Unix Process Management Process management is an integral part of any modern day operating system (OS). The OS must allocate resources to processes, enable processes to share and exchange information, protect the resources of each process from other processes and enable synchronisation among processes

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Presentation on Unix
Process Management

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3. Presentation on
Process Management
By: Arshad Ruman
Email Id:
arshadruman@gmail.com
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4. Contents
1.Process Concept:
2.Process Scheduling:
3.Operations On Process:
4.Cooperating Process:
5.Inter Process Communication:
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5. Process Concept
Classes:
Batch Processing(60’s)
Multiprogramming(70’s)
Time Sharing(70’s)
Real Time(80’s)
Distributed(90’s)
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6. OS Performs following Actions While
creating Process:
 Assign Process Id and Priority
Allocating Memory and other resources
Set up the Process environment
Creating PCB
Return Process Id
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7. Process States
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8. Process Control Block(PCB)
Process ID
Priority
Process State
PSW
CPU register
Event Information
Memory Allocation
Resource Held
PCB Pointer
Process
Scheduling
Information
PSW & CPU reg
information
Info for which
process is waiting
Pointer to another
PCB
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9. Interaction Of Processes
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10. Process Scheduling Queues
 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.
 Process migration between the various
queues
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11. Scheduling
Activity of SELECTING the next request to be
handled by SERVER.
 Two fundamental Techniques:
1: Pre-emption Of Request
2:Reordering Of Request
Linux Process:
1: Normal or Real Time
2: Priority
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12. Representation of Process
Scheduling
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13. Four Events Of Scheduler
1: Arrival:
A request is arrived to system.
2:Scheduling:
Scheduler selects one request for servicing.
3:Pre-emption:
Request is Preempted to service other request.
4:Completion:
Process request gets completed.
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14. Schedulers
Long-term scheduler (or job scheduler) –
selects which processes should be brought
into the ready queue.
 Short-term scheduler (or CPU scheduler) –
selects which process should be executed
next and allocates CPU.
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15. Addition of Medium Term
Scheduling
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16. Context Switch
When CPU switches to another process, the
system must save the state of the old process and
load the saved state for the new process.
Context-switch time is overhead; the system
does no useful work while switching.
 Time dependent on hardware support.
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17. Process Creation
Parent process create children processes, which, in turn create
other processes, forming a tree of processes.
 Resource sharing
Parent and children share all resources.
Children share subset of parent’s resources.
Child will not exceed resource limits on that process.
 Execution
Parent and children execute concurrently.
Parent waits until children terminate.
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18. Process Creation (Cont.)
 Address space
Child duplicate of parent.
Child has a program loaded into it.
 UNIX examples
fork system call creates new process
exec system call used after a fork to
replace the process’ memory space with a
new program.
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19. Processes Tree on a UNIX System
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20. Process Termination
Process executes last statement and asks the operating
system to decide it (exit).
Output data from child to parent (via wait).
Process’ resources are deallocated by operating
system.
 Parent may terminate execution of children processes (abort).
Child has exceeded allocated resources.
Task assigned to child is no longer required.
Parent is exiting.
Operating system does not allow child to continue if its parent
terminates.
 Cascading termination.
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21. Cooperating Processes
Independent process cannot affect or be affected by the
execution of another process.
 Cooperating process can affect or be affected by the
execution of another process.
 Advantages of process cooperation
Information sharing
Computation speed-up
Modularity
Convenience
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22. Producer-Consumer Problem
Paradigm for cooperating processes, producer
process produces information that is consumed
by a consumer process.
unbounded-buffer places no practical
limit on the size of the buffer.
bounded-buffer assumes that there is a
fixed buffer size.
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23. Interprocess Communication
(IPC)
Mechanism for processes to communicate and to
synchronize their actions.
 Message system – processes communicate with each
other without resorting to shared variables.
 IPC facility provides two operations:
send(message) – message size fixed or variable
receive(message)
 If P and Q wish to communicate, they need to:
establish a communication link between them
exchange messages via send/receive
 Implementation of communication link
physical (e.g., shared memory, hardware bus)
logical (e.g., logical properties)
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24. Shared data
#define BUFFER_SIZE 10
Typedef struct {
. . .
} item;
item buffer[BUFFER_SIZE];
int in = 0;
int out = 0;
Solution is correct, but can only use BUFFER_SIZE-1
elements
Bounded-Buffer – Shared-Memory Solution
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Thank You
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