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DefaultPromise LateListener notification order

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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 2015-11-16 22:31:52 -08:00 committed by Norman Maurer
parent 1ba3a66ff7
commit cd859a7a4d
2 changed files with 163 additions and 53 deletions
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17
common/src/main/java/io/netty/util/concurrent/DefaultPromise.java
View File

@ -18,6 +18,7 @@ package io.netty.util.concurrent;
import io.netty.util.Signal;
import io.netty.util.internal.EmptyArrays;
import io.netty.util.internal.InternalThreadLocalMap;
import io.netty.util.internal.OneTimeTask;
import io.netty.util.internal.PlatformDependent;
import io.netty.util.internal.StringUtil;
import io.netty.util.internal.logging.InternalLogger;
@ -27,7 +28,7 @@ import java.util.ArrayDeque;
import java.util.concurrent.CancellationException;
import java.util.concurrent.TimeUnit;
import static java.util.concurrent.TimeUnit.*;
import static java.util.concurrent.TimeUnit.MILLISECONDS;
public class DefaultPromise<V> extends AbstractFuture<V> implements Promise<V> {
@ -576,7 +577,7 @@ public class DefaultPromise<V> extends AbstractFuture<V> implements Promise<V> {
if (listeners instanceof DefaultFutureListeners) {
final DefaultFutureListeners dfl = (DefaultFutureListeners) listeners;
execute(executor, new Runnable() {
execute(executor, new OneTimeTask() {
@Override
public void run() {
notifyListeners0(DefaultPromise.this, dfl);
@ -586,7 +587,7 @@ public class DefaultPromise<V> extends AbstractFuture<V> implements Promise<V> {
} else {
final GenericFutureListener<? extends Future<V>> l =
(GenericFutureListener<? extends Future<V>>) listeners;
execute(executor, new Runnable() {
execute(executor, new OneTimeTask() {
@Override
public void run() {
notifyListener0(DefaultPromise.this, l);
@ -612,7 +613,9 @@ public class DefaultPromise<V> extends AbstractFuture<V> implements Promise<V> {
private void notifyLateListener(final GenericFutureListener<?> l) {
final EventExecutor executor = executor();
if (executor.inEventLoop()) {
if (listeners == null && lateListeners == null) {
// Execute immediately if late listeners is empty. This allows subsequent late listeners
// that are added after completion to be notified immediately and preserver order.
if (listeners == null && (lateListeners == null || lateListeners.isEmpty())) {
final InternalThreadLocalMap threadLocals = InternalThreadLocalMap.get();
final int stackDepth = threadLocals.futureListenerStackDepth();
if (stackDepth < MAX_LISTENER_STACK_DEPTH) {
@ -658,7 +661,7 @@ public class DefaultPromise<V> extends AbstractFuture<V> implements Promise<V> {
}
}
execute(eventExecutor, new Runnable() {
execute(eventExecutor, new OneTimeTask() {
@Override
public void run() {
notifyListener0(future, l);
@ -752,7 +755,7 @@ public class DefaultPromise<V> extends AbstractFuture<V> implements Promise<V> {
if (listeners instanceof GenericProgressiveFutureListener[]) {
final GenericProgressiveFutureListener<?>[] array =
(GenericProgressiveFutureListener<?>[]) listeners;
execute(executor, new Runnable() {
execute(executor, new OneTimeTask() {
@Override
public void run() {
notifyProgressiveListeners0(self, array, progress, total);
@ -761,7 +764,7 @@ public class DefaultPromise<V> extends AbstractFuture<V> implements Promise<V> {
} else {
final GenericProgressiveFutureListener<ProgressiveFuture<V>> l =
(GenericProgressiveFutureListener<ProgressiveFuture<V>>) listeners;
execute(executor, new Runnable() {
execute(executor, new OneTimeTask() {
@Override
public void run() {
notifyProgressiveListener0(self, l, progress, total);

199
common/src/test/java/io/netty/util/concurrent/DefaultPromiseTest.java
View File

