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/*
* OutputBarrier.java February 2014
*
* Copyright (C) 2014, Niall Gallagher <niallg@users.sf.net>
*
* 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.simpleframework.http.socket.service;
import static java.util.concurrent.TimeUnit.MILLISECONDS;
import java.io.IOException;
import java.util.concurrent.locks.ReentrantLock;
import org.simpleframework.http.Request;
import org.simpleframework.transport.Channel;
import org.simpleframework.transport.ByteWriter;
/**
* The <code>OutputBarrier</code> is used to ensure that control
* frames and data frames do not get sent at the same time. Sending
* both at the same time could lead to the status checking thread
* being blocked and this could eventually exhaust the thread pool.
*
* @author Niall Gallagher
*/
class OutputBarrier {
/**
* This is used to check if there is an operation in progress.
*/
private final ReentrantLock lock;
/**
* This is the underlying sender used to send the frames.
*/
private final ByteWriter writer;
/**
* This is the TCP channel the frames are delivered over.
*/
private final Channel channel;
/**
* This is the length of time to wait before failing to lock.
*/
private final long duration;
/**
* Constructor for the <code>OutputBarrier</code> object. This
* is used to ensure that if there is currently a blocking write
* in place that the <code>SessionChecker</code> will not end up
* being blocked if it attempts to send a control frame.
*
* @param request this is the request to get the TCP channel from
* @param duration this is the length of time to wait for the lock
*/
public OutputBarrier(Request request, long duration) {
this.lock = new ReentrantLock();
this.channel = request.getChannel();
this.writer = channel.getWriter();
this.duration = duration;
}
/**
* This method is used to send all frames. It is important that
* a lock is used to protect this so that if there is an attempt
* to send out a control frame while the connection is blocked
* there is an exception thrown.
*
* @param frame this is the frame to send over the TCP channel
*/
public void send(byte[] frame) throws IOException {
try {
if(!lock.tryLock(duration, MILLISECONDS)) {
throw new IOException("Transport lock could not be acquired");
}
try {
writer.write(frame);
writer.flush(); // less throughput, better latency
} finally {
lock.unlock();
}
} catch(Exception e) {
throw new IOException("Error writing to transport", e);
}
}
}
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