Operating Systems: Process Management and Interprocess Communication, Study notes of Computer Science

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Operating SystemsOperating Systems

CMPSC 473 CMPSC 473

Process Management Process Management

January 31, 2008 - Lecture January 31, 2008 - Lecture 55

Instructor: Trent Jaeger Instructor: Trent Jaeger

• Last class:
  • Process Creation
• Today:
  • Process Management

Process State

• What do we need to track about a process?

Process Control Block

• State of running process
• Linked list of process control information Process id Program Counter … Other registers Process state Ptr to linked list Main Memory (RAM) OS Processes

/proc File System

• Linux and Solaris
  • ls /proc
  • A directory for each process
• Various process information or ways to write to the

process

• /proc//io -- I/O statistics
• /proc//environ -- Environment variables (in binary)
• /proc//stat -- process status and info

Context Switch

• OS switches from one execution context to another
  • One process to another process
  • Interrupt handling
  • Process to kernel ( mode transition , not context switch)
• Current Process to New Process
  • Save the state of the current process
    • Process control block which describes the state of the process in the CPU
  • Load the saved context for the new process
    • Load the new process’s process control block into OS and registers
  • Start the new process
• Does this differ if we are running an interrupt handler?

Context Switch

• No useful work is being done during a context

switch

• Speed it up
• Hardware support
• Multiple register sets (Sun UltraSPARC)
• However, hardware optimization may conflict
• TLB flush is necessary
• Different virtual to physical mappings on different processes

Process Description Summary

• Serves two purposes
  • Track per process resources
  • Save process state on context switch
• Process control block
  • Represents both aspects
  • CPU state
    • Progam counter, registers
  • Resources
    • Linked lists of pages, child processes, files, etc.

Process Scheduling

• What do we need to know about processes to

choose the next one to run?

• Actual scheduling details/algorithms will be discussed later

Scheduling Processes

• Processes transition among execution states

State Transitions

• New Process ==> Ready
  • Allocate resources
  • End of process queue
• Ready ==> Running
  • Head of process queue
  • Scheduled
• Running ==> Ready
  • Interrupt (Timer)
  • Back to end of process queue

State Transitions:

Page Fault Handling

• Running ==> Waiting
  • Page fault exception (similar for syscall or I/O interrupt)
  • Wait for event
• Waiting ==> Ready
  • Event has occurred (page fault serviced)
  • End of process queue (or head?)
• Ready ==> Running
  • As before…

Interprocess Communication

Process Communication

• Processes need to share information
  • Don’t work in isolation
• Discuss a variety of ways
  • Doesn’t include normal files and signals