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<meta name="DC.Title" content="Identify a call stack entry" />
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<meta name="abstract" content="If a CL procedure is to send a message to an OPM program or another ILE procedure, you must identify the call stack entry to which the message is sent." />
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<title>Identify a call stack entry</title>
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<body id="callid"><a name="callid"><!-- --></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">Identify a call stack entry</h1>
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<div><p>If a CL procedure is to send a message to an OPM program or another
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ILE procedure, you must identify the call stack entry to which the message
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is sent.</p>
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<div class="section"> <p>The message is sent to the call message queue of the identified
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call stack entry.</p>
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<p>The TOPGMQ parameter of the <span class="cmdname">Send Program
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Message (SNDPGMMSG)</span> command is used to identify the call stack entry
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to which a message is sent. Identification of a call stack entry consists
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of the following two parts: </p>
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<ul><li>Specification of a base entry <p>This specification identifies a program
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or procedure within the call stack (this is element 2 of TOPGMQ).</p>
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</li>
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<li>Offset specification of a base entry <p>The offset specification (element
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1 of TOPGMQ) identifies if you send the message to the base (*SAME) or if
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you send the message to the caller of the base (*PRV).</p>
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</li>
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</ul>
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<p>The specification TOPGMQ(*PRV *) identifies the base entry as
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being the one in which the procedure using the <span class="cmdname">Send Program Message
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(SNDPGMMSG)</span> command is running. The offset is specified as being
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one entry previous to that base. This specification identifies the caller
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of the procedure which is using the command.</p>
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<p>To understand how to identify
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the base entry, element 2 of TOPGMQ, you also need to understand the call
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stack when an ILE program is running. Two programs are used to illustrate
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this. Program CLPGM1 is an OPM CL program and Program CLPGM2 is an ILE program.
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Since program CLPGM2 is ILE, it can consist of several procedures, such as:
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CLPROC1, CLPROC2, CLPROC3, and CLPROC4. At runtime the following calls take
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place: </p>
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<ul><li>CLPGM1 is called first.</li>
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<li>CLPGM1 calls CLPGM2.</li>
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<li>CLPGM2 calls CLPROC1.</li>
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<li>CLPROC1 calls CLPROC2.</li>
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<li>CLPROC2 calls CLPROC3 or CLPROC4.</li>
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</ul>
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<div class="p">This figure below illustrates the following considerations:<ul><li>There is a one-to-one correspondence between a call stack entry and an
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OPM program; for each call of an OPM program, one new entry is added to the
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call stack.</li>
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<li>An ILE program, as a unit, is not represented on the stack; instead, when
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an ILE program is called, one entry is added to the stack for each procedure
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that is called in the program. As a result, you send a message to an ILE procedure,
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not to an ILE program.</li>
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</ul>
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</div>
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<div class="note"><span class="notetitle">Note:</span> The first procedure to run when an ILE program is called is
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the Program Entry Procedure (PEP) for the program. In CL, this procedure (_CL_PEP)
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is generated by the system and calls the first procedure you provide. In this
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example, the entry for the PEP is between the entry for the OPM program CLPGM1
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and the entry for the procedure CLPROC1.</div>
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<div class="fignone" id="callid__sndfig1"><a name="callid__sndfig1"><!-- --></a><span class="figcap">Figure 1. Example
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of runtime call stack with an OPM program and an ILE program with multiple
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procedures</span><br /><img src="rbafn563.gif" alt="" /><br /></div>
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</div>
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</div>
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<div>
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<ul class="ullinks">
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<li class="ulchildlink"><strong><a href="callcmdbase.htm">Use the command as a base</a></strong><br />
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To use the program or procedure that runs the <span class="cmdname">Send Program
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Message (SNDPGMMSG)</span> command as the base call stack entry, you can
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use the TOPGMQ parameter.</li>
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<li class="ulchildlink"><strong><a href="callidbyname.htm">Identify the base entry by name</a></strong><br />
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You can identify the base call stack entry by providing the name of the OPM program or ILE procedure running in that entry.</li>
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<li class="ulchildlink"><strong><a href="callpgmasbase.htm">Use the program boundary as a base</a></strong><br />
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You can specify the program boundary as the base call stack entry by using the *PGMBDY special value.</li>
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<li class="ulchildlink"><strong><a href="callrecentasbase.htm">Use the most recently called procedure as a base</a></strong><br />
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You can specify the most recently called procedure as the base call stack entry by using the *PGMNAME special value.</li>
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<li class="ulchildlink"><strong><a href="callcontrolasbase.htm">Use a control boundary as a base</a></strong><br />
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You can identify the base call stack entry as the one at the nearest control boundary by using the special value *CTLBDY.</li>
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<li class="ulchildlink"><strong><a href="callservicepgms.htm">Considerations for service programs</a></strong><br />
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This topic describes differences between ILE programs and ILE service programs.</li>
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</ul>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="msgcl.htm" title="Various message types are described in this topic. Use the Send Program Message (SNDPGMMSG) command or the Send User Message (SNDUSRMSG) command to send a message from a CL procedure or program.">Send messages from a CL program</a></div>
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</div>
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<div class="relconcepts"><strong>Related concepts</strong><br />
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<div><a href="msgcallqueue.htm" title="A call message queue is used to send messages between one program or procedure and another program or procedure.">Call message queue</a></div>
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<div><a href="callcmdbase.htm" title="To use the program or procedure that runs the Send Program Message (SNDPGMMSG) command as the base call stack entry, you can use the TOPGMQ parameter.">Use the command as a base</a></div>
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</div>
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</div>
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</body>
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