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Fix event loop shutdown timing fragility (#9639)

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Motivation

The current event loop shutdown logic is quite fragile and in the
epoll/NIO cases relies on the default 1 second wait/select timeout that
applies when there are no scheduled tasks. Without this default timeout
the shutdown would hang indefinitely.

The timeout only takes effect in this case because queued scheduled
tasks are first cancelled in
SingleThreadEventExecutor#confirmShutdown(), but I _think_ even this
isn't robust, since the main task queue is subsequently serviced which
could result in some new scheduled task being queued with much later
deadline.

It also means shutdowns are unnecessarily delayed by up to 1 second.

Modifications

- Add/extend unit tests to expose the issue
- Adjust SingleThreadEventExecutor shutdown and confirmShutdown methods
to explicitly add no-op tasks to the taskQueue so that the subsequent
event loop iteration doesn't enter blocking wait (as looks like was
originally intended)

Results

Faster and more robust shutdown of event loops, allows removal of the default wait timeout.
This is a port of https://github.com/netty/netty/pull/9616
This commit is contained in:
Norman Maurer 2019-10-08 12:00:59 +04:00 committed by GitHub
parent 4a5bff2d42
commit ec8e8bd515
No known key found for this signature in database
GPG Key ID: 4AEE18F83AFDEB23
7 changed files with 231 additions and 9 deletions
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12
common/src/main/java/io/netty/util/concurrent/SingleThreadEventExecutor.java
View File

@ -442,7 +442,7 @@ public class SingleThreadEventExecutor extends AbstractScheduledEventExecutor im
}
protected void wakeup(boolean inEventLoop) {
if (!inEventLoop || state == ST_SHUTTING_DOWN) {
if (!inEventLoop) {
// Use offer as we actually only need this to unblock the thread and if offer fails we do not care as there
// is already something in the queue.
taskQueue.offer(WAKEUP_TASK);
@ -551,8 +551,11 @@ public class SingleThreadEventExecutor extends AbstractScheduledEventExecutor im
}
if (wakeup) {
taskQueue.offer(WAKEUP_TASK);
if (!addTaskWakesUp) {
wakeup(inEventLoop);
}
}
return terminationFuture();
}
@ -603,9 +606,12 @@ public class SingleThreadEventExecutor extends AbstractScheduledEventExecutor im
}
if (wakeup) {
taskQueue.offer(WAKEUP_TASK);
if (!addTaskWakesUp) {
wakeup(inEventLoop);
}
}
}
@Override
public final boolean isShuttingDown() {
@ -652,7 +658,7 @@ public class SingleThreadEventExecutor extends AbstractScheduledEventExecutor im
if (gracefulShutdownQuietPeriod == 0) {
return true;
}
wakeup(true);
taskQueue.offer(WAKEUP_TASK);
return false;
}
@ -665,7 +671,7 @@ public class SingleThreadEventExecutor extends AbstractScheduledEventExecutor im
if (nanoTime - lastExecutionTime <= gracefulShutdownQuietPeriod) {
// Check if any tasks were added to the queue every 100ms.
// TODO: Change the behavior of takeTask() so that it returns on timeout.
wakeup(true);
taskQueue.offer(WAKEUP_TASK);
try {
Thread.sleep(100);
} catch (InterruptedException e) {

124
testsuite/src/main/java/io/netty/testsuite/transport/AbstractSingleThreadEventLoopTest.java Normal file
View File

