Envoy Application Programming Manual

Software Concepts
Envoy Application Programming Manual—427159-001
2-12
Point-to-Point Operation
Point-to-Point Operation
Figure 2-3 shows the use of file-system procedure calls and error returns and the effects
of the various line states in a point-to-point configuration. Two NonStop™ Himalaya
servers are connected to one another over a nonswitched point-to-point line. An
application process in each system acts as a station.
Because the connection is permanently established, the only action necessary to
establish communication with the other station is to call the OPEN procedure. The line
is named $BSC1 in System A and $LINE1 in System B (the line names are designated
during system generation):
Process in System A:
Process in System B:
Note that data communications lines are always opened for exclusive read-write access
regardless of what value you supply in the OPEN call (in the above case, the flags
parameter is omitted entirely).
Next, while each process is idle, the processes monitor the line for incoming messages
(Example 2-3
) by calling the READ procedure. While waiting for incoming messages,
the READs periodically complete with an error 162 (operation timed out). (The timeout
period is specified at system generation and can be altered by a call to the SETMODE
procedure.)
Figure 2-3. Point-to-Point Operation
lname [0:11] := [“$BSC1 “,9*[“ “]];
CALL OPEN (lname,lfnum);
lname [0:11] := [“$LINE1”,9*[“ ”]];
CALL OPEN (lname,lfnum);
012CDT .CDD
Application
Process No. 1
Application
Process No. 2
Server A Server B
Nonswitched
Point-to-Point Line
$BSC1 $LINE1