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Recent questions tagged semaphore

6 votes

2 answers

91

ISRO-DEC2017-70
A counting semaphore was initialized t o $7$. Then $\text{20 P (wait)}$ operations and$\text{x V (signal)}$ operations were completed on this semaphore. If the final value of semaphore is $5$, then the value $x$ will be $0$ $13$ $18$ $5$

gatecse asked in Operating System Dec 17, 2017

3.2k views

0 votes

1 answer

92

Problem regarding mutual exclusion
Process P1 Process P2 P(S1) P(S1) P(S2) P(S2) Critical Section Critical Section V(S2) V(S1) V(S1) V(S2) In one of the Gateoverflow tests, this question was given and it was told that in the above case mutual exclusion is not ... section. As far as the order of unlocking, I dont see a problem there. Can someone please explain why mutual exclusion is not guaranteed?

humblefool asked in Operating System Dec 13, 2017

899 views

1 vote

0 answers

93

Bounded Wait
Process Pi repeat flag[i] = true; while ( flag[j] ) do no-op; < critical - section > flag[i] = false; < remainder - section > until false; Note : "i" refer0s to current process and "j" refers to another process. How Bounded Wait is satisfied here?

Shubhanshu asked in Operating System Dec 7, 2017

1.9k views

1 vote

2 answers

94

Starvation (Binary Semaphore )
Given Processes P1: Wait(Sx); Wait(Sy); Do something;Signal(Sx); Signal(Sy); and Process P2: Wait(Sx); Wait(Sy); Do something;Signal(Sy); Signal(Sx); . Will it ever lead to starvation ?

sumit chakraborty asked in Operating System Nov 26, 2017

by sumit chakraborty

960 views

2 votes

2 answers

95

Semaphores { Ace }
Pseudocode: Int x = 0 , y =20; Semaphores SX=1 , SY= 1; Parbegin Begin P(SX) , P(SY) ; X=X+1; V(SY), V(SX); End Begin P(SY) , P(SX) ; X=Y+2; V(SX), V(SY); End Parend Question: Final Values of X? I am getting 1, 22 and deadlock. How come answer is 22, 23 and deadlock possible??

vishwa ratna asked in Operating System Nov 8, 2017

by vishwa ratna

663 views

1 vote

1 answer

96

Ace Test Series: Operating System - Semaphore
It says as follows: Pseudocode Integer X = 0 , Y = 23 ; Semaphore mx = 1 , my = Null ; Codebegin Begin P(mx); x= x+1; V(my); End Begin P(my); x= y+1; V(mx); End Question: Possible final values of X?? I tried to find the values and i concluded that 1 and 24 could be the final values but solution says only 24 :( Any idea??

vishwa ratna asked in Operating System Nov 8, 2017

by vishwa ratna

951 views

1 vote

2 answers

97

Parshu gate asked in Operating System Nov 6, 2017

832 views

4 votes

2 answers

98

Semaphore
mutex a = 1,b = 0; For P(0): while(1) { P(a); print(1); v(b); } For P(1): while(1) { P(b); print(0); v(a); } Now obviously the output printed is 10101010..... But my doubt is if they ask a regular expression for this question, then what would it be? $(10)*$ or $1 + (10)*$ So my question is will the semaphores always wakeup the process? Can I get a single $"1"$ ?

Neelay Upadhyaya asked in Operating System Oct 31, 2017

by Neelay Upadhyaya

1.8k views

0 votes

3 answers

99

Process Synchronisation ( binary semaphores)
Consider the below program as two concurrent processes: Semaphore x:= 0; P1: repeat forever P2: repeat forever 1.V(x); 4. P(x); 2.Compute; 5.Compute; 3.P(x); 6.V(x); Consider the following statements about process P1 & P2: (1) ... chance to run , and it wil starve (THIS IS WHAT I THOUGHT THE ANSWER SHOULD BE , PLEASE COMMENT, IF I AM WRONG ANYWHERE)

