locktablevti.java

derby database source code.good for you.

/*

   Derby - Class org.apache.derby.impl.services.locks.LockTableVTI

   Copyright 1999, 2004 The Apache Software Foundation or its licensors, as applicable.

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

      http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.

 */

package org.apache.derby.impl.services.locks;

import org.apache.derby.iapi.services.locks.Latch;

import java.util.Hashtable;
import java.util.Vector;
import java.util.Enumeration;
import java.util.NoSuchElementException;

import java.util.ListIterator;
import java.util.List;

/**
	This provides an Enumeration of Latch's
	from a clone of the lock table. A Latch is badly named,
	it represents lock information.
 */
class LockTableVTI implements Enumeration
{
	// the clonedLockTable temporarily holds a copy of the lock table.
	//
	// The copy is necessary because the real lock manager needs to be single
	// threaded while a snap shot is made.  After the copy is made, it can take
	// its time digesting the information without blocking the real lock
	// manager.

	private final LockSet clonedLockTable;
	private final Enumeration outerControl;
	private Control control;
	private ListIterator grantedList;
	private ListIterator waitingList;
	private Latch nextLock;

	LockTableVTI(LockSet clonedLockTable)
	{
		this.clonedLockTable = clonedLockTable;

		outerControl = clonedLockTable.elements();
	}


	public boolean hasMoreElements() {

		if (nextLock != null)
			return true;

		for (;;) {

			if (control == null) {
				if (!outerControl.hasMoreElements())
					return false;
//System.out.println("new control lock ");

				control = (Control) outerControl.nextElement();

				List granted = control.getGranted();
				if (granted != null)
					grantedList = granted.listIterator();


				List waiting = control.getWaiting();
				if (waiting != null)
					waitingList = waiting.listIterator();

				nextLock = control.getFirstGrant();
				if (nextLock == null) {

					nextLock = getNextLock(control);
				}
				
			} else {
				nextLock = getNextLock(control);
			}


			if (nextLock != null)
				return true;

			control = null;
		}
	}

	private Latch getNextLock(Control control) {
		Latch lock = null;
//System.out.println("next lock ");
		if (grantedList != null) {
			if (grantedList.hasNext()) {
				lock = (Lock) grantedList.next();
			}
			else
				grantedList = null;
		}

		if (lock == null) {
			if (waitingList != null) {
				if (waitingList.hasNext()) {
					lock = (Lock) waitingList.next();
				}
				else
					waitingList = null;
			}
		}

		return lock;
	}

	public Object nextElement() {

		if (!hasMoreElements())
			throw new NoSuchElementException();

		Latch ret = nextLock;

		nextLock = null;
		return ret;
	}
}