1. Chapter 3
Process Management

2. Process definition A process is a program in execution
Process needs resources : CPU time
memory to
files accomplish
I/O device its tasks
These resources are allocated to process when it is created or during execution
Process is the unit of work of system
System consists of collection of processes

3. Process OS processes execute system code, user code
Processes can be executed concurrently (parallel) or sequential
Program can be single thread or Multithreading
Thread is a sequence of instructions that can be managed independently
Thread is the component of process
Multithreading more than one thread in the same process share resources and memory

4. Multithreading process

5. Process concept What to call the CPU activities ? (CPU Cycle)
All kind of CPU activities are called process
Batch system time shared single user OS
system
Execute jobs
execute task run several programs
Is an operating system
that work without
the interaction
of user
Are process

6. Process Process is more than program code, it includes:
Current activity represented by the value of program counter
Content of processor registers
Stack which contains temporary data (function, parameters, return address, local variable) in which is inserted data used during instruction execution
Data section : which include global variables
Heap that is memory dynamically allocated during process runtime

7. click
program
Loaded into
memory
Passive
CPU
In execution
process
Active
But
Not yet
process PC
In which
instruction
Data
section
heap
Memory
Content of
registers
Stack

8. are variables declared at the beginning of the program and
Global variables :
are variables declared at the beginning
of the program and
can be used in any part of the program
Local variables :
are variables declared inside part
of the program and
can be used only inside this part of the program
When the user click two times on a program
It creates two separate processes
With two stacks and two heaps …..

9. Process state The state is part of the current activity of the process
The process can have the following states:
New : created
Running instructions are being executed
Waiting the process waits some event like I/O
Ready the process is waiting to be assigned a processor
Terminated the process finished execution
In each instant only one process can be running on a processor

10. Diagram of Process State

11. Process control block PCB
Each process in operating system is represented by PCB that contains information about the process . It contains the following information :
process state : new , running, waiting, ready , terminating
PC Program counter that indicates the address of next instruction to be executed (this information must be saved when an interrupt is happened)
CPU registers : type , index of registers, stack , pointers

12. Process control block PCB continue
CPU scheduling : information , priorities
Memory management information : limit registers, page table segment, table depend on memory used by OS
Accounting information : amount of CPU, real time used, tile limits, account number, job or process number
I/O status information : list of I/O devices allocated to the process , list of open file….

13. Click
New
program 1
Running 3
passive
CPU 3
registers 7 2 PC 6
I/O 4
Ready
Scheduling
Interrupt
Segment
Page 5
Memory

14. Threads A process is a program that perform single thread
Ex: word cannot type and control errors at the same time
New OS can support more than one thread at time

16. Process scheduling
The objective of multiprogramming is to have some process running at all times to maximize the CPU utilization
Time sharing is to switch the CPU among processes so, the user can interact with program while in execution
needs process scheduling
Selects the available process for program execution on the CPU

17. Process scheduling One process no need for scheduling
More than one process ……..scheduling

18. Ready Queue And Various I/O Device Queues

19. Scheduling queue Process enter The system Memory system P P C C B B
Ready queue
Job queue
Waiting or
Ready processes
Linked list

20. Scheduling queue
Header contains pointer to the first and last PCB (Program Control Block) that contains information about process
Each PCB contains a pointer to the next process to be executed in this queue
ready waiting
for I/O
device queue
each device has
its own queue
keyboard
Mouse
CPU

21. Scheduler
OS must select which process enter each queue, this selection is done by scheduler
Many processes enter the system ….. All are sent to the queue …. Spooling
Scheduler choose ………. Long term scheduler
………..short term scheduler

22. Long term scheduler
Choose one process from spooler and load it into memory
Execute 1 process each 100 milliseconds + it takes 10 millisecond for deciding which process is assigned …… during this time the memory is idle ….that means time is wasted
One minute between create each process , it select
I/O bound process
Is a process that spends more CPU bound process
Time in I/O operation than more computation
A CPU operation time

23. If all processes are CPU bound waiting queue will be empty
I/O bound
CPU bound
Mixed
If all processes
I/O bound
Ready queue
Will be
Empty
If all processes are CPU bound waiting queue will be empty
Unix and Windows has no long term scheduler

24. Swapping
Swapping means move some process from short term memory to midterm memory
All that is done by scheduling algorithms

25. Context switch
When an interrupt is happened the state of the process is saved …….PCB
Process ……………state saved
To resume activity ……. State restore
Context switch when the kernel switch between state saved to state restore
It adds overhead on the system because the system does nothing useful

26. Operation on processes
The processes in most systems can be executed in parallel can be created and deleted dynamically
Process creation :
a process is created using create process system call
A process can create many other processes . The first is called Parent and the subsequent processes are called children forming a tree of processes
a process is identified using unique process identifier Pid that is an integer number

27. Process creation
Consider a process needs resources, when a process is created the resources are allocated to it by its parent. If no available resources it can obtain a subset of the parent’s resources.
The parent can distribute resources between its children without overloading the system
Resources allocated to a child process must be passed by away of the parent

28. Process creation (continue)
When a process creates a sub process, there are two possibilities :
Execution memory addresses
Parent and the parent parent and the child
Child are wait until its child use the uses new
Executed child end execution same memory memory
Concurrently space space

