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

Writing Pathsend Requesters

NonStop TS/MP Pathsend and Server Programming Manual–132500

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Context-Sensitive Pathsend Programming

If you are writing a context-sensitive Pathsend program, you must follow the guidelines

in the previous subsection, Basic Pathsend Programming, and also perform additional

programming tasks. This subsection describes these additional tasks and other

considerations for context-sensitive programming.

Context-sensitive Pathsend programming involves establishing a dialog between a

requester and a server process in a server class, and then sending messages within the

dialog. After the dialog is established, the same server process is used for all the

messages in the dialog; therefore, the server can retain context between send operations.

A requester starts a dialog by calling SERVERCLASS_DIALOG_BEGIN_. This

procedure returns a dialog identifier to be used on subsequent server-class send

operations, which are made by calling SERVERCLASS_DIALOG_SEND_. The

requester can use multiple calls to SERVERCLASS_DIALOG_BEGIN_, and the

resulting dialog identifiers, to engage in multiple simultaneous dialogs. As in the

context-free case, the requester can call SERVERCLASS_SEND_INFO_ after a server-

class send operation to get detailed information about send initiation and completion

errors.

Either the requester or the server can abort the dialog, but only the server can end it.

(The server aborts the dialog by returning file-system error 1 (FEEOF) in its reply; it

ends the dialog by returning file-system error 0 (FEOK).) To abort the dialog, the

requester calls SERVERCLASS_DIALOG_ABORT_. The requester calls

SERVERCLASS_DIALOG_END_ to clean up resources after the server has ended or

aborted the dialog.

As in context-free programming, the requester can perform context-sensitive server-class

send operations either waited or nowait. The requester receives an error indication if the

server process has terminated or if it has ended or aborted the dialog.

To participate in a dialog with a context-sensitive Pathway requester, a server must

perform additional tasks besides those required of all servers. These additional tasks are

described under Writing Context-Sensitive Servers

in Section 4.

Using Context-Sensitive Requesters With Context-Free Servers

Context-sensitive requesters can perform single-send dialogs with Pathway servers that

are coded to be context-free. However, if these servers check for system messages and

they use the Common Run-Time Environment (CRE), they must be modified to

recognize and respond to Pathsend dialog abort system messages. Section 4, Writing

Pathway Servers, describes how to code servers to handle these system messages.

Resource Utilization

On a requester’s first SERVERCLASS_DIALOG_BEGIN_ call, an extended segment is

added to the requester’s segment space for use as a workspace. This segment can be up

to 64 KB in size. It is deallocated when the requester process is terminated.