How to allow certain threads to have priority in locking a mutex use PTHREADS

Question

Assume that the following code is being executed by 10 threads.

pthread_mutex_lock(&lock)
Some trivial code
pthread_mutex_unlock(&lock)

Answer 1

Alternatively you may just introduce another lock for higher priority threads. consider the following pseudo-code (i am not familiar with the pthread semantics, but i believe this is not hard to map the code to the needed calls)

EDIT (thanx JosephH)

introducing the exec semaphore set to 3 (number of high-prio threads) note that pend(exec,3); means that this pend will sleep until all 3 slots are available and will consume them all

//init
exec = semaphore(3,3);

//========================

if this is NOT thread (t1,t2,t3)
    lock(low_prio);
    sem_pend(exec,3);
else
    sem_pend(exec,1);
lock(high_prio);
//...
unlock(high_prio);
if this is NOT thread (t1,t2,t3)
    sem_release(exec,3);
    sleep(0); //yield();  //ensures that sem_pend(exec,1) is executed
    unlock(low_prio);
else
    sem_release(exec,1);