By default, THT creates a sub-interp per page within which Tcl
For simple CGI mode,
this is not all that important. However, when running any other mode
(eg. FastCGI), this is critical.
It means that
built-ins and libraries do not need to be recompiled for each request.
Moreover interp deletion
provides an efficient and effective cleanup between requests.
A separate interp make for
a clear isolation between built-ins and user code.
It can also be used to limit access to sensitive commands
their behavior. This approach also leaves open the future use of threads.
THT also provides a -safe option for making the
sub-interp use Safe-Tcl.
Going the other way, a -subinterp option can
even eval pages in the toplevel interp.
Any way you slice it, interps provide great flexibility.
Access to built-in commands in THT is managed through interp aliases.
The built-in procs themselves reside in the toplevel interp, and thus do not require
a re-bytecompiling for each page. The only limits this
places on built-in code is
with upvar and uplevel. However, these are easily worked
around, and in principle large libraries shouldn't be difficult
to develop as built-ins. This should allow a relatively small resource footprint per page-render.
© 2008 Peter MacDonald