1. Lecture 4
Interprocess and Scheduling
4.1. Interprocess communication
4.2. Classical IPC problems
4.3. Scheduling
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2. Interprocess Communication
Race Conditions
Two processes want to access shared memory at same time
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3. Critical Regions (1)
Four conditions to provide mutual exclusion
1. No two processes simultaneously in critical region
2. No assumptions made about speeds or numbers of CPUs
3. No process running outside its critical region may block
another process
4. No process must wait forever to enter its critical region
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4. Critical Regions (2)
Mutual exclusion using critical regions
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5. Mutual Exclusion with Busy Waiting (1)
Proposed solution to critical region problem
(a) Process 0.
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(b) Process 1.
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6. Mutual Exclusion with Busy Waiting (2)
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Peterson's solution for achieving mutual exclusion 6

7. Mutual Exclusion with Busy Waiting (3)
Entering and leaving a critical region using the
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8. Sleep and Wakeup
Producer-consumer http://fasilkom.narotama.ac.id/ fatal race condition8
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problem with

9. Semaphores
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producer-consumer problem using semaphores 9

10. Mutexes
Implementation of mutex_lock and mutex_unlock
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11. Monitors (1)
Sistem Operasi Example of a monitor
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12. Monitors (2)
• Outline of producer-consumer problem with monitors
– only one monitor procedure active at one time
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– buffer has N slots 12

13. Monitors (3)
Solution to producer-consumer problem in Java (part 1)
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14. Monitors (4)
Solution to producer-consumer problem in Java (part 2)
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15. Message Passing
The producer-consumer problem with N messages
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16. Barriers
• Use of a barrier
– processes approaching a barrier
– all processes but one blocked at barrier
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– last process arrives, all are let through 16

17. Dining Philosophers (1)
• Philosophers eat/think
• Eating needs 2 forks
• Pick one fork at a time
• How to prevent deadlock
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18. Dining Philosophers (2)
A nonsolution to the dining philosophers problem
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19. Dining Philosophers (3)
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Solution to dining philosophers problem (part 1) 19

20. Dining Philosophers (4)
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Solution to dining philosophers problem (part 2) 20

21. The Readers and Writers Problem
A solution to the readers and writers problem
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22. The Sleeping Barber Problem (1)
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23. The Sleeping Barber Problem (2)
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Solution to sleeping barber problem. 23

24. Scheduling
Introduction to Scheduling (1)
• Bursts of CPU usage alternate with periods of I/O wait
– a CPU-bound process
– an I/O bound process
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25. Introduction to Scheduling (2)
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26. Scheduling in Batch Systems (1)
An example of shortest job first scheduling
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27. Scheduling in Batch Systems (2)
Sistem Operasi Three level scheduling
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28. Scheduling in Interactive Systems (1)
• Round Robin Scheduling
– list of runnable processes
– list of runnable processes after B uses up its quantum
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29. Scheduling in Interactive Systems (2)
A scheduling algorithm with four priority classes
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30. Scheduling in Real-Time Systems
Schedulable real-time system
• Given
– m periodic events
– event i occurs within period Pi and requires Ci
seconds
• Then the load can only be handled if
m
Ci
∑ P ≤1
i =1
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31. Policy versus Mechanism
• Separate what is allowed to be done with
how it is done
– a process knows which of its children threads
are important and need priority
• Scheduling algorithm parameterized
– mechanism in the kernel
• Parameters filled in by user processes
– policy set by user process
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32. Thread Scheduling (1)
Possible scheduling of user-level threads
• 50-msec process quantum
• threads run http://fasilkom.narotama.ac.id/
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5 msec/CPU burst 32

33. Thread Scheduling (2)
Possible scheduling of kernel-level threads
• 50-msec process quantum
• threads run http://fasilkom.narotama.ac.id/
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34. Question ?
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