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<h1 class="topictitle1">Threads on <span class="keyword">i5/OS™</span></h1>
<div><p>All programs have at least one thread, referred to as the <em>initial
thread</em>. In a program with multiple threads, each thread runs its code
independently of the other threads in the program.</p>
<p>A <em>process</em> is the container for the
memory and resources of the program. On IBM<sup>®</sup> <span><img src="eserver.gif" alt="eServer" /></span> iSeries™ systems,
a job represents a process. Each process has at least one thread (task) in
which the program runs its code. The first thread in a process is referred
to as the initial thread. Some processes are capable of supporting additional
threads, which are called secondary threads. </p>
<p>The concepts that are described here pertain to all programming languages.
For details about how each language enables a concept, refer to the programmer's
guide for that specific language.</p>
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<div>
<ul class="ullinks">
<li class="ulchildlink"><strong><a href="rzahwkerco.htm">Thread models</a></strong><br />
There are different models of thread usage: user threads and kernel threads.</li>
<li class="ulchildlink"><strong><a href="rzahwrogco.htm">Thread program models</a></strong><br />
There are different models for creating multithread programs.</li>
<li class="ulchildlink"><strong><a href="rzahwourco.htm">Jobs and job resources</a></strong><br />
A <em>job</em> is a container for storage and other resources. A
job cannot run by itself. </li>
<li class="ulchildlink"><strong><a href="rzahwcesco.htm">Thread-private data and thread-specific data</a></strong><br />
Threads cannot share certain resources. Data that threads cannot share between themselves are called thread-private data.</li>
<li class="ulchildlink"><strong><a href="rzahweadco.htm">Multithreaded program startup commands</a></strong><br />
To call a multithreaded Integrated Language
Environment<sup>®</sup> (ILE) program, the job in which the program is called must
be capable of supporting multiple threads (multithread-capable). Multithreaded Java™ programs
can be called in most jobs (some system jobs restrict the types of programs
that can be called).</li>
<li class="ulchildlink"><strong><a href="rzahwgrxco.htm">Activation groups and threads</a></strong><br />
All programs and service programs are activated within a substructure of a job that is called an activation group. This substructure contains the resources necessary to run the programs, including static and heap storage, and temporary data management resources.</li>
<li class="ulchildlink"><strong><a href="rzahwcmnco.htm">Communications considerations for multithreaded programming</a></strong><br />
The only threadsafe communications protocol supported on <span class="keyword">i5/OS™</span> is sockets.</li>
<li class="ulchildlink"><strong><a href="rzahwdbcco.htm">Database considerations for multithreaded programming</a></strong><br />
You should consider these items when using databases in multithreaded programs.</li>
<li class="ulchildlink"><strong><a href="rzahwdmcco.htm">Data management considerations for multithreaded programming</a></strong><br />
You should consider several topics when managing data in a multithreaded program.</li>
<li class="ulchildlink"><strong><a href="rzahwfscco.htm">File system considerations for multithreaded programming</a></strong><br />
You should consider several topics when working with file systems in multithreaded programs.</li>
<li class="ulchildlink"><strong><a href="rzahwprcco.htm">Printer file considerations for multithreaded programming</a></strong><br />
Only printer files opened with SPOOL(*YES) are allowed in a job that is capable of multithread operations.</li>
</ul>
<div class="familylinks">
<div class="parentlink"><strong>Parent topic:</strong> <a href="rzahwovepo.htm" title="A thread is the path taken by a program while running, the steps performed, and the order in which the steps are performed.">Multithreaded applications</a></div>
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