NIKU asked in Operating System Oct 28, 2017

by NIKU

1.0k views

0 votes

1 answer

100

Process Synchronisation
11. Consider the following program: Const int n= 10 int Count= 0 Void A( ) { int i; for(i= 1 to n) Count= Count + 1; } Main ( ) { Par begin A( ); A( ); A( ); A( ); Par end } What is the minimum and maximum possible value of count after the ... 40 (b) 2, 40 (c) 3, 40 (d) 4, 40 NOTE: I am not able to understand what does "par begin" and "par end" indicates

NIKU asked in Operating System Oct 28, 2017

by NIKU

587 views

1 vote

1 answer

101

Proces Synchronisation
Consider the following algorithm as a solution to the Critical Section problem. The process shares two variables: var flag: array [0 .1] of Boolean; turn= 0 ..1; Initially flag [0]= flag [1]= false; turn= 0 (or) 1; the structure of process Pi is like repeat flag[i ... flag [i]= true & turn= j; (d) flag [i]= false & turn= i; Solution: Option (a) (need the explanation)

NIKU asked in Operating System Oct 26, 2017

by NIKU

1.2k views

3 votes

4 answers

102

Process Synchronisation
Consider the below Algorithm: P0: Process= 0 P1: Process= 1 other= 1-Process other= 1-Process while (flag!= Process); while (flag!= Process); Enter CS Enter CS flag= other. flag= other. (a) The ... guarantees Mutual Exclusion (b) The algorithm is busy waiting solution (c) The algorithm does not guarantee progress (d) The algorithm guarantee Bounded waiting

NIKU asked in Operating System Oct 26, 2017

by NIKU

1.6k views

2 votes

2 answers

103

Process Synchronisation Of Operating System
Consider the below Algorithm where flag and lock are global variables: P0: P1: while (flag= =1 && lock= = 0); while (flag= = 0 && lock= = 1); Enter CS Enter CS lock= 0 flag= 0 flag= 1 lock= 1 (a) The above algorithm is deadlock free (b) The above algorithm guarantees Mutual Exclusion (c) Both (a) & (b) (d) None of the above

NIKU asked in Operating System Oct 26, 2017

by NIKU

1.5k views

0 votes

1 answer

104

Semaphores
s = 0 initially A : down(s) B : down(s) CS CS up(s) up(s) C : down(s) D : up(s) CS CS up(s) down(s) E : up(s) F : up(s) CS CS down(s) down(s) What is the maximum value of s? Doubt : I think max value of s should be 1 as P and V are atomic operations. Also nowhere the value of s is stored in memory here. But the answer given is 3. What concept am I missing?

just_bhavana asked in Operating System Sep 27, 2017

by just_bhavana

293 views

1 vote

1 answer

105

UGC NET CSE | December 2009 | Part 2 | Question: 38
A semaphore count of negative n means (s = – n) that the queue contains ________ waiting processes. (A) n + 1 (B) n (C) n – 1 (D) 0

rishu_darkshadow asked in Operating System Sep 17, 2017

by rishu_darkshadow

1.1k views

3 votes

1 answer

106

Counting Semaphores
2. Assume that ‘C’ is a Counting Semaphore initialized to value ‘10’. Consider the following program segment: P(C); V(C); P(C); P(C); P(C); V(C); V(C) V(C); V(C); V(C); P(C); V(C); V(C); P(C) What is the value of C? a) 8 b)10 c)12 d)14

ashutoshaay26 asked in Operating System Sep 3, 2017

by ashutoshaay26

4.8k views

0 votes

1 answer

107

Operation System -> Process Synchronisation -> Counting Semaphores
Struct Semaphore { int value; Queue type L; } Down (Semaphore S) { S.value = S.value -1; if(S.value<0) { put process in L; sleep(); } else return; } Up(Semaphore S) { S.value = S. ... I'm wrong somewhere, please correct me. I referred Tanenbaum and Galvin but didn't find any such explanation for Counting Semaphores)

rakeshgsharma asked in Operating System Aug 23, 2017

by rakeshgsharma

684 views

3 votes

1 answer

108

Producer Consumer Problem
Consider the producer-consumer problem solution using semaphore. Which of the following condition below synchronization mechanism satisfies. Mutual Exclusion Bounded Waiting Progress Architecural Neutral mutex buffer_mutex; // similar to "semaphore buffer_mutex = ... buffer_mutex); item = removeItemFromBuffer(); up(buffer_mutex); up(emptyCount); consumeItem(item); } }

