Refine locking.

Closes: #4429
Original Pull Request: #4431

Author: christophstrobl

Diff for: spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/MongoOperations.java

@@ -18,8 +18,12 @@
 import java.util.Collection;
 import java.util.List;
 import java.util.Set;
+import java.util.concurrent.atomic.AtomicReference;
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReentrantLock;
 import java.util.function.Consumer;
 import java.util.function.Supplier;
+import java.util.function.UnaryOperator;
 import java.util.stream.Stream;
 
 import org.bson.Document;
@@ -188,16 +192,19 @@ default SessionScoped withSession(Supplier<ClientSession> sessionProvider) {
 
 		return new SessionScoped() {
 
-			private final Object lock = new Object();
-			private @Nullable ClientSession session = null;
+			private final Lock lock = new ReentrantLock();
+			private @Nullable ClientSession session;
 
 			@Override
 			public <T> T execute(SessionCallback<T> action, Consumer<ClientSession> onComplete) {
 
-				synchronized (lock) {
+				lock.lock();
+				try {
 					if (session == null) {
 						session = sessionProvider.get();
 					}
+				} finally {
+					lock.unlock();
 				}
 
 				try {

Diff for: spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/convert/LazyLoadingProxyFactory.java

@@ -22,6 +22,9 @@
 import java.io.ObjectOutputStream;
 import java.io.Serializable;
 import java.lang.reflect.Method;
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReadWriteLock;
+import java.util.concurrent.locks.ReentrantReadWriteLock;
 import java.util.function.Supplier;
 
 import org.aopalliance.intercept.MethodInterceptor;
@@ -134,7 +137,8 @@ public Object createLazyLoadingProxy(MongoPersistentProperty property, DbRefReso
 		}
 
 		return prepareProxyFactory(propertyType,
-				() -> new LazyLoadingInterceptor(property, callback, source, exceptionTranslator)).getProxy(LazyLoadingProxy.class.getClassLoader());
+				() -> new LazyLoadingInterceptor(property, callback, source, exceptionTranslator))
+						.getProxy(LazyLoadingProxy.class.getClassLoader());
 	}
 
 	/**
@@ -171,6 +175,8 @@ public static class LazyLoadingInterceptor
 			}
 		}
 
+		private final ReadWriteLock lock = new ReentrantReadWriteLock();
+
 		private final MongoPersistentProperty property;
 		private final DbRefResolverCallback callback;
 		private final Object source;
@@ -339,25 +345,29 @@ private void readObject(ObjectInputStream in) throws IOException {
 		}
 
 		@Nullable
-		private synchronized Object resolve() {
+		private Object resolve() {
 
-			if (resolved) {
+			lock.readLock().lock();
+			try {
+				if (resolved) {
 
-				if (LOGGER.isTraceEnabled()) {
-					LOGGER.trace(String.format("Accessing already resolved lazy loading property %s.%s",
-							property.getOwner() != null ? property.getOwner().getName() : "unknown", property.getName()));
+					if (LOGGER.isTraceEnabled()) {
+						LOGGER.trace(String.format("Accessing already resolved lazy loading property %s.%s",
+								property.getOwner() != null ? property.getOwner().getName() : "unknown", property.getName()));
+					}
+					return result;
 				}
-				return result;
+			} finally {
+				lock.readLock().unlock();
 			}
 
-			try {
-				if (LOGGER.isTraceEnabled()) {
-					LOGGER.trace(String.format("Resolving lazy loading property %s.%s",
-							property.getOwner() != null ? property.getOwner().getName() : "unknown", property.getName()));
-				}
-
-				return callback.resolve(property);
+			if (LOGGER.isTraceEnabled()) {
+				LOGGER.trace(String.format("Resolving lazy loading property %s.%s",
+						property.getOwner() != null ? property.getOwner().getName() : "unknown", property.getName()));
+			}
 
+			try {
+				return executeWhileLocked(lock.writeLock(), () -> callback.resolve(property));
 			} catch (RuntimeException ex) {
 
 				DataAccessException translatedException = exceptionTranslator.translateExceptionIfPossible(ex);
@@ -370,6 +380,16 @@ private synchronized Object resolve() {
 						translatedException != null ? translatedException : ex);
 			}
 		}
+
+		private static <T> T executeWhileLocked(Lock lock, Supplier<T> stuff) {
+
+			lock.lock();
+			try {
+				return stuff.get();
+			} finally {
+				lock.unlock();
+			}
+		}
 	}
 
 }

Diff for: spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/messaging/CursorReadingTask.java

