 8170870: https://bugs.openjdk.java.net/browse/JDK-8170870

[David Holmes]

Hi Harold,

On 8/12/2016 4:43 AM, harold seigel wrote:
> Hi,
>
> Please review this fix for bug JDK-8170870.  The fix synchronizes access
> to the class loaders' PackageEntryTable and ModuleEntryTable structures
> by requiring callers of ClassLoaderData::modules_do() and
> ClassLoaderData::packages_do() to lock the Module_lock.
>
> The lock is needed because even during a safepoint one thread could be
> removing items from the tables while another thread is reading the
> tables.  For example, unloading a class could cause an event collection
> framework's JVM support to read the tables during a ClassUnload event
> while the VM is removing entries from these structures for modules and
> packages whose class loader got unloaded.

Sorry I don't follow this - what threads are executing code in the VM 
_during_ a safepoint ??

Also it is unclear to me whether it is safe to acquire the Module_lock 
during a safepoint - that requires no code holding the Modules_lock can 
ever block at a safepoint.

Thanks,
David
-----

> The fix also cleans up management of package qualified export lists.
>
> Open Webrev:
> http://cr.openjdk.java.net/~hseigel/bug_8170870/webrev/index.html
>
> JBS Bug:  https://bugs.openjdk.java.net/browse/JDK-8170870
>
> The fix was tested with the JCK Lang and vm tests, the JTreg hotspot,
> java/io, java/lang, and java/util tests and the nsk cololocated and the
> non-colocated tests.
>
> Thanks, Harold
>