@ -0,0 +1,124 @@
/*
* Copyright 2019 The Netty Project
*
* The Netty Project licenses this file to you under the Apache License,
* version 2.0 (the "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at:
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations
* under the License.
*/
package io.netty.testsuite.transport;
import static org.junit.Assert.assertFalse;
import static org.junit.Assert.assertTrue;
import static org.junit.Assert.fail;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.RejectedExecutionException;
import java.util.concurrent.TimeUnit;
import io.netty.channel.ChannelHandler;
import io.netty.channel.IoHandlerFactory;
import io.netty.channel.MultithreadEventLoopGroup;
import org.junit.Test;
import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.EventLoop;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.ServerChannel;
import io.netty.channel.local.LocalAddress;
import io.netty.channel.local.LocalServerChannel;
import io.netty.util.concurrent.EventExecutor;
import io.netty.util.concurrent.Future;
public abstract class AbstractSingleThreadEventLoopTest {
@Test
@SuppressWarnings("deprecation")
public void shutdownBeforeStart() throws Exception {
EventLoopGroup group = new MultithreadEventLoopGroup(newIoHandlerFactory());
assertFalse(group.awaitTermination(2, TimeUnit.MILLISECONDS));
group.shutdown();
assertTrue(group.awaitTermination(200, TimeUnit.MILLISECONDS));
}
@Test
public void shutdownGracefullyZeroQuietBeforeStart() throws Exception {
EventLoopGroup group = new MultithreadEventLoopGroup(newIoHandlerFactory());
assertTrue(group.shutdownGracefully(0L, 2L, TimeUnit.SECONDS).await(200L));
}
// Copied from AbstractEventLoopTest
@Test(timeout = 5000)
public void testShutdownGracefullyNoQuietPeriod() throws Exception {
EventLoopGroup loop = new MultithreadEventLoopGroup(newIoHandlerFactory());
ServerBootstrap b = new ServerBootstrap();
b.group(loop)
.channel(serverChannelClass())
.childHandler(new ChannelHandler() { });
// Not close the Channel to ensure the EventLoop is still shutdown in time.
ChannelFuture cf = serverChannelClass() == LocalServerChannel.class
? b.bind(new LocalAddress("local")) : b.bind(0);
cf.sync().channel();
Future<?> f = loop.shutdownGracefully(0, 1, TimeUnit.MINUTES);
assertTrue(loop.awaitTermination(600, TimeUnit.MILLISECONDS));
assertTrue(f.syncUninterruptibly().isSuccess());
assertTrue(loop.isShutdown());
assertTrue(loop.isTerminated());
}
@Test
public void shutdownGracefullyBeforeStart() throws Exception {
EventLoopGroup group = new MultithreadEventLoopGroup(newIoHandlerFactory());
assertTrue(group.shutdownGracefully(200L, 1000L, TimeUnit.MILLISECONDS).await(500L));
}
@Test
public void gracefulShutdownAfterStart() throws Exception {
EventLoop loop = new MultithreadEventLoopGroup(newIoHandlerFactory()).next();
final CountDownLatch latch = new CountDownLatch(1);
loop.execute(new Runnable() {
@Override
public void run() {
latch.countDown();
}
});
// Wait for the event loop thread to start.
latch.await();
// Request the event loop thread to stop.
loop.shutdownGracefully(200L, 3000L, TimeUnit.MILLISECONDS);
// Wait until the event loop is terminated.
assertTrue(loop.awaitTermination(500L, TimeUnit.MILLISECONDS));
assertRejection(loop);
}
private static final Runnable NOOP = new Runnable() {
@Override
public void run() { }
};
private static void assertRejection(EventExecutor loop) {
try {
loop.execute(NOOP);
fail("A task must be rejected after shutdown() is called.");
} catch (RejectedExecutionException e) {
// Expected
}
}
protected abstract IoHandlerFactory newIoHandlerFactory();
protected abstract Class<? extends ServerChannel> serverChannelClass();
}

33
testsuite/src/main/java/io/netty/testsuite/transport/LocalSingleThreadEventLoopTest.java Normal file
View File

@ -0,0 +1,33 @@
/*
* Copyright 2019 The Netty Project
*
* The Netty Project licenses this file to you under the Apache License,
* version 2.0 (the "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at:
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations
* under the License.
*/
package io.netty.testsuite.transport;
import io.netty.channel.IoHandlerFactory;
import io.netty.channel.ServerChannel;
import io.netty.channel.local.LocalHandler;
import io.netty.channel.local.LocalServerChannel;
public class LocalSingleThreadEventLoopTest extends AbstractSingleThreadEventLoopTest {
@Override
protected IoHandlerFactory newIoHandlerFactory() {
return LocalHandler.newFactory();
}
@Override
protected Class<? extends ServerChannel> serverChannelClass() {
return LocalServerChannel.class;
}
}

33
testsuite/src/main/java/io/netty/testsuite/transport/NioSingleThreadEventLoopTest.java Normal file
View File

