| /* |
| * Licensed to the Apache Software Foundation (ASF) under one or more |
| * contributor license agreements. See the NOTICE file distributed with |
| * this work for additional information regarding copyright ownership. |
| * The ASF 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 org.apache.catalina.valves; |
| |
| import java.io.IOException; |
| import java.util.concurrent.Semaphore; |
| |
| import javax.servlet.ServletException; |
| |
| import org.apache.catalina.LifecycleException; |
| import org.apache.catalina.LifecycleState; |
| import org.apache.catalina.connector.Request; |
| import org.apache.catalina.connector.Response; |
| |
| |
| /** |
| * <p>Implementation of a Valve that limits concurrency.</p> |
| * |
| * <p>This Valve may be attached to any Container, depending on the granularity |
| * of the concurrency control you wish to perform. Note that internally, some |
| * async requests may require multiple serial requests to complete what - to the |
| * user - appears as a single request.</p> |
| * |
| * @author Remy Maucherat |
| */ |
| public class SemaphoreValve extends ValveBase { |
| |
| //------------------------------------------------------ Constructor |
| public SemaphoreValve() { |
| super(true); |
| } |
| |
| |
| // ----------------------------------------------------- Instance Variables |
| |
| /** |
| * Semaphore. |
| */ |
| protected Semaphore semaphore = null; |
| |
| |
| // ------------------------------------------------------------- Properties |
| |
| |
| /** |
| * Concurrency level of the semaphore. |
| */ |
| protected int concurrency = 10; |
| public int getConcurrency() { return concurrency; } |
| public void setConcurrency(int concurrency) { this.concurrency = concurrency; } |
| |
| |
| /** |
| * Fairness of the semaphore. |
| */ |
| protected boolean fairness = false; |
| public boolean getFairness() { return fairness; } |
| public void setFairness(boolean fairness) { this.fairness = fairness; } |
| |
| |
| /** |
| * Block until a permit is available. |
| */ |
| protected boolean block = true; |
| public boolean getBlock() { return block; } |
| public void setBlock(boolean block) { this.block = block; } |
| |
| |
| /** |
| * Block interruptibly until a permit is available. |
| */ |
| protected boolean interruptible = false; |
| public boolean getInterruptible() { return interruptible; } |
| public void setInterruptible(boolean interruptible) { this.interruptible = interruptible; } |
| |
| |
| /** |
| * Start this component and implement the requirements |
| * of {@link org.apache.catalina.util.LifecycleBase#startInternal()}. |
| * |
| * @exception LifecycleException if this component detects a fatal error |
| * that prevents this component from being used |
| */ |
| @Override |
| protected synchronized void startInternal() throws LifecycleException { |
| |
| semaphore = new Semaphore(concurrency, fairness); |
| |
| setState(LifecycleState.STARTING); |
| } |
| |
| |
| /** |
| * Stop this component and implement the requirements |
| * of {@link org.apache.catalina.util.LifecycleBase#stopInternal()}. |
| * |
| * @exception LifecycleException if this component detects a fatal error |
| * that prevents this component from being used |
| */ |
| @Override |
| protected synchronized void stopInternal() throws LifecycleException { |
| |
| setState(LifecycleState.STOPPING); |
| |
| semaphore = null; |
| } |
| |
| |
| // --------------------------------------------------------- Public Methods |
| |
| /** |
| * Do concurrency control on the request using the semaphore. |
| * |
| * @param request The servlet request to be processed |
| * @param response The servlet response to be created |
| * |
| * @exception IOException if an input/output error occurs |
| * @exception ServletException if a servlet error occurs |
| */ |
| @Override |
| public void invoke(Request request, Response response) |
| throws IOException, ServletException { |
| |
| if (controlConcurrency(request, response)) { |
| boolean shouldRelease = true; |
| try { |
| if (block) { |
| if (interruptible) { |
| try { |
| semaphore.acquire(); |
| } catch (InterruptedException e) { |
| shouldRelease = false; |
| permitDenied(request, response); |
| return; |
| } |
| } else { |
| semaphore.acquireUninterruptibly(); |
| } |
| } else { |
| if (!semaphore.tryAcquire()) { |
| shouldRelease = false; |
| permitDenied(request, response); |
| return; |
| } |
| } |
| getNext().invoke(request, response); |
| } finally { |
| if (shouldRelease) { |
| semaphore.release(); |
| } |
| } |
| } else { |
| getNext().invoke(request, response); |
| } |
| |
| } |
| |
| |
| /** |
| * Subclass friendly method to add conditions. |
| * @param request |
| * @param response |
| */ |
| public boolean controlConcurrency(Request request, Response response) { |
| return true; |
| } |
| |
| |
| /** |
| * Subclass friendly method to add error handling when a permit isn't |
| * granted. |
| * @param request |
| * @param response |
| * @throws IOException |
| * @throws ServletException |
| */ |
| public void permitDenied(Request request, Response response) |
| throws IOException, ServletException { |
| // NO-OP by default |
| } |
| |
| |
| } |