Quiz 4                                  Due 11/24/09

1.  Describe two ways to detach a thread.

2.  Why would creating dozens of joinable pthreads within a process be
a disadvantage?
  
3.  Thread 2 issues a pthread_cancel(3) on thread 3.  Is thread 3
automatically terminated?  Explain.
  
4.  The function testandsetonce.c from our textbook is shown below.
It is one way to guarantee that a mutex variable is initialized 
just once.
  
#include <pthread.h>

int testandsetonce(int *ovalue) {
   static int done = 0; 
   static pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;
   int error;   
   if (error = pthread_mutex_lock(&lock))
      return error; 
   *ovalue = done;
   done = 1; 
   return pthread_mutex_unlock(&lock);
}

a)  What is the purpose of the static keyword on the variables
done and lock.

b)  What is another way of guaranteeing that a synchronization
variable is initialized only once?

5.  Why are semaphores considered more flexible than mutex lock
variables?