Helper Mutex

Jan Burse, created Aug 30. 2016

package matula.util.misc;
/**
* <p>This class provides a slotted mutex object.</p>
* <p/>
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* otherwise agreed upon, XLOG Technologies GmbH makes no warranties
* regarding the provided information. XLOG Technologies GmbH assumes
* no liability that any problems might be solved with the information
* provided by XLOG Technologies GmbH.
* <p/>
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* <p/>
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* of the information is only allowed for non-commercial uses. Selling,
* giving away or letting of the execution of the library is prohibited.
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* for execution provided this comment remains unchanged.
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*/
public final class Mutex extends AbstractLock {
private Thread locked;
/**
* <p>Acquire the lock.</p>
* <p>Blocks if lock is already held.</p>
*
* @throws InterruptedException If the request was cancelled.
*/
public void acquire()
throws InterruptedException {
Thread thread = Thread.currentThread();
synchronized (this) {
if (locked == thread)
throw new IllegalStateException("alread_locked");
while (locked != null)
this.wait();
locked = thread;
}
}
/**
* <p>Attempt the lock.</p>
* <p>Fails if lock is already held.</p>
*
* @return True if lock was acquired, or false otherwise.
*/
public boolean attempt() {
Thread thread = Thread.currentThread();
synchronized (this) {
if (locked == thread)
throw new IllegalStateException("alread_locked");
if (locked == null) {
locked = thread;
return true;
} else {
return false;
}
}
}
/**
* <p>Acquire the lock or time-out.</p>
*
* @param sleep The time-out.
* @return True if lock was acquired, or false otherwise.
* @throws InterruptedException If the request was cancelled.
*/
public boolean attempt(long sleep)
throws InterruptedException {
Thread thread = Thread.currentThread();
long when = System.currentTimeMillis() + sleep;
synchronized (this) {
if (locked == thread)
throw new IllegalStateException("alread_locked");
while (locked != null && sleep > 0) {
this.wait(sleep);
sleep = when - System.currentTimeMillis();
}
if (sleep > 0) {
locked = thread;
return true;
} else {
return false;
}
}
}
/**
* <p>Release the lock.</p>
*/
public void release() {
Thread thread = Thread.currentThread();
synchronized (this) {
if (locked != thread)
throw new IllegalStateException("not_locked");
locked = null;
this.notifyAll();
}
}
}
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