Exchange/SNA Manual

READ Procedure
Exchange/SNA System Procedure Calls
104700 Tandem Computers Incorporated 5–17
tag
INT(32):value
identifies individual nowait I/O operations when a single file can have two or
more nowait I/O operations outstanding at the same time. The value of tag is a
unique, arbitrary value that your program defines for each nowait I/O operation.
A subsequent call to AWAITIO that completes this I/O operation returns this
value to your program, identifying this I/O operation as the nowait I/O operation
that just completed.
If your program has no more than one outstanding nowait I/O operation against a
single file at one time, you can omit this parameter. In this case, the file number
returned by AWAITIO uniquely identifies the I/O operation that was completed.
If you opened the line server for wait I/O operations, omit this parameter.
Considerations The READ procedure causes the line server to accept response units (RUs) transmitted
by the host to the specified subdevice. Each RU can contain one or more records. The
line server disassembles the RUs into individual records and returns the records to
your program one at time (one per call to READ).
If you opened the Exchange/SNA line server for nowait I/O, you must call AWAITIO
to complete an I/O operation initiated by a call to READ. In general, you should not
specify a time limit on the AWAITIO call in console operations—specify timeout =OD
when you call AWAITIO to check for completion. If you do choose to place a time
limit in a READ console operation and the READ call times out, you should
immediately call READ again.