Helge Bahmann wrote:
why would you ever want to use a mutex that does not properly inform the system scheduler until when the calling thread should be suspended (in case of contention) for "true" inter-thread (or even inter-process) coordination?
When you believe that the probability of contention is very small, and you care only about average and not worst-case performance, and you wish to avoid the overhead (e.g. time or code or data size) of "properly informing" the system scheduler. Earlier in this thread, Stefan Strasser wrote:
a mutex template with a parameter on what to do to waste some time (this_fiber::yield, this_thread::yield, spinning...) could clean this up
Yes. I implemented something like this that could either spin, or call sched_yield, or (on Linux) call futex_wait. It's basically a Futex-based mutex that implements the other behaviours by replacing the futex with something trivial. See http://svn.chezphil.org/libpbe/trunk/include/Mutex.hh and Futex.hh, Yield.hh, Spin.hh in the same directory. I've discussed the relative performance of these things on this list in the past. Regards, Phil.