TS/MP 2.5 Pathsend and Server Programming Manual

You can use a GDSX as a front-end process to the TCP and SCREEN COBOL requestors to
communicate with devices not directly supported by the TCP. Use of the GDSX product is described
in the Extended General Device Support (GDSX) Manual.
The Pathsend Environment
The Pathsend environment includes Pathsend processes and ACS subsystem processes:
• Pathsend processes, written as a part of your application, use Pathsend procedure calls to
make requests to server-classes.
• ACS subsystem processes, supplied by HP, control communication between Pathsend processes
and Pathway server-classes.
Pathsend Processes
When writing programs to run as Pathsend processes, you use a set of procedures that are part
of the Guardian procedure library. These procedures allow you to send request messages to server
processes within a server-class and to receive the servers’ replies. You can call the Pathsend
procedures from programs written in C, C++, COBOL85, Pascal, TAL, or pTAL.
Pathsend procedure calls are provided for both context-free and context-sensitive communication
with servers. A context-free server accepts a single message from a requestor, performs the requested
tasks, and issues a single reply to respond to the requestor. After the reply message is issued, the
server retains no information (context) that can be used in subsequent requests. A context-sensitive
server engages in a multiple-message communication, or dialog, with a requestor. Between
messages, the server retains information (context) pertaining to the dialog.
The use of the Pathsend procedure calls is described in chapter 3, “Writing Pathsend Requestors”
(page 50), and their syntaxes is described in chapter 5, “Pathsend Procedure Call Reference”
(page 74). Design considerations related to context-free and context-sensitive servers are discussed
in chapter 2, “Designing Your Application” (page 28).
ACS Subsystem Processes
ACS Subsystem processes, together with the PATHMON process, perform link-management functions
for Pathsend processes (Process Broker [PB] and ROUT). A link is a connection to a server process.
An ACS Subsystem process executes in each processor, or CPU of a system. As a link manager,
ACS Subsystem processes (PB and ROUT) are responsible for managing links on behalf of all the
Pathsend processes executing in its processor.
If you have the TS/MP software installed on your system, ACS Subsystem processes are automatically
started in each processor. You cannot start ACS Subsystem processes with a RUN command.
Figure 2 (page 23) shows a sample Pathsend environment in which Pathsend processes and ACS
Subsystem processes reside in the same processor on system \A. ACS Subsystem process (ROUT)
sets up communication to the Pathway server-class on system \B through the PATHMON process
controlling the server-class. The role of the PATHMON process in establishing this communication
is described in chapter 3, “Writing Pathsend Requestors” (page 50).
As shown in the figure, only server-class control information is passed to the ACS Subsystem ROUT
process; the application data moves directly from the Pathsend requestor process to the server
process.
22 Introduction to Pathway Application Programming