setcheckinsemaphore.java

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package org.jasig.portal.utils;

import java.util.Set;

/**
 * This is a weird semaphore that makes every thread wait, until
 * all of Strings from a given set have been "checked in".
 *
 * @author <a href="mailto:[e-mail]">Peter Kharchenko</a>
 * @version $Revision: 1.1 $
 */
public class SetCheckInSemaphore {
    private Set registry;

    /**
     * Creates a new <code>CountDownSemaphore</code> instance.
     *
     * @param registrySet a <code>Set</code> of key objects
     * that will have to be "checked in" before any waiting threads are allowed to proceed.
     */
    public SetCheckInSemaphore(Set registrySet) {
        this.registry=registrySet;
    }

    /**
     * Checks in with a given name, and waits for others.
     *
     * @param key an <code>Object</code> value
     */
    public synchronized void checkInAndWaitOn(Object key) {
        registry.remove(key);
        while(!registry.isEmpty()) {
            try {
                this.wait();
            } catch (InterruptedException ie) {}
        }
        this.notifyAll();
    }

    /**
     * Check in a key, but do not wait on the semaphore.
     *
     * @param key an <code>Object</code> value
     */
    public synchronized void checkIn(Object key) {
        registry.remove(key);
        if(registry.isEmpty()) {
            this.notifyAll();
        }
    }

    /**
     * Wait on the semaphore, without checking in any keys.
     *
     */
    public synchronized void waitOn() {
        while(!registry.isEmpty()) {
            try {
                this.wait();
            } catch (InterruptedException ie) {}
        }
    }

    /**
     * Checks in all the remaining values, so that all
     * threads can proceed immediately.
     *
     */
    public synchronized void checkInAll() {
        registry.clear();
        this.notifyAll();
    }

}