org.apache.xmlbeans.impl.common.Mutex Maven / Gradle / Ivy
/* Copyright 2004 The Apache Software Foundation
*
* 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.
*/
package org.apache.xmlbeans.impl.common;
public class Mutex
{
private Thread owner = null; // Owner of mutex, null if nobody
private int lock_count = 0;
/**
* Acquire the mutex. The mutex can be acquired multiple times
* by the same thread, provided that it is released as many
* times as it is acquired. The calling thread blocks until
* it has acquired the mutex. (There is no timeout).
*/
public synchronized void acquire() throws InterruptedException
{
while (tryToAcquire() == false)
{
wait();
}
}
/**
* Attempts to acquire the mutex. Returns false (and does not
* block) if it can't get it.
*/
public synchronized boolean tryToAcquire()
{
// Try to get the mutex. Return true if you got it.
if( owner == null )
{
owner = Thread.currentThread();
lock_count = 1;
return true;
}
if( owner == Thread.currentThread() )
{
++lock_count;
return true;
}
return false;
}
/**
* Release the mutex. The mutex has to be released as many times
* as it was acquired to actually unlock the resource. The mutex
* must be released by the thread that acquired it
*
* @throws IllegalStateException (a RuntimeException) if a thread
* other than the current owner tries to release the mutex.
*/
public synchronized void release()
{
if (owner != Thread.currentThread())
throw new IllegalStateException("Thread calling release() doesn't own mutex");
if (--lock_count <= 0)
{
owner = null;
notify();
}
}
}