org.zkoss.util

Class WaitLock

java.lang.Object

org.zkoss.util.WaitLock

public class WaitLock
extends Object

A simple lock used to implement load-on-demand mechanism. Typical use: a thread, say A, checks whether a resource is loaded, and put a WaitLock instance if not loaded yet. Then, another thread, say B, if find WaitLock, it simply calls waitUntilUnlock(int) to wait. Meanwhile, once A completes the loading, it put back the resource and calls unlock().

WaitLock lock = null;
for (;;) {
        synchronized (map) {
                Object o = map.get(key);
                if (o == null) {
                        map.put(key, lock = new WaitLock());
                        break; //go to load resource
                }
        }
        if (o instanceof MyResource)
                return (MyResource)o;
        if (!((Lock)o).waitUntilUnlock(60000))
                log.waring("Takes too long");
}
//load resource
try {
        ....
        synchronized (map) {
                map.put(key, resource);
        }
        return resource;
} catch (Throwable ex) {
        synchronized (map) {
                map.remove(key);
        }
        throw SystemException.Aide.wrap(ex);
} finally {
        lock.unlock();
}

Author:

tomyeh

Constructor Summary

Constructors

Constructor and Description
WaitLock() Once created, it is default to be locked.

Method Summary

Modifier and Type	Method and Description
void	unlock() Unlocks any other threads blocked by waitUntilUnlock(int).
boolean	waitUntilUnlock(int timeout) Waits this lock to unlock.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

WaitLock

public WaitLock()

Once created, it is default to be locked. In other words, other thread's invocation of waitUntilUnlock(int) won't return until unlock() is called.

Method Detail

waitUntilUnlock

public boolean waitUntilUnlock(int timeout)

Waits this lock to unlock.

Returns:

whether it is unlocked successfully

Throws:

SystemException - if this thread is interrupted

PotentialDeadLockException - if the thread itself creates this lock. In other words, it tried to wait for itself to complete.

unlock

public void unlock()

Unlocks any other threads blocked by waitUntilUnlock(int).