CS 3733 Operating Systems

Reading: Chapter 2.3, 2.4 and 2.5 of PUP

• Relationships between processes
  • Independent:
    • Can affect or be affected by other processes.
    • State not shared by other processes.
    • Execution is reproducible.
    • Execution can be stopped and restarted without causing ill effects.
  • Cooperating:
    • State may be shared.
    • Result of execution can not be predicted in advance.
    • Nondeterministic.

• Operations on Processes
  • Creation
    • A process may create other processes.
    • The creating process is called the parent
    • The created process is called the child
    • Resources of the parent may be shared among children or the children may get completely new resources.
    • Parent might execute concurrently or might wait for all children to complete.
  • Destruction
  • Changing State of Process

• Processes in Unix
  • Child processes are created with the fork system call.
  • The new process has a copy of the address space of parent.
  • Both processes continue execution after the fork
  • The fork returns 0 to the child and the Child's PID to the parent.

• Code Examples
  • Example 2.3 PUP: What is the value of x for each process?
  • Example 2.4 PUP: Parent and child print different messages.
  • Example 2.5 PUP: A chain of processes, the parent always breaks.
  • Example 2.6 PUP: A fan of processes, the child breaks.
  • Example 2.7 PUP: A tree of processes, only break when error.

SKILL: Understand the basics of process creation in Unix