TMF Application Programmer's Guide (G06.24+)

TMF Programming Environment

HP NonStop TMF Application Programmer’s Guide—522419-004

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The Requester/Server Model

Many business applications that run on HP systems use the requester/server

application design model to obtain input from end users and apply it to a database.

In the most elementary case, a requester is the process that receives the initial request

to perform a business operation requiring modification of a database. The requester

then initiates a TMF transaction, calls one or more server processes to make the

necessary changes to the database, terminates the transaction, and responds to the

end user (or to the application module that represents an end user).

In reality, however, application modules are usually much more complex than that.

Requester and server modules can be designed to work on more than one transaction

at a time; this is referred to as “multithreaded operation.” In addition to delegating the

work for a particular transaction to one or more servers, a requester can update a

database directly. Furthermore, a single application module can even function

simultaneously as a requester for some transactions and as a server for others.

TMF requesters can be coded in C, C++, COBOL85, FORTRAN, Pascal, SCREEN

COBOL, or TAL.

TMF servers can be coded in C, C++, COBOL85, FORTRAN, Pascal, or TAL.

Within the TMF environment, requesters and servers communicate with one another

over the message system.

To communicate with a server, a requester must first open the server process by using

the OPEN system procedure. The OPEN procedure includes, as its first parameter,

the server process’ name instead of a file name. All necessary process names, in local

and network form, can be predefined so that the particular processes are known

throughout both the system and the network.

To send a request to a server and receive a reply, the requester uses the WRITEREAD

procedure (specifying the filenumber returned by OPEN). Note that SCREEN

COBOL requesters use the SEND verb to communicate with servers.

After opening a server, a requester will often leave it open indefinitely. Eventually,

however, the requester terminates its communication path to the server by using the

CLOSE system procedure.

To communicate with a requester, a server must open a special file named $RECEIVE.

Thereafter, the server accepts work request messages from requesters by using the

READUPDATE system procedure to read from $RECEIVE. When the server has

completed all of the operations associated with a particular work request, it responds to

the requester by using the REPLY system procedure.