RFR 8171971: Fix timing bug in JVM management of package export lists

[serguei.spitsyn at oracle.com]

+1

Thanks,
Serguei


On 1/20/17 05:55, Lois Foltan wrote:
> Looks good.
> Lois
>
> On 1/19/2017 6:38 PM, harold seigel wrote:
>> Hi,
>>
>> Here is an updated webrev containing the changes that you suggested.
>>
>> http://cr.openjdk.java.net/~hseigel/bug_8171971.2/webrev/index.html
>>
>> Could you take another look?
>>
>> Thanks, Harold
>>
>> On 1/19/2017 1:37 PM, harold seigel wrote:
>>> Hi Karen, Lois,
>>>
>>> Thanks for the review!  Please see comments in-line.
>>>
>>> Harold
>>>
>>>
>>> On 1/19/2017 11:54 AM, Karen Kinnear wrote:
>>>> Harold,
>>>>
>>>> Thank you for doing this. And for the comments on the states.
>>>>
>>>> Looks good. I believe that the changes you have made have fixed the 
>>>> timing holes. Thank you.
>>>>
>>>> 1) packageEntry.hpp: 145: set_unqual_exported()
>>>> It would be helpful to have a comment that this explicitly sets 
>>>> PKG_EXP_UNQUALIFIED and clears PKG_EXP_ALLUNNAMED.
>>> Done
>>>>
>>>> I realized my concept of states is slightly different,
>>>> with AllUnnamed, NamedExports and AllUnnamed+NamedExports being 
>>>> different states. In future, when we rework this
>>>> for performance, let’s revisit the states.
>>> Agreed
>>>>
>>>>> On Jan 19, 2017, at 10:14 AM, Lois Foltan <lois.foltan at oracle.com 
>>>>> <mailto:lois.foltan at oracle.com>> wrote:
>>>>>
>>>>>
>>>>> On 1/18/2017 10:05 AM, harold seigel wrote:
>>>>>> Hi,
>>>>>>
>>>>>> Please review this fix for the package export timing holes 
>>>>>> discussed in JDK-8171971.  The fix reduces the number of 
>>>>>> PackageEntry fields that are used to maintain a package's export 
>>>>>> state and uses the Module_lock to protect all access to these 
>>>>>> fields.
>>>>>>
>>>>>> Also, in cases where a package transitions from having qualified 
>>>>>> exports to being unqualifiedly exported, it fixes the cleanup of 
>>>>>> its qualified export list by removing the 
>>>>>> _exported_pending_delete field and using just 
>>>>>> is_unqual_exported() to determine when the qualified exports list 
>>>>>> can be purged (at a safepoint).
>>>>>>
>>>>>> Open Webrev: 
>>>>>> http://cr.openjdk.java.net/~hseigel/bug_8171971/webrev/ 
>>>>>> <http://cr.openjdk.java.net/%7Ehseigel/bug_8171971/webrev/>
>>>>>>
>>>>>> JBS Bug: https://bugs.openjdk.java.net/browse/JDK-8171971
>>>>>>
>>>>>> The fix was tested with the hotspot, java/lang, java/util, 
>>>>>> java/io, JFR, and other JTReg tests, the JCK lang and VM tests, 
>>>>>> RBT tier2 - tier5 tests on LinuxX64, and the colocated and 
>>>>>> non-colocated NSK tests.
>>>>>
>>>>> Hi Harold,
>>>>>
>>>>> Looks good! A couple of comments in 
>>>>> src/share/vm/classfile/packageEntry.hpp:
>>>>>
>>>>> - line #133, the method has_qual_exports_list().  A comment should 
>>>>> be added ahead of this method to indicate that even if the 
>>>>> _qualified_exports list is empty the package is still considered 
>>>>> qualifiedly exported and a similar comment should be added to 
>>>>> PackageEntry::purge_qualified_exports().  During a GC safepoint, 
>>>>> it could be the scenario that all modules on a given package's 
>>>>> qualified export list die, thus leaving an allocated but empty 
>>>>> _qualified_exports field.  If the _qualified_exports GrowableArray 
>>>>> was deleted in that scenario, then according to the new 
>>>>> _exports_flag and a NULL value for _qualified_exports, the package 
>>>>> would erroneously not be considered qualifiedly exported anymore.
>>> Good point.  I added the comments.
>>>> So not deleting the GrowableArray today is deliberate, because the 
>>>> transition from qualifiedly exported to not exported is not 
>>>> currently valid.
>>>> Agreed, we may want to revisit that in future.
>>>>
>>>> 2) Harold, could you possibly add that state change to the comment 
>>>> to the “A package cannot transition from”, i.e. after line 58?
>>> Done
>>>>> This can be reworked in the future to have the _exports_flag 
>>>>> contain definitions for all possible states.  Relying on the state 
>>>>> of whether _qualified_exports field is NULL or not can be 
>>>>> problematic, but I think your changes do improve upon ensuring a 
>>>>> PackageEntry maintains a valid state.
>>>>>
>>>>> - line #86 - please add a blank line for readability
>>> okay
>>>>> - line #139 & #143 please out the return expression in parentheses.
>>> (okay)
>>>>>
>>>>> Thanks,
>>>>> Lois
>>>>>
>>>>>>
>>>>>> Thanks, Harold
>>>>
>>>> thanks,
>>>> Karen
>>>>
>>>
>>
>