Helfer LockerRead

Jan Burse, erstellt 18. Aug 2019
package matula.util.misc;
import matula.util.data.SetHash;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
/**
* <p>This class provides a slotted and escalable read 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 LockerRead implements Lock {
SetHash<Thread> set = new SetHash<Thread>();
private final Locker parent;
/**
* <p>Create a read lock.</p>
*
* @param p The read write state.
*/
LockerRead(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 (set.getKey(thread) != null)
throw new IllegalStateException("alread_locked");
while (parent.write.otherWriter(thread))
parent.wait();
set.add(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 (set.getKey(thread) != null)
throw new IllegalStateException("alread_locked");
if (!parent.write.otherWriter(thread)) {
set.add(thread);
return true;
} else {
return false;
}
}
}
/**
* <p>Acquire the read 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 (set.getKey(thread) != null)
throw new IllegalStateException("alread_locked");
while (parent.write.otherWriter(thread) && sleep > 0) {
parent.wait(sleep);
sleep = when - System.currentTimeMillis();
}
if (sleep > 0) {
set.add(thread);
return true;
} else {
return false;
}
}
}
/**
* <p>Release a read lock.</p>
*
* @throws IllegalStateException If the write lock was not yet acquired.
*/
public void unlock() throws IllegalStateException {
Thread thread = Thread.currentThread();
synchronized (parent) {
if (set.getKey(thread) == null)
throw new IllegalStateException("not_locked");
set.remove(thread);
parent.notifyAll();
}
}
/**
* <p>Retrieve a condition.</p>
*
* @return The condition.
*/
public Condition newCondition() {
throw new IllegalArgumentException("not supported");
}
/**
* <p>Determine the number of other readers.</p>
*
* @param thread The current thread.
* @return The number of other readers.
*/
int otherReaders(Thread thread) {
if (set.getKey(thread) != null) {
return set.size - 1;
} else {
return set.size;
}
}
}

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