Class Latch

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. ]