@ -22,9 +22,13 @@ import java.util.concurrent.BlockingQueue;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;
import static org.hamcrest.CoreMatchers.*;
import static org.junit.Assert.*;
import static org.hamcrest.CoreMatchers.is;
import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertSame;
import static org.junit.Assert.assertThat;
import static org.junit.Assert.assertTrue;
@SuppressWarnings("unchecked")
public class DefaultPromiseTest {
@ -83,54 +87,56 @@ public class DefaultPromiseTest {
@Test
public void testListenerNotifyOrder() throws Exception {
EventExecutor executor = new TestEventExecutor();
final BlockingQueue<FutureListener<Void>> listeners = new LinkedBlockingQueue<FutureListener<Void>>();
int runs = 100000;
try {
final BlockingQueue<FutureListener<Void>> listeners = new LinkedBlockingQueue<FutureListener<Void>>();
int runs = 100000;
for (int i = 0; i < runs; i++) {
final Promise<Void> promise = new DefaultPromise<Void>(executor);
final FutureListener<Void> listener1 = new FutureListener<Void>() {
@Override
public void operationComplete(Future<Void> future) throws Exception {
listeners.add(this);
}
};
final FutureListener<Void> listener2 = new FutureListener<Void>() {
@Override
public void operationComplete(Future<Void> future) throws Exception {
listeners.add(this);
}
};
final FutureListener<Void> listener4 = new FutureListener<Void>() {
@Override
public void operationComplete(Future<Void> future) throws Exception {
listeners.add(this);
}
};
final FutureListener<Void> listener3 = new FutureListener<Void>() {
@Override
public void operationComplete(Future<Void> future) throws Exception {
// Ensure listener4 is notified *after* this method returns to maintain the order.
future.addListener(listener4);
listeners.add(this);
}
};
for (int i = 0; i < runs; i++) {
final Promise<Void> promise = new DefaultPromise<Void>(executor);
final FutureListener<Void> listener1 = new FutureListener<Void>() {
@Override
public void operationComplete(Future<Void> future) throws Exception {
listeners.add(this);
}
};
final FutureListener<Void> listener2 = new FutureListener<Void>() {
@Override
public void operationComplete(Future<Void> future) throws Exception {
listeners.add(this);
}
};
final FutureListener<Void> listener4 = new FutureListener<Void>() {
@Override
public void operationComplete(Future<Void> future) throws Exception {
listeners.add(this);
}
};
final FutureListener<Void> listener3 = new FutureListener<Void>() {
@Override
public void operationComplete(Future<Void> future) throws Exception {
listeners.add(this);
future.addListener(listener4);
}
};
GlobalEventExecutor.INSTANCE.execute(new Runnable() {
@Override
public void run() {
promise.setSuccess(null);
}
});
GlobalEventExecutor.INSTANCE.execute(new Runnable() {
@Override
public void run() {
promise.setSuccess(null);
}
});
promise.addListener(listener1).addListener(listener2).addListener(listener3);
promise.addListener(listener1).addListener(listener2).addListener(listener3);
assertSame("Fail during run " + i + " / " + runs, listener1, listeners.take());
assertSame("Fail during run " + i + " / " + runs, listener2, listeners.take());
assertSame("Fail during run " + i + " / " + runs, listener3, listeners.take());
assertSame("Fail during run " + i + " / " + runs, listener4, listeners.take());
assertTrue("Fail during run " + i + " / " + runs, listeners.isEmpty());
assertSame("Fail 1 during run " + i + " / " + runs, listener1, listeners.take());
assertSame("Fail 2 during run " + i + " / " + runs, listener2, listeners.take());
assertSame("Fail 3 during run " + i + " / " + runs, listener3, listeners.take());
assertSame("Fail 4 during run " + i + " / " + runs, listener4, listeners.take());
assertTrue("Fail during run " + i + " / " + runs, listeners.isEmpty());
}
} finally {
executor.shutdownGracefully(0, 0, TimeUnit.SECONDS).sync();
}
