Various C system-oriented projects
A memory allocator, a preemptive process scheduler, synchronization exercises using mutexes and semaphores, a simplified UNIX shell… Multiple courses proposed small projects around the C programming language and low-level programming.
Simplified shell
Here is an example ensishell session, showing redirections, background
processes and time limits. This project was a good opportunity to discover the
standard programming interfaces for pipes, file descriptors and signal
handling.
$ ./ensishell
Terminaison asynchrone (sec. 5.4) ; Limitations du temps de calcul (sec. 5.6)
ensishell>ls
ensishell.c présentation_alloc.pdf readcmd.c testshell.expect
jobs.c présentation.odp readcmd.h trap_sig.sh
jobs.h présentation.pdf Shell_print.pdf
Makefile présentation_shell.pdf Sujet_shell.pdf
ensishell>ls | grep ".c$"
ensishell.c
jobs.c
readcmd.c
ensishell>
ensishell>sleep 10 &
background (&)
ensishell>liste_ps
7747 sleep 10 &
ensishell># Wait 10 seconds
ensishell: Background process 7747 terminated.
ensishell>ulimit 1
ensishell>yes >/dev/null
out: /dev/null
# 1 second later, process is terminated
ensishell>
Toy operating system
I remember calculating memory addresses by hand and casting them into pointers to read and write the contents.
The operating system project, on the other hand, was designed to make us discover low-level memory manipulation, processor-specific operations such as registering an interruption handler, saving all register contents before performing a context switch, and so on. I ended with a process scheduler that used interruptions to preemptively switch between processes, and time quanta to know which one to choose. Processes could sleep for some time and be awakened automatically, and the scheduler could be configured either to do as little context switches as possible, either to be more interactive by interleaving active processes.