Homework 2

1. Do book problems 3.4, 3.5, 3.11
2. Do book problems 4.1, 4.2, 4.4.
3. Hello World 2: Electric Boogaloo. You will write a simple Hello World program in C, but there's a catch. You will need to launch two threads, one that prints "hello", and one that prints " world!". You will need a semaphore to make sure that they get printed in the correct order.

   Things to remember:

   • You create a thread with:

     int pthread_create(pthread_t *thread, const pthread_attr_t *attr, void  *(*start_routine)(void*), void * arg);
                                    ^                       ^                     ^                           ^      
                                    |                       |                     |                           | 
                                    |                       |                     |                           | 
                           thread variable   we'll always be using NULL    thread function    arguments for thread function
     

     For example:

     void *listenerThread(void *p);
     pthread_t lt;
     pthread_create(&lt,NULL,listenerThread,NULL);
     

   • Include pthread.h and compile with the -pthread flag
   • Semaphores are created as a variable of type sem_t
   • They are initialized with sem_init()

     int sem_init(sem_t *sem, int pshared, unsigned int value);
                          ^          ^                    ^
                          |          |                    |
                          |          |                    |
           pointer to seamphore  0 for threads     initial value
     
     sem_t foo;
     sem_init(&foo,0,0);
     

   • You block on a semaphore with:

     int sem_wait(sem_t *sem);
     
     sem_wait(&foo);
     

   • You increment a semaphore with:

     int sem_post(sem_t *sem);
     
     sem_post(&foo);
     

   • Include semaphor.h
4. Due Jan 24. The written portion in class, the code at midnight.