executor.shutdownGracefully().sync();
}
@Test
@ -144,7 +150,7 @@ public class DefaultPromiseTest {
@Test(timeout = 2000)
public void testPromiseListenerAddWhenCompleteFailure() throws Exception {
testPromiseListenerAddWhenComplete(new RuntimeException());
testPromiseListenerAddWhenComplete(fakeException());
}
@Test(timeout = 2000)
@ -152,6 +158,103 @@ public class DefaultPromiseTest {
testPromiseListenerAddWhenComplete(null);
}
@Test(timeout = 2000)
public void testLateListenerIsOrderedCorrectlySuccess() throws InterruptedException {
final EventExecutor executor = new TestEventExecutor();
try {
testLateListenerIsOrderedCorrectly(null);
} finally {
executor.shutdownGracefully(0, 0, TimeUnit.SECONDS).sync();
}
}
@Test(timeout = 2000)
public void testLateListenerIsOrderedCorrectlyFailure() throws InterruptedException {
final EventExecutor executor = new TestEventExecutor();
try {
testLateListenerIsOrderedCorrectly(fakeException());
} finally {
executor.shutdownGracefully(0, 0, TimeUnit.SECONDS).sync();
}
}
/**
* This test is mean to simulate the following sequence of events, which all take place on the I/O thread:
* <ol>
* <li>A write is done</li>
* <li>The write operation completes, and the promise state is changed to done</li>
* <li>A listener is added to the return from the write. The {@link FutureListener#operationComplete()} updates
* state which must be invoked before the response to the previous write is read.</li>
* <li>The write operation</li>
* </ol>
*/
private static void testLateListenerIsOrderedCorrectly(Throwable cause) throws InterruptedException {
final EventExecutor executor = new TestEventExecutor();
try {
final AtomicInteger state = new AtomicInteger();
final CountDownLatch latch1 = new CountDownLatch(1);
final CountDownLatch latch2 = new CountDownLatch(2);
final Promise<Void> promise = new DefaultPromise<Void>(executor);
// Add a listener before completion so "lateListener" is used next time we add a listener.
promise.addListener(new FutureListener<Void>() {
@Override
public void operationComplete(Future<Void> future) throws Exception {
assertTrue(state.compareAndSet(0, 1));
}
});
// Simulate write operation completing, which will execute listeners in another thread.
if (cause == null) {
promise.setSuccess(null);
} else {
promise.setFailure(cause);
}
// Add a "late listener"
promise.addListener(new FutureListener<Void>() {
@Override
public void operationComplete(Future<Void> future) throws Exception {
assertTrue(state.compareAndSet(1, 2));
latch1.countDown();
}
});
// Wait for the listeners and late listeners to be completed.
latch1.await();
assertEquals(2, state.get());
// This is the important listener. A late listener that is added after all late listeners
// have completed, and needs to update state before a read operation (on the same executor).
executor.execute(new Runnable() {
@Override
public void run() {
promise.addListener(new FutureListener<Void>() {
@Override
public void operationComplete(Future<Void> future) throws Exception {
assertTrue(state.compareAndSet(2, 3));
latch2.countDown();
}
});
}
});
// Simulate a read operation being queued up in the executor.
executor.execute(new Runnable() {
@Override
public void run() {
// This is the key, we depend upon the state being set in the next listener.
assertEquals(3, state.get());
latch2.countDown();
}
});
latch2.await();
} finally {
executor.shutdownGracefully(0, 0, TimeUnit.SECONDS).sync();
}
}
private static void testPromiseListenerAddWhenComplete(Throwable cause) throws InterruptedException {
final CountDownLatch latch = new CountDownLatch(1);
final Promise<Void> promise = new DefaultPromise<Void>(ImmediateEventExecutor.INSTANCE);
@ -227,4 +330,8 @@ public class DefaultPromiseTest {
}
}
}
private static RuntimeException fakeException() {
return new RuntimeException("fake exception");
}
}