Pathway/XM System Management Manual

Overview of Configuring and Managing Pathway/XM
Compaq NonStop™ Pathway/XM System Management Manual—426761-001
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Terminal Control Processes (TCPs)
Terminal Control Processes (TCPs)
Terminal control processes (TCPs) provide terminal management and transaction
control. A TCP is a multithreaded process that interprets compiled SCREEN COBOL
requester programs (screen programs) in the user’s application, executing the
appropriate program instructions for each I/O device or process the TCP is configured to
handle.
In the Pathway/XM environment, additional TCPs are created as needed to balance
transaction workload. The Pathway/XM configuration includes TCP templates, each of
which can be applied to multiple TCPs.
A TCP coordinates communication between screen programs and their I/O devices or
processes and, with the help of the PATHMON process, establishes links between the
screen programs and server processes. The TCP also performs the following tasks:
•
Verifies and stores terminal context data and terminal control logic
•
Gathers statistics about TERM objects, the server processes, and itself
•
Reports operating errors and status information to the PATHMON process
•
Provides integrity across failure situations
Because it is a multithreaded process, a TCP can concurrently manage many user
terminals and execute many screen programs. To accomplish these tasks, the TCP runs
its terminal tasks as threads, interleaving the concurrent processing of requests
originating from many I/O devices or processes. This multithreading allows the TCP to
handle complex groups of operations for many users at the same time.
The TCP manages the operation of multiple I/O devices by maintaining separate screen
program code and data areas for each device under its control. In addition to managing
operation of terminals, the TCP supports card readers, local printers, and bar-code
readers when they are attached to terminals.
Link Control Service (LCS) Processes
The link control service (LCS) processes manage transaction requests to distributed
server classes. One LCS process is provided for each distributed server class under each
PATHMON process running in the Pathway/XM environment. Each LCS process acts
as a proxy server; it manages the resources of its server class, controls the server-class
transaction queue, and forwards requests to server processes.
Router Processes
Router processes manage links between browser-based web clients or socket-based
intelligent devices (IDS requesters) and the TCPs. The router processes are listener
processes that detect connection requests on a socket or an http connection, determine
from the TCP which TERM objects are available, and distribute the requests to the
TERM objects. Thereafter, the clients or requesters communicate directly with the
assigned TERM objects. The TERM object selection algorithm is designed to maintain a
balanced workload.