closeScope0 should not walk all threads

[tajila]

Java_jdk_internal_misc_ScopedMemoryAccess_closeScope0 can be updated to only walk threads that can run java code. currently it walks all vmthreads.

	J9VMThread *walkThread = J9_LINKED_LIST_START_DO(vm->mainThread);
		while (NULL != walkThread) {
			J9StackWalkState walkState;
			walkState.walkThread = walkThread;
			walkState.flags = J9_STACKWALK_ITERATE_FRAMES | J9_STACKWALK_ITERATE_O_SLOTS;
			walkState.skipCount = 0;
			walkState.userData1 = (void *)scope;
			walkState.userData2 = (void *)&scopeNotFound;
			walkState.frameWalkFunction = closeScope0FrameWalkFunction;
			walkState.objectSlotWalkFunction = closeScope0OSlotWalkFunction;

			vm->walkStackFrames(walkThread, &walkState);
			if (JNI_FALSE == *(jboolean *)walkState.userData2) {
				/* scope found */
				break;
			}

			walkThread = J9_LINKED_LIST_NEXT_DO(vm->mainThread, walkThread);
		}
		vmFuncs->releaseExclusiveVMAccess(currentThread);

The use of VM_VMHelpers::threadCanRunJavaCode(walkThread) can identify the threads that need to be walked.

[tajila]

@EricYangIBM Please take a look

[gacholio]

Threads which can't run java code will have trivial stacks. Is this an API worthy of optimization?

[tajila]

Its a trivial change, theres no risk in doing it.