The Fastcond project

This provides an alternate implementation of posix condition variables, based only on posix semaphores.

They can be used instead of regular pthread_cond_t objects subject to the following restrictions:

• They don't obey any non-default pthread_condattr_t attributes
• They don't provide cancellation points.
• They cannot be initialized with a static initializer

Two versions are provided, the weak and the strong condition variables. This terminology is my own.

• The weak version relaxes one of the classic condition cariable promises, namely that one of the treads already waiting gets awoken by a pthread_cond_signal() (or all of them in case of a pthread_cond_broadcast()), and instead, guarantees only that a thread will wake up. I.e. it is possible that a thread which has not yet started to wait, will be the one woken up.

• At the cost of some sligt added complexity, the strong version will uphold the aforementioned promise.

Interestingly, tests on multicore machines show that the both versions outperform the regular pthread_cond_t primitives, and the strong type results in much lower latency.

This could be used as a drop-in replacement in many multithreaded programs where latency is of prime importance.