| /** |
| * 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.activemq.thread; |
| |
| /** |
| * A Valve is a synchronization object used enable or disable the "flow" of |
| * concurrent processing. |
| * |
| * |
| */ |
| public final class Valve { |
| |
| private final Object mutex = new Object(); |
| private boolean on; |
| private int turningOff; |
| private int usage; |
| |
| public Valve(boolean on) { |
| this.on = on; |
| } |
| |
| /** |
| * Turns the valve on. This method blocks until the valve is off. |
| * |
| * @throws InterruptedException if wait is interrupted |
| */ |
| public void turnOn() throws InterruptedException { |
| synchronized (mutex) { |
| while (on) { |
| mutex.wait(); |
| } |
| on = true; |
| mutex.notifyAll(); |
| } |
| } |
| |
| public boolean isOn() { |
| synchronized (mutex) { |
| return on; |
| } |
| } |
| |
| /** |
| * Turns the valve off. This method blocks until the valve is on and the |
| * valve is not in use. |
| * |
| * @throws InterruptedException if wait is interrupted |
| */ |
| public void turnOff() throws InterruptedException { |
| synchronized (mutex) { |
| if (turningOff < 0) { |
| throw new IllegalStateException("Unbalanced turningOff: " + turningOff); |
| } |
| try { |
| ++turningOff; |
| while (usage > 0 || !on) { |
| mutex.wait(); |
| } |
| on = false; |
| mutex.notifyAll(); |
| } finally { |
| --turningOff; |
| } |
| } |
| } |
| |
| /** |
| * Increments the use counter of the valve. This method blocks if the valve |
| * is off, or is being turned off. |
| * |
| * @throws InterruptedException if wait is interrupted |
| */ |
| public void increment() throws InterruptedException { |
| synchronized (mutex) { |
| if (turningOff < 0) { |
| throw new IllegalStateException("Unbalanced turningOff: " + turningOff); |
| } |
| if (usage < 0) { |
| throw new IllegalStateException("Unbalanced usage: " + usage); |
| } |
| // Do we have to wait for the value to be on? |
| while (turningOff > 0 || !on) { |
| mutex.wait(); |
| } |
| usage++; |
| } |
| } |
| |
| /** |
| * Decrements the use counter of the valve. |
| */ |
| public void decrement() { |
| synchronized (mutex) { |
| usage--; |
| if (turningOff < 0) { |
| throw new IllegalStateException("Unbalanced turningOff: " + turningOff); |
| } |
| if (usage < 0) { |
| throw new IllegalStateException("Unbalanced usage: " + usage); |
| } |
| if (turningOff > 0 && usage < 1) { |
| mutex.notifyAll(); |
| } |
| } |
| } |
| |
| } |