Processes, Process Control Block, Process Scheduling.pdf

Operating Systems
Chapter 3: Processes
Lecturer: Dalya Samer
Operating System Concepts – 10th
Edition Silberschatz, Galvin and Gagne ©2018
Chapter 3 Outlines

▪ Process Concept
▪ Process Scheduling
▪ Operations on Processes
▪ Interprocess Communication
Operating System Concepts – 10
3.2 Silberschatz, Galvin and Gagne ©2018 th
Edition

Process Concept(1/2)
Program vs. Process
▪ A program is a passive entity such as the file that contains the
list of instructions stored on a disk always referred to as an
executable file.
▪ A program becomes a process when an executable file is
loaded into the memory and then becomes an active entity.
▪ The fundamental task of any operating system is the process
management.
▪ Processes include not only a text but also include a set of
resources such as open files and pending signals. Processes
also contain internal kernel data, processor state, an address
space, and a data section

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Process Concept(2/2)
➢OS must allocate resources to processes, enable sharing of
information, protect resources, and enable the synchronization
among processes.

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Process Elements (1/2)
▪ Segments of a process represents the following components:
➢ Text Section: the program code. This is typically read-only,
and might be shared by a number of processes.
➢ Data Section: containing global variables.
➢ Heap: containing memory dynamically allocated during run
time.
➢ Stack: containing temporary data.
• Function parameters, return addresses, local variables.

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Process Elements (2/2) •Process in

Memory
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Process Control Block (PCB) (1/2)

• For better control of processes,
operating
systems need to consider their dynamic
behaviors.
• Each process is represented in the OS by
a
Process Control Block (PCB).
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❑Process Control Block (PCB) (1/3)
➢ Process identification information:
•Process identifier: numeric identifiers represent the
unique process identifier .
•User identifier: the user who is responsible for the job).
•Identifier of the parent process that created this
process.

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➢ Processor state Information
•Process state – running, waiting, etc
➢ Program counter
•location of instruction to next execute

➢ CPU registers
• contents of all process-centric registers
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➢ CPU scheduling information
▪ priorities, scheduling queue pointers
➢ Memory-management information
▪ memory allocated to the process

➢Accounting information
▪ CPU used, clock time elapsed since start, time limits
➢ I/O status information
▪ I/O devices allocated to
process, list of open files
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Process State (1/3)
▪ As a process executes, it changes state
➢New: The process is being created
➢Running: Instructions are being executed

➢Waiting: The process is waiting for some event to
occur
➢Ready: The process is waiting to be assigned to a
processor
➢Terminated: The process has finished execution
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Process State (2/3)
•Diagram of Process State

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Process State (3/3)

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CPU Switch From Process to
Process

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Process Scheduling (1/2) ▪ Job
queue – set of all processes in the system
▪ Ready queue – set of all processes residing in main memory,
ready and waiting to execute
▪ Device queues – set of processes waiting for an I/O device
• Processes migrate among the various queues

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Process Scheduling (2/2)
•Representation of Process Scheduling

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Schedulers (1/2)

▪ Short-term scheduler (or CPU scheduler)
➢ Selects which process should be executed next and
allocates CPU.
➢ Invoked frequently (milliseconds) → (must be fast).
▪ Long-term scheduler (or job scheduler)
➢ Selects which processes should be brought into the ready
queue.
➢ Invoked infrequently (seconds, minutes) → (may be
slow).
➢ Controls the degree of multiprogramming.
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Schedulers (2/2)
▪ Medium-term scheduler
➢ Can be added if degree of multiple programming needs to
decrease
➢ Remove process from memory, store on disk, bring back
in from disk to continue execution: swapping

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Interprocess Communication(1/2)
▪ Processes within a system may be independent or cooperating ▪
Cooperating process can affect or be affected by other processes,
including sharing data
▪ Cooperating processes need interprocess communication (IPC)
▪ Two models of IPC
➢Shared memory
➢Message passing

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Interprocess Communication(2/2)
(a) Shared memory. (b) Message passing.

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End of Chapter 3

Processes, Process Control Block, Process Scheduling.pdf

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