91 lines
5.9 KiB
HTML
91 lines
5.9 KiB
HTML
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PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<meta name="DC.Title" content="Data management considerations for multithreaded programming" />
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<meta name="abstract" content="You should consider several topics when managing data in a multithreaded program." />
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<title>Data management considerations for multithreaded programming</title>
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<body id="rzahwdmc-dmcco"><a name="rzahwdmc-dmcco"><!-- --></a>
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<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
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<h1 class="topictitle1">Data management considerations for multithreaded programming</h1>
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<div><p>You should consider several topics when managing data in a multithreaded
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program.</p>
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<div class="section"><ul><li>File open operations:<p>Only integrated file system stream files, printer
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files, distributed data management (DDM) files of type *IP, and local database
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files can be opened in a multithread-capable job. Attempts to open *FILE objects
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other than print files, type *IP DDM files, or local database files cause
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a CPF4380 escape message to be sent to the function that opens
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the file. The CPF4380 escape message signals that open attributes are not
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valid in a multithreaded process. Local database files include physical and
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logical files. Loosely coupled parallel (LCP) files are not local and send
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the CPF4380 escape message when a function tries to open the file. Local database
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files also do not include save files (*SAVF), which are device files, or other
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communications files. You cannot open a printer file by specifying SPOOL(*NO).
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If you specify SPOOL(*NO) when trying to open the print file, the CPF4380
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escape message is sent to the function that tried to open the print file.</p>
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<p>Multithread-capable
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jobs allow shared opens. However, an open data path (ODP) cannot be shared
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between threads. If a file is opened SHARE(*YES) and OPNSCOPE(*ACTGRPDFN)
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is specified, any subsequent shared open within the same thread that is running
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in the same activation group can share the ODP. If a file is opened SHARE(*YES)
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with OPNSCOPE(*JOB) specified, any subsequent shared open of the file within
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the same thread can share the ODP.</p>
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</li>
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<li>File overrides:<p> Multithreaded applications can only issue overrides
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in their initial thread. Any attempt to issue an override in a secondary
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thread returns the CPF180C escape message. Only overrides with job-level and
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activation group-level scope affect secondary threads; overrides of call-level
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scope are not visible. Overrides of all scope levels can affect initial threads.
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You can use three different types of file override commands: <span class="cmdname">Override
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with Database File (OVRDBF)</span>, <span class="cmdname">Override with Printer File
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(OVRPRTF)</span>, and <span class="cmdname">Override with Message File (OVRMSGF)</span>.</p>
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<p>You
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can delete overrides in the initial thread, but not in secondary threads,
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by calling the Delete Override (DLTOVR) command. DLTOVR returns the CPF180C
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escape message if thrown against a secondary thread.</p>
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</li>
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<li>Reclaim resources commands:<p>None of the commands that
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reclaim resources are threadsafe because the <span class="keyword">i5/OS™</span> operating
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system does not track resources. The operating system cannot identify which
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resources are in use by which threads. You cannot call the <span class="cmdname">Reclaim
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Resources (RCLRSC)</span> and <span class="cmdname">Reclaim Activation Group (RCLACTGRP)</span> commands
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in secondary threads. <span class="cmdname">RCLRSC</span> and <span class="cmdname">RCLACTGRP</span> can
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be called in the initial thread of a multithread-capable job (<span class="parmname">ALWMLTTHD(*YES)</span>)
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if secondary user threads are not present. If secondary user threads are present
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in the job, these commands send a CPF180B escape message to the caller of
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the command.</p>
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</li>
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</ul>
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</div>
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</div>
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<div>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="rzahwas4co.htm" title="All programs have at least one thread, referred to as the initial thread. In a program with multiple threads, each thread runs its code independently of the other threads in the program.">Threads on i5/OS</a></div>
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</div>
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<div class="relref"><strong>Related reference</strong><br />
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<div><a href="rzahwprcco.htm" title="Only printer files opened with SPOOL(*YES) are allowed in a job that is capable of multithread operations.">Printer file considerations for multithreaded programming</a></div>
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</div>
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</div>
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</body>
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</html>
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