foundation/org.eclipse.persistence.core/src/main/java/org/eclipse/persistence/internal/helper/DeferredLockManager.java

/*
 * Copyright (c) 1998, 2021 Oracle and/or its affiliates. All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v. 2.0 which is available at
 * http://www.eclipse.org/legal/epl-2.0,
 * or the Eclipse Distribution License v. 1.0 which is available at
 * http://www.eclipse.org/org/documents/edl-v10.php.
 *
 * SPDX-License-Identifier: EPL-2.0 OR BSD-3-Clause
 */

// Contributors:
//     Oracle - initial API and implementation from Oracle TopLink
package org.eclipse.persistence.internal.helper;

import java.util.*;

/**
 * INTERNAL:
 * <p>
 * <b>Purpose</b>: Be used for deadlock avoidance through allowing detection and resolution.
 *
 * <p>
 * <b>Responsibilities</b>:
 * <ul>
 * <li> Keep track of all deferred locks of each thread.
 * <li> Keep track of all active locks of each thread..
 * <li> Maintain the depth of the each thread.
 * </ul>
 */
public class DeferredLockManager {
    protected Vector<ConcurrencyManager> deferredLocks;
    protected Vector<ConcurrencyManager> activeLocks;
    protected int threadDepth;
    protected boolean isThreadComplete;

    public static boolean SHOULD_USE_DEFERRED_LOCKS = true;

    /**
     * DeferredLockManager constructor comment.
     */
    public DeferredLockManager() {
        super();
        this.deferredLocks = new Vector<>(1);
        this.activeLocks = new Vector<>(1);
        this.threadDepth = 0;
        this.isThreadComplete = false;
    }

    /**
     * add a concurrency manager as active locks to the DLM
     */
    public void addActiveLock(Object manager) {
        getActiveLocks().addElement((ConcurrencyManager) manager);
    }

    /**
     * add a concurrency manager as deferred locks to the DLM
     */
    public void addDeferredLock(Object manager) {
        getDeferredLocks().addElement((ConcurrencyManager) manager);
    }

    /**
     * decrement the depth of the thread
     */
    public void decrementDepth() {
        threadDepth--;
    }

    /**
     * Return a set of the active locks from the DLM
     */
    public Vector<ConcurrencyManager> getActiveLocks() {
        return activeLocks;
    }

    /**
     * Return a set of the deferred locks
     */
    public Vector<ConcurrencyManager> getDeferredLocks() {
        return deferredLocks;
    }

    /**
     * Return the depth of the thread associated with the DLM, being used to release the lock
     */
    public int getThreadDepth() {
        return threadDepth;
    }

    /**
     * Return if there are any deferred locks.
     */
    public boolean hasDeferredLock() {
        return !getDeferredLocks().isEmpty();
    }

    /**
     * increment the depth of the thread
     */
    public void incrementDepth() {
        threadDepth++;
    }

    /**
     * Return if the thread is complete
     */
    public boolean isThreadComplete() {
        return isThreadComplete;
    }

    /**
     * Release the active lock on the DLM
     */
    public void releaseActiveLocksOnThread() {
        Vector<ConcurrencyManager> activeLocks = getActiveLocks();
        if (!activeLocks.isEmpty()) {
            for (Enumeration<ConcurrencyManager> activeLocksEnum = activeLocks.elements();
                     activeLocksEnum.hasMoreElements();) {
                ConcurrencyManager manager = activeLocksEnum.nextElement();
                manager.release();
            }
        }
        setIsThreadComplete(true);
    }

    /**
     * set a set of the active locks to the DLM
     */
    public void setActiveLocks(Vector<ConcurrencyManager> activeLocks) {
        this.activeLocks = activeLocks;
    }

    /**
     * set a set of the deferred locks to the DLM
     */
    public void setDeferredLocks(Vector<ConcurrencyManager> deferredLocks) {
        this.deferredLocks = deferredLocks;
    }

    /**
     * set if the thread is complete in the given DLM
     */
    public void setIsThreadComplete(boolean isThreadComplete) {
        this.isThreadComplete = isThreadComplete;
    }
}