Update acquireVThreadInspector and enterVThreadTransitionCritical

VM is entered by the invocation of internalEnterVMFromJNI. VM is exited by the invocation of internalExitVMToJNI VM is always entered before acquireVThreadInspector and enterVThreadTransitionCritical are invoked. In these functions, the goal can be achieved by just releasing and re-acquiring VM access. The new changes just release and re-acquire VM access instead of exiting and entering the VM. This has less overhead. Addresses: eclipse-openj9#18420 (comment) Signed-off-by: Babneet Singh <[email protected]>
babsingh · Nov 9, 2023 · 5035035 · 5035035
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commit 5035035
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diff --git a/runtime/j9vm/javanextvmi.cpp b/runtime/j9vm/javanextvmi.cpp
@@ -274,10 +274,10 @@ enterVThreadTransitionCritical(J9VMThread *currentThread, jobject thread)
 
 	while(!objectAccessBarrier.inlineMixedObjectCompareAndSwapU64(currentThread, threadObj, vm->virtualThreadInspectorCountOffset, 0, (U_64)-1)) {
 		/* Thread is being inspected or unmounted, wait. */
-		vmFuncs->internalExitVMToJNI(currentThread);
+		vmFuncs->internalReleaseVMAccess(currentThread);
 		VM_AtomicSupport::yieldCPU();
 		/* After wait, the thread may suspend here. */
-		vmFuncs->internalEnterVMFromJNI(currentThread);
+		vmFuncs->internalAcquireVMAccess(currentThread);
 		threadObj = J9_JNI_UNWRAP_REFERENCE(thread);
 	}
 }

diff --git a/runtime/vm/ContinuationHelpers.cpp b/runtime/vm/ContinuationHelpers.cpp
@@ -539,10 +539,10 @@ acquireVThreadInspector(J9VMThread *currentThread, jobject thread, BOOLEAN spin)
 	vthreadInspectorCount = J9OBJECT_I64_LOAD(currentThread, threadObj, vm->virtualThreadInspectorCountOffset);
 	if (vthreadInspectorCount < 0) {
 		/* Thread is in transition, wait. */
-		vmFuncs->internalExitVMToJNI(currentThread);
+		vmFuncs->internalReleaseVMAccess(currentThread);
 		VM_AtomicSupport::yieldCPU();
 		/* After wait, the thread may suspend here. */
-		vmFuncs->internalEnterVMFromJNI(currentThread);
+		vmFuncs->internalAcquireVMAccess(currentThread);
 		if (spin) {
 			goto retry;
 		} else {