When Apache is started, (or when child Apache processes are started if a threaded Tcl is used), Rivet_InitTclStuff is called, which creates a new interpreter, or one interpreter per virtual host, depending on the configuration. It also initializes various things, like the RivetChan channel system, creates the Rivet-specific Tcl commands, and executes Rivet's init.tcl. The caching system is also set up, and if there is a GlobalInitScript, it is run.

The RivetChan system was created in order to have an actual Tcl channel that we could redirect standard output to. This lets us use, for instance, the regular puts command in .rvt pages. It works by creating a channel that buffers output, and, at predetermined times, passes it on to Apache's IO system. Tcl's regular standard output is replaced with an instance of this channel type, so that, by default, output will go to the web page.

When a Rivet page is requested, it is transformed into an ordinary Tcl script by parsing the file for the <? ?> processing instruction tags. Everything outside these tags becomes a large puts statement, and everything inside them remains Tcl code.

Each .rvt file is evaluated in its own ::request namespace, so that it is not necessary to create and tear down interpreters after each page. By running in its own namespace, though, each page will not run afoul of local variables created by other scripts, because they will be deleted automatically when the namespace goes away after Apache finishes handling the request.

After a script has been loaded and parsed into it's "pure Tcl" form, it is also cached, so that it may be used in the future without having to reload it (and re-parse it) from the disk. The number of scripts stored in memory is configurable. This feature can significantly improve performance.