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

<concept id="GUID-088DC096-0CC7-5510-8D71-7DAF5961A681" xml:lang="en"><title>Using

Critical Sections</title><shortdesc>This document describes how to use critical sections.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

<p>Critical sections are provided to serialise access to shared resources.

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

<p>A critical section can only be used by threads within the same process;

it <i>cannot</i> be used to control access to a resource shared by threads

across different processes. To serialise access to a resource shared by threads

across more than one process, use a mutex.</p>

<p>While a critical section is used to serialise access to a general resource,

it is used, typically, to serialise access to a section of re-entrant code

which cannot be executed concurrently by more than one thread within a process.

A critical section only allows one thread into a controlled section, forcing

other threads, that try to gain access to that critical section, to wait until

the first thread has exited from that section.</p>

<p>Note that threads which do not attempt to gain access to the critical section

are not blocked.</p>

<p>A critical section is implemented using a semaphore.</p>

<p>Access to a critical section object is through an <codeph>RCriticalSection</codeph> handle.</p>

</conbody></concept>