multithreading - C Programming: Debugging with pthreads

Question

One of the hardest things for me to initially adjust to was my first intense experience programming with pthreads in C. I was used to knowing exactly what the next line of code to be run would be and most of my debugging techniques centered around that expectation.

What are some good techniques to debugging with pthreads in C? You can suggest personal methodologies without any added tools, tools you use, or anything else that helps you debug.

P.S. I do my C programming using gcc in linux, but don't let that necessarily restrain your answer

Answer 1

Valgrind is an excellent tool to find race conditions and pthreads API misuses. It keeps a model of program memory (and perhaps of shared resources) accesses and will detect missing locks even when the bug is benign (which of course means that it will completely unexpectedly become less benign at some later point).

To use it, you invoke valgrind --tool=helgrind, here is its manual. Also, there is valgrind --tool=drd (manual). Helgrind and DRD use different models so they detect overlapping but possibly different set of bugs. False positives also may occur.

Anyway, valgrind has saved countless hours of debugging (not all of them though :) for me.