TS/MP Pathsend and Server Programming Manual (H06.05+, J06.03+)

Server Classes
Server classes provide these benefits:
• You can minimize use of system resources—for example, processes and file opens—because
server classes are shared and highly utilized.
• You can maximize performance because server classes allow multiple copies of server processes
to run concurrently in multiple processors.
• Based on configuration settings determined by the system manager or operator, the PATHMON
process can dynamically create additional server processes within the server class to maintain
acceptable throughput as the workload increases.
• 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 API, provided in the TS/MP product
• The SCREEN COBOL language, provided in the Pathway/iTS product
Requesters written using these two interfaces are briefly described in the following paragraphs. In
addition, other HP products are available to assist you in writing requesters and clients that
communicate with Pathway servers. These products include the RSC/MP product and the POET
for workstation clients and the Extended General Device Support (GDSX) product for front-end and
back-end processes.
Section 2, “Designing Your Application” (page 29), provides additional information about how
Pathsend requesters, SCREEN COBOL requesters, RSC/MP and POET clients, and GDSX processes
can be used in Pathway applications.
Pathsend Requesters
The Pathsend procedure calls and the LINKMON process or the ACS subsystem processes 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
contextsensitive servers.
Pathsend requesters support these 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 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 therefore 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.
22 Introduction to Pathway Application Programming