TS/MP Pathsend and Server Programming Manual (G06.24+, H06.03+)

Introduction to Pathway Application Programming
NonStop TS/MP Pathsend and Server Programming Manual–132500
1-9
Requesters
•
By temporarily freezing and stopping the server class and changing configuration
parameters, the system manager or operator can adjust the number of servers that are
active at any one time to suit response-time requirements.
•
The system manager or operator can balance the workload over multiple processes
and across multiple processors, which provides fault tolerance in addition to load
balancing: if a processor fails, the server class is still available.
Requesters
The Pathway application programming environment provides two programming
interfaces for requesters:
•
The Pathsend application program interface (API), provided in the NonStop TS/MP
product
•
The SCREEN COBOL language, provided in the Pathway/TS product
Requesters written using these two interfaces are briefly described in the following
paragraphs. In addition, other Tandem products are available to assist you in writing
requesters and clients that communicate with Pathway servers. These products include
the Remote Server Call (RSC) product and the Pathway Open Environment Toolkit
(POET) for workstation clients and the Extended General Device Support (GDSX)
product for front-end and back-end processes.
Section 2, Designing Your Application
, provides additional information about how
Pathsend requesters, SCREEN COBOL requesters, RSC and POET clients, and GDSX
processes can be used in Pathway applications.
Pathsend Requesters
The Pathsend procedure calls and the LINKMON process allow Guardian processes to
access Pathway server classes. The Pathsend procedures bring the benefits of Pathway
server classes to a wide range of requesters, providing flexibility in application design.
They also provide high performance for requesters that do not need a complex,
multithreaded interface to terminals or intelligent devices. Finally, they provide support
for both context-free and context-sensitive servers.
Pathsend requesters support the following features:
•
Use of the TMF subsystem
•
Automatic retry of I/O operations to a server process if the primary process of a
server process pair fails, through use of the Guardian file system
The Extended General Device Support (GDSX) product provides a set of “pseudo
Pathway procedures” that allow you to call Pathsend procedures in the user-supplied part
of a GDSX program. A GDSX process can thus function as a Pathsend requester. GDSX
processes can communicate with devices by means of a number of data communications
protocols, as described in the Extended General Device Support (GDSX) Manual.