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

[Lois Foltan]

On 4/14/2016 4:23 PM, Dean Long wrote:
> Do the inc_keep_alive()  and dec_keep_alive() updates need to be 
> atomic by any chance?

Thanks Dean for the review and good point.  I will make that change and 
send out an updated webrev.
Lois

>
> 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
>