/*
Wotonomy: OpenStep design patterns for pure Java applications.
Copyright (C) 2002 Israfil consulting Services Corporation

This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.

This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public
License along with this library; if not, see http://www.gnu.org

$Id: NSMultiReaderLock.java 893 2006-02-16 13:22:23Z cgruber $

*/

package net.wotonomy.foundation;

import EDU.oswego.cs.dl.util.concurrent.ReentrantWriterPreferenceReadWriteLock;

/**
 * A Read-Write lock that allows unlimited number of calling threads to acquire
 * read locks, but only one thread to acquire a write lock. It is also
 * reentrant, allowing each thread to re-acquire it's lock recursively. For that
 * reason it is somewhat slower, as there is a hash lookup when attempting to
 * acquire and release reader locks. Of course a writer lock is quite a bit
 * slower than a reader lock. A write lock is mutally exclusive with read locks,
 * though a thread that has obtained a read-lock may be promoted to a write lock
 * and vice versa when conditions permit.
 *
 * @author cgruber@israfil.net
 * @author $Author: cgruber $
 * @version $Revision: 893 $
 */
public class NSMultiReaderLock extends ReentrantWriterPreferenceReadWriteLock implements NSLocking {

	NSMutableDictionary<Thread, Integer> _readerSuspended = new NSMutableDictionary<>();

	public NSMultiReaderLock() {
	}

	public void lockForReading() {
		try {
			readerLock_.acquire();
		} catch (InterruptedException interruptedexception) {
			// Null behavior, as notify() is already called
			// by acquire();
			// We may want to log here.
		}
	}

	public void unlockForReading() {
		readerLock_.release();
	}

	@Override
	public void lock() {
		lockForWriting();
	}

	public void lockForWriting() {
		try {
			writerLock_.acquire();
		} catch (InterruptedException interruptedexception) {
			// Null behavior, as notify() is already called
			// by acquire();
			// We may want to log here.
		}
	}

	@Override
	public void unlock() {
		unlockForWriting();
	}

	public void unlockForWriting() {
		writerLock_.release();
	}

	/** @see com.webobjects.foundation.NSMultiReaderLock#suspendReaderLock() */
	public void suspendReaderLocks() {
		Thread thisThread = Thread.currentThread();
		Integer suspendedReaders = (Integer) _readerSuspended.get(thisThread);
		if (suspendedReaders != null && suspendedReaders.intValue() > 0)
			return;
		// logic is to override startRead / endRead and ensure that the suspension
		// isn't improperly stopped.
		throw new UnsupportedOperationException("Not Yet Implemented");
	}

	/** @see com.webobjects.foundation.NSMultiReaderLock#retrieveReaderLock() */
	public void retrieveReaderLocks() {
		Thread thisThread = Thread.currentThread();
		Integer suspendedReaders = (Integer) _readerSuspended.get(thisThread);
		if (suspendedReaders != null && suspendedReaders.intValue() > 0)
			return;
		// logic is to override startRead / endRead and ensure that the suspension
		// isn't improperly stopped.
		throw new UnsupportedOperationException("Not Yet Implemented");
	}

	public boolean tryLockForWriting() {
		try {
			return writerLock_.attempt(0);
		} catch (InterruptedException interruptedexception) {
			// notify() is already called by attempt();
			// We may want to log here.
			return false;
		}
	}

	public boolean tryLockForReading() {
		try {
			return readerLock_.attempt(0);
		} catch (InterruptedException interruptedexception) {
			// notify() is already called by attempt();
			// We may want to log here.
			return false;
		}
	}

	@Override
	public String toString() {
		throw new UnsupportedOperationException("Not Yet Implemented");
	}

	protected String _padString(long l, int i) {
		throw new UnsupportedOperationException("Not Yet Implemented");
	}

	protected String _padString(String s, int i, boolean flag) {
		throw new UnsupportedOperationException("Not Yet Implemented");
	}

}
/*
 * $Log$ Revision 1.2 2006/02/16 13:15:00 cgruber Check in all sources in
 * eclipse-friendly maven-enabled packages.
 *
 * Revision 1.2 2003/08/06 23:07:52 chochos general code cleanup (mostly,
 * removing unused imports)
 *
 * Revision 1.1 2002/07/14 21:56:16 mpowers Contributions from cgruber.
 *
 * Revision 1.2 2002/06/26 00:40:22 cgruber Add implementation, using
 * ReentrantWriterPreferenceReadWriteLock as a base.
 * 
 * suspendReaderLocks and retreiveReaderLocks is the one that's likeliest to be
 * a pain.
 *
 * Revision 1.1 2002/06/25 07:52:57 cgruber Add quite a few abstract classes,
 * interfaces, and classes. All API consistent with WebObjects, but with no
 * implementation, nor any private or package access members from the original.
 *
 */