>>>Jonathan Clark said:
> Could you point me to any place that explains the ability of the
> tclhttpd to handle simultaneous hits from multiple clients- does this
> involve locking?
> Thankyou,
> Jonathan.
By default, TclHttpd uses non-blocking, event-driven I/O to multiplex itself
among
multiple client hits. It takes 1000's of hits daily on big web sites.
What happens when the server blocks while servicing a request?
There are 3 answers:
1) If the request is for a CGI application, then TclHttpd runs the
CGI process and communicates with it via a pipe. The Tcl event loop means
that TclHttpd only runs when there is data available on the pipe.
So, the CGI process can block arbitrarily long and TclHttpd is free
to service other I/O requests, such as connections from new clients.
2) If the server would block because the client has a slow network
connection, then because it uses non-blocking I/O, well, it doesn't block.
Instead, it relies on the Tcl event loop to trigger a fileevent when
there is new data comming from the client, or when the write socket to
the client drains its output buffer.
3) If the server blocks for some other reason it can indeed starve clients.
The most typical example is if you make SQL calls to a database server directly
from TclHttpd. Those calls will block until the SQL server returns the answer.
Right now the OraTcl and SybTcl interfaces do not really support a non-blocking
interface that will free up TclHttpd to get back into its event loop.
So:
3a) don't do that - if you are just serving files and short-running
dynamic pages, then it doesn't matter. So what if you use some CPU time
to compute a page. Passing that request off to another process (a la Apache)
or another thread (a la AOLserver) only helps on a multiprocessor.
On a uniprocessor, those approaches just add overhead.
3b) or, enable threading the TclHttpd. This requires a recompile of
Tcl with the --enable-thread configure option, and the use of the Thread
extension. You can get this with TclHttpd "Bundled distribution".
With threading, TclHttpd can pass requests to worker threads.
I've expanded this answer into the web page at
http://dev.scriptics.com/tclhttpd/threading.html
-- Brent Welch <bre...@in...>
http://www.interwoven.com
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