1. Advanced UNIX programming
Fall 2002
Instructor: Ashok Srinivasan
Lecture 20
Acknowledgements: The syllabus and power point presentations are modified versions of those by T. Baker and X. Yuan

2. Announcements Reading assignment Chapters 5 Chapter 6
Section 6.3 and 6.8
You may need to refer to other sections occasionally, especially sections 6.4 and 6.7

3. Week 8 Topics Client-Server design Client-server design alternatives
Concurrent server
Programming assignment 3 discussion
Client-server design alternatives
Server with multiplexed I/O
Preforked server

4. Client-Server design
Concurrent server

5. Concurrent server See example2[abc].c
Use a new child process to handle a new connection request
Advantages
Simple program
Large number of connections
Main limitation: too much overhead

6. Server crashing What happens to the client when the server crashes?
How can we make the client anticipate the problem?
example1a.c
The client has two places that can block – it may not be able to detect that something is wrong
Solution
I/O multiplexing – check the file descriptor before performing a blocking operation
Mechanism: select