| /* |
| * 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.geode.internal.util.concurrent; |
| |
| import java.util.concurrent.Semaphore; |
| import java.util.concurrent.TimeUnit; |
| |
| |
| /** |
| * A special purpose semaphore that allows reentrancy. With this semaphore, a thread will only |
| * acquire a real permit the first time it calls acquire. After that, the thread can call acquire |
| * repeatedly, and it won't affect the semaphore count until the thread calls release the same |
| * number of times as acquire. |
| * |
| * This semaphore currently only supports a thread acquiring and releasing a single permit at a |
| * time. |
| * |
| * If a thread does not hold the semaphore, but still decrements it, then it will increase the |
| * permits of the semaphore, just like a regular semaphore. |
| * |
| * This semaphore is useful for allowing only a limited number of threads to enter a block of code, |
| * while allowing a single thread to try to enter that block several times in it's call stack. |
| * |
| */ |
| public class ReentrantSemaphore extends Semaphore { |
| private final ThreadLocal<Integer> holdCount = new ThreadLocal<Integer>(); |
| |
| public ReentrantSemaphore(int permits) { |
| super(permits); |
| } |
| |
| public ReentrantSemaphore(int permits, boolean fair) { |
| super(permits, fair); |
| } |
| |
| @Override |
| public void acquire() throws InterruptedException { |
| if (incHoldCount()) { |
| super.acquire(); |
| } |
| } |
| |
| @Override |
| public void acquireUninterruptibly() { |
| if (incHoldCount()) { |
| super.acquireUninterruptibly(); |
| } |
| } |
| |
| @Override |
| public boolean tryAcquire() { |
| if (incHoldCount()) { |
| boolean result = super.tryAcquire(); |
| if (!result) { |
| decHoldCount(); |
| } |
| return result; |
| } else { |
| return true; |
| } |
| } |
| |
| @Override |
| public boolean tryAcquire(long timeout, TimeUnit unit) throws InterruptedException { |
| if (incHoldCount()) { |
| boolean result = super.tryAcquire(); |
| if (!result) { |
| decHoldCount(); |
| } |
| return result; |
| } else { |
| return true; |
| } |
| } |
| |
| @Override |
| public void release() { |
| if (decHoldCount()) { |
| super.release(); |
| } |
| } |
| |
| @Override |
| public void acquire(int permits) throws InterruptedException { |
| throw new UnsupportedOperationException( |
| "ReentrantSemaphore doesn't support a single thread using more than one permit"); |
| } |
| |
| @Override |
| public void acquireUninterruptibly(int permits) { |
| throw new UnsupportedOperationException( |
| "ReentrantSemaphore doesn't support a single thread using more than one permit"); |
| } |
| |
| @Override |
| public boolean tryAcquire(int permits) { |
| throw new UnsupportedOperationException( |
| "ReentrantSemaphore doesn't support a single thread using more than one permit"); |
| } |
| |
| @Override |
| public boolean tryAcquire(int permits, long timeout, TimeUnit unit) throws InterruptedException { |
| throw new UnsupportedOperationException( |
| "ReentrantSemaphore doesn't support a single thread using more than one permit"); |
| } |
| |
| @Override |
| public void release(int permits) { |
| throw new UnsupportedOperationException( |
| "ReentrantSemaphore doesn't support a single thread using more than one permit"); |
| } |
| |
| private boolean incHoldCount() { |
| Integer count = holdCount.get(); |
| if (count != null) { |
| holdCount.set(Integer.valueOf(count.intValue() + 1)); |
| return false; |
| } |
| { |
| holdCount.set(Integer.valueOf(1)); |
| return true; |
| } |
| } |
| |
| private boolean decHoldCount() { |
| Integer count = holdCount.get(); |
| if (count == null) { |
| return true; |
| } |
| if (count.intValue() == 1) { |
| holdCount.remove(); |
| return true; |
| } else { |
| holdCount.set(Integer.valueOf(count.intValue() - 1)); |
| return false; |
| } |
| } |
| |
| public boolean tryAcquireMs(long timeout) throws InterruptedException { |
| return tryAcquire(timeout, TimeUnit.MILLISECONDS); |
| } |
| |
| public boolean tryAcquireMs(int permits, long timeout) throws InterruptedException { |
| return tryAcquire(permits, TimeUnit.MILLISECONDS); |
| } |
| } |