Open System Services System Calls Reference Manual (G06.28+, H06.05+)

System Functions (s and S) SPT_READUPDATEX(2)
Interprocess communication
SPT_READUPDATEX() reads a message from the $RECEIVE file that
is answered in a later call to the Guardian REPLYX procedure. Each
message read by SPT_READUPDATEX() must be replied to in a
corresponding call to REPLYX.
For programming information about the READUPDATEX procedure, see the
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Programmer’s Guide and the Guardian Programmer’s Guide.
Considerations
Buffer use SPT_READUPDATEX() is intended for use with 32-bit extended
addresses. Therefore, the data buffer for SPT_READUPDATEX() can
be either in the caller’s stack segment or any extended data segment.
Random processing and positioning
A call to SPT_READUPDATEX() returns the record from the current
position in the file. Because SPT_READUPDATEX() is designed for
random processing, it cannot be used for successive positioning through
a subset of records as the SPT_READX() function does. Rather,
SPT_READUPDATEX() reads a record after a call to the Guardian
POSITION or KEYPOSITION procedure, in anticipation of a subse-
quent update through a call to the Guardian WRITEUPDATEX pro-
cedure.
Calling SPT_READUPDATEX() after SPT_READX()
A call to SPT_READUPDATEX() after a call to SPT_READX(),
without intermediate positioning, returns the same record as the call to
SPT_READX( ).
Waited SPT_READUPDATEX()
If a waited SPT_READUPDATEX() call is executed, the count_read
parameter indicates the number of bytes actually read.
Nowait I/O and SPT_READUPDATEX()
If a nowait SPT_READUPDATEX() call is executed, count_read has
no meaning and can be omitted. The count of the number of bytes read
is obtained when the I/O operation completes through the
count_transferred parameter of the Guardian AWAITIOX procedure.
The SPT_READUPDATEX() function must complete with a
corresponding call to the Guardian AWAITIOX procedure when used
with a file that is opened for nowait I/O.
Default locking mode action
If the default locking mode is in effect when a call to
SPT_READUPDATEX() is made to a locked file or record, but the
filenum of the locked file differs from the filenum in the call, the caller of
SPT_READUPDATEX() is suspended and queued in the locking queue
behind other processes attempting to access the file or record.
Use on OSS objects
This procedure operates only on Guardian objects. If an OSS file is specified, Guardian file-
system error 2 occurs.
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