CODEWITHSUNDEEP
cpthreads
Harry
Harry

Reputation: 3110

multiple condition variables in c

I am developing an application in C where in thread A have to wait for three events(like reception of data) from 3 different threads namely B, C, D. I am able to implement for a single event using pthread_cond_wait, pthread_cond_signal and mutex but I want to expand this concept to multiple events using single condition variable and single mutex. Can somebody please help me in resolving this issue.

Thanks in advance.

Upvotes: 2

Views: 3444

Answers (1)

caf
caf

Reputation: 239341

There's really nothing tricky to it: presuming for one event you have code in thread A like:

pthread_mutex_lock(&lock);
while (!event_b_pending)
    pthread_cond_wait(&cond, &lock);

/* Process Event B */

with code in thread B like:

pthread_mutex_lock(&lock);
event_b_pending = 1;
pthread_cond_signal(&cond);
pthread_mutex_unlock(&lock);

Then for three events, you would change thread A to:

pthread_mutex_lock(&lock);
while (!event_b_pending && !event_c_pending && !event_d_pending)
    pthread_cond_wait(&cond, &lock);

if (event_b_pending)
{
    /* Process Event B */
}

if (event_c_pending)
{
    /* Process Event C */
}

if (event_d_pending)
{
    /* Process Event D */
}

with threads C and D working like thread B (except setting the appropriate flag).

Upvotes: 5

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