Helper Mutex

Jan Burse, created Aug 15. 2016

package example06;
/**
* <p>Java code for the object of the mutex example.</p>
* <p>This class provides a mutex object.</p>
* <p/>
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*/
public final class Mutex {
private boolean locked;
/**
* <p>Create a new mutex.</p>
*/
public Mutex() {
}
/**
* <p>Acquire the lock.</p>
* <p>Acquiring a lock is not reentrant, the current implementation
* is simple, we do not keep a counter, only a flag. So when the
* same process tries to acquire the same lock again, it will block
* and this will get unnoticed.</p>
* <p>Acquiring a lock is cancellable by calling the method
* interrupt() on the blocking thread. The cancellation will leave
* the lock properly in locked state.</p>
*
* @throws InterruptedException If the request was cancelled.
*/
public void acquire() throws InterruptedException {
synchronized (this) {
while (locked)
this.wait();
locked = true;
}
}
/**
* <p>Release the lock.</p>
* <p>Releasing does not check the owner, the current implementation
* is simple, we do not keep the owner. So a process can acquire
* the lock and a different process can release the lock.</p>
*
* @throws IllegalStateException If the lock was not yet acquired.
*/
public void release() {
synchronized (this) {
if (!locked)
throw new IllegalStateException();
locked = false;
this.notifyAll();
}
}
}
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