@@ -18,6 +18,8 @@
 import java.time.Duration;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.TimeUnit;
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReentrantLock;
 import java.util.function.Supplier;
 
 import org.springframework.dao.DataAccessResourceFailureException;
@@ -39,7 +41,7 @@
  */
 abstract class CursorReadingTask<T, R> implements Task {
 
-	private final Object lifecycleMonitor = new Object();
+	private final Lock lock = new ReentrantLock();
 
 	private final MongoTemplate template;
 	private final SubscriptionRequest<T, R, RequestOptions> request;
@@ -86,19 +88,14 @@ public void run() {
 					}
 				} catch (InterruptedException e) {
 
-					synchronized (lifecycleMonitor) {
-						state = State.CANCELLED;
-					}
+					doWhileLocked(lock, () -> state = State.CANCELLED);
 					Thread.currentThread().interrupt();
 					break;
 				}
 			}
 		} catch (RuntimeException e) {
 
-			synchronized (lifecycleMonitor) {
-				state = State.CANCELLED;
-			}
-
+			doWhileLocked(lock, () -> state = State.CANCELLED);
 			errorHandler.handleError(e);
 		}
 	}
@@ -114,40 +111,40 @@ public void run() {
 	 */
 	private void start() {
 
-		synchronized (lifecycleMonitor) {
+		doWhileLocked(lock, () -> {
 			if (!State.RUNNING.equals(state)) {
 				state = State.STARTING;
 			}
-		}
+		});
 
 		do {
 
-			boolean valid = false;
+			// boolean valid = false;
 
-			synchronized (lifecycleMonitor) {
+			boolean valid = executeWhileLocked(lock, () -> {
 
-				if (State.STARTING.equals(state)) {
+				if (!State.STARTING.equals(state)) {
+					return false;
+				}
 
-					MongoCursor<T> cursor = execute(() -> initCursor(template, request.getRequestOptions(), targetType));
-					valid = isValidCursor(cursor);
-					if (valid) {
-						this.cursor = cursor;
-						state = State.RUNNING;
-					} else if (cursor != null) {
-						cursor.close();
-					}
+				MongoCursor<T> cursor = execute(() -> initCursor(template, request.getRequestOptions(), targetType));
+				boolean isValid = isValidCursor(cursor);
+				if (isValid) {
+					this.cursor = cursor;
+					state = State.RUNNING;
+				} else if (cursor != null) {
+					cursor.close();
 				}
-			}
+				return isValid;
+			});
 
 			if (!valid) {
 
 				try {
 					Thread.sleep(100);
 				} catch (InterruptedException e) {
 
-					synchronized (lifecycleMonitor) {
-						state = State.CANCELLED;
-					}
+					doWhileLocked(lock, () -> state = State.CANCELLED);
 					Thread.currentThread().interrupt();
 				}
 			}
@@ -163,15 +160,15 @@ private void start() {
 	@Override
 	public void cancel() throws DataAccessResourceFailureException {
 
-		synchronized (lifecycleMonitor) {
+		doWhileLocked(lock, () -> {
 
 			if (State.RUNNING.equals(state) || State.STARTING.equals(state)) {
 				this.state = State.CANCELLED;
 				if (cursor != null) {
 					cursor.close();
 				}
 			}
-		}
+		});
 	}
 
 	@Override
@@ -181,10 +178,7 @@ public boolean isLongLived() {
 
 	@Override
 	public State getState() {
-
-		synchronized (lifecycleMonitor) {
-			return state;
-		}
+		return executeWhileLocked(lock, () -> state);
 	}
 
 	@Override
@@ -220,13 +214,12 @@ private void emitMessage(Message<T, R> message) {
 	@Nullable
 	private T getNext() {
 
-		synchronized (lifecycleMonitor) {
+		return executeWhileLocked(lock, () -> {
 			if (State.RUNNING.equals(state)) {
 				return cursor.tryNext();
 			}
-		}
-
-		throw new IllegalStateException(String.format("Cursor %s is not longer open", cursor));
+			throw new IllegalStateException(String.format("Cursor %s is not longer open", cursor));
+		});
 	}
 
 	private static boolean isValidCursor(@Nullable MongoCursor<?> cursor) {
@@ -263,4 +256,23 @@ private <V> V execute(Supplier<V> callback) {
 			throw translated != null ? translated : e;
 		}
 	}
+
+	private static void doWhileLocked(Lock lock, Runnable action) {
+
+		executeWhileLocked(lock, () -> {
+			action.run();
+			return null;
+		});
+	}
+
+	@Nullable
+	private static <T> T executeWhileLocked(Lock lock, Supplier<T> stuff) {
+
+		lock.lock();
+		try {
+			return stuff.get();
+		} finally {
+			lock.unlock();
+		}
+	}
 }