PRINCIPLES OF OPERATING SYSTEMS Tutorial-4: Multi-process and Multi-threaded Programming CPSC 457, Spring 2015 May 28/29, 2015 Department of Computer Science, University of Calgary

Outline  Multi-process Programming  Process ids  Process creation  Process wait and exec family of functions Exercise - 1  Multi-threaded programming  Thread creation  Thread wait (join)  Parameter passing Exercise - 2 2

Process Execution  When a child process is created…  The parent may continue to execute concurrently with its children  At some point the parent shall wait until each of its children have terminated  Otherwise zombie processes may remain in the system. 3

Example Code #include int main () Ref: Example1.c { printf("Hello World\n"); fork(); printf("Goodbye World\n"); } How many prints of ”Hello World” and ”Goodbye World”? 4

 wait()  Wait for one of the child processes to terminate  exec()  Replace current process image with new one  Signals  Communicating with processes  Special messages to the processes  More on this topic in later tutorial 5

Exercise - 1  Overview  Discussion  Sample codes 6

Review: Threads  Threads in a process allow multiple executions to take place in the same process environment  A thread is a  Mini-process within a process.  Threads are scheduled independently 7 shared unshared

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 8

Review: 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) 9

Example Code  Refer example-0.c  Discussion 10

Exercise - 2  Overview  Discussion 11