/*
* 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.queue;
import java.io.IOException;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.TimeUnit;
import io.netty.buffer.ChannelBuffer;
import io.netty.channel.Channel;
import io.netty.channel.ChannelEvent;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.ChannelStateEvent;
import io.netty.channel.ExceptionEvent;
import io.netty.channel.MessageEvent;
import io.netty.channel.SimpleChannelUpstreamHandler;
import io.netty.util.internal.DeadLockProofWorker;
import io.netty.util.internal.QueueFactory;
/**
* Emulates blocking read operation. This handler stores all received messages
* into a {@link BlockingQueue} and returns the received messages when
* {@link #read()}, {@link #read(long, TimeUnit)}, {@link #readEvent()}, or
* {@link #readEvent(long, TimeUnit)} method is called.
* <p>
* Please note that this handler is only useful for the cases where there are
* very small number of connections, such as testing and simple client-side
* application development.
* <p>
* Also, any handler placed after this handler will never receive
* {@code messageReceived}, {@code exceptionCaught}, and {@code channelClosed}
* events, hence it should be placed in the last place in a pipeline.
* <p>
* Here is an example that demonstrates the usage:
* <pre>
* {@link BlockingReadHandler}<{@link ChannelBuffer}> reader =
* new {@link BlockingReadHandler}<{@link ChannelBuffer}>();
* {@link ChannelPipeline} p = ...;
* p.addLast("reader", reader);
*
* ...
*
* // Read a message from a channel in a blocking manner.
* try {
* {@link ChannelBuffer} buf = reader.read(60, TimeUnit.SECONDS);
* if (buf == null) {
* // Connection closed.
* } else {
* // Handle the received message here.
* }
* } catch ({@link BlockingReadTimeoutException} e) {
* // Read timed out.
* } catch (IOException e) {
* // Other read errors
* }
* </pre>
*
* @param <E> the type of the received messages
*/
public class BlockingReadHandler<E> extends SimpleChannelUpstreamHandler {
private final BlockingQueue<ChannelEvent> queue;
private volatile boolean closed;
/**
* Creates a new instance with the default unbounded {@link BlockingQueue}
* implementation.
*/
public BlockingReadHandler() {
this(QueueFactory.createQueue(ChannelEvent.class));
}
/**
* Creates a new instance with the specified {@link BlockingQueue}.
*/
public BlockingReadHandler(BlockingQueue<ChannelEvent> queue) {
if (queue == null) {
throw new NullPointerException("queue");
}
this.queue = queue;
}
/**
* Returns the queue which stores the received messages. The default
* implementation returns the queue which was specified in the constructor.
*/
protected BlockingQueue<ChannelEvent> getQueue() {
return queue;
}
/**
* Returns {@code true} if and only if the {@link Channel} associated with
* this handler has been closed.
*
* @throws IllegalStateException
* if this handler was not added to a {@link ChannelPipeline} yet
*/
public boolean isClosed() {
return closed;
}
/**
* Waits until a new message is received or the associated {@link Channel}
* is closed.
*
* @return the received message or {@code null} if the associated
* {@link Channel} has been closed
* @throws IOException
* if failed to receive a new message
* @throws InterruptedException
* if the operation has been interrupted
*/
public E read() throws IOException, InterruptedException {
ChannelEvent e = readEvent();
if (e == null) {
return null;
}
if (e instanceof MessageEvent) {
return getMessage((MessageEvent) e);
} else if (e instanceof ExceptionEvent) {
throw (IOException) new IOException().initCause(((ExceptionEvent) e).getCause());
} else {
throw new IllegalStateException();
}
}
/**
* Waits until a new message is received or the associated {@link Channel}
* is closed.
*
* @param timeout
* the amount time to wait until a new message is received.
* If no message is received within the timeout,
* {@link BlockingReadTimeoutException} is thrown.
* @param unit
* the unit of {@code timeout}
*
* @return the received message or {@code null} if the associated
* {@link Channel} has been closed
* @throws BlockingReadTimeoutException
* if no message was received within the specified timeout
* @throws IOException
* if failed to receive a new message
* @throws InterruptedException
* if the operation has been interrupted
*/
public E read(long timeout, TimeUnit unit) throws IOException, InterruptedException {
ChannelEvent e = readEvent(timeout, unit);
if (e == null) {
return null;
}
if (e instanceof MessageEvent) {
return getMessage((MessageEvent) e);
} else if (e instanceof ExceptionEvent) {
throw (IOException) new IOException().initCause(((ExceptionEvent) e).getCause());
} else {
throw new IllegalStateException();
}
}
/**
* Waits until a new {@link ChannelEvent} is received or the associated
* {@link Channel} is closed.
*
* @return a {@link MessageEvent} or an {@link ExceptionEvent}.
* {@code null} if the associated {@link Channel} has been closed
* @throws InterruptedException
* if the operation has been interrupted
*/
public ChannelEvent readEvent() throws InterruptedException {
detectDeadLock();
if (isClosed()) {
if (getQueue().isEmpty()) {
return null;
}
}
ChannelEvent e = getQueue().take();
if (e instanceof ChannelStateEvent) {
// channelClosed has been triggered.
assert closed;
return null;
} else {
return e;
}
}
/**
* Waits until a new {@link ChannelEvent} is received or the associated
* {@link Channel} is closed.
*
* @param timeout
* the amount time to wait until a new {@link ChannelEvent} is
* received. If no message is received within the timeout,
* {@link BlockingReadTimeoutException} is thrown.
* @param unit
* the unit of {@code timeout}
*
* @return a {@link MessageEvent} or an {@link ExceptionEvent}.
* {@code null} if the associated {@link Channel} has been closed
* @throws BlockingReadTimeoutException
* if no event was received within the specified timeout
* @throws InterruptedException
* if the operation has been interrupted
*/
public ChannelEvent readEvent(long timeout, TimeUnit unit) throws InterruptedException, BlockingReadTimeoutException {
detectDeadLock();
if (isClosed()) {
if (getQueue().isEmpty()) {
return null;
}
}
ChannelEvent e = getQueue().poll(timeout, unit);
if (e == null) {
throw new BlockingReadTimeoutException();
} else if (e instanceof ChannelStateEvent) {
// channelClosed has been triggered.
assert closed;
return null;
} else {
return e;
}
}
private void detectDeadLock() {
if (DeadLockProofWorker.PARENT.get() != null) {
throw new IllegalStateException(
"read*(...) in I/O thread causes a dead lock or " +
"sudden performance drop. Implement a state machine or " +
"call read*() from a different thread.");
}
}
@Override
public void messageReceived(ChannelHandlerContext ctx, MessageEvent e)
throws Exception {
getQueue().put(e);
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, ExceptionEvent e)
throws Exception {
getQueue().put(e);
}
@Override
public void channelClosed(ChannelHandlerContext ctx, ChannelStateEvent e)
throws Exception {
closed = true;
getQueue().put(e);
}
@SuppressWarnings("unchecked")
private E getMessage(MessageEvent e) {
return (E) e.getMessage();
}
}