[foreign] RFR 8209151: StdLibTest fails intermittently

[Maurizio Cimadamore]

Thanks for testing, I will push and then we'll see if it got better for 
real ;-))


Maurizio


On 10/08/18 14:28, Sundararajan Athijegannathan wrote:
> The changes look good.
>
> PS. I stress tests earlier round of patch - which did resulted in NPE 
> at times. With the current patch, I no longer see NPE (on Mac) in 
> multi-round stress test of StdLibTest
>
> -Sundar
>
> On 10/08/18, 4:23 PM, Maurizio Cimadamore wrote:
>> http://cr.openjdk.java.net/~mcimadamore/panama/codecache-lock-v2/
>>
>> Maurizio
>>
>>
>> On 10/08/18 07:37, Sundararajan Athijegannathan wrote:
>>> I get 404. Is the URL correct?
>>>
>>> -Sundar
>>>
>>> On 10/08/18, 5:25 AM, Maurizio Cimadamore wrote:
>>>> New revision:
>>>>
>>>> http://cr.openjdk.java.net/~mcimadamore/panama/codecache-lock_v2/
>>>>
>>>> I realized that there was another bug lurking: in NativeInvoker we 
>>>> try to hold onto the UpcallHandler objects to prevent early 
>>>> deallocation (via the UpcallStub's Cleaner). We do so by stashing 
>>>> all the created handlers into an array list, which is held in a 
>>>> local variable. Unfortunately, JIT optimization can cause this list 
>>>> to be collected before the native method invocation is even started 
>>>> - and this can trigger spurious NPE from Java code.
>>>>
>>>> I've fixed this by adding a reachability fence on the list (thx 
>>>> John for the neat trick!).
>>>>
>>>> Maurizio
>>>>
>>>>
>>>> On 08/08/18 19:07, Maurizio Cimadamore wrote:
>>>>> The logic for retrieving and clearing native code blobs is race-y 
>>>>> - it is sometimes possible for the binder code to retrieve a stale 
>>>>> code blob that has just been deleted by the cleaner thread. This 
>>>>> causes Hotspot crashes (around NativeInvoker::free_upcall_stub) 
>>>>> and, sometimes, Java NPEs too in that area.
>>>>>
>>>>> The fix is to guard the code that accesses the CodeCache under the 
>>>>> corresponding lock (this idiom is present elsewhere in the hotspot 
>>>>> code, but I missed it the first time around).
>>>>>
>>>>> With the locking logic in place, I've been able to run the test 60 
>>>>> consecutive times w/o failures (w/o the patch I'd get a failure 
>>>>> within 10 attempts).
>>>>>
>>>>> Webrev:
>>>>>
>>>>> http://cr.openjdk.java.net/~mcimadamore/panama/codecache-lock/
>>>>>
>>>>> Maurizio
>>>>>
>>>>
>>