How to utilize a thread pool with pthreads?

I have a queue of jobs and I want to make a pool of four threads where I can throw my jobs at. What I am stuck at is in how to make the threads and keep them suspended while there is no work.

JOB QUEUE        | job1 | job2 | job3 | job4 | ..

THREAD POOL      | thread1 | thread2 | thread3 | thread4 |

To create the threads I have currently at the initialisation point:

for (t=0; t<num_of_threads; t++){
    pthread_create(&(threads[t]), NULL, doSth2, NULL);
}

Where num_of_threads=4 and doSth2 is a function with nothing inside. So once I have created the 4 threads and they are done with doSth2, how can I give them new work to do, without killing them?