Latch.java

/*-
 * See the file LICENSE for redistribution information.
 *
 * Copyright (c) 2002-2006
 *      Sleepycat Software.  All rights reserved.
 *
 * $Id: Latch.java,v 1.1 2006/05/06 09:00:33 ckaestne Exp $
 */

package com.sleepycat.je.latch;

import com.sleepycat.je.DatabaseException;
import com.sleepycat.je.RunRecoveryException;

public interface Latch {

    /**
     * Set the latch name, used for latches in objects instantiated from
     * the log.
     */
    public void setName(String name);

    /**
     * Acquire a latch for exclusive/write access.
     *
     * <p>Wait for the latch if some other thread is holding it.  If there are
     * threads waiting for access, they will be granted the latch on a FIFO
     * basis.  When the method returns, the latch is held for exclusive
     * access.</p>
     *
     * @throws LatchException if the latch is already held by the calling
     * thread.
     *
     * @throws RunRecoveryException if an InterruptedException exception
     * occurs.
     */
    public void acquire()
	throws DatabaseException;

    /**
     * Acquire a latch for exclusive/write access, but do not block if it's not
     * available.
     *
     * @return true if the latch was acquired, false if it is not available.
     *
     * @throws LatchException if the latch is already held by the calling
     * thread.
     */
    public boolean acquireNoWait()
	throws LatchException;

    /**
     * Release the latch.  If there are other thread(s) waiting for the latch,
     * one is woken up and granted the latch. If the latch was not owned by 
     * the caller, just return;
     */
    public void releaseIfOwner();

    /**
     * Release the latch.  If there are other thread(s) waiting for the latch,
     * they are woken up and granted the latch.
     *
     * @throws LatchNotHeldException if the latch is not currently held.
     */
    public void release()
	throws LatchNotHeldException;

    /**
     * Return true if the current thread holds this latch.
     *
     * @return true if we hold this latch.  False otherwise.
     */
    public boolean isOwner();

    /**
     * Used only for unit tests.
     *
     * @return the thread that currently holds the latch for exclusive access.
     */
    public Thread owner();

    /**
     * Return the number of threads waiting.
     *
     * @return the number of threads waiting for the latch.
     */
    public int nWaiters();

    /**
     * @return a LatchStats object with information about this latch.
     */
    public LatchStats getLatchStats();

    /**
     * Formats a latch owner and waiters.
     */
    public String toString();
}