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<concept id="GUID-3DE276E8-D2C7-5297-AF3B-40B0B8733572" xml:lang="en"><title>Inter-thread

Data Transfer</title><shortdesc>The mechanism for copying data between threads is called inter-thread

data transfer and is handled by the four functions provided by the <codeph>RThread</codeph> handle.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

<p>Data can be passed between threads. The threads can be in the same process

or in different processes. The functions provides by the <xref href="GUID-B0E661BC-4058-3256-B9C3-5A4FD52F6DE5.dita"><apiname>RThread</apiname></xref> class

are:</p>

<ul>

<li id="GUID-416730EC-5719-5633-A51A-50B0E3AAD8F4"><p><codeph>ReadL()</codeph> </p> </li>

<li id="GUID-B4EF1893-D469-541A-898E-AEC8DBF1BD3A"><p><codeph>WriteL()</codeph> </p> </li>

<li id="GUID-7550CBE4-FEBF-51E5-AB0D-80729D7CAC95"><p><codeph>GetDesLength()</codeph> </p> </li>

<li id="GUID-0B8127FB-9FE1-5EAA-9B8B-3F0BC9F4AAF5"><p><codeph>GetDesMaxLength()</codeph> </p> </li>

</ul>

<p>The functions are used in the implementation of the <codeph>RMessage</codeph> class

which, in turn, is used for passing information between clients and servers.</p>

<p>The <codeph>ReadL()</codeph> and <codeph>WriteL()</codeph> functions, which

transfer data, assume that both source and target data are descriptors.</p>

<p>Typically, code executing in the current thread will have a handle to another

thread. The code in the <i>current</i> thread copies data <i>from</i> the <i>other</i> thread,

represented by an <codeph>RThread</codeph> handle, by calling its <codeph>ReadL()</codeph> function.

Copying data <i>to</i> the <i>other</i> thread is similar, but is done using

the <codeph>WriteL()</codeph> function. The following diagram illustrates

this:</p>

<fig id="GUID-7A4E3725-E6DA-566D-86E0-2941A8D96ACE">

<image href="GUID-40C995CA-9906-59D8-A5E7-08F592031AEE_d0e247945_href.png" placement="inline"/>

</fig>

<p>The source or target location in the <i>other</i> thread is identified

by pointer. The pointer only has meaning within the context of that thread;

attempting to reference the pointer directly from within the <i>current</i> thread

is meaningless and may cause an exception.</p>