Envoy Application Programming Manual

Envoy Application Programming Manual—427159-001
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C
File-System Procedures
Appendix C summarizes the various Guardian 90 file-system procedures that an
application program uses to interact with asynchronous and byte synchronous data
communications lines. The procedures are described fully in the Guardian Procedure
Calls Reference Manual. The Guardian Procedure Calls Reference Manual provides an
overview of the use of the file-system procedures. For each procedure, this appendix
presents the syntax as it applies to Envoy, discusses the more important aspects of the
procedure, and then gives a few sample calls.
For ease of reference, the procedures are presented in alphabetical order:
AWAITIO[X]
CANCEL
CHANGELIST
CLOSE
CONTROL
DEFINELIST
DEVICEINFO
FILEINFO
HALTPOLL
OPEN
READ[X]
SETMODE
SETMODENOWAIT
WRITE[X]
WRITEREAD[X]
General Characteristics
This subsection outlines the general parameters and conventions used to describe the
Guardian 90 file-system procedures used by Envoy.
Wait and Nowait I/O
When you open a communications line, one of the things that you specify is whether
you wish to use wait or nowait I/O. With wait I/O, each individual file-system procedure
call within the application program must be completed before control passes to the
subsequent instruction or statement. With nowait I/O, certain procedure calls initiate the
specified operation and then pass control immediately to the subsequent instruction or
statement. Such I/O calls are logically completed by a corresponding AWAITIO[X] call
later in the program.
If a line is opened for nowait I/O, the following procedure calls must be completed by a
corresponding AWAITIO[X] call:
CONTROL
READ[X]
SETMODENOWAIT