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<concept id="GUID-9D00655C-AFBA-5DF7-B11B-6B2355BDF08D" xml:lang="en"><title>Using

Semaphores</title><shortdesc>This document describes how to use semaphores.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

<p>Semaphores are provided to synchronise co-operating threads. They are Kernel

objects and, as such, are managed by the Kernel.</p>

<p>Access to a semaphore is through an RSemaphore handle.</p>

<p>The semaphores are counting semaphores, having a <codeph>TInt</codeph> count

value that is incremented by calling the <codeph>Signal()</codeph> member

function of the semaphore handle and decremented by calling the <codeph>Wait()</codeph> member

function of the semaphore handle. A semaphore with a negative value implies

that a thread must wait for the completion of some event.</p>

<p>The mechanism by which a thread waits on a semaphore is part of the overall

management of thread scheduling.</p>

<p>For general applications, it is not common to explicitly create a semaphore;

most applications are interested in making asynchronous requests to service

providers. When a thread is created, a <keyword>request         semaphore</keyword> is

also created that support asynchronous requests.</p>

<p>After making one or more asynchronous requests, a thread calls User::WaitForAnyRequest()

to wait for one of the requests to complete or calls User::WaitForRequest()

to wait for a specific request to complete. A service provider calls User::RequestComplete()

to signal request completion.</p>