// Copyright (c) 2003-2007, Jodd Team (jodd.sf.net). All Rights Reserved.
package jodd.util;
/**
* Provides simple mutual exclusion.
* <p>
* Interesting, the previous implementation based on Leslie Lamport's
* "Fast Mutal Exclusion" algorithm was not working, proabably due wrong
* implementation.
* <p>
* Object (i.e. resource) that uses Mutex must be accessed only between
* {@link #lock()} and {@link #unlock()}.
*/
public class Mutex {
private Thread owner;
/**
* Blocks execution and acquires a lock. If already inside of critical block,
* it simply returs.
*/
public synchronized void lock() {
Thread currentThread = Thread.currentThread();
if (owner == currentThread) {
return;
}
while (owner != null) {
try {
wait();
} catch (InterruptedException iex) {
notify();
}
}
owner = currentThread;
}
/**
* Acquires a lock. If lock already acquired, returns <code>false</code>,
*/
public synchronized boolean tryLock() {
Thread currentThread = Thread.currentThread();
if (owner == currentThread) {
return true;
}
if (owner != null) {
return false;
}
owner = currentThread;
return true;
}
/**
* Releases a lock.
*/
public synchronized void unlock() {
owner = null;
notify();
}
}
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