Exchange/RJE Manual

CANCEL Procedure
Exchange/RJE System Procedure Calls
104698 Tandem Computers Incorporated 5–9
CANCEL Procedure The CANCEL procedure cancels the oldest outstanding I/O operation against a file
opened for nowait I/O.
CALL CANCEL ( filenum );
filenum
INT:value
is the file number of the Exchange/RJE line server. This number is returned by the
call to OPEN that established communication with the line server.
Line Activity None.
Considerations The CANCEL procedure cancels the oldest outstanding I/O operation on the specified
file. In the case of the Exchange/RJE line server, there can be only one outstanding
I/O operation at a time. The CANCEL procedure always cancels the most recently
requested I/O operation against the line server.
If the operation has already taken place (the block has been sent, for example), the
CANCEL procedure has no effect on the physical I/O operation. If the operation has
not yet occurred (the remote system has not yet bid for the line during an initial
receive operation, for example), the CANCEL procedure does cancel the physical I/O
operation. There is no way to guarantee that the CANCEL procedure can stop the
physical I/O operation. However, the CANCEL procedure always eliminates the need
to call AWAITIO to complete the canceled I/O operation.
A wait I/O operation cannot be canceled; it will already have completed before control
is returned to your program.