RFR (S): JDK-8152949: Jigsaw crash when Klass in _fixup_module_field_list is unloaded

[Dean Long]

Do the inc_keep_alive()  and dec_keep_alive() updates need to be atomic 
by any chance?

dl

On 4/14/2016 12:29 PM, Lois Foltan wrote:
> Hello,
>
> Please review the following fix:
>
> Webrev:
>       http://cr.openjdk.java.net/~lfoltan/bug_jdk8152949/
>
> Bug: Jigsaw crash when Klass in _fixup_module_field_list is unloaded
>       https://bugs.openjdk.java.net/browse/JDK-8152949
>
> Summary:
> Prior to java.base being defined to the VM by the module system 
> initialization, classes loaded must be saved on a fixup list in order 
> to later have their java.lang.Class' module field patched with 
> java.base's java.lang.reflect.Module object once java.base is 
> defined.  Before module system initialization is complete, all classes 
> loaded must have java.base as their defining module and be loaded by 
> the boot loader.   It was erroneously assumed that all classes placed 
> on the module fixup list therefore would not die before java.base was 
> defined.  This assumption did not hold for anonymous classes which 
> have a shorter lifetime than the boot loader.  Test cases run with a 
> small heap, -Xmx2m, would cause GC to unload the anonymous classes on 
> the fixup list, later causing issues when an attempt was made to patch 
> these classes with java.base's java.lang.reflect.Module object.  Thank 
> you to Per Liden and Stefan Karlsson for contributing this fix for the 
> runtime team.
>
> Test:
> - java/lang, java/util, java/io, all Hotspot jtreg tests, Hotspot 
> colocated tests & noncolo.quick.testlist
> - several iterations of ConcurrentLinkedQueue/RemoveLeak.java which 
> exhibited the problem