Re: [gentoo-user] OT: pthreads condition variable/mutex question

[Alec Ten Harmsel]

2014-08-13 12:21 GMT-05:00 Grant Edwards <grant.b.edwards@×××××.com>:
> This is not Gentoo specific, and while I'm doing my prototyping and
> development on a Gentoo system, the eventual target is not going to be
> running Gentoo -- so feel free to ignore this thread or throw things
> at me.

You're close enough ;) I'll try to answer to the best of my ability,
which is admittedly not much.

> I'm trying to figure out how to synchronize threads which may be in
> different processes.  Basically, I want thread A to be able to wake up
> any number of other threads B, C, D, ... who are all blocking until A
> says "go" (and who may or may not be in other processes).

Without knowing what you're doing, this sounds like a bad idea; if you
*need* to synchronize threads, why aren't they running in the same process?

If it's going to be running on Linux, you can send signals through the
kernel's signal API; specifically HUP, USR1, and USR2 might be of
interest to you.

> A condition variable in shared memory is the closest thing I have
> found, and my test applications are working OK (so far).  But, I'm
> unclear on the purpose of the mutex whose address you pass to
> pthread_cond_wait().

I'm too much of a rookie to know how to do this; how are you sharing
memory between processes?

> The mutex appears to be there to serialize access to some user-defined
> variable(s) (outside the condition variable itself) which I don't
> have. So all the mutex locking/unlocking and resultant blocking of B,
> C, D is just wasted overhead and pointless latency.

This is definitely not a task for mutexes, a boolean or signaling would
work much better.

I'm not sure what exactly you're trying to do, but I hope this helps. If
you can be more specific about the relationships between processes, I
might be able to help more.

Alec