Re: Sockets: TMTOWTDI (BWWIB)?

First, I'd recommend a good TCP/IP book. I learned from the Comer/Stevens series. I would recommend you pick up one of the following: Internetworking with TCP/IP, Volume III, BSD version, Windows version, linux/POSIX version. http://www.bookpool.com is a good place to get technical books at a discount. Somebody else here might have some other book recommendations but I've always heard good reviews about this series.

As far as handling connections goes, you have the following choice:

Accept a connection, read the request, generate and send the response, close the socket. This only works for a very lightly loaded server, small amounts of data, responses that can be generated quickly. This is the simplest way to put a server together.
Fork a new process for each connection. On unix-like systems, this works out well because it doesn't take much to fork. On some other systems, creating a new process by forking takes a lot of time or resources and is highly discouraged. Since it sounds like you're working on Windows, you probably don't want to go this way. This method works if each client can be handled individually. In your case, I think your server is going to be a multi-client controller so your clients need to pass information between them through your server. If you go the fork route, you'll also be messing with inter-process communication (IPC) on your server machine to do this. This takes a lot of coordination (locking, queuing, shared memory, etc.) You might run into system limits on the number of child processes or a limit on process per user.
select() or poll() would allow one process to handle multiple clients asynchronously. The select() or poll() call is told what handles to inspect and returns a list of handles that have data ready or are ready to accept data. This is a fairly efficient way of doing what you need. Some operating systems, I think Windows included, may have a limit on the number of network handles you can use with these calls. Also, some operating systems won't allow you to specify non-socket handles which could cause problems if you also need to synchronize on other things. Here you might run into limits on handle counts.
Create a new thread for each client. This method is similar to the multi-process model. You still need to figure out how to pass information between threads and how to synchronize but the solutions in a threaded model are simpler than in a multi-process model. You'll have the same handle count limits here as in the select() model.

Which way is best is for you to decide. What works best on one platform may not work well at all on another. Try to separate your network interface from the rest of your code so that you can try implementing it in different ways.

As a disclaimer, I've written many network servers but usually in C/C++. I've never tried to do one in perl.

---
print map { my ($m)=1<<hex($_)&11?' ':'';
$m.=substr('AHJPacehklnorstu',hex($_),1) }
split //,'2fde0abe76c36c914586c';
[download]

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Re^2: Sockets: TMTOWTDI (BWWIB)? by Ionizor (Pilgrim) on Dec 17, 2002 at 05:15 UTC
Thank you. I found this thread very helpful and informative. Unfortunately the book you've noted is a bit out of my price range and my Christmas gifts have already been bought. I've eliminated the "open, read, write, close" model because the overhead is too high. I want the server to be able to handle a load of a few hundred concurrent users, even if it doesn't ever scale that high in actuality. Given the problems with fork() in Windows I've eliminated it as well as I don't currently have a Unix machine to test on. This may change in future. This leaves me with threads and select(). I am still weighing the benefits and drawbacks but I'm leaning towards select() switching. I've taken your advice and the model I've drawn up for the server has the networking core abstracted with an API so I can switch the underlying implementation as it becomes prudent to do so. Is there a specific reason you've never written network servers in Perl? (i.e. am I missing something important?) Thank you once again for sharing your perspective.	[reply]
Re: Re: Re: Sockets: TMTOWTDI (BWWIB)? by pfaut (Priest) on Dec 17, 2002 at 15:21 UTC
Is there a specific reason you've never written network servers in Perl? (i.e. am I missing something important?) You're not missing anything. Most of the network servers I've written have been done as part of my job. The situations called for coding in C/C++. Most of my personal stuff has been written to run as web-based applications and are written in perl. `--- print map { my ($m)=1<<hex($_)&11?' ':''; $m.=substr('AHJPacehklnorstu',hex($_),1) } split //,'2fde0abe76c36c914586c';` [download]	[reply] [d/l]