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).

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Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
protected static class	FIFOSemaphore.FIFOWaitQueue Simple linked list queue used in FIFOSemaphore.

Nested classes/interfaces inherited from class EDU.oswego.cs.dl.util.concurrent.QueuedSemaphore

QueuedSemaphore.WaitQueue

Field Summary

Fields inherited from class EDU.oswego.cs.dl.util.concurrent.QueuedSemaphore

wq_

Fields inherited from class EDU.oswego.cs.dl.util.concurrent.Semaphore

permits_

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
FIFOSemaphore(long initialPermits) Create a Semaphore with the given initial number of permits.

Method Summary

Methods inherited from class EDU.oswego.cs.dl.util.concurrent.QueuedSemaphore

acquire, attempt, getSignallee, precheck, recheck, release, release

Methods inherited from class EDU.oswego.cs.dl.util.concurrent.Semaphore

permits

Methods inherited from class java.lang.Object

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

Constructor Detail

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.