Foundation University Islamabad
Processes
Operating Systems
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A set of lecture notes from a university course on Operating Systems, focusing on the topic of processes. The notes cover the definition of a process, the control flow of a process, process types, how the operating system creates a process, private address spaces of a process, the five-state process model, context switching, and creating new processes using the fork() system call. The document also includes examples and explanations of how parent and child processes can communicate.
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2020/2021
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Operating Systems
LECTURE#
Processes Processes
Dr. Shariq BASHIR
Operating Systems
FALL 2019
Operating Systems
Course Learning Objectives
- Study the fundamental concepts of operating system design and implementation.
- Understand the interaction between user- level applications and the underlying operating system.
- Practical understanding of operating system topics such as processes/threads, file systems, and memory management.
Operating Systems 4
“ “TentativeTentative”” GradingGrading
- (^) Assignments 15%
- (^) Quizzes /Class Test 10%
- (^) Midterm 25%
- (^) Final Exam 50%
5
What If No Operating System? What If No Operating System?
- (^) All we have is bare hardware
- (^) You want to run a program (^) How do you load it? (^) How do you run it? (^) What happens when it completes?
- (^) Need at least some minimal Operating System (OS) to do these functions
Operating Systems
- (^) A computer program in execution on a machine is a process
- (^) More formally:
- (^) A Sequential Stream of Execution in its own address space
Process
7
Operating SystemsControl Flow of a
Process
- (^) Computers do Only One Thing
- (^) From startup to shutdown, a CPU simply reads and executes a sequence of instructions, one at a time. Physical control flow Time
Operating Systems
Process Types
- (^) If all processes are I/O bound,
- (^) System will go free
- (^) If all processes are CPU bound,
- (^) Devices will go unused
- (^) System will again be unbalanced 10
Operating Systems
How OS Creates a Process
- (^) Assign a unique process identifier
- (^) Allocate space to the process
- (^) Creates process control block
- (^) Ex: add new process to linked list used for scheduling processes
Operating SystemsPrivate Address Spaces of a
Process
- (^) Each process has its own private address space Heap Segment run-time heap (managed by malloc) Stack Segment user stack (created at runtime) Code Segment 0 %esp (stack pointer) memory invisible to user code 0xc 0x 0x Data Segment loaded from the executable file 0xffffffff
Operating Systems
Five-State Process Model
New New Exit Exit Admit Release Running Running Ready Ready Dispatch Time-out Blocked Blocked Event occurs (^) Event wait 14
Operating Systems
CPU Switch From Process to
Process
- (^) Part of OS (Operating System) responsible for switching the processor among the processes is called Dispatcher 16
Operating Systems
Context Switching Example
Tim eoutI/O Tim eout Tim eout
Operating Systems
Trace from Processors point of view
Tim eoutI/O Tim eout Tim eout
Operating Systems
- (^) Processes may themselves go on to create new processes
- (^) A new process is created by a fork() system call (in case of only linux) 20