Protothreads and Other Wicked C Tricks

lwb writes "For those of you interested in interesting hard-core C programming tricks: Adam Dunkels' protothreads library implements an unusually lightweight type of threads. Protothreads are not real threads, but rather something in between an event-driven state machine and regular threads. But they are implemented in 100% portable ANSI C and with an interesting but quite unintuitive use of the switch/case construct. The same trick has previously been used by Simon Tatham to implement coroutines in C. The trick was originally invented by Tom Duff and dubbed Duff's device. You either love it or you hate it!"

Comments

Re:I guess the idea is it's extremely portable.

[twiddlingbits]

It is bound to a paticular KIND of OS. This code would not work right in a pre-emptive multi-tasking OS unless it was the highest priority task. It works best without an OS as it makes it's own blocking.

I read his paper where he said "writing an event-driven system is hard". I guess he has never heard of a using Finite State Automata for the design? State machines are very simple to program. An event driven system is not at all hard to write, although you often times do have to have some deep hardware and/or procesor knowledge to do it well. I wrote many of them in the 1980's when I did embedded C code for DOD work, although I have not done so in quite a few years. Once Ada came along everyone abandoned C as too obtuse for embedded work for the DOD. I once did benchmarks that showed decent C code without strong optimization outperformed Ada code, but C was dead already in their minds. I'm glad to see some folks are still interested in it on the commercial side of programming. After all we can't write everything in Java ;)