Date: Wed, 13 Nov 1996 12:38:09 -0700 (MST) From: Terry Lambert <terry@lambert.org> To: stesin@gu.net (Andrew Stesin) Cc: hackers@freebsd.org, squid-users@nlanr.net Subject: Re: Programming technique for non-forking servers? Message-ID: <199611131938.MAA22676@phaeton.artisoft.com> In-Reply-To: <Pine.BSI.3.95.961113122121.8648B-100000@creator.gu.kiev.ua> from "Andrew Stesin" at Nov 13, 96 12:32:33 pm
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> can anyone point me to some book, or URL(s), where the
> programming technique for writing non-forking network server
> daemons is described in details? with caveats, non-obvious
> places...
The Stevens books cover it...
> Yes, there are sources, but I'd really like to read
> some general theory on the subject.
The general theory is that you change a blocking call into a non-blocking
call + a context switch.
In other words, it's state-machine based event driven multithreading.
,------> wait for packet
| |
| v
| select() o-----------------------.
| | socket A | socket B
| v v
| f(context A) f(context B)
| \ /
| \ /
| \ /
| \ /
| \ /
| v
| o packet processing function f()
| |
| v
| o any additional processing
| |
`------------------------'
In addition, the packet may be a connect() request from a remote client;
if so, you need to:
1) accept the connection to bind it to a local socket
2) add the socket to the list of fd's that the select is
listening to
3) continue processing
so the main loop looks like:
/*
* init
*/
create connect_socket for incoming connections
post listen() on socket connect_socket
init default fd_set default_read_mask to contain connect_socket
set max_fd to connect_socket + 1
initialize context_list to NULL
/*
* main loop
*/
while( 1) {
copy default_read_mask to real_read_mask
select( max_fd, real_read_mask)
/*
* if we got here, a socket event has occurred;
* real_read_mask will now contain the fd's
* (sockets) which you must do processing on.
*/
/* check for incoming connections, first thing*/
if( FD_ISSET( connect_socket, &real_read_mask)) {
/* clear so we don't hit it in processing loop*/
FD_CLR( connect_socket, &real_read_mask)
/* generate default context for new connection*/
ctxp = new_context();
add_context( ctxp, context_list);
ctxp->state = 0;
ctxp->fd = accept( connect_socket)
/* accept events on this context*/
FD_SET(ctxp->fd, &default_read_mask)
}
/* process all contexts which aren't incoming connections*/
for( ctxp = context_list; ctxp = ctxp->next) {
if( FD_ISSET( ctxp->fd, &real_read_mask)) {
handle_event( ctxp);
}
}
}
Terry Lambert
terry@lambert.org
---
Any opinions in this posting are my own and not those of my present
or previous employers.
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