Operating Systems - William Stallings Persian Chapter5-2 semaphore Function Mutual exclusion and synchronization mahmood alemi Ahmad niroomand

1. Mutual Exclusion and
Synchronization

4. Wikipedia

5. We have features for every step of the way

6. Design, organize, and collaborate

7. Semaphore


o
o




8. Stylize, edit, and animate your media

9. Broadcast and compress for seamless delivery

10. semSignal semWait 
semWait 
wait



13. semaphore s=1;
P0 () P1 ()
{ {
semWait (s); semWait (s);
<CS> <CS>
semSignal (s); semSignal (s);
} }

15. •
n •
•
15

16. semaphore s=1;
P0 () P1 ()
{ {
semWaitB (s); semWaitB (s);
<CS> <CS>
semSignalB (s); semSignalB (s);
} }
16

17. Producer and Consumer
•
•
–
•
–
17

18. •
•
–
–
•
–
18

19. producer: consumer:
while (true) while (true)
{ {
/* produce item v */ while (in <= out)
b[in] = v; /* do nothing */;
in++
} w = b[out];
out = (out + 1);
/* consume item w */
}
19

20. n
delay
(n=1)
20

21. 21

22. 22

23. n
wait
23

24. y x •
z
x Processes
z y
W(z) z n>=0 y x
W(y) z n>=0 y n>=1 x
W(x) z y x
z n>=0 y x
<CS>
S(x) (n>=0) z z •
S(y) y z
S(z) x y y
..
x
24

25. S a P3 P2 P1 •
S semWait W semSignal
P1 P2 P3 P2 P1 P3 P2 P2 P3 P1
W(a) W(a) S(a) W(a) S(a) S(a) W(a) W(a) S(a) W(a)
•
P3 P2 P1 •
P2 P3 P1 •
P1 P3 P2 •
25

26. P1 P2 P3 P2 P1 P3 P2 P2 P3 P1
W(a) W(a) S(a) W(a) S(a) S(a) W(a) W(a) S(a) W(a)
a 0 -1 0 -1 0 1 0 -1 0 -1
P2 P2 P2 P1
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27. 27

28. 28

29. n n •
n
•
•
•
–
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30. •
30

31. 31

32. Monitor
•
•
•
–
–
–
•
32

33. 33

34. cwait(c) •
c
csignal (c) •
cwait
wait/signal •
34

35. 35

36. •
•
•
36

37. •
37

38. mayconsume •
capacity
•
mayproduce
mayproduce •
38