Process Synchronization overview

1. By
CHITRAKANT BANCHHOR
IT, MITCOE, Pune
By
CHITRAKANT BANCHHOR
IT, MITCOE, Pune

2. ••
••

4. CHITRAKANT BANCHHOR

5. Parallelism is the quality of occurring at the same timeParallelism is the quality of occurring at the same time
Two tasks are parallel if they are performed at the same time

6. Concurrency is an illusion of parallelism.Concurrency is an illusion of parallelism.

7. P1
P2

8. Principle
of
concurrency
Concurrency
in
single processor machine
Concurrency
in
multiple processor machine

10. Process 1:
Process 2:
Concurrency in Single processor systemConcurrency in Single processor system
Figure:Figure: Concurrent processing in Uniprocessor system
Time
Process 2:
Process 3:

11. Modern Operating Systems are multiprocessor systems.Modern Operating Systems are multiprocessor systems.
They run many process concurrently to achieve better resource utilization.They run many process concurrently to achieve better resource utilization.

12. Concurrent processing in Multiprocessor systemConcurrent processing in Multiprocessor system
Time

13. CHITRAKANT BANCHHOR

17. P0:
Read(A);
A = A – 100;
Write(A);
P1:
Read(A);
A = A + 200;
Write(A);
P0:
Read(A);
A = A – 100;
Write(A);
P1:
Read(A);
A = A + 200;
Write(A);
P0:
Read(A);
A = A – 100;
Write(A);
P1:
Read(A);
A = A + 200;
Write(A);
P0:
Read(A);
A = A – 100;
Write(A);
P1:
Read(A);
A = A + 200;
Write(A);

21. Critical section refers to the code segment of a process, whereby itCritical section refers to the code segment of a process, whereby it
accesses a shared resourceaccesses a shared resource

22. P1P0 P1

25. (a)(a) P0 followed by P1.P0 followed by P1.
(b) P1 followed by P0.(b) P1 followed by P0.

26. P1 P2 Pn

27. P1 P2 Pn

28. CHITRAKANT BANCHHOR

29. dodo
{{
Entry Section
Critical Section
Reminder Section
Exit Section
Critical Section
} while(1);} while(1);

35. If no process is in critical section, can decide quickly who entersIf no process is in critical section, can decide quickly who enters

36. Normally the upper bound is 1.Normally the upper bound is 1.

37. CHITRAKANT BANCHHOR

39. AlgorithmAlgorithm -- 11

40. int turn = 0; /* Initial value of turn can be set to 0 or 1*/
P0:P0:
do{
while (turn == 1); /* Keep looping as long as turn equals 1*/
/* This is entry section*/
<Critical Section><Critical Section>
turn = 1; /*Enable P1 to enter Critical Section*/
/*This is exit section*/
<Remainder Section><Remainder Section>
}while(1);
P1:P1:
do{
while (turn == 0); /* Keep looping as long as turn equals 0*/
/* This is the entry section*/
<Critical Section><Critical Section>
turn = 0; /*Enable P0 to enter Critical Section*/
/*This is the exit section*/
<Remainder Section><Remainder Section>
}while(1);

41. ••

42. Thus the requirement of mutual exclusion is satisfiedThus the requirement of mutual exclusion is satisfied

44. SITUATION - I :

45. SITUATION I - 2:

47. typedef enum boolean { false, true };
boolean flag[2];

48. Mutual Exclusion satisfied.Mutual Exclusion satisfied.

50. Peterson's algorithm

51. int turn; /*Initial Value does not matter*/
boolean flag[2]; /*Initially set to false*/

53. CHITRAKANT BANCHHOR

56. int S = 1; /* Let S be a Binary semaphore, initialized to 1 */

57. void wait( int *S )
{
while( *S == 0 );
/* Keep looping here as long as S is 0*/
*S - -
}

58. void signal ( int *S )
{
*S++;
}

59. A process Pi can be synchronized for accessing of its critical section
as follows:

60. CHITRAKANT BANCHHORCHITRAKANT BANCHHOR