Switching to Blackboard

1
Switching to Blackboard

• All assignments will be submitted through
  blackboard
• To access, you need to do the following
• Get your UNET id and set a password. Contact UNET
  helpdesk or the IT helpdesk if necessary.
• Can also call 800 number on blackboard homepage.
• http//www.courses.maine.edu/
• All future homework/projects must be submitted
  via the digital dropbox on blackboard.

2
Proposed Schedule Modification

• Reschedule preliminary 1 to Monday, October 4th.
• Reschedule due date for project part 1 to
  Wednesday October 6th.

3
Midterm

• READING
• You are responsible for all of the material
  covered in the book
• up to (but not including) Section 2.3.7
  except for the following sections
• Chapter 1 1.2.1, 1.2.2, 1.2.4, 1.2.5, 1.3,
  1.5.8, 1.7 to the end of the chapter.
• Chapter 2 2.2.6, 2.3.7 to the end of the
  chapter.
• Also responsible for all class slides!!
• Please make sure you review the material
  carefully because large pieces of it is not
  covered in the book.

4
Dining Philosophers (1)

• Philosophers eat/think
• Eating needs 2 forks
• Pick one fork at a time
• How to prevent deadlock

5
Dining Philosophers

• A nonsolution to the dining philosophers problem

6
Dining Philosophers

• Solution to dining philosophers problem (part 1)

7
Dining Philosophers

• Solution to dining philosophers problem (part 2)

8

T T T T
T
State Array S Array
Mutex 1
NULL
Mutex.queue
P0 take_forks(0) down(mutex)
test(0)
9

E T T T
T
State Array S Array
Mutex 0
NULL
2 1 1 1
1
Mutex.queue
P0 take_forks(0) down(mutex)
test(0)
10

E T T T
T
State Array S Array
Mutex 0
NULL
1 0 0 0
0
Mutex.queue
P0 take_forks(0) down(mutex)
test(0) up(mutex) down(S0)

11

E T T T
T
State Array S Array
Mutex 1
NULL
Mutex.queue
P0 take_forks(0) down(mutex)
test(0) up(mutex) down(S0)
// falls through to //critical
section Preempted
12

E T T T
T
State Array S Array
Mutex 1
NULL
1 1 1 1
1
Mutex.queue
P0 take_forks(0) down(mutex)
test(0) down(S0) Preempted P2
take_forks(2) down(mutex)
13

E T T T
T
State Array S Array
Mutex 0
NULL
1 1 1 1
1
Mutex.queue
P0 take_forks(0) down(mutex)
test(0) down(S0) Preempted P2
take_forks(2) down(mutex)
14

E T E T
T
State Array S Array
Mutex 0
NULL
1 1 2 1
1
Mutex.queue
P0 take_forks(0) down(mutex)
test(0) down(S0) Preempted P2
take_forks(2) down(mutex) test(2)

15

E T T T
T
State Array S Array
Mutex 0
NULL
1 1 1 1
1
Mutex.queue
P0 take_forks(0) down(mutex)
test(0) down(S0) Preempted P2
take_forks(2) down(mutex) test(2)

16

E T E T
T
State Array S Array
Mutex 0
NULL
1 1 2 1
1
Mutex.queue
P0 take_forks(0) down(mutex)
test(0) down(S0) Preempted P2
take_forks(2) down(mutex) test(2)
up(mutex) down(S2)
17

E T E T
T
State Array S Array
Mutex 1
NULL
1 1 1 1
1
Mutex.queue
P0 take_forks(0) down(mutex)
test(0) down(S0) Preempted P2
take_forks(2) down(mutex) test(2)
up(mutex) down(S2) //falls
through semaphore //and enters critical
section.
18

E T E T
T
State Array S Array
Mutex 1
NULL
1 1 1 1
1
Mutex.queue
P0 take_forks(0) down(mutex)
test(0) down(S0) Preempted P2
take_forks(2) down(mutex) test(2)
up(mutex) down(S2) eat()
!!!
P3 take_forks(3) down(mutex) test(3)
up(mutex) down(S3)
19

E T E H
T
State Array S Array
Mutex 1
NULL
1 1 1 0
1
Mutex.queue
S3.queue
P0 take_forks(0) down(mutex)
test(0) down(S0) Preempted P2
take_forks(2) down(mutex) test(2)
up(mutex) down(S2) eat()
!!!
P3 take_forks(3) down(mutex) test(3)
up(mutex) down(S3)
P3
20

E T E H
T
State Array S Array
Mutex 1
NULL
1 1 1 0
1
Mutex.queue
S3.queue
P0 take_forks(0) down(mutex)
test(0) down(S0) Preempted P2
take_forks(2) down(mutex) test(2)
up(mutex) down(S2) eat()
!!!
P3 take_forks(3) down(mutex) test(3)
up(mutex) down(S3) P2
put_forks(2) down(mutex)
set state2 Thinking.
test(1)
P3
21

E T T H
T
State Array S Array
Mutex 0
NULL
1 1 1 0
1
Mutex.queue
S3.queue
P0 take_forks(0) down(mutex)
test(0) down(S0) Preempted P2
take_forks(2) down(mutex) test(2)
up(mutex) down(S2) eat()
!!!
P3 take_forks(3) down(mutex) test(3)
up(mutex) down(S3) P2
put_forks(2) down(mutex)
set state2 Thinking.
test(1) //left neighbor not //hungry.

P3
22

E T T H
T
State Array S Array
Mutex 0
NULL
1 1 1 0
1
Mutex.queue
S3.queue
P0 take_forks(0) down(mutex)
test(0) down(S0) Preempted P2
take_forks(2) down(mutex) test(2)
up(mutex) down(S2) eat()
!!!
P3 take_forks(3) down(mutex) test(3)
up(mutex) down(S3) P2
put_forks(2) down(mutex)
set state2 Thinking.
test(1) test(3)

P3
23

E T T T
T
State Array S Array
Mutex 0
NULL
1 1 1 1
1
Mutex.queue
P0 take_forks(0) down(mutex)
test(0) down(S0) Preempted P2
take_forks(2) down(mutex) test(2)
up(mutex) down(S2) eat()
!!!
P3 take_forks(3) down(mutex) test(3)
up(mutex) down(S3) P2
put_forks(2) down(mutex)
set state2 Thinking.
test(1) test(3)

24
Dining Philosophers

• Solution to dining philosophers problem (part 2)

25
Create Deadlock
down(Sx) up (mutex)