29. Process creation in Unix
Creating new process is done by Fork () call system
The new process consists on copying the address space of the original process
The two processes continue execution after fork system call with one difference that the returned value of fork () function is 0 for child process and is not zero for parent process
parent and child can communicate to each other and the parent can create more child and uses the wait () system call and manage memory address space
The child process inherits privileges from its parent

30. Process Creation

31. C Program Forking Separate Process
#include <sys/types.h>
#include <studio.h>
#include <unistd.h>
int main() {
pid_t pid;
/* fork another process */
pid = fork();
if (pid < 0) { /* error occurred */
fprintf(stderr, "Fork Failed");
return 1; }
else if (pid == 0) { /* child process */
execlp("/bin/ls", "ls", NULL);
else { /* parent process */
/* parent will wait for the child */
wait (NULL);
printf ("Child Complete");
return 0;

32. A Tree of Processes on Solaris

33. Windows creating process
Creating process in windows is done using Win 32 API using create process () system call that means loading the program into memory and load mspaint.exe application for execution.

34. Process terminate
Process terminate when it finishes executing its final statement and asks the OS to delete it by using exit () system call
The parent process resume activity using wait () system call
All resources (physical and virtual memory, open files, I/O buffer ) are de-allocated by OS
A process is terminate when it ends execution or by other process (parent)

35. Process terminate A parent terminate child process if :
Child process has exceeds the use of some resources
The task assigned to child is no longer needed
If the parent is exiting the OS does not permit to child to continue execution.

36. Inter-process communication
Processes executing concurrently in OS can be either independent or cooperating processes
A process is independent if cannot affect or be affected by the other processes executed in the system
Any process that does not share data with other processes is independent
Cooperating process may share data with other processes (child)

37. Why cooperating ? Information sharing
Computation speedup, if we want a task to run faster, we divide it into subtasks and are executed in parallel . Speedup is allowed when more than one processor works together
Modularity : dividing the system into modules or functions or threads
Convenience : allows multi operations in parallel

38. Communication between processes
Cooperating process must communicate to each other .
Types of communication
Inter-process remote call indirect
Communication

39. Inter-process communication
Memory shared message passing
Part of memory is used communicating
Between the two processes processes
Both processes can read exchange data and
And write to this region information by away
of kernel

40. Shared Memory Allows maximum Speedup and Convenience
For communication
No need for kernel
Intervention
Is faster than
Message passing

41. Message passing Useful for By away Exchanging small Of kernel
Amount of data
By away
Of kernel
Easy to
Implement
No conflict

42. How to share
Establishing the region to be shared between the communicating processes from the memory address space assigned
Creating one process ……address space
Another process ….new address space
Generally OS prevent that one process accesses the resources of another process…..the two processes must cooperate to remove the restrictions
Both processes can read and write on the region without the OS control but not simultanously
Part
shared

43. Example of Cooperating processes
Producer
Consumer
Consume information
Produce information
Unlimited
buffer
buffer
Shared memory
Limited
Buffer
size

44. Explanation of producer- consumer example
Producer produces data stored in the buffer, the buffer is emptied by the consumer
To allow this paradigm to work correctly, consumer and producer must be synchronized To
To access shared
data
Consumer must
Consume only
The data produced by
The producer
The buffer is implemented using circular array with
two pointers in and out
In point to the next position in the buffer
Out points to the first position in the buffer
In==out mean buffer empty
(in+1)%buffer size == out means buffer full

45. Message passing system
Processes communicate and synchronized without sharing memory
Distributed systems over network
Chat
send (message) receive (message)

46. Indirect communication
Message passing
communication
Direct communication
Indirect communication
synchronization
Synchronous
asynchronous
buffering
Automatic
Explicit
buffer
Each process want to send
Message must explicit
The name of the sender
Send (P, message)
By a way of third part
server

47. Link property in direct communication
Link automatically
Established between
Two processes
(after knowing process
identity
Exist only
One link
Link associated
between two processes
Full duplex

48. Naming mechanism for direct communication
Symmetric
Only by message name
Send( process name , message )
Receive (process name , message)
(router)
Asymmetric
By ID
Send (process name, message)
Receive ( id, message)
Is less desirable , it requires
More work
(switch)

49. Link property for indirect communication
Link is established
Between two processes if
They share
Some resources
Example : mail box
Between the
communicating
Processes
May be
Different links
router
Link may be used by
More than one process

50. Example
P1 send message to A “ send (A, message)”, A want to respond to P1, P2,P3 that share the same mailbox which will receive the message b?
The answer is depend on the link property :
Each link can only one process
Be shared can execute receive who receive
Between only operation at time operation
Two processes must be selected
(round robin)

51. Synchronization Communication between two processes is done by send or receive operations
After send Block non block Block sending The process blocks Sending message send Until the previous Message arrive At destination
After receive block non block The process block Receiving until Ending processing

52. Synchronization Send(block) ……… Receive (block) ……
Sender : send message + block …….wait
Receiver : receive message +block ……….end block
rendezvous
Resume activity

53. No waiting in the buffer Packet arrived will be sent
Buffering
Zero capacity
No waiting in the buffer
Packet arrived will be sent
Sender :send + block
Bounded capacity
Length n
When becoming full
Blocking receive
Unbounded capacity
Never blocking
Send or
receive