Hi Peter,
This stuff always gives me a headache :-)
IIUC it’s all idempotent stuff, and the final field in NamedFunction should
take care of certain things.
Claes, was it intentional that you call function.resolve() after the array
store? You might need to reverse that and place a Unsafe.storeFence between
them if it is required that the published and visible function be resolved.
Paul.
> On 12 Nov 2015, at 17:26, Peter Levart <peter.lev...@gmail.com> wrote:
>
> Hi Claes,
>
> I have one concern...
>
> 645 private static NamedFunction getConstantFunction(int idx) {
> 646 NamedFunction function = FUNCTIONS[idx];
> 647 if (function != null) {
> 648 return function;
> 649 }
> 650 return setCachedFunction(idx, makeConstantFunction(idx));
> 651 }
> 652
> 653 private static synchronized NamedFunction setCachedFunction(int idx,
> final NamedFunction function) {
> 654 // Simulate a CAS, to avoid racy duplication of results.
> 655 NamedFunction prev = FUNCTIONS[idx];
> 656 if (prev != null) {
> 657 return prev;
> 658 }
> 659 FUNCTIONS[idx] = function;
> 660 function.resolve();
> 661 return function;
> 662 }
>
>
> Above is a classical double-checked locking idiom, but it is not using
> volatile variable to publish the NamedFunction instance. I wonder if this is
> safe. Even if the FUNCTIONS[idx] slot was a volatile variable, you would
> publish new instance before resolving it. Is it OK to publish unresolved
> NamedFunction(s)? There is a NamedFunction.resolvedHandle() instance method
> that makes sure NamedFunction is resolved before returning a MethodHandle,
> but there are also usages of dereferencing NamedFunction.resolvedHandle field
> directly in code. Are you sure that such unresolved or almost resolved
> instance of NamedFunction is never used in such places where
> NamedFunction.resolvedHandle field is dereferenced directly?
>
> In original code those NamedFunctions were resolved in static initializer so
> they were published properly.
>
> Regards, Peter
>
> On 11/12/2015 04:55 PM, Claes Redestad wrote:
>>
>> On 2015-11-12 14:47, Paul Sandoz wrote:
>>>> On 11 Nov 2015, at 15:32, Claes Redestad <claes.redes...@oracle.com> wrote:
>>>>
>>>> Paul,
>>>>
>>>> On 2015-11-10 11:55, Paul Sandoz wrote:
>>>>> DirectMethodHandle
>>>>> —
>>>>> 682 private static @Stable NamedFunction[] FUNCTIONS = new
>>>>> NamedFunction[NF_LIMIT];
>>>>>
>>>>> Invokers
>>>>> —
>>>>> 442 private static @Stable NamedFunction[] FUNCTIONS = new
>>>>> NamedFunction[NF_LIMIT];
>>>>>
>>>>> MethodHandleImpl
>>>>> —
>>>>> 1627 private static @Stable NamedFunction[] FUNCTIONS = new
>>>>> NamedFunction[NF_LIMIT];
>>>>>
>>>>>
>>>>> To be complete you could add “final”, thus it makes it clear that @Stable
>>>>> refers specifically to the array element.
>>>>>
>>>>> Paul.
>>>> Thanks for having a look and catching this:
>>>>
>>>> http://cr.openjdk.java.net/~redestad/8142334/webrev.03
>>>>
>>>> - added final keyword to FUNCTIONS and HANDLES
>>>> - added @Stable to ARRAYS, FILL_ARRAYS, and FILL_ARRAY_TO_RIGHT
>>>>
>>> MethodHandleImpl.java
>>> —
>>>
>>> 1413 private static final @Stable MethodHandle[] FILL_ARRAYS = new
>>> MethodHandle[FILL_ARRAYS_COUNT + 1];
>>> 1414
>>> 1415 private static MethodHandle getFillArray(int count) {
>>> 1416 assert (count > 0 && count <= FILL_ARRAYS_COUNT);
>>>
>>> Why FILL_ARRAYS_COUNT + 1 rather than FILL_ARRAYS_COUNT?
>>>
>>> Based on the previous code I would have expected the bounds to be:
>>>
>>> 0 < count < FILL_ARRAYS_COUNT
>>>
>>> Paul.
>>
>> Yes. Updated http://cr.openjdk.java.net/~redestad/8142334/webrev.03 in-place.
>>
>> /Claes
>
>
