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Process. Additional references: Operating Systems: Internals and Design Principles 5e– William Stallings - Pearson. This lecture slide uses images/slides from other references also. . Free memory. User task. Monitor / Kernel. Single tasking. Life is simple here

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process

Process

Additional references:

Operating Systems: Internals and Design Principles 5e– William Stallings - Pearson

This lecture slide uses images/slides from other references also.

single tasking

Free memory

User task

Monitor / Kernel

Single tasking
  • Life is simple here
    • Have only one task running
  • Task directly loaded
    • What will you do to execute such a task?
  • What if more than one process?
linux process run time memory
Linux process’ run-time memory
  • Process
    • Code
    • Data part

Fig courtesy: Computer Systems: a programmer’s perspective

process4
Process
  • Program has just code  NOT Live entity
  • Process with data, work-space
    • Stack
    • Heap
  • Open files
    • File descriptors
    • Other primitives
      • ipc, memory, …
  • Execution snapshots
    • Register content
      • Program counter
      • General purpose registers
question
Question???
  • How are multiple processes handled?
  • How does process management take place?
    • Creation, deletion,…
  • What to do when a process performs I/O?
  • How to ensure all processes get a chance to execute?
  • Can processes communicate among one another?
    • If so, how?
  • What are the desirable features?
a simple scenario two state process model
A simple scenario: Two-State Process Model
  • Process may be in one of two states
    • Running
    • Not-running
not running process in a queue

Both are 2 different scenarios

Not-Running Process in a Queue

What processes are in queue?

Process timed out

Process gone for I/O

process contd
Process (contd.)
  • Not-running
    • Ready to run given chance
    • Blocked/waiting for event
  • Why not three states then?
three state model

Dispatch

Admit

Release

Ready

Running

Time out

Event Occurs

Event Wait

Blocked

Three state model
four state model

Dispatch

Admit

Release

New

Ready

Running

Time out

Event Occurs

Event Wait

Blocked

Four state model
  • Need to create process
    • Process control block
    • Verify availability of resources

What about termination?

five state model

Dispatch

Admit

Exit

Terminate

New

Ready

Running

Time out

Event Occurs

Event Wait

Blocked

Five state model
  • Terminate
    • To wrap up process
    • Wait conditions before termination
suspended processes
Suspended Processes
  • Processor is faster than I/O so all processes could be waiting for I/O
  • Swap these processes to disk to free up more memory
  • Blocked state becomes suspend state when swapped to disk
one suspend state 6 state model
One Suspend State (6 state model)
  • Suspend does not show those that can run once in memory
  • Two new states
    • Blocked/Suspend
    • Ready/Suspend