DefaultPromise LateListener notification order
Motivation: There is a notification ordering issue in DefaultPromise when the lateListener collection is in use. The ordering issue can be observed in situations where a late listener is added to a Future returned from a write operation. It is possible that this future will run after a read operation scheduled on the I/O thread, even if the late listener is added on the I/O thread. This can lead to unexpected ordering where a listener for a write operation which must complete in order for the read operation to happen is notified after the read operation is done. Modifications: - If the lateListener collection becomes empty, it should be treated as though it was null when checking if lateListeners can be notified immediatley (instead of executing a task on the executor) Result: Ordering is more natural and will not be perceived as being out of order relative to other tasks on the same executor.
This commit is contained in:
Scott Mitchell
Norman Maurer
parent
01da38d21a
commit
eed8fe5d27
@ -18,6 +18,7 @@ package io.netty.util.concurrent;
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import io.netty.util.Signal;
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import io.netty.util.internal.EmptyArrays;
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import io.netty.util.internal.InternalThreadLocalMap;
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import io.netty.util.internal.OneTimeTask;
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import io.netty.util.internal.PlatformDependent;
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import io.netty.util.internal.StringUtil;
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import io.netty.util.internal.logging.InternalLogger;
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@ -27,7 +28,7 @@ import java.util.ArrayDeque;
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import java.util.concurrent.CancellationException;
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import java.util.concurrent.TimeUnit;
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import static java.util.concurrent.TimeUnit.*;
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import static java.util.concurrent.TimeUnit.MILLISECONDS;
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public class DefaultPromise<V> extends AbstractFuture<V> implements Promise<V> {
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@ -576,7 +577,7 @@ public class DefaultPromise<V> extends AbstractFuture<V> implements Promise<V> {
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if (listeners instanceof DefaultFutureListeners) {
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final DefaultFutureListeners dfl = (DefaultFutureListeners) listeners;
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execute(executor, new Runnable() {
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execute(executor, new OneTimeTask() {
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@Override
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public void run() {
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notifyListeners0(DefaultPromise.this, dfl);
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@ -586,7 +587,7 @@ public class DefaultPromise<V> extends AbstractFuture<V> implements Promise<V> {
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} else {
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final GenericFutureListener<? extends Future<V>> l =
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(GenericFutureListener<? extends Future<V>>) listeners;
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execute(executor, new Runnable() {
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execute(executor, new OneTimeTask() {
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@Override
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public void run() {
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notifyListener0(DefaultPromise.this, l);
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@ -612,7 +613,9 @@ public class DefaultPromise<V> extends AbstractFuture<V> implements Promise<V> {
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private void notifyLateListener(final GenericFutureListener<?> l) {
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final EventExecutor executor = executor();
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if (executor.inEventLoop()) {
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if (listeners == null && lateListeners == null) {
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// Execute immediately if late listeners is empty. This allows subsequent late listeners
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// that are added after completion to be notified immediately and preserver order.
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if (listeners == null && (lateListeners == null || lateListeners.isEmpty())) {
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final InternalThreadLocalMap threadLocals = InternalThreadLocalMap.get();
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final int stackDepth = threadLocals.futureListenerStackDepth();
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if (stackDepth < MAX_LISTENER_STACK_DEPTH) {
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@ -658,7 +661,7 @@ public class DefaultPromise<V> extends AbstractFuture<V> implements Promise<V> {
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}
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}
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execute(eventExecutor, new Runnable() {
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execute(eventExecutor, new OneTimeTask() {
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@Override
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public void run() {
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notifyListener0(future, l);
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@ -752,7 +755,7 @@ public class DefaultPromise<V> extends AbstractFuture<V> implements Promise<V> {
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if (listeners instanceof GenericProgressiveFutureListener[]) {
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final GenericProgressiveFutureListener<?>[] array =
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(GenericProgressiveFutureListener<?>[]) listeners;
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execute(executor, new Runnable() {
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execute(executor, new OneTimeTask() {
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@Override
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public void run() {
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notifyProgressiveListeners0(self, array, progress, total);
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@ -761,7 +764,7 @@ public class DefaultPromise<V> extends AbstractFuture<V> implements Promise<V> {
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} else {
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final GenericProgressiveFutureListener<ProgressiveFuture<V>> l =
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(GenericProgressiveFutureListener<ProgressiveFuture<V>>) listeners;
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execute(executor, new Runnable() {
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execute(executor, new OneTimeTask() {
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@Override
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public void run() {
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notifyProgressiveListener0(self, l, progress, total);
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@ -23,9 +23,13 @@ import java.util.concurrent.CountDownLatch;
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import java.util.concurrent.Executors;
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import java.util.concurrent.LinkedBlockingQueue;
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import java.util.concurrent.TimeUnit;
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import java.util.concurrent.atomic.AtomicInteger;
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import static org.hamcrest.CoreMatchers.*;
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import static org.junit.Assert.*;
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import static org.hamcrest.CoreMatchers.is;
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import static org.junit.Assert.assertEquals;
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import static org.junit.Assert.assertSame;
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import static org.junit.Assert.assertThat;
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import static org.junit.Assert.assertTrue;
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@SuppressWarnings("unchecked")
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public class DefaultPromiseTest {
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@ -84,6 +88,7 @@ public class DefaultPromiseTest {
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@Test
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public void testListenerNotifyOrder() throws Exception {
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EventExecutor executor = new TestEventExecutor();
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try {
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final BlockingQueue<FutureListener<Void>> listeners = new LinkedBlockingQueue<FutureListener<Void>>();
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int runs = 100000;
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@ -110,9 +115,8 @@ public class DefaultPromiseTest {
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final FutureListener<Void> listener3 = new FutureListener<Void>() {
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@Override
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public void operationComplete(Future<Void> future) throws Exception {
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// Ensure listener4 is notified *after* this method returns to maintain the order.
