Helper LockerWrite

Jan Burse, created Aug 18. 2019
package matula.util.misc;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
/**
* <p>This class provides a write lock object.</p>
* <p/>
* Warranty & Liability
* To the extent permitted by applicable law and unless explicitly
* 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/>
* Rights & License
* All industrial property rights regarding the information - copyright
* and patent rights in particular - are the sole property of XLOG
* Technologies GmbH. If the company was not the originator of some
* excerpts, XLOG Technologies GmbH has at least obtained the right to
* reproduce, change and translate the information.
* <p/>
* Reproduction is restricted to the whole unaltered document. Reproduction
* of the information is only allowed for non-commercial uses. Selling,
* giving away or letting of the execution of the library is prohibited.
* The library can be distributed as part of your applications and libraries
* for execution provided this comment remains unchanged.
* <p/>
* Restrictions
* Only to be distributed with programs that add significant and primary
* functionality to the library. Not to be distributed with additional
* software intended to replace any components of the library.
* <p/>
* Trademarks
* Jekejeke is a registered trademark of XLOG Technologies GmbH.
*/
final class LockerWrite implements Lock {
Thread locked;
private final Locker parent;
/**
* <p>Create a write lock.</p>
*
* @param p The read write state.
*/
LockerWrite(Locker p) {
parent = p;
}
/**
* <p>Acquire the lock.</p>
* <p>Blocks if lock is already held.</p>
*/
public void lock() {
throw new IllegalArgumentException("not supported");
}
/**
* <p>Acquire the lock.</p>
* <p>Blocks if lock is already held.</p>
*
* @throws InterruptedException If the request was cancelled.
*/
public void lockInterruptibly() throws InterruptedException {
Thread thread = Thread.currentThread();
synchronized (parent) {
if (locked == thread)
throw new IllegalStateException("alread_locked");
while (parent.read.otherReaders(thread) != 0 ||
locked != null)
parent.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 tryLock() {
Thread thread = Thread.currentThread();
synchronized (parent) {
if (locked == thread)
throw new IllegalStateException("alread_locked");
if (parent.read.otherReaders(thread) == 0 &&
locked == null) {
locked = thread;
return true;
} else {
return false;
}
}
}
/**
* <p>Acquire the write lock or time-out.</p>
* <p>Blocks if lock is already held and while not time-out.</p>
*
* @param sleep The time-out.
* @param tu The time unit.
* @return True if lock was acquired, or false otherwise.
* @throws InterruptedException If the request was cancelled.
*/
public boolean tryLock(long sleep, TimeUnit tu)
throws InterruptedException {
sleep = tu.toMillis(sleep);
Thread thread = Thread.currentThread();
long when = System.currentTimeMillis() + sleep;
synchronized (parent) {
if (locked == thread)
throw new IllegalStateException("alread_locked");
while ((parent.read.otherReaders(thread) != 0 ||
locked != null) && sleep > 0) {
parent.wait(sleep);
sleep = when - System.currentTimeMillis();
}
if (sleep > 0) {
locked = thread;
return true;
} else {
return false;
}
}
}
/**
* <p>Release the write lock.</p>
*/
public void unlock() {
Thread thread = Thread.currentThread();
synchronized (parent) {
if (locked != thread)
throw new IllegalStateException("not_locked");
locked = null;
parent.notifyAll();
}
}
/**
* <p>Retrieve a condition.</p>
*
* @return The condition.
*/
public Condition newCondition() {
throw new IllegalArgumentException("not supported");
}
/**
* <p>Determine wether there is another writer.</p>
*
* @param thread The current thread.
* @return True if there is another writer, otherwise false.
*/
boolean otherWriter(Thread thread) {
return (locked != null && locked != thread);
}
}

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