Guardian Procedure Calls Reference Manual (G06.25+)

Guardian Procedure Calls (W-Z)
Guardian Procedure Calls Reference Manual—522629-013
16-24
WRITEREAD[X] Procedures
Considerations
•
WRITEREAD versus WRITEREADX
Use WRITEREAD when the buffer has a 16-bit address, and use WRITEREADX
when the buffer has a 32-bit extended address. Therefore, the data buffer for
WRITEREADX can be either in the caller’s stack segment or any extended data
segment.
•
Waited I/O READ
If a waited I/O WRITEREAD[X] is executed, the
count-read parameter indicates
the number of bytes actually read.
•
Nowait I/O READ
If a nowait I/O WRITEREAD[X] 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
AWAITIO[X] procedure.
The WRITEREAD[X] procedure must complete with a corresponding call to the
AWAITIO[X] procedure when used with a file that is opened nowait. If
WRITEREADX is used, you must call AWAITIOX to complete the I/O. If
WRITEREAD is used, you can use either AWAITIO or AWAITIOX to complete the
I/O.
You should not change the contents of the data buffer between the initiation and
completion of a nowait WRITEREAD operation. This is because a retry can copy
the data again from the user buffer and cause the wrong data to be written. You
should avoid sharing a buffer between a WRITEREAD and another I/O operation
because this creates the possibility of changing the contents of the data buffer
before the write is completed.
•
Carriage return/line feed sequence after the write
There is no carriage return/line feed sequence sent to the terminal after the write
part of the operation.
Considerations for WRITEREADX Only
•
The buffer and count transferred may be in the user stack or in an extended data
segment. The buffer and count transferred cannot be in the user code space.
•
If the buffer or count transferred is in a selectable extended data segment, the
segment must be in use at the time of the call. Flat segments allocated by a
process are always accessible to the process.
•
If the file is opened for nowait I/O, and the buffer is in an extended data segment,
you cannot deallocate or reduce the size of the extended data segment before the
I/O completes with a call to AWAITIOX or is canceled by a call to CANCEL or
CANCELREQ.