145 lines
8.6 KiB
HTML
145 lines
8.6 KiB
HTML
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<meta name="DC.Title" content="INVITE (Invite) keyword for display files" />
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<meta name="abstract" content="Use this file- or record-level keyword to invite the device for a later read operation." />
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<title>INVITE (Invite) keyword for display files</title>
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<body id="rzakcmstdfinv"><a name="rzakcmstdfinv"><!-- --></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">INVITE (Invite) keyword for display files</h1>
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<div><p>Use this file- or record-level keyword to invite the device for
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a later read operation.</p>
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<div class="section"><p>To send an invite to a specific device, your program sends an
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output operation to the device with the INVITE keyword in effect. If the record
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format used has output-capable fields, the data is sent to the device before
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the device is invited.</p>
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<p>This keyword has no parameters.</p>
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<p>INVITE
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must be used if the display file can have multiple acquired devices and your
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program does read from invited devices operations. This is because a read
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from invited devices to a multiple device display file only returns a record
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from one of the devices that was invited. If you want all the acquired devices
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to be able to return data, an output operation with INVITE in effect must
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be sent to each device before the read from invited devices. Even if there
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is only one device acquired on the multiple device file, the device must be
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invited via INVITE before a read from invited devices.</p>
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<p>INVITE also gives
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you the ability to create a subset of acquired devices that are eligible to
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respond on a read from invited devices. For example, if ten devices are currently
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acquired to the file but only three devices were invited, the next read from
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invited devices operation returns a record from one of the three invited devices.
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This is true even if the other devices have data available.</p>
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<p>INVITE provides
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some performance improvement. Normally a read request is issued to a device
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when your program sends an input operation. However, INVITE allows you to
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request the read when you issue the output operation. After the output operation
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is complete, your program can do other processing while the device is issuing
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data and the <span class="keyword">i5/OS™</span> operating
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system is processing the received data. This can be a significant improvement
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if the device is remote.</p>
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<p>For specific instructions on when an invite
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operation is necessary and how to specify a read from invited devices operation
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in your program, see the appropriate high-level language manual.</p>
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<p>INVITE
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cannot be specified at both the file and record level and cannot be specified
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with the subfile keyword (SFL).</p>
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<p>Option indicators are valid for this
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keyword.</p>
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</div>
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<div class="section"><h4 class="sectiontitle">Special considerations when using the INVITE keyword</h4><div class="p">The
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following list shows special considerations when you use the INVITE keyword:
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<ul><li id="rzakcmstdfinv__sp1"><a name="rzakcmstdfinv__sp1"><!-- --></a>An input operation sent to a specific device does not require
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an invite operation. Input operations with a specified record format name
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or device are directed to one device. If that device has an invite outstanding
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at the time of the input operation, the invite operation is deleted after
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the input operation is completed.</li>
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<li>Once an invite operation has been sent to a device,
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the only valid operations (in addition to a read operation from invited devices)
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are as follows: <ul><li>An input operation to a specific device.</li>
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<li>An output operation with data that tries to cancel the invite operation.
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If the cancel operation is successful, the data is written. If INVITE was
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in effect on the output operation, the device is invited again. If the cancel
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is not successful (because the data has already been received by the system),
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the output operation fails. Your program must perform an input operation to
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process the data. The input operation erases the invite for that device.</li>
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</ul>
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</li>
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<li>On a read operation from invited devices operation to a display file,
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only data from devices with an outstanding invite operation are considered.
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The input operation waits for data from any of the invited devices. (See the
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WAITRCD parameter on the Create Display File (CRTDSPF) and Change Display
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File (CHGDSPF) commands.) If none of the invited devices responds before the
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wait time ends, a notify message is sent and no data is returned. All invited
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devices remain invited.</li>
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<li>If more than one device acquired to the display file has an invite outstanding,
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a read from invited devices operation returns the next available record from
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one of the invited devices. If records are received from more than one device
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before this input operation, the other records are kept for subsequent input
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operations.</li>
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<li>When a read operation from invited devices operation to a display file
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returns a record to your program from an invited device, the invite operation
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for that device is deleted. Other devices that have an invite outstanding
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remain invited. The device that sent the record your program read must be
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invited again if you want to receive data from this device on a later read
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from invited devices operation.</li>
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<li>If no device was invited or if a device was invited but the job was canceled
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with the controlled option, a read operation from invited devices
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operation to a display file results in a notify message and no data is returned
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to your program. All invited devices remain invited.</li>
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<li>If you want to invite a device but have no data to send it, issue an output
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operation using a record format containing no output-capable fields with INVITE
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in effect.</li>
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<li>After the first record is received from an invited display device, the
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device should not be re-invited until all the record formats on the display
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with input-capable fields are read by your program. Your program can read
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those other record formats if you specify the record format name and the device
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name on the read operation.</li>
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<li>If your display file has the delayed write option (DFRWRT(*YES) parameter
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on the (Create Display File (CRTDSPF) and Change Display File (CHGDSPF) commands),
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an output operation with the INVITE keyword in effect causes the delayed output
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to appear on the display before the device is invited.</li>
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</ul>
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</div>
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</div>
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<div class="example"><h4 class="sectiontitle">Example</h4><p>The following example shows how to specify
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the INVITE keyword.</p>
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<pre>|...+....1....+....2....+....3....+....4....+....5....+....6....+....7....+....8
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00010A 01 INVITE
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00020A R RCD1
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00030A FLD1 10 2 2
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00030A FLD2 5 2 24
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A</pre>
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<p>INVITE is in effect only when option indicator 01 is
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set on.</p>
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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="rzakcmstkeyent.htm" title="You type the keyword entries that define display files in positions 45 through 80 (functions).">DDS keyword entries for display files (positions 45 through 80)</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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