Re: Co-thread for parallel processing

[Bogdan Cristea <cristeab@gmail.com>]

On Friday 02 December 2011 10:23:49 you wrote:
> My program use co-threads, because creating and reinitialize thread is
> expensive, it first create threads and reuse them. The main thread
> will send each co-thread a event (through condition variable)
> simultaneously to do task in parallel way. Each co-thread has variety
> work-time, let say it can be (in miliseconds) 200ms, 130ms, 317ms,
> 90ms etc to get result to be consumed by main thread.
> 
> Here I did to wake-up all threads in the main thread:
> 
> .....
> for (i = 0; i < nthread; i++)
>     pthread_cond_broadcast(&cond);
> wait_all_worker(); /* wait for all worker threads to finish */
> get_all_worker_result(); /* get result from all worker thread */
> ...
> 
> 
> And worker-thread routines:
> 
> ...
> for (;;) {
>   pthread_mutex_lock();
>   pthread_cond_wait();
>   pthread_mutex_unlock();
> 
>   do_work();
>   fill_result();
> }
> ....
> 
> My dilema is:
> 
> 1. What the proper way to the main thread to wait for all co-threads
> until finished?

I would use  a semaphore which should be locked by the treads once the 
condition variable is set en unlocked when the result is available for the 
main thread.

> 2. After calling pthread_cond_signal() or pthread_cond_broadcast()
> followed by sleep()/nanosleep(),
>     the condition variable looks like not signaled, (the co-thread
> routine doesn't run). What make this?

I don't understand, please provide a working example

-- 
Bogdan