Ernest Nana Baffour, Systems Software Engineer

The problem

I had been calling malloc for two years without knowing what it did with the 24 bytes I asked for, or why a program that frees everything can still keep growing.

What I did

• Version one was a single free list with first fit, growing the heap with sbrk. Every free walked the whole list, so it was slow.
• I split free blocks into 12 size classes and added boundary tags, so a freed block merges with its neighbours in constant time.
• Anything over 128 KiB now goes straight to mmap.
• Each thread got its own arena and lock.

The problem

I wanted to know how Vim draws a screen. A terminal is a stream of bytes in both directions, and nothing on it moves unless you tell it to.

What I did

• I started from antirez's kilo tutorial, then rewrote its storage and rendering.
• Raw mode comes from termios, and every frame is drawn with VT100 escape codes.
• Each line lives in a gap buffer, so typing in the middle of a long line doesn't move the rest of it.
• Search, C syntax highlighting and saving came last.

The problem

My operating systems course covered fork and exec in one slide. I wanted to see what happens between cat and grep when I type a pipe.

What I did

• A tokenizer that understands quotes comes first. Each command then runs with fork, execvp and waitpid.
• Redirection is open plus dup2, and a pipeline is one pipe per |.
• The shell ignores SIGINT and each child restores it, so Ctrl+C stops the program and not the shell.