RFR: 8193222: EnsureLocalCapacity() should maintain capacity requests through multiple calls

[David Holmes]

Thanks Coleen!

David

On 12/12/2017 8:53 AM, coleen.phillimore at oracle.com wrote:
> 
> This looks good to me.  I've reviewed both the code and the test.
> 
> Thanks,
> Coleen
> 
> On 12/11/17 5:18 PM, David Holmes wrote:
>> Ping! Very simple, and trying to get in before cutoff.
>>
>> Thanks,
>> David
>>
>> On 10/12/2017 3:39 PM, David Holmes wrote:
>>> bug: https://bugs.openjdk.java.net/browse/JDK-8193222
>>> webrev: http://cr.openjdk.java.net/~dholmes/8193222/webrev/
>>>
>>> In product mode, for hotspot, EnsureLocalCapacity is a no-op as there 
>>> is no artificial limit applied for local refs.
>>>
>>> With -Xcheck:jni the checked mode was augmented to watch for 
>>> "excessive" use of local refs and to produce a warning if that 
>>> happened e.g.:
>>>
>>>   WARNING: JNI local refs: 41, exceeds capacity: 40
>>>
>>> That was added under JDK-8043224.
>>>
>>> The problem is that the code always modifies the planned capacity 
>>> (that expected before warnings should be used) without regard for the 
>>> fact the existing capacity may be higher than that requested. As a 
>>> result if you have a call chain like:
>>>
>>> void foo() {  // C code
>>>    env->EnsureLocalCapacity(60); // needs lots of local refs
>>>    ...
>>>    JNU_GetPlatformsString(...)
>>>        env->EnsureLocalCapacity(5); // lower than 60!
>>>     ...
>>>     // create 60 local refs
>>> }
>>>
>>> upon return the warning will be issued because the number of local 
>>> refs exceeds the most recent call to EnsureLocalCapacity.
>>>
>>> A simple fix is for EnsureLocalCapacity to only raise the planned 
>>> capacity, not lower it. That fits with the notion of "ensuring" there 
>>> is sufficient space - the function is not SetLocalcapacity. It also 
>>> fits with the way PushLocalFrame(capacity) increases the planned 
>>> capacity by "capacity" but PopLocalFrame does not reduce it again.
>>>
>>> New test added.
>>>
>>> Tested through JPRT.
>>>
>>> Thanks,
>>> David
>