1. Cs561 Presenter: QIAOQIAO CHEN Spring 2012
Process
Cs561
Presenter: QIAOQIAO CHEN
Spring 2012
Process
11/22/2018

2. Lecture Outline Definition of a Process Anatomy of a Process
Process States
Context Switch
Process Manipulation
Thread
Process
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3. What is a Process? A Process is an execution stream
A Process is the basic unit of execution
Process examples: shell, web browser
It needs resources to run (minimum):
Memory
CPU registers
Process
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4. Anatomy of a Process Processes are separated from each other Process
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5. Organization of Processes
Two concepts
Uniprogramming – only one process is handled at a time
Multiprogramming – multiple processes running at a time
Resource Sharing?
Process
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6. Process states
New (also called created) – process awaits admission to “ready” state.
Ready (also called waiting) – waiting for execution on CPU.
Running – when it is chosen for execution.
Blocked – by some events, such as I/O.
Terminated – after execution or explicitly being killed.
Process
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7. Context Switch How does OS implement process abstraction?
Key Idea: switch from one process to another
Process
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8. Process Manipulation
In Unix OS, there functions for process creation, deletion, signaling and controlling.
fork(), exec(), wait(), exit(), kill(), sleep(), ptrace(), etc.
Process
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9. Process Manipulation continue
Process creation using fork().
Creates a child process that inherits
identical copy of all parent’s memory and variables
copy identical CUP registers of parent process
Fork() return 0 to child, non-zero to parent
After fork(), two processes are running at parallel.
Why people say fork() is expensive?
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10. Fork() continue
Example of Unix fork():
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11. Process manipulation continue
Terminate a process after its job done, using exit()
Take the results as an argument
Close up things
Deallocate memory and OS data structures that support this process
Checks if parent process is alive:
yes – hold the results until parent asks for them (zombie child)
no – Deallocate data structure, now the process is dead.
Clean up all zombie child processes.
Process
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12. Thread A thread is also a stream of execution.
Difference between threads and processes:
Thread ≈ function, process ≈ program
One thread is bound to one process
Multiple threads can access the same memory
Context switch in threads? Much cheaper!
Process
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13. References
Martin C, Rinard, “Process and Threads”, available at
“OS structure, Processes & Processes Management”, available at 9.pdf
Process
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