On 2014-08-13, Andrés Becerra Sandoval <[email protected]> wrote:
> In short:
>
> Withouth the use of the lock, the condition variable and a shared
> variable in concert you can get in trouble!
That is often true, but
1) I don't have a shared variable that I want to associate with the
condition variable. There is some shared data, but I'm going to
use means other than a mutex to control access to it.
2) In most of the examples presented in that article the shared
variable is an int that is set to 0 or 1 by one thread and is
tested for non-zero value by the other. I'm not aware of any CPU
on which Linux runs where those operations can result in a race
condition thus requiring a mutex. [Yes I know that isn't
guaranteed by the C language definiton, but one can verify that
it's true.]
If I create a shared mutex just to make pthread_cond_wait happy, and
one of the "clients" (the ones calling pthread_cond_wait) dies while
holding the mutex, then it deadlocks all of the other clients. To be
safe it seems one should create a private mutex for each thread that's
going to call pthread_cond_wait(). Private mutexes should be very
little overhead in the uncontended case, so that's an option.
--
Grant Edwards grant.b.edwards Yow! I wonder if I should
at put myself in ESCROW!!
gmail.com
