Thread: pthread_mutex

Do I have to declare a pthread_mutex as an extern so that I may use it in a different program?

I want to control one program by playing with the mutex in another program.

First your implementation has to support the _POSIX_THREAD_PROCESS_SHARED option.
Then you have to create a pthread_mutexattr_t with the PTHREAD_PROCESS_SHARED attribute.
Then you use some shared memory mechanism to host the actual pthread_mutex_t.

More info with an implemenation here: http://www.opengroup.org/onlinepubs/...r_destroy.html

gg

I'm using a fast mutex implementation.

I think I'm running into some race condition - since the processes are running at different rates.

Are you talking about futex's? Because those are tricky...http://people.redhat.com/drepper/futex.pdf

Another alternative is a Sys-V or Posix semaphore.

gg

by fast mutex I was referring to the default instantiation of a mutex using P_THREAD_INSTAN.... somthing or the other.

futexes sound cool, I'll have to dig into that.

What do you mean by Sys-V?

Ah - ok. Futexes are probably a little more "low-level" than what you need.

To use a pthread_mutex_t across processes, you'll need to follow the steps in my first posting. But it's probably easier to just use a semaphore.

SYSV is short-hand for, and most commonly refers to "Unix System 5, Release 4". Another common acronym is "SVR4". http://en.wikipedia.org/wiki/SysV

Semaphores in the SVR4 specification come from <sys/sem.h> and include the functions semctl(), semget(), and semop().

The Single Unix Specification, aka POSIX, has their own semaphore api from <semaphore.h> and include the functions sem_init(), sem_post(), sem_wait(), sem_destroy(), etc...

gg