Durgesh Singh asked in Operating System Jul 22, 2017

by Durgesh Singh

2.6k views

1 vote

1 answer

109

Counting Semaphore
If value of counting semaphore value is 7, and then 20 P operations and 'x' V operations are performed. Now value of semaphore is 5. What is x?? iam getting ans as 18. please correct me if Iam wrong.

AnilGoudar asked in Operating System May 12, 2017

1.2k views

5 votes

2 answers

110

ISRO2017-71
At a particular time the value of counting semaphore is 10. It will become 7 after: 3 V operations 3 P operations 5 V operations and 2 P operations 2 V operations and 5 P operations

sh!va asked in Operating System May 7, 2017

by sh!va

13.5k views

3 votes

3 answers

111

Finding initial values of counting semaphore
Below are four concurrent processes and three counting semaphores. What must be the initial values of the three semaphores, so that output “TGE” is obtained?

GateAspirant999 asked in Operating System Feb 14, 2017

by GateAspirant999

2.5k views

2 votes

1 answer

112

Test by Bikram | Mock GATE | Test 3 | Question: 48
The following five concurrent processes operate on counting semaphore variable $\left ( S \right )$, which is initialized to $0$. P1 : wait$\left ( s \right )$ ; $cs$ ; signal$\left ( s \right )$ ; P2 : wait$\left ( s \right )$ ; $cs$ ; ... signal$\left ( s \right )$ ; $cs$ ; wait $\left ( s \right )$; The maximum possible value of $S$ is ______.

Bikram asked in GATE Feb 9, 2017

by Bikram

422 views

0 votes

0 answers

113

Semaphore
Let S be the binary semaphore variable S = 0 initially. Assume that no blocked processes exist in the system. The following signal (V), wait (P) operations are performed. The number of blocked processes at the end are _________. 4 P, 6 V, 9 P, 13 V, 14 P

srestha asked in Operating System Feb 5, 2017

1.7k views

0 votes

2 answers

114

Self Doubt (Semaphores)
struct Semaphore { enum value(0,1); Queue type L; } Down (Semaphore S) { if(S.value==1) { S.value=0; } else { put process(PCB) in S.L; sleep(); } } Up(Semaphore S) { if(S.L is empty) { S.value=1; } else { select a process from S.L; ... and goes to sleep. P0 comes out and exeutes the else part of Up and wakes P1 up. Now how will P1 enter the CS, since S.value is still 0?

Samujjal Das asked in Operating System Feb 5, 2017

by Samujjal Das

4.0k views

1 vote

1 answer

115

MadeEasy Subject Test: Operating System - Semaphores

vaishali jhalani asked in Operating System Jan 30, 2017

by vaishali jhalani

575 views

1 vote

1 answer

116

Semaphore bounded wait
Does semaphore solution fulfill the condition of bounded wait for more than 2 processes I know we can implement the waiting list in such a way that makes it satisfy bounded wait but what is the standard?

Pankaj Joshi asked in Operating System Jan 12, 2017

by Pankaj Joshi

1.5k views

0 votes

2 answers

117

sanyam53 asked in Operating System Jan 10, 2017

1.0k views

0 votes

1 answer

118

Correct order of semaphores

vaishali jhalani asked in Operating System Jan 7, 2017

by vaishali jhalani

1.1k views

0 votes

1 answer

119

monty asked in Operating System Jan 6, 2017

by monty

943 views

0 votes

1 answer

120

[Strong/Weak Semaphore] Operating system Chapter -5 William Stallings 7th Edition
How the processes are removