Package 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 Details

    • 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 Details

    • 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).