EDU.oswego.cs.dl.util.concurrent

Class Latch

java.lang.Object

EDU.oswego.cs.dl.util.concurrent.Latch

All Implemented Interfaces:

Sync

public class Latch
extends java.lang.Object
implements Sync

A latch is a boolean condition that is set at most once, ever. Once a single release is issued, all acquires will pass.

Sample usage. Here are a set of classes that use a latch as a start signal for a group of worker threads that are created and started beforehand, and then later enabled.

 class Worker implements Runnable {
   private final Latch startSignal;
   Worker(Latch l) { startSignal = l; }
    public void run() {
      startSignal.acquire();
      doWork();
   }
   void doWork() { ... }
 }

 class Driver { // ...
   void main() {
     Latch go = new Latch();
     for (int i = 0; i < N; ++i) // make threads
       new Thread(new Worker(go)).start();
     doSomethingElse();         // don't let run yet 
     go.release();              // let all threads proceed
   } 
 }

[ Introduction to this package. ]

Field Summary

Fields

Modifier and Type	Field and Description
protected boolean	latched_

Fields inherited from interface EDU.oswego.cs.dl.util.concurrent.Sync

ONE_CENTURY, ONE_DAY, ONE_HOUR, ONE_MINUTE, ONE_SECOND, ONE_WEEK, ONE_YEAR

Constructor Summary

Constructors

Constructor and Description
Latch()

Method Summary

Modifier and Type	Method and Description
void	acquire() Wait (possibly forever) until successful passage.
boolean	attempt(long msecs) Wait at most msecs to pass; report whether passed.
void	release() Enable all current and future acquires to pass

Methods inherited from class java.lang.Object

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

Field Detail

latched_

protected boolean latched_

Constructor Detail

Latch

public Latch()

Method Detail

acquire

public void acquire()
             throws java.lang.InterruptedException

Description copied from interface: Sync

Wait (possibly forever) until successful passage. Fail only upon interuption. Interruptions always result in `clean' failures. On failure, you can be sure that it has not been acquired, and that no corresponding release should be performed. Conversely, a normal return guarantees that the acquire was successful.

Specified by:

acquire in interface Sync

Throws:

java.lang.InterruptedException

attempt

public boolean attempt(long msecs)
                throws java.lang.InterruptedException

Description copied from interface: Sync

Wait at most msecs to pass; report whether passed.

The method has best-effort semantics: The msecs bound cannot be guaranteed to be a precise upper bound on wait time in Java. Implementations generally can only attempt to return as soon as possible after the specified bound. Also, timers in Java do not stop during garbage collection, so timeouts can occur just because a GC intervened. So, msecs arguments should be used in a coarse-grained manner. Further, implementations cannot always guarantee that this method will return at all without blocking indefinitely when used in unintended ways. For example, deadlocks may be encountered when called in an unintended context.

Specified by:

attempt in interface Sync

Parameters:

msecs - the number of milleseconds to wait. An argument less than or equal to zero means not to wait at all. However, this may still require access to a synchronization lock, which can impose unbounded delay if there is a lot of contention among threads.

Returns:

true if acquired

Throws:

java.lang.InterruptedException

release

public void release()

Enable all current and future acquires to pass

Specified by:

release in interface Sync