com.gemstone.gemfire.internal.util.concurrent.ReentrantSemaphore Maven / Gradle / Ivy
/*
* Copyright (c) 2010-2015 Pivotal Software, Inc. All rights reserved.
*
* Licensed 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. See accompanying
* LICENSE file.
*/
package com.gemstone.gemfire.internal.util.concurrent;
import java.util.concurrent.Semaphore;
import java.util.concurrent.TimeUnit;
import com.gemstone.gemfire.internal.concurrent.S;
/**
* 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.
* @author dsmith
*
*/
public class ReentrantSemaphore extends Semaphore implements S {
private final ThreadLocal holdCount = new ThreadLocal();
/**
* @param permits
*/
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);
}
}