Merge pull request eclipse-openj9#18630 from amicic/alreadyHaveExclus…

…ive-v0.43.0 (0.43) Prevent requesting exclusive, if already acquired
thallium · Dec 14, 2023 · 54becab · 54becab
2 parents 8d1235c + a1b3ec7
commit 54becab
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Showing 3 changed files with 33 additions and 5 deletions.
diff --git a/runtime/jvmti/jvmtiClass.c b/runtime/jvmti/jvmtiClass.c
@@ -1233,10 +1233,14 @@ redefineClassesCommon(jvmtiEnv* env,
 		/* Eliminate dark matter so that none will be encountered in prepareToFixMemberNames(). */
 		UDATA savedAllowUserHeapWalkFlag = vm->requiredDebugAttributes & J9VM_DEBUG_ATTRIBUTE_ALLOW_USER_HEAP_WALK;
 		vm->requiredDebugAttributes |= J9VM_DEBUG_ATTRIBUTE_ALLOW_USER_HEAP_WALK;
-		/* J9MMCONSTANT_EXPLICIT_GC_RASDUMP_COMPACT allows the GC to run while the current thread is holding
-		 * exclusive VM access.
-		 */
-		vm->memoryManagerFunctions->j9gc_modron_global_collect_with_overrides(currentThread, J9MMCONSTANT_EXPLICIT_GC_RASDUMP_COMPACT);
+
+		/* This is to help with Metronome to avoid requesting Exclusive if we already have SafePoint, which may not look as Exclusive to the requester thread */
+		vm->alreadyHaveExclusive = TRUE;
+
+		vm->memoryManagerFunctions->j9gc_modron_global_collect_with_overrides(currentThread, J9MMCONSTANT_EXPLICIT_GC_EXCLUSIVE_VMACCESS_ALREADY_ACQUIRED);
+
+		vm->alreadyHaveExclusive = FALSE;
+
 		if (0 == savedAllowUserHeapWalkFlag) {
 			/* Clear the flag to restore its original value. */
 			vm->requiredDebugAttributes &= ~J9VM_DEBUG_ATTRIBUTE_ALLOW_USER_HEAP_WALK;

diff --git a/runtime/oti/j9nonbuilder.h b/runtime/oti/j9nonbuilder.h
@@ -5912,6 +5912,7 @@ typedef struct J9JavaVM {
 	UDATA addModulesCount;
 	UDATA safePointState;
 	UDATA safePointResponseCount;
+	BOOLEAN alreadyHaveExclusive;
 	struct J9VMRuntimeStateListener vmRuntimeStateListener;
 #if defined(J9VM_INTERP_ATOMIC_FREE_JNI_USES_FLUSH)
 #if defined(J9UNIX) || defined(AIXPPC)

diff --git a/runtime/vm/VMAccess.cpp b/runtime/vm/VMAccess.cpp
@@ -755,6 +755,11 @@ acquireExclusiveVMAccessFromExternalThread(J9JavaVM * vm)
 	UDATA vmResponsesExpected = 0;
 	UDATA jniResponsesExpected = 0;
 
+	/* If exclusive has already been acquired, nothing need be done here */
+	if (vm->alreadyHaveExclusive) {
+		return;
+	}
+
 	synchronizeRequestsFromExternalThread(vm, TRUE);
 
 	/* Post the halt request to all threads */
@@ -836,6 +841,12 @@ void
 releaseExclusiveVMAccessFromExternalThread(J9JavaVM * vm)
 {
 	J9VMThread * currentThread;
+
+	/* If exclusive has already been acquired, nothing need be done here */
+	if (vm->alreadyHaveExclusive) {
+		return;
+	}
+
 	Assert_VM_true(J9_XACCESS_EXCLUSIVE == vm->exclusiveAccessState);
 
 	/* Acquire these monitors in the same order as in allocateVMThread to prevent deadlock */
@@ -913,6 +924,11 @@ requestExclusiveVMAccessMetronomeTemp(J9JavaVM *vm, UDATA block, UDATA *vmRespon
 	UDATA jniResponsesExpected = 0;
 	*gcPriority = J9THREAD_PRIORITY_MAX;
 
+	/* If exclusive has already been acquired, nothing need be done here */
+	if (vm->alreadyHaveExclusive) {
+		return FALSE;
+	}
+
 	/* Check if another party is requesting X access already. */
 	if (FALSE == synchronizeRequestsFromExternalThread(vm, block)) {
 		/* Yes, there was another party requesting X access, but because we did not want to block,
@@ -1010,7 +1026,14 @@ waitForExclusiveVMAccessMetronome(J9VMThread * vmThread, UDATA responsesRequired
 void
 waitForExclusiveVMAccessMetronomeTemp(J9VMThread * vmThread, UDATA vmResponsesRequired, UDATA jniResponsesRequired)
 {
-	waitForResponseFromExternalThread(vmThread->javaVM, vmResponsesRequired, jniResponsesRequired);
+	J9JavaVM *vm = vmThread->javaVM;
+
+	/* If exclusive has already been acquired, nothing need be done here */
+	if (vm->alreadyHaveExclusive) {
+		return;
+	}
+
+	waitForResponseFromExternalThread(vm, vmResponsesRequired, jniResponsesRequired);
 
 	VM_VMAccess::backOffFromSafePoint(vmThread);