/*
* Copyright 2011 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.handler.execution;
import java.util.concurrent.Executor;
import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.Channel;
import io.netty.channel.ChannelDownstreamHandler;
import io.netty.channel.ChannelEvent;
import io.netty.channel.ChannelHandler;
import io.netty.channel.ChannelHandler.Sharable;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.ChannelPipelineFactory;
import io.netty.channel.ChannelState;
import io.netty.channel.ChannelStateEvent;
import io.netty.channel.ChannelUpstreamHandler;
import io.netty.channel.Channels;
import io.netty.util.ExternalResourceReleasable;
import io.netty.util.internal.ExecutorUtil;
/**
* Forwards an upstream {@link ChannelEvent} to an {@link Executor}.
* <p>
* {@link ExecutionHandler} is often used when your {@link ChannelHandler}
* performs a blocking operation that takes long time or accesses a resource
* which is not CPU-bound business logic such as DB access. Running such
* operations in a pipeline without an {@link ExecutionHandler} will result in
* unwanted hiccup during I/O because an I/O thread cannot perform I/O until
* your handler returns the control to the I/O thread.
* <p>
* In most cases, an {@link ExecutionHandler} is coupled with an
* {@link OrderedMemoryAwareThreadPoolExecutor} because it guarantees the
* correct event execution order and prevents an {@link OutOfMemoryError}
* under load:
* <pre>
* public class DatabaseGatewayPipelineFactory implements {@link ChannelPipelineFactory} {
*
* <b>private final {@link ExecutionHandler} executionHandler;</b>
*
* public DatabaseGatewayPipelineFactory({@link ExecutionHandler} executionHandler) {
* this.executionHandler = executionHandler;
* }
*
* public {@link ChannelPipeline} getPipeline() {
* return {@link Channels}.pipeline(
* new DatabaseGatewayProtocolEncoder(),
* new DatabaseGatewayProtocolDecoder(),
* <b>executionHandler, // Must be shared</b>
* new DatabaseQueryingHandler());
* }
* }
* ...
*
* public static void main(String[] args) {
* {@link ServerBootstrap} bootstrap = ...;
* ...
* <b>{@link ExecutionHandler} executionHandler = new {@link ExecutionHandler}(
* new {@link OrderedMemoryAwareThreadPoolExecutor}(16, 1048576, 1048576))
* bootstrap.setPipelineFactory(
* new DatabaseGatewayPipelineFactory(executionHandler));</b>
* ...
* bootstrap.bind(...);
* ...
*
* while (!isServerReadyToShutDown()) {
* // ... wait ...
* }
*
* bootstrap.releaseExternalResources();
* <b>executionHandler.releaseExternalResources();</b>
* }
* </pre>
*
* Please refer to {@link OrderedMemoryAwareThreadPoolExecutor} for the
* detailed information about how the event order is guaranteed.
*
* <h3>SEDA (Staged Event-Driven Architecture)</h3>
* You can implement an alternative thread model such as
* <a href="http://en.wikipedia.org/wiki/Staged_event-driven_architecture">SEDA</a>
* by adding more than one {@link ExecutionHandler} to the pipeline.
*
* <h3>Using other {@link Executor} implementation</h3>
*
* Although it's recommended to use {@link OrderedMemoryAwareThreadPoolExecutor},
* you can use other {@link Executor} implementations. However, you must note
* that other {@link Executor} implementation might break your application
* because they often do not maintain event execution order nor interact with
* I/O threads to control the incoming traffic and avoid {@link OutOfMemoryError}.
*
* @apiviz.landmark
* @apiviz.has java.util.concurrent.ThreadPoolExecutor
*/
@Sharable
public class ExecutionHandler implements ChannelUpstreamHandler, ChannelDownstreamHandler, ExternalResourceReleasable {
private final Executor executor;
private final boolean handleDownstream;
/**
* Creates a new instance with the specified {@link Executor}.
* Specify an {@link OrderedMemoryAwareThreadPoolExecutor} if unsure.
*/
public ExecutionHandler(Executor executor) {
this(executor, false);
}
/**
* Creates a new instance with the specified {@link Executor}.
* Specify an {@link OrderedMemoryAwareThreadPoolExecutor} if unsure.
*/
public ExecutionHandler(Executor executor, boolean handleDownstream) {
if (executor == null) {
throw new NullPointerException("executor");
}
this.executor = executor;
this.handleDownstream = handleDownstream;
}
/**
* Returns the {@link Executor} which was specified with the constructor.
*/
public Executor getExecutor() {
return executor;
}
/**
* Shuts down the {@link Executor} which was specified with the constructor
* and wait for its termination.
*/
@Override
public void releaseExternalResources() {
Executor executor = getExecutor();
ExecutorUtil.terminate(executor);
if (executor instanceof ExternalResourceReleasable) {
((ExternalResourceReleasable) executor).releaseExternalResources();
}
}
@Override
public void handleUpstream(
ChannelHandlerContext context, ChannelEvent e) throws Exception {
executor.execute(new ChannelUpstreamEventRunnable(context, e));
}
@Override
public void handleDownstream(
ChannelHandlerContext ctx, ChannelEvent e) throws Exception {
// check if the read was suspend
if (!handleReadSuspend(ctx, e)) {
if (handleDownstream) {
executor.execute(new ChannelDownstreamEventRunnable(ctx, e));
} else {
ctx.sendDownstream(e);
}
}
}
/**
* Handle suspended reads
*/
protected boolean handleReadSuspend(ChannelHandlerContext ctx, ChannelEvent e) {
if (e instanceof ChannelStateEvent) {
ChannelStateEvent cse = (ChannelStateEvent) e;
if (cse.getState() == ChannelState.INTEREST_OPS &&
(((Integer) cse.getValue()).intValue() & Channel.OP_READ) != 0) {
// setReadable(true) requested
boolean readSuspended = ctx.getAttachment() != null;
if (readSuspended) {
// Drop the request silently if MemoryAwareThreadPool has
// set the flag.
e.getFuture().setSuccess();
return true;
}
}
}
return false;
}
}