title: threads inside a thread?
body: <p>I wanna implement divide and conquer using pthread, but I don't know what will happen if I create more threads in a thread. </p>
  
  <p>From my understanding, if the machine has a 2-core processor, it can only process 2 threads at the same time. If there are more than 2 threads, other threads have to wait for the resources, so if I create more and more threads while I'm going deeper, actually it may not increase the speed of the algorithm since only 2 threads can be processed at the same time.</p>
  
  <p>I do some research online and it seems the threads at upper level can be inactive, only the ones at the deepest level stay active. How to achieve this? Also if an upper thread stays inactive, does it affect the lower thread?</p>