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    10 <!DOCTYPE concept

    11   PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">

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

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

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

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

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

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

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

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

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

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

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

    23 management of thread scheduling.</p>

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

    25 most applications are interested in making asynchronous requests to service

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

    27 also created that support asynchronous requests.</p>

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

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

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

    31 to signal request completion.</p>

    32 </conbody></concept>