ScopedMemoryAccess closeScope0 synchronization

There are gaps where async exceptions are not processed in time (e.g. JIT compiled code in a loop). Threads will wait in closeScope0 until J9VMThread->scopedError (async exception) is transferred to J9VMThread->currentException. The wait prevents a MemorySession to be closed until no more operations are being performed on it. Related: eclipse-openj9#13211 Signed-off-by: Babneet Singh <[email protected]>
babsingh · May 2, 2024 · 0de9810 · 0de9810
1 parent fab1bbd
commit 0de9810
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diff --git a/runtime/jcl/common/jdk_internal_misc_ScopedMemoryAccess.cpp b/runtime/jcl/common/jdk_internal_misc_ScopedMemoryAccess.cpp
@@ -86,6 +86,8 @@ Java_jdk_internal_misc_ScopedMemoryAccess_closeScope0(JNIEnv *env, jobject insta
 					setHaltFlag(walkThread, J9_PUBLIC_FLAGS_CLOSE_SCOPE);
 					walkThread->scopedError = errorObj;
 					walkThread->closeScopeObj = closeScopeObj;
+					/* Atomic add is not needed since exclusive VM access has been acquired. */
+					vm->closeScopeNotifyCount += 1;
 #else /* JAVA_SPEC_VERSION >= 22 */
 					scopeFound = JNI_TRUE;
 					break;
@@ -99,6 +101,21 @@ Java_jdk_internal_misc_ScopedMemoryAccess_closeScope0(JNIEnv *env, jobject insta
 	}
 
 	vmFuncs->internalExitVMToJNI(currentThread);
+
+#if JAVA_SPEC_VERSION >= 22
+	/* There are gaps where async exceptions are not processed in time
+	 * (e.g. JIT compiled code in a loop). Wait until J9VMThread->scopedError
+	 * (async exception) is transferred to J9VMThread->currentException. The
+	 * wait prevents a MemorySession to be closed until no more operations are
+	 * being performed on it.
+	 */
+	omrthread_monitor_enter(vm->closeScopeMutex);
+	while (0 != vm->closeScopeNotifyCount) {
+		omrthread_monitor_wait(vm->closeScopeMutex);
+	}
+	omrthread_monitor_exit(vm->closeScopeMutex);
+#endif /* JAVA_SPEC_VERSION >= 22 */
+
 #if JAVA_SPEC_VERSION <= 21
 	return !scopeFound;
 #endif /* JAVA_SPEC_VERSION <= 21 */

diff --git a/runtime/oti/j9nonbuilder.h b/runtime/oti/j9nonbuilder.h
@@ -6049,6 +6049,10 @@ typedef struct J9JavaVM {
 	/* Pool for allocating J9MemberNameListNode. */
 	struct J9Pool *memberNameListNodePool;
 #endif /* defined(J9VM_OPT_OPENJDK_METHODHANDLE) */
+#if JAVA_SPEC_VERSION >= 22
+	omrthread_monitor_t closeScopeMutex;
+	UDATA closeScopeNotifyCount;
+#endif /* JAVA_SPEC_VERSION >= 22 */
 } J9JavaVM;
 
 #define J9VM_PHASE_STARTUP  1

diff --git a/runtime/vm/AsyncMessageHandler.cpp b/runtime/vm/AsyncMessageHandler.cpp
@@ -143,20 +143,37 @@ javaCheckAsyncMessages(J9VMThread *currentThread, UDATA throwExceptions)
 #if JAVA_SPEC_VERSION >= 22
 		/* Check for a close scope request. */
 		if (J9_ARE_ANY_BITS_SET(publicFlags, J9_PUBLIC_FLAGS_CLOSE_SCOPE)) {
+			bool notifyThreads = false;
 			if (hasMemoryScope(currentThread, currentThread->closeScopeObj)) {
 				if (throwExceptions) {
 					currentThread->currentException = currentThread->scopedError;
 					currentThread->scopedError = NULL;
 					currentThread->closeScopeObj = NULL;
 					clearEventFlag(currentThread, J9_PUBLIC_FLAGS_CLOSE_SCOPE);
 					result = J9_CHECK_ASYNC_THROW_EXCEPTION;
+					notifyThreads = true;
 				} else {
 					VM_VMHelpers::indicateAsyncMessagePending(currentThread);
 				}
 			} else {
 				currentThread->scopedError = NULL;
 				currentThread->closeScopeObj = NULL;
 				clearEventFlag(currentThread, J9_PUBLIC_FLAGS_CLOSE_SCOPE);
+				notifyThreads = true;
+			}
+			if (notifyThreads) {
+				J9JavaVM *vm = currentThread->javaVM;
+				/* Notify all threads that are waiting in ScopedMemoryAccess closeScope0
+				 * to continue since the MemorySession(s) will no longer be used and it
+				 * is safe to close them.
+				 */
+				omrthread_monitor_enter(vm->closeScopeMutex);
+				Assert_VM_true(vm->closeScopeNotifyCount > 0);
+				vm->closeScopeNotifyCount -= 1;
+				if (0 == vm->closeScopeNotifyCount) {
+					omrthread_monitor_notify_all(vm->closeScopeMutex);
+				}
+				omrthread_monitor_exit(vm->closeScopeMutex);
 			}
 			break;
 		}

diff --git a/runtime/vm/jvminit.c b/runtime/vm/jvminit.c
@@ -1025,6 +1025,13 @@ freeJavaVM(J9JavaVM * vm)
 	}
 #endif /* defined(J9VM_OPT_CRIU_SUPPORT) */
 
+#if JAVA_SPEC_VERSION >= 22
+	if (NULL != vm->closeScopeMutex) {
+		omrthread_monitor_destroy(vm->closeScopeMutex);
+		vm->closeScopeMutex = NULL;
+	}
+#endif /* JAVA_SPEC_VERSION >= 22 */
+
 	j9mem_free_memory(vm);
 
 	if (NULL != tmpLib->self_handle) {

diff --git a/runtime/vm/vmthinit.c b/runtime/vm/vmthinit.c
@@ -99,6 +99,10 @@ UDATA initializeVMThreading(J9JavaVM *vm)
 		omrthread_monitor_init_with_name(&vm->delayedLockingOperationsMutex, 0, "Delayed locking operations mutex") ||
 #endif /* defined(J9VM_OPT_CRIU_SUPPORT) */
 
+#if JAVA_SPEC_VERSION >= 22
+		omrthread_monitor_init_with_name(&vm->closeScopeMutex, 0, "ScopedMemoryAccess closeScope0 mutex") ||
+#endif /* JAVA_SPEC_VERSION >= 22 */
+
 		initializeMonitorTable(vm)
 	)
 	{