001/** 002 * Licensed to the Apache Software Foundation (ASF) under one or more 003 * contributor license agreements. See the NOTICE file distributed with 004 * this work for additional information regarding copyright ownership. 005 * The ASF licenses this file to You under the Apache License, Version 2.0 006 * (the "License"); you may not use this file except in compliance with 007 * the License. You may obtain a copy of the License at 008 * 009 * http://www.apache.org/licenses/LICENSE-2.0 010 * 011 * Unless required by applicable law or agreed to in writing, software 012 * distributed under the License is distributed on an "AS IS" BASIS, 013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 014 * See the License for the specific language governing permissions and 015 * limitations under the License. 016 */ 017package org.apache.activemq.thread; 018 019/** 020 * A Valve is a synchronization object used enable or disable the "flow" of 021 * concurrent processing. 022 * 023 * 024 */ 025public final class Valve { 026 027 private final Object mutex = new Object(); 028 private boolean on; 029 private int turningOff; 030 private int usage; 031 032 public Valve(boolean on) { 033 this.on = on; 034 } 035 036 /** 037 * Turns the valve on. This method blocks until the valve is off. 038 * 039 * @throws InterruptedException if wait is interrupted 040 */ 041 public void turnOn() throws InterruptedException { 042 synchronized (mutex) { 043 while (on) { 044 mutex.wait(); 045 } 046 on = true; 047 mutex.notifyAll(); 048 } 049 } 050 051 public boolean isOn() { 052 synchronized (mutex) { 053 return on; 054 } 055 } 056 057 /** 058 * Turns the valve off. This method blocks until the valve is on and the 059 * valve is not in use. 060 * 061 * @throws InterruptedException if wait is interrupted 062 */ 063 public void turnOff() throws InterruptedException { 064 synchronized (mutex) { 065 if (turningOff < 0) { 066 throw new IllegalStateException("Unbalanced turningOff: " + turningOff); 067 } 068 try { 069 ++turningOff; 070 while (usage > 0 || !on) { 071 mutex.wait(); 072 } 073 on = false; 074 mutex.notifyAll(); 075 } finally { 076 --turningOff; 077 } 078 } 079 } 080 081 /** 082 * Increments the use counter of the valve. This method blocks if the valve 083 * is off, or is being turned off. 084 * 085 * @throws InterruptedException if wait is interrupted 086 */ 087 public void increment() throws InterruptedException { 088 synchronized (mutex) { 089 if (turningOff < 0) { 090 throw new IllegalStateException("Unbalanced turningOff: " + turningOff); 091 } 092 if (usage < 0) { 093 throw new IllegalStateException("Unbalanced usage: " + usage); 094 } 095 // Do we have to wait for the value to be on? 096 while (turningOff > 0 || !on) { 097 mutex.wait(); 098 } 099 usage++; 100 } 101 } 102 103 /** 104 * Decrements the use counter of the valve. 105 */ 106 public void decrement() { 107 synchronized (mutex) { 108 usage--; 109 if (turningOff < 0) { 110 throw new IllegalStateException("Unbalanced turningOff: " + turningOff); 111 } 112 if (usage < 0) { 113 throw new IllegalStateException("Unbalanced usage: " + usage); 114 } 115 if (turningOff > 0 && usage < 1) { 116 mutex.notifyAll(); 117 } 118 } 119 } 120 121}