Lecture Notes

Notes (handout) Notes (overhead presentation) Relevant textbook material
Introduction Introduction  
The client-server model The client-server model Chapter 2
Concurrency Concurrency Chapter 3
Application program interfaces APIs Chapter 4, Chapter 5, part of Chapter 6
Client design Client Chapter 6 (the TCP part)
Server design Server design Chapters 8 (the TCP part) and 13; critical regions1
Multithreaded servers Multithreaded servers Chapter 122
Managing concurrency Managing concurrency Chapter 16
Multiservice servers Multiservice servers Chapter 15
Practical issues Practical issues Sections 30.1 to 30.23
Logging and debugging Logging and debugging The remainder of Chapter 30, extra
Deadlock and starvation Deadlock and starvation Chapter 31
Secure programming Secure programming Based on the Secure programs howto3
The User Datagram Protocol UDP Sections 6.18 to 6.24, 8.19, 8.22, 8.27, 8.28
The Internet Protocol IP RFC 791, routing algorithms extra
Socket programming on other platforms Other platforms N/A4
Multi-file programs Multi-file programs N/A5

Lecture recording

My lectures are recorded, as follows:

There are two videos for each recorded lecture, one featuring the camera feed and the other featuring a capture of the front desk screen. The audio track is the same for both videos. It is difficult to recommend one stream over another generally, since depending on the lecture things may happen on the screen or on the whiteboard. You may want to run both streams simultaneously (one of them muted).

Note: Reusing a Socket

When you use the close command to close a socket your program tells the system that it is done with using the respective socket. The socket is however not deallocated, and even the port binding created by your program is still in place. Since nobody is using it, the port binding will eventually time out (according to the TCP timeout value, typically of the order of minutes) and die, but you get in the meantime slapped with an “port already in use” error if you want to bind another socket to the same port. This could become a serious nuisance when one uses thread preallocation, and especially when this is combined with dynamic reconfiguration.

This kind of behaviour occurs when the client does not shut down the socket. Indeed, the TCP stack on the server side assumes that communication will come from the client in the future unless the client has sent an end of file. But then the end of file is sent only upon shoudown. One solution is thus to convince one's clients to be well-behaved, but this is no real solution from the server's programmer point of view (typically the server's programmer has no control over the clients).

I could find no server-side solution to convince a socket to just die for good (should anybody know one, I would be very interested to hear about it). So I will present here the next best thing, a workaround. The workaround consists in convincing your socket to tell bind to reuse the initially provided address. You can do this by modifying the properties of the socket as follows (with sd the descriptor of your master socket):

    int reuse = 1;
    setsockopt(sd, SOL_SOCKET, SO_REUSEADDR, &reuse, sizeof(reuse));

This must be done after creating the socket and before binding it. See the manual page of socket in Section 7 for details on this and other options, and of course the manual page for setsockopt.

Finally, it is worth pointing out that when a client dies in an uncivilized manner the server receives a SIGPIPE signal from its TCP stack. This may be be used as well in the context of this problem (though I don't really know how).

You may also be interested in this explanation of what happens when a socket closes.


... regions1
The code for critical regions discussed in these slides is here.
... Chapter 122
The code for critical regions discussed in these slides is here.
Exploiting buffer oferflows is explained in details in the classic “Smashing the Stack for Fun and Profit.” A couple of examples are from this paper on race conditions
... N/A4
Microsoft provides a very concise getting started document, with just the basics (which is all you need to create socket applications in Windows since you already know the rest of the story). To dig further you may want to look at the following quite extensive winsock programmer's FAQ
... N/A5
More information on the matter of programming with multiple modules can be found on the Web here (continued in the next section; previous section also worth a look). See the reference material for more details on makefiles.