@ -0,0 +1,33 @@
/*
* Copyright 2019 The Netty Project
*
* The Netty Project licenses this file to you under the Apache License,
* version 2.0 (the "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at:
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations
* under the License.
*/
package io.netty.testsuite.transport;
import io.netty.channel.IoHandlerFactory;
import io.netty.channel.ServerChannel;
import io.netty.channel.nio.NioHandler;
import io.netty.channel.socket.nio.NioServerSocketChannel;
public class NioSingleThreadEventLoopTest extends AbstractSingleThreadEventLoopTest {
@Override
protected IoHandlerFactory newIoHandlerFactory() {
return NioHandler.newFactory();
}
@Override
protected Class<? extends ServerChannel> serverChannelClass() {
return NioServerSocketChannel.class;
}
}

15
transport-native-epoll/src/test/java/io/netty/channel/epoll/EpollEventLoopTest.java
View File

@ -18,8 +18,11 @@ package io.netty.channel.epoll;
import io.netty.channel.DefaultSelectStrategyFactory;
import io.netty.channel.EventLoop;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.IoHandlerFactory;
import io.netty.channel.ServerChannel;
import io.netty.channel.SingleThreadEventLoop;
import io.netty.channel.unix.FileDescriptor;
import io.netty.testsuite.transport.AbstractSingleThreadEventLoopTest;
import io.netty.util.concurrent.DefaultThreadFactory;
import io.netty.util.concurrent.Future;
import io.netty.util.concurrent.ThreadPerTaskExecutor;
@ -35,7 +38,7 @@ import static org.junit.Assert.assertFalse;
import static org.junit.Assert.assertNull;
import static org.junit.Assert.assertTrue;
public class EpollEventLoopTest {
public class EpollEventLoopTest extends AbstractSingleThreadEventLoopTest {
@Test
public void testScheduleBigDelayNotOverflow() {
@ -111,4 +114,14 @@ public class EpollEventLoopTest {
timerFd.close();
}
}
@Override
protected IoHandlerFactory newIoHandlerFactory() {
return EpollHandler.newFactory();
}
@Override
protected Class<? extends ServerChannel> serverChannelClass() {
return EpollServerSocketChannel.class;
}
}

17
transport-native-kqueue/src/test/java/io/netty/channel/kqueue/KQueueEventLoopTest.java
View File

@ -17,7 +17,10 @@ package io.netty.channel.kqueue;
import io.netty.channel.EventLoop;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.IoHandlerFactory;
import io.netty.channel.MultithreadEventLoopGroup;
import io.netty.channel.ServerChannel;
import io.netty.testsuite.transport.AbstractSingleThreadEventLoopTest;
import io.netty.util.concurrent.Future;
import org.junit.Test;
@ -26,11 +29,11 @@ import java.util.concurrent.TimeUnit;
import static org.junit.Assert.assertFalse;
import static org.junit.Assert.assertTrue;
public class KQueueEventLoopTest {
public class KQueueEventLoopTest extends AbstractSingleThreadEventLoopTest {
@Test
public void testScheduleBigDelayNotOverflow() {
EventLoopGroup group = new MultithreadEventLoopGroup(1, KQueueHandler.newFactory());
EventLoopGroup group = new MultithreadEventLoopGroup(1, newIoHandlerFactory());
final EventLoop el = group.next();
Future<?> future = el.schedule(() -> {
@ -41,4 +44,14 @@ public class KQueueEventLoopTest {
assertTrue(future.cancel(true));
group.shutdownGracefully();
}
@Override
protected IoHandlerFactory newIoHandlerFactory() {
return KQueueHandler.newFactory();
}
@Override
protected Class<? extends ServerChannel> serverChannelClass() {
return KQueueServerSocketChannel.class;
}
}

2
transport/src/test/java/io/netty/channel/AbstractEventLoopTest.java
View File

@ -38,7 +38,7 @@ public abstract class AbstractEventLoopTest {
b.bind(0).sync().channel();
Future<?> f = loop.shutdownGracefully(0, 1, TimeUnit.MINUTES);
assertTrue(loop.awaitTermination(2, TimeUnit.SECONDS));
assertTrue(loop.awaitTermination(600, TimeUnit.MILLISECONDS));
assertTrue(f.syncUninterruptibly().isSuccess());
assertTrue(loop.isShutdown());
assertTrue(loop.isTerminated());