Communication Systems and Networks

Communication Systems and Networks

(Deadlocks)Deadlocks)) (Deadlocks)deadlocks)) (Deadlocks)preemptable non preemptable) (Deadlocks)os)trich algorithm) (Deadlocks)detection and recovery)) (Deadlocks)deadlock avoidance) (Deadlocks)deadlock prevention)

process1() CD process2() CD. . ; / semaphore cd=1, tp=1; void process1(){ while(true){ down(&cd); down(&tp); in= readCD(); writeTp(in); up(&cd);

up(&tp); } } void process2(){ while(true){ down(&tp); down(&cd); in= readTp(); writeCD(in); up(&cd); up(&tp); } } (Deadlock)!!! Preemptable res)ources)

(Deadlocks) ) Non-Preemptable res)ources) (Deadlocks) ). preemptable. ; preemptable. ; non preemptable .

. (Deadlocks)hold and wait).

non-preemption (Deadlocks)circular wait conditions)) . P (Deadlocks)proces)s)) R (Deadlocks)res)ource) R R R2 P P

R1 R P H P R A R1

B R2 C R3 A R2 B R3 C R1 C R1 R2 R3 (Deadlocks)os)trich algorithm) (Deadlocks)detection and recovery))

(Deadlocks)deadlock avoidance) (Deadlocks)deadlock prevention) (Deadlocks)os)trich algorithm) (Deadlocks)reboot)! . (Deadlocks) ) . .

Unix Windows) ; (Deadlocks)Detection and Recovery)) preemption rollback .

: ; preemption rollback (Deadlocks)checkpoints))

(Deadlocks), ) , . (Deadlocks)kill) . : . :

(Deadlocks) ); A. Tanenbaum: 170. A B C D R1 R2 R3 C

D R2 R3 A B C D R1

R2 R3 . . . . . A B C D R1

R2 R3 L= L= R1 A R2 C R3 D R2 n m (Deadlocks)clas)s)es)) Ej 1jm.

n C ij i 1 Aj E j Ri A (Deadlocks) Rij Aj 1 j m)

Ci (Deadlocks)available res)ources)). . E 4 2 3 1 A 2 1 0 0 0 0 1 0 C 2 0 0 1 0 1 2 0 2 0 0 1 R 1 0 1 0

2 1 0 0 3 =[2 2 2 0] 2, =[4 2 2 1] ;

(Deadlocks)utilization) (Deadlocks)thres)hold). bus)y) waiting! (Deadlocks)Deadlock Avoidance) (Deadlocks)s)afe and uns)afe s)tates))

. CD writer 2 CD writer 1

(Deadlocks)Bankers) algorithm) , (Deadlocks) ) . , . E 4 2 3 1 A 2 1 0 0 0 0 1 0

C 2 0 0 1 0 1 2 0 2 0 0 1 R 1 0 1 01 2 1 0 0 (Deadlocks) ). 2 4. 3 =[2 2 2 0].

(Deadlocks)hold and wait).

non-preemption (Deadlocks)circular wait conditions)) . .

.., ! s)pooling (Deadlocks)hold and wait). .

! . non-preemption . (Deadlocks)circular wait conditions)) .., (Deadlocks)1) , (Deadlocks)2) s)canner, (Deadlocks)3) plotter (Deadlocks)4)

, . (Deadlocks)) . Two-Phas)e Locking

. . (Deadlocks)Starvation)

.. Las)t In Firs)t Out (Deadlocks)LIFO) Shorter job firs)t : Firs)t In Firs)t Out (Deadlocks)FIFO)

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