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future.addListener(listener4);
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listeners.add(this);
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future.addListener(listener4);
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}
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};
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@ -125,13 +129,15 @@ public class DefaultPromiseTest {
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promise.addListener(listener1).addListener(listener2).addListener(listener3);
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assertSame("Fail during run " + i + " / " + runs, listener1, listeners.take());
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assertSame("Fail during run " + i + " / " + runs, listener2, listeners.take());
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assertSame("Fail during run " + i + " / " + runs, listener3, listeners.take());
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assertSame("Fail during run " + i + " / " + runs, listener4, listeners.take());
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assertSame("Fail 1 during run " + i + " / " + runs, listener1, listeners.take());
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assertSame("Fail 2 during run " + i + " / " + runs, listener2, listeners.take());
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assertSame("Fail 3 during run " + i + " / " + runs, listener3, listeners.take());
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assertSame("Fail 4 during run " + i + " / " + runs, listener4, listeners.take());
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assertTrue("Fail during run " + i + " / " + runs, listeners.isEmpty());
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}
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executor.shutdownGracefully().sync();
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} finally {
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executor.shutdownGracefully(0, 0, TimeUnit.SECONDS).sync();
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}
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}
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@Test
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@ -145,7 +151,7 @@ public class DefaultPromiseTest {
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@Test(timeout = 2000)
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public void testPromiseListenerAddWhenCompleteFailure() throws Exception {
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testPromiseListenerAddWhenComplete(new RuntimeException());
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testPromiseListenerAddWhenComplete(fakeException());
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}
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@Test(timeout = 2000)
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@ -153,6 +159,103 @@ public class DefaultPromiseTest {
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testPromiseListenerAddWhenComplete(null);
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}
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@Test(timeout = 2000)
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public void testLateListenerIsOrderedCorrectlySuccess() throws InterruptedException {
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final EventExecutor executor = new TestEventExecutor();
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try {
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testLateListenerIsOrderedCorrectly(null);
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} finally {
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executor.shutdownGracefully(0, 0, TimeUnit.SECONDS).sync();
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}
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}
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@Test(timeout = 2000)
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public void testLateListenerIsOrderedCorrectlyFailure() throws InterruptedException {
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final EventExecutor executor = new TestEventExecutor();
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try {
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testLateListenerIsOrderedCorrectly(fakeException());
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} finally {
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executor.shutdownGracefully(0, 0, TimeUnit.SECONDS).sync();
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}
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}
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/**
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* This test is mean to simulate the following sequence of events, which all take place on the I/O thread:
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* <ol>
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* <li>A write is done</li>
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* <li>The write operation completes, and the promise state is changed to done</li>
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* <li>A listener is added to the return from the write. The {@link FutureListener#operationComplete()} updates
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* state which must be invoked before the response to the previous write is read.</li>
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* <li>The write operation</li>
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* </ol>
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*/
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private static void testLateListenerIsOrderedCorrectly(Throwable cause) throws InterruptedException {
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final EventExecutor executor = new TestEventExecutor();
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try {
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final AtomicInteger state = new AtomicInteger();
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final CountDownLatch latch1 = new CountDownLatch(1);
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final CountDownLatch latch2 = new CountDownLatch(2);
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final Promise<Void> promise = new DefaultPromise<Void>(executor);
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// Add a listener before completion so "lateListener" is used next time we add a listener.
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promise.addListener(new FutureListener<Void>() {
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@Override
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public void operationComplete(Future<Void> future) throws Exception {
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assertTrue(state.compareAndSet(0, 1));
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}
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});
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// Simulate write operation completing, which will execute listeners in another thread.
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if (cause == null) {
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promise.setSuccess(null);
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} else {
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promise.setFailure(cause);
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}
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// Add a "late listener"
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promise.addListener(new FutureListener<Void>() {
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@Override
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public void operationComplete(Future<Void> future) throws Exception {
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assertTrue(state.compareAndSet(1, 2));
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latch1.countDown();
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}
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});
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// Wait for the listeners and late listeners to be completed.
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latch1.await();
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assertEquals(2, state.get());
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// This is the important listener. A late listener that is added after all late listeners
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// have completed, and needs to update state before a read operation (on the same executor).
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executor.execute(new Runnable() {
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@Override
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public void run() {
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promise.addListener(new FutureListener<Void>() {
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@Override
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public void operationComplete(Future<Void> future) throws Exception {
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assertTrue(state.compareAndSet(2, 3));
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latch2.countDown();
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}
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});
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}
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});
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// Simulate a read operation being queued up in the executor.
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executor.execute(new Runnable() {
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@Override
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public void run() {
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// This is the key, we depend upon the state being set in the next listener.
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assertEquals(3, state.get());
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latch2.countDown();
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}
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});
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latch2.await();
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} finally {
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executor.shutdownGracefully(0, 0, TimeUnit.SECONDS).sync();
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}
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}
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private static void testPromiseListenerAddWhenComplete(Throwable cause) throws InterruptedException {
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final CountDownLatch latch = new CountDownLatch(1);
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final Promise<Void> promise = new DefaultPromise<Void>(ImmediateEventExecutor.INSTANCE);
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@ -228,4 +331,8 @@ public class DefaultPromiseTest {
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}
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}
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}
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private static RuntimeException fakeException() {
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return new RuntimeException("fake exception");
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}
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}
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