/*
* 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
/**
* The descriptive information related to this implementation.
*/
private static final String info =
"org.apache.catalina.valves.SemaphoreValve/1.0";
/**
* 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
/**
* Return descriptive information about this Valve implementation.
*/
@Override
public String getInfo() {
return (info);
}
/**
* 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
}
}