Introduction

Before beginning: Read this lab tutorial; it has some useful tips for programming in the C environment.

This project is a warm-up for operating systems class. It serves to get you into the mindset of a C programmer, something you will become quite familiar with over the next few months. It also gets you familliar with poking around large code bases, which is useful post-school. Finally, it's fun!

The basic idea is to work with memcached, a widely-used networked caching system. Many distributed services in the world are built on top of it.

You'll be adding a small feature to memcached for this project. Read below for details!

Background

Download and Build

To start using memcached, first you have to download it. This is readily done as follows:

prompt> curl -O http://www.memcached.org/files/memcached-1.6.17.tar.gz

Now you have obtained the tar'd and gzip'd source code. To build memcached, just follow these steps:

prompt> tar xvzf memcached-1.6.17.tar.gz
prompt> cd memcached-1.6.17
prompt> ./configure
prompt> make

At this point, a lot of stuff will happen to build memcached, but hopefully it just works and you are ready to try it out!

Run

Now we will run memcached. For this, it is best to have two terminal windows open; we will assume these are on the same computer (they can be on different ones - this is a network server after all! - but then the instructions will be slightly different).

In the first terminal, we will run memcached. To do so, from the build directory, type the following:

prompt> ./memcached

To stop running it at any time, just hit control c (i.e., hold down the control key and hit the c key). This will send a SIGINT signal to memcached, which it will catch but in response it will exit. Try it!

Now, let's assume that memcached is running. In the second terminal window, we will attach to it and put some data into it, using a simple telnet session (if you don't know what telnet is, look it up!). We can do so as follows:

telnet 127.0.0.1 11211

If this is successful, it will say something like this:

Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.

If not, it will say:

Trying 127.0.0.1...
telnet: connect to address 127.0.0.1: Connection refused
telnet: Unable to connect to remote host

(in which case, memcached probably isn't running).

Hopefully, it works! If so, we're now ready to type something into this second window, to send memcached a command. How exciting!

Feature

Tips

Here are some tips:

Start small, and get things working incrementally.
Testing is critical. A great programmer we once knew said you have to write five to ten lines of test code for every line of code you produce; testing your code to make sure it works is crucial. Write tests to see if your code handles all the cases you think it should. Be as comprehensive as you can be. Of course, when grading your projects, we will be. Thus, it is better if you find your bugs first, before we do.
Keep old versions around. Keep copies of older versions of your program around, as you may introduce bugs and not be able to easily undo them. A simple way to do this is to keep copies around, by explicitly making copies of the file at various points during development. For example, let's say you get a simple version of kv.c working (say, that just reads in the file); type cp kv.c kv.v1.c to make a copy into the file kv.v1.c. More sophisticated developers use version control systems such as git; such a tool is well worth learning, so do it!