Java tutorial
/* * Copyright 2002-2018 the original author or authors. * * 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 * * https://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.springframework.web.socket.handler; import java.io.IOException; import java.util.Queue; import java.util.concurrent.LinkedBlockingQueue; import java.util.concurrent.atomic.AtomicInteger; import java.util.concurrent.locks.Lock; import java.util.concurrent.locks.ReentrantLock; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.springframework.web.socket.CloseStatus; import org.springframework.web.socket.WebSocketMessage; import org.springframework.web.socket.WebSocketSession; /** * Wrap a {@link org.springframework.web.socket.WebSocketSession WebSocketSession} * to guarantee only one thread can send messages at a time. * * <p>If a send is slow, subsequent attempts to send more messages from other threads * will not be able to acquire the flush lock and messages will be buffered instead. * At that time, the specified buffer-size limit and send-time limit will be checked * and the session will be closed if the limits are exceeded. * * @author Rossen Stoyanchev * @author Juergen Hoeller * @since 4.0.3 */ public class ConcurrentWebSocketSessionDecorator extends WebSocketSessionDecorator { private static final Log logger = LogFactory.getLog(ConcurrentWebSocketSessionDecorator.class); private final int sendTimeLimit; private final int bufferSizeLimit; private final OverflowStrategy overflowStrategy; private final Queue<WebSocketMessage<?>> buffer = new LinkedBlockingQueue<>(); private final AtomicInteger bufferSize = new AtomicInteger(); private volatile long sendStartTime; private volatile boolean limitExceeded; private volatile boolean closeInProgress; private final Lock flushLock = new ReentrantLock(); private final Lock closeLock = new ReentrantLock(); /** * Basic constructor. * @param delegate the {@code WebSocketSession} to delegate to * @param sendTimeLimit the send-time limit (milliseconds) * @param bufferSizeLimit the buffer-size limit (number of bytes) */ public ConcurrentWebSocketSessionDecorator(WebSocketSession delegate, int sendTimeLimit, int bufferSizeLimit) { this(delegate, sendTimeLimit, bufferSizeLimit, OverflowStrategy.TERMINATE); } /** * Constructor that also specifies the overflow strategy to use. * @param delegate the {@code WebSocketSession} to delegate to * @param sendTimeLimit the send-time limit (milliseconds) * @param bufferSizeLimit the buffer-size limit (number of bytes) * @param overflowStrategy the overflow strategy to use; by default the * session is terminated. * @since 5.1 */ public ConcurrentWebSocketSessionDecorator(WebSocketSession delegate, int sendTimeLimit, int bufferSizeLimit, OverflowStrategy overflowStrategy) { super(delegate); this.sendTimeLimit = sendTimeLimit; this.bufferSizeLimit = bufferSizeLimit; this.overflowStrategy = overflowStrategy; } /** * Return the configured send-time limit (milliseconds). * @since 4.3.13 */ public int getSendTimeLimit() { return this.sendTimeLimit; } /** * Return the configured buffer-size limit (number of bytes). * @since 4.3.13 */ public int getBufferSizeLimit() { return this.bufferSizeLimit; } /** * Return the current buffer size (number of bytes). */ public int getBufferSize() { return this.bufferSize.get(); } /** * Return the time (milliseconds) since the current send started, * or 0 if no send is currently in progress. */ public long getTimeSinceSendStarted() { long start = this.sendStartTime; return (start > 0 ? (System.currentTimeMillis() - start) : 0); } @Override public void sendMessage(WebSocketMessage<?> message) throws IOException { if (shouldNotSend()) { return; } this.buffer.add(message); this.bufferSize.addAndGet(message.getPayloadLength()); do { if (!tryFlushMessageBuffer()) { if (logger.isTraceEnabled()) { logger.trace(String.format( "Another send already in progress: " + "session id '%s':, \"in-progress\" send time %d (ms), buffer size %d bytes", getId(), getTimeSinceSendStarted(), getBufferSize())); } checkSessionLimits(); break; } } while (!this.buffer.isEmpty() && !shouldNotSend()); } private boolean shouldNotSend() { return (this.limitExceeded || this.closeInProgress); } private boolean tryFlushMessageBuffer() throws IOException { if (this.flushLock.tryLock()) { try { while (true) { WebSocketMessage<?> message = this.buffer.poll(); if (message == null || shouldNotSend()) { break; } this.bufferSize.addAndGet(-message.getPayloadLength()); this.sendStartTime = System.currentTimeMillis(); getDelegate().sendMessage(message); this.sendStartTime = 0; } } finally { this.sendStartTime = 0; this.flushLock.unlock(); } return true; } return false; } private void checkSessionLimits() { if (!shouldNotSend() && this.closeLock.tryLock()) { try { if (getTimeSinceSendStarted() > getSendTimeLimit()) { String format = "Send time %d (ms) for session '%s' exceeded the allowed limit %d"; String reason = String.format(format, getTimeSinceSendStarted(), getId(), getSendTimeLimit()); limitExceeded(reason); } else if (getBufferSize() > getBufferSizeLimit()) { switch (this.overflowStrategy) { case TERMINATE: String format = "Buffer size %d bytes for session '%s' exceeds the allowed limit %d"; String reason = String.format(format, getBufferSize(), getId(), getBufferSizeLimit()); limitExceeded(reason); break; case DROP: int i = 0; while (getBufferSize() > getBufferSizeLimit()) { WebSocketMessage<?> message = this.buffer.poll(); if (message == null) { break; } this.bufferSize.addAndGet(-message.getPayloadLength()); i++; } if (logger.isDebugEnabled()) { logger.debug("Dropped " + i + " messages, buffer size: " + getBufferSize()); } break; default: // Should never happen.. throw new IllegalStateException("Unexpected OverflowStrategy: " + this.overflowStrategy); } } } finally { this.closeLock.unlock(); } } } private void limitExceeded(String reason) { this.limitExceeded = true; throw new SessionLimitExceededException(reason, CloseStatus.SESSION_NOT_RELIABLE); } @Override public void close(CloseStatus status) throws IOException { this.closeLock.lock(); try { if (this.closeInProgress) { return; } if (!CloseStatus.SESSION_NOT_RELIABLE.equals(status)) { try { checkSessionLimits(); } catch (SessionLimitExceededException ex) { // Ignore } if (this.limitExceeded) { if (logger.isDebugEnabled()) { logger.debug("Changing close status " + status + " to SESSION_NOT_RELIABLE."); } status = CloseStatus.SESSION_NOT_RELIABLE; } } this.closeInProgress = true; super.close(status); } finally { this.closeLock.unlock(); } } @Override public String toString() { return getDelegate().toString(); } /** * Enum for options of what to do when the buffer fills up. * @since 5.1 */ public enum OverflowStrategy { /** * Throw {@link SessionLimitExceededException} that would will result * in the session being terminated. */ TERMINATE, /** * Drop the oldest messages from the buffer. */ DROP } }