author | Graeme Price <GRAEME.PRICE@NOKIA.COM> |
Fri, 15 Oct 2010 14:32:18 +0100 | |
changeset 15 | 307f4279f433 |
parent 7 | 51a74ef9ed63 |
permissions | -rw-r--r-- |
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<?xml version="1.0" encoding="utf-8"?> |
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<!-- Copyright (c) 2007-2010 Nokia Corporation and/or its subsidiary(-ies) All rights reserved. --> |
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<!-- This component and the accompanying materials are made available under the terms of the License |
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"Eclipse Public License v1.0" which accompanies this distribution, |
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and is available at the URL "http://www.eclipse.org/legal/epl-v10.html". --> |
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<!-- Initial Contributors: |
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Nokia Corporation - initial contribution. |
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Contributors: |
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--> |
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<!DOCTYPE concept |
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PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd"> |
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<concept id="GUID-9D00655C-AFBA-5DF7-B11B-6B2355BDF08D" xml:lang="en"><title>Using |
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Semaphores</title><shortdesc>This document describes how to use semaphores.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody> |
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<p>Semaphores are provided to synchronise co-operating threads. They are Kernel |
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objects and, as such, are managed by the Kernel.</p> |
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<p>Access to a semaphore is through an RSemaphore handle.</p> |
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<p>The semaphores are counting semaphores, having a <codeph>TInt</codeph> count |
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value that is incremented by calling the <codeph>Signal()</codeph> member |
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function of the semaphore handle and decremented by calling the <codeph>Wait()</codeph> member |
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function of the semaphore handle. A semaphore with a negative value implies |
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that a thread must wait for the completion of some event.</p> |
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<p>The mechanism by which a thread waits on a semaphore is part of the overall |
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management of thread scheduling.</p> |
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<p>For general applications, it is not common to explicitly create a semaphore; |
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most applications are interested in making asynchronous requests to service |
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providers. When a thread is created, a <keyword>request semaphore</keyword> is |
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also created that support asynchronous requests.</p> |
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<p>After making one or more asynchronous requests, a thread calls User::WaitForAnyRequest() |
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to wait for one of the requests to complete or calls User::WaitForRequest() |
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to wait for a specific request to complete. A service provider calls User::RequestComplete() |
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to signal request completion.</p> |
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</conbody></concept> |