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Prohibit blocking operations in IO threads #434
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150 changes: 150 additions & 0 deletions
150
driver/src/main/java/org/neo4j/driver/internal/async/EventLoopGroupFactory.java
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,150 @@ | ||
| /* | ||
| * Copyright (c) 2002-2017 "Neo Technology," | ||
| * Network Engine for Objects in Lund AB [http://neotechnology.com] | ||
| * | ||
| * This file is part of Neo4j. | ||
| * | ||
| * Licensed 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 org.neo4j.driver.internal.async; | ||
|
|
||
| import io.netty.bootstrap.Bootstrap; | ||
| import io.netty.channel.Channel; | ||
| import io.netty.channel.EventLoopGroup; | ||
| import io.netty.channel.nio.NioEventLoopGroup; | ||
| import io.netty.channel.socket.nio.NioSocketChannel; | ||
| import io.netty.util.concurrent.DefaultThreadFactory; | ||
| import io.netty.util.concurrent.FastThreadLocalThread; | ||
|
|
||
| import java.util.concurrent.Executor; | ||
| import java.util.concurrent.Future; | ||
| import java.util.concurrent.ThreadFactory; | ||
|
|
||
| import org.neo4j.driver.v1.Session; | ||
|
|
||
| /** | ||
| * Manages creation of Netty {@link EventLoopGroup}s, which are basically {@link Executor}s that perform IO operations. | ||
| */ | ||
| public final class EventLoopGroupFactory | ||
| { | ||
| private static final String THREAD_NAME_PREFIX = "Neo4jDriverIO"; | ||
| private static final int THREAD_PRIORITY = Thread.MAX_PRIORITY; | ||
|
|
||
| private EventLoopGroupFactory() | ||
| { | ||
| } | ||
|
|
||
| /** | ||
| * Get class of {@link Channel} for {@link Bootstrap#channel(Class)} method. | ||
| * | ||
| * @return class of the channel, which should be consistent with {@link EventLoopGroup}s returned by | ||
| * {@link #newEventLoopGroup()} and {@link #newEventLoopGroup(int)}. | ||
| */ | ||
| public static Class<? extends Channel> channelClass() | ||
| { | ||
| return NioSocketChannel.class; | ||
| } | ||
|
|
||
| /** | ||
| * Create new {@link EventLoopGroup} with specified thread count. Returned group should by given to | ||
| * {@link Bootstrap#group(EventLoopGroup)}. | ||
| * | ||
| * @param threadCount amount of IO threads for the new group. | ||
| * @return new group consistent with channel class returned by {@link #channelClass()}. | ||
| */ | ||
| public static EventLoopGroup newEventLoopGroup( int threadCount ) | ||
| { | ||
| return new DriverEventLoopGroup( threadCount ); | ||
| } | ||
|
|
||
| /** | ||
| * Create new {@link EventLoopGroup} with default thread count. Returned group should by given to | ||
| * {@link Bootstrap#group(EventLoopGroup)}. | ||
| * | ||
| * @return new group consistent with channel class returned by {@link #channelClass()}. | ||
| */ | ||
| public static EventLoopGroup newEventLoopGroup() | ||
| { | ||
| return new DriverEventLoopGroup(); | ||
| } | ||
|
|
||
| /** | ||
| * Assert that current thread is not an event loop used for async IO operations. This check is needed because | ||
| * blocking API methods like {@link Session#run(String)} are implemented on top of corresponding async API methods | ||
| * like {@link Session#runAsync(String)} using basically {@link Future#get()} calls. Deadlocks might happen when IO | ||
| * thread executes blocking API call and has to wait for itself to read from the network. | ||
| * | ||
| * @throws IllegalStateException when current thread is an event loop IO thread. | ||
| */ | ||
| public static void assertNotInEventLoopThread() throws IllegalStateException | ||
| { | ||
| if ( Thread.currentThread() instanceof DriverThread ) | ||
| { | ||
| throw new IllegalStateException( | ||
| "Blocking operation can't be executed in IO thread because it might result in a deadlock. " + | ||
| "Please do not use blocking API when chaining futures returned by async API methods." ); | ||
| } | ||
| } | ||
|
|
||
| /** | ||
| * Same as {@link NioEventLoopGroup} but uses a different {@link ThreadFactory} that produces threads of | ||
| * {@link DriverThread} class. Such threads can be recognized by {@link #assertNotInEventLoopThread()}. | ||
| */ | ||
| private static class DriverEventLoopGroup extends NioEventLoopGroup | ||
| { | ||
| DriverEventLoopGroup() | ||
| { | ||
| } | ||
|
|
||
| DriverEventLoopGroup( int nThreads ) | ||
| { | ||
| super( nThreads ); | ||
| } | ||
|
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||
| @Override | ||
| protected ThreadFactory newDefaultThreadFactory() | ||
| { | ||
| return new DriverThreadFactory(); | ||
| } | ||
| } | ||
|
|
||
| /** | ||
| * Same as {@link DefaultThreadFactory} created by {@link NioEventLoopGroup} by default, except produces threads of | ||
| * {@link DriverThread} class. Such threads can be recognized by {@link #assertNotInEventLoopThread()}. | ||
| */ | ||
| private static class DriverThreadFactory extends DefaultThreadFactory | ||
| { | ||
| DriverThreadFactory() | ||
| { | ||
| super( THREAD_NAME_PREFIX, THREAD_PRIORITY ); | ||
| } | ||
|
|
||
| @Override | ||
| protected Thread newThread( Runnable r, String name ) | ||
| { | ||
| return new DriverThread( threadGroup, r, name ); | ||
| } | ||
| } | ||
|
|
||
| /** | ||
| * Same as default thread created by {@link DefaultThreadFactory} except this dedicated class can be easily | ||
| * recognized by {@link #assertNotInEventLoopThread()}. | ||
| */ | ||
| private static class DriverThread extends FastThreadLocalThread | ||
| { | ||
| DriverThread( ThreadGroup group, Runnable target, String name ) | ||
| { | ||
| super( group, target, name ); | ||
| } | ||
| } | ||
| } | ||
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I think we should stick with
Thread.NORM_PRIORITY. Maybe we can depend on a system property to override the default, if such a requirement arises.There was a problem hiding this comment.
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MAX_PRIORITYis what netty uses inside. Here I'm basically duplicating default behaviour just to create threads of our own class. Such thread can then be easily detected with simpleinstanceof.