RFR 8199868: Support JNI critical functions in object pinning API

[Roman Kennke]

One more thing: we might want to move the entry points from
SharedRuntime to CollectedHeap.

Roman

> Ping!!!! anyone? please!
> 
> - Zhengyu
> 
> On 05/02/2018 05:12 PM, Per Liden wrote:
>> Hi,
>>
>> On 05/02/2018 09:41 PM, Zhengyu Gu wrote:
>>> Hi,
>>>
>>> Can I have reviews for this RFR?
>>>
>>> This patch completes object pinning for JNI critical section,
>>> provides critical native support.
>>>
>>> The approach is quite straightforward:
>>>
>>> During generating native wrapper for critical native method, it
>>> generates runtime call to pin every array argument, before unpacks them.
>>>
>>> For pinned objects, it also needs to save them for unpinning after
>>> JNI function call completes.
>>>
>>> If argument is passed on stack, it saves pinned object at the
>>> original slot (as pin_object() may move the object). For register
>>> based arguments, it reuses oop handle area (where GCLocker based
>>> implementation saves register based arguments for safepoints).
>>>
>>> Currently, only Shenandoah uses object pinning for JNI critical
>>> section, this patch has been baked quite some time there. However, I
>>> am new to Runtime Stub code, I would appreciate your comments and
>>> suggestions.
>>>
>>> I rebased patch to jdk/jdk repo.
>>>
>>> Webrev: http://cr.openjdk.java.net/~zgu/8199868/webrev.02/
>>
>> Just want to say that I would really like to see this patch go in. As
>> mentioned, it completes the object pinning story and it's useful for
>> other GCs too (at least ZGC and possibly G1). However, I also agree
>> with Aleksey that some one who really knows this code needs to review
>> this. Unfortunately that's not me. Anyone?
>>
>> cheers,
>> Per
>>
>>>
>>> Thanks,
>>>
>>> -Zhengyu
>>>
>>>
>>> On 04/06/2018 10:35 PM, Zhengyu Gu wrote:
>>>> Offline discussion with Aleksey, he suggested that
>>>> pin/unpin_critical_native_array methods can be made more generic as
>>>> pin/unpin_object.
>>>>
>>>> Updated webrev: http://cr.openjdk.java.net/~zgu/8199868/webrev.01/
>>>>
>>>> Test:
>>>>    Reran all tests, submit-hs tests still clean.
>>>>
>>>> Thanks,
>>>>
>>>> -Zhengyu
>>>>
>>>> On 04/06/2018 08:55 AM, Aleksey Shipilev wrote:
>>>>> On 04/04/2018 07:47 PM, Zhengyu Gu wrote:
>>>>>> Please review this patch that adds JNI critical native support to
>>>>>> object pinning.
>>>>>>
>>>>>> Shenandoah does not block GC while JNI critical session is in
>>>>>> progress. This patch allows it to pin
>>>>>> all incoming array objects before critical native call, and unpin
>>>>>> them after call completes.
>>>>>>
>>>>>>
>>>>>> Bug: https://bugs.openjdk.java.net/browse/JDK-8199868
>>>>>> Webrev: http://cr.openjdk.java.net/~zgu/8199868/webrev.00/
>>>>>
>>>>> Looks good to me, but somebody more savvy with runtime stub
>>>>> generation should take a closer look.
>>>>>
>>>>> *) Should probably be "Why we are here?"
>>>>>
>>>>> 2867   assert(Universe::heap()->supports_object_pinning(), "Why we
>>>>> here?");
>>>>>
>>>>> 2876   assert(Universe::heap()->supports_object_pinning(), "Why we
>>>>> here?");
>>>>>
>>>>>
>>>>> Thanks,
>>>>> -Aleksey
>>>>>