EDU.oswego.cs.dl.util.concurrent
Class FIFOSemaphore

java.lang.Object
  EDU.oswego.cs.dl.util.concurrent.Semaphore
      EDU.oswego.cs.dl.util.concurrent.QueuedSemaphore
          EDU.oswego.cs.dl.util.concurrent.FIFOSemaphore

All Implemented Interfaces:

Sync

public class FIFOSemaphore

extends QueuedSemaphore

A First-in/First-out implementation of a Semaphore. Waiting requests will be satisified in the order that the processing of those requests got to a certain point. If this sounds vague it is meant to be. FIFO implies a logical timestamping at some point in the processing of the request. To simplify things we don't actually timestamp but simply store things in a FIFO queue. Thus the order in which requests enter the queue will be the order in which they come out. This order need not have any relationship to the order in which requests were made, nor the order in which requests actually return to the caller. These depend on Java thread scheduling which is not guaranteed to be predictable (although JVMs tend not to go out of their way to be unfair).

[ Introduction to this package. ]

FIFOSemaphore

public FIFOSemaphore(long initialPermits)

Create a Semaphore with the given initial number of permits. Using a seed of one makes the semaphore act as a mutual exclusion lock. Negative seeds are also allowed, in which case no acquires will proceed until the number of releases has pushed the number of permits past 0.