Class 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. ]

    • Constructor Summary

      Constructors 
      Constructor Description
      Latch()  
    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method 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