Guardian Programmer's Guide

Communicating With Processes
Guardian Programmer’s Guide — 421922-014
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Sending and Receiving Messages: An Introduction
information to child processes by way of a Startup message (see Section 8,
Communicating With a TACL Process).
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Permits user processes to receive system messages.
A process sends a message to another process by opening the recipient process file
and writing a message to it. A process receives a message—whether the message is
a request from another user process or a system message—by reading from a special
file called $RECEIVE. Figure 6-1 shows these concepts.
Communication with other processes is done using procedure calls to the file system.
The relevant procedures are introduced below:
Figure 6-1. Sending and Receiving Messages
AWAITIO[X] Checks for completion of I/O for any system
procedure. Specific to process communication, it
checks for completion of read operations pending on
the $RECEIVE file; AWAITIO checks READ and
READUPDATE operations, and AWAITIOX checks
READX and READUPDATEX operations as well as
for READ and READUPDATE.
CANCEL Cancels the oldest outstanding operation on a
process or $RECEIVE file.
CANCELREQ Cancels a message identified by a tag value.
CONTROL Issues CONTROL operations to a process that
simulates an I/O device.
CONTROLBUF Issues CONTROLBUF operations to a process that
simulates an I/O device.
FILE_CLOSE_ Terminates access to a process file or to the
$RECEIVE file.
VST033.VSD
VST033.VSD