Quadcap Embeddable Database

com/quadcap/sql/lock/Lock.java

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package com.quadcap.sql.lock;

/* Copyright 1999 - 2003 Quadcap Software.  All rights reserved.
 *
 * This software is distributed under the Quadcap Free Software License.
 * This software may be used or modified for any purpose, personal or
 * commercial.  Open Source redistributions are permitted.  Commercial
 * redistribution of larger works derived from, or works which bundle
 * this software requires a "Commercial Redistribution License"; see
 * http://www.quadcap.com/purchase.
 *
 * Redistributions qualify as "Open Source" under  one of the following terms:
 *   
 *    Redistributions are made at no charge beyond the reasonable cost of
 *    materials and delivery.
 *
 *    Redistributions are accompanied by a copy of the Source Code or by an
 *    irrevocable offer to provide a copy of the Source Code for up to three
 *    years at the cost of materials and delivery.  Such redistributions
 *    must allow further use, modification, and redistribution of the Source
 *    Code under substantially the same terms as this license.
 *
 * Redistributions of source code must retain the copyright notices as they
 * appear in each source code file, these license terms, and the
 * disclaimer/limitation of liability set forth as paragraph 6 below.
 *
 * Redistributions in binary form must reproduce this Copyright Notice,
 * these license terms, and the disclaimer/limitation of liability set
 * forth as paragraph 6 below, in the documentation and/or other materials
 * provided with the distribution.
 *
 * The Software is provided on an "AS IS" basis.  No warranty is
 * provided that the Software is free of defects, or fit for a
 * particular purpose.  
 *
 * Limitation of Liability. Quadcap Software shall not be liable
 * for any damages suffered by the Licensee or any third party resulting
 * from use of the Software.
 */

import com.quadcap.util.collections.ArrayQueue;

import com.quadcap.util.Debug;

/**
 * A mapped, instantiated lock object.
 *
 * @author Stan Bailes
 */
public class Lock implements Comparable {
    static Lock                 tombstone       = new Lock();
    
    String                      name;
    final int[]                 heldCount       = new int[LockMode.MAX];
    int                         refCount        = 0;
    private Lock                parent          = null;
    ArrayQueue                  waitQueue       = null;
    Object                      sync            = new Object();

    /**
     * Default constructor
     */
    protected Lock() {}

    /**
     * Initialization/recycling
     */
    public void init(Lock parent, String name) {
        this.parent = parent;
        this.name = name;
    }

    /**
     * Return this lock's name
     */
    final String getName() { return name; }

    final int getHeldCount(int mode) {
        return heldCount[mode];
    }

    final int incrHeldCount(int mode) {
        return ++heldCount[mode];
    }
    final int decrHeldCount(int mode) {
        return --heldCount[mode];
    }

    final int getHeldCount() {
        int sum = 0;
        for (int i = 0; i < LockMode.MAX; i++) sum += heldCount[i];
        return sum;
    }

    final void addWaitQueue(Transaction t) {
        synchronized (sync) {
            if (waitQueue == null) waitQueue = new ArrayQueue(2, -1);
            waitQueue.addBack(t);
        }
    }

    final boolean hasWaiters() {
        synchronized (sync) {
            return waitQueue == null ? false : waitQueue.size() > 0;
        }
    }

    final Transaction popWaitQueue() {
        Transaction ret = null;
        synchronized (sync) {
            if (waitQueue != null) ret = (Transaction)waitQueue.popFront();
        }
        return ret;
    }

    final Transaction headWaitQueue() {
        Transaction ret = null;
        synchronized (sync) {
            if (waitQueue != null) ret = (Transaction)waitQueue.head();
        }
        return ret;
    }

    final boolean couldLock(int mode) {
        switch (mode) {
        case LockMode.S:
            return (heldCount[LockMode.X] == 0 &&
                    heldCount[LockMode.IX] == 0 &&
                    heldCount[LockMode.SIX] == 0);
        case LockMode.IS:
            return heldCount[LockMode.X] == 0;
        case LockMode.X:
            return (heldCount[LockMode.X] == 0 &&
                    heldCount[LockMode.IX] == 0 &&
                    heldCount[LockMode.SIX] == 0 &&
                    heldCount[LockMode.IS] == 0 &&
                    heldCount[LockMode.S] == 0);
        case LockMode.IX:
            return (heldCount[LockMode.X] == 0 &&
                    heldCount[LockMode.S] == 0 &&
                    heldCount[LockMode.SIX] == 0);          
        case LockMode.SIX:
            return (heldCount[LockMode.X] == 0 &&
                    heldCount[LockMode.S] == 0 &&
                    heldCount[LockMode.IX] == 0 &&
                    heldCount[LockMode.SIX] == 0);
        default:
            throw new RuntimeException("Bad lock mode: " + mode);
        }
    }

    final boolean couldPromote(int fromMode, int toMode) {
        int savc = heldCount[fromMode];
        heldCount[fromMode] = 0;
        boolean could = couldLock(toMode);
        heldCount[fromMode] = savc;
        return could;
    }

    public int compareTo(Object obj) {
        return name.compareTo(((Lock)obj).name);
    }

    public boolean equals(Object obj) {
        return 0 == compareTo(obj);
    }

    public int hashCode() {
        return name.hashCode();
    }

    public Lock getParent() { return parent; }
    
    //#ifdef DEBUG
    public String toString() {
        return dump();
    }

    public String dump() {
        StringBuffer sb = new StringBuffer();
        sb.append(name);
        sb.append(": ");
        for (int i = 0; i < LockMode.MAX; i++) {
            if (heldCount[i] > 0) {
                sb.append("{");
                sb.append(LockMode.toString(i));
                sb.append(",");
                sb.append(Integer.toString(heldCount[i]));
                sb.append("} ");
            }
        }
        Transaction t = headWaitQueue();
        if (t != null) {
            sb.append("wait=T:");
            sb.append(String.valueOf(t.getTransactionId()));
            if (waitQueue.size() > 1) {
                sb.append(" + ");
                sb.append(waitQueue.size() - 1);
                sb.append(" other");
                if (waitQueue.size() > 2) sb.append('s');
            }
        }
        return sb.toString();
    }
    //#endif
}