PRINCIPLES OF OPERATING SYSTEMS Lecture 6: Processes CPSC 457, Spring 2015 May 21, 2015 M. Reza Zakerinasab Department of Computer Science, University of Calgary

Review: Threads  Threads in a process allow multiple executions to take place in the same process environment  A thread is a unit of execution of a process.  Basically, mini-processes within a process.  Threads are scheduled independently and can make system calls simultaneously  A thread requires an address space and other resources  but it can share many of those resources with other threads 2 shared unshared

Review: Processes vs. Threads Processes  Processes are used when the tasks are essentially unrelated  Each process has its own address space and PCB  Address spaces are protected from each other  Switching between processes is done at the kernel level  Owned by one or more users 3 Threads  Threads are used when tasks are actually part of the same job  Threads belonging to the same process share the process’ address space, code data, and files, but not the registers and stack  No address space protections  Switching between threads can be done at either the user level or the kernel level  Usually own by a single user

Review: Thread Libraries  A thread library provides the programmer with an API for creating and managing threads.  Three main libraries in use today  POSIX Pthreads  Win32  Java 4

Review: How to Use Pthreads Library?  Include the Pthreads library  #include  Create your thread  pthread_create(thread, attr, start_routine, arg)  thread: pointer to the created object  attr: joinable, detached, … You can use NULL most of the time.  start_routine: routine to be executed by the new thread  arg: a single argument for the start_routine  Destroy your thread when it is done  pthread_exit(status)  Make sure the process waits for the threads to finish  pthread_join(thread, status) 5

Example Code Slide (Replace this) 6 #include #define NUMBER_OF_THREADS 10 void *print_hello_world(void * tid) { printf("Hello Word. Greetings from thread %d\n", tid); pthread_exit(0); } int main(int argc, char *argv[]) { pthread_t threads[NUMBER_OF_THREADS]; int status, i; for (i = 0; i < NUMBER_OF_THREADS; i++){ printf("Main here, Creating thread %d\n", i); status = pthread_create(&threads[i], NULL, print_hello_world, (void *) i); if (status != 0) { printf("Oops, pthread_create returned error code %d\n", status); exit(-1); } } exit(0); } What is missing?