Administration and Programming Guide for OS/400

About Persistent Macros

When using persistent macros, Net.Data runs in a special persistent CGI process of the Web server, receives input through standard input and environment variables, and provides data through standard output. However, after the output is returned to the Web server, The Web server does not have to terminate the Net.Data process. Instead, the process remains active, waiting for a response from the user through the Web browser. Because the process does not terminate, Net.Data can maintain state information for the macro and can leave transactions open.

Net.Data communicates to the Web server that it wants to run in a persistent CGI process by sending the server a new HTTP header. Support for the new header, "Accept-HTSession", has been added to the AS/400 HTTP Server in version 4, release 3 (V4R3). Net.Data decides what HTTP headers to send to the server when it sends its first output, because the headers must precede the output. This has the following implications to you when developing a persistent macro:

• Net.Data must know at the time the first output is generated from the macro whether or not this is to be a persistent macro.
• Using the new persistent macro built-in functions, you must specify the macro is persistent before any output is generated.

These restrictions will be noted in the documentation that follows.

The characteristics of persistent Net.Data processes are very similar to those of standard Net.Data processes with the following exceptions:

• They run in a pseudo-connection-oriented environment. The connection between Net.Data and the Web server is persistent, but the connection between the browser and the Web server still has no connection.
• They can have long running transactions. Because a single Net.Data process can span multiple browser requests, transactions can be left open and committed or rolled-back as appropriate based on subsequent browser requests or error conditions.
• A persistent Net.Data process can consume more system resources because it can remain active for potentially long periods of time. Care must be taken in the management of those resources.
• Portability is reduced because the Web server must contain support for persistence.