Class NullSync

  extended by EDU.oswego.cs.dl.util.concurrent.NullSync
All Implemented Interfaces:

public class NullSync
extends java.lang.Object
implements Sync

A No-Op implementation of Sync. Acquire never blocks, Attempt always succeeds, Release has no effect. However, acquire and release do detect interruption and throw InterruptedException. Also, the methods are synchronized, so preserve memory barrier properties of Syncs.

NullSyncs can be useful in optimizing classes when it is found that locking is not strictly necesssary.

[ Introduction to this package. ]

Field Summary
Fields inherited from interface EDU.oswego.cs.dl.util.concurrent.Sync
Constructor Summary
Method Summary
 void acquire()
          Wait (possibly forever) until successful passage.
 boolean attempt(long msecs)
          Wait at most msecs to pass; report whether passed.
 void release()
          Potentially enable others to pass.
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail


public NullSync()
Method Detail


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


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
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.
true if acquired


public void release()
Description copied from interface: Sync
Potentially enable others to pass.

Because release does not raise exceptions, it can be used in `finally' clauses without requiring extra embedded try/catch blocks. But keep in mind that as with any java method, implementations may still throw unchecked exceptions such as Error or NullPointerException when faced with uncontinuable errors. However, these should normally only be caught by higher-level error handlers.

Specified by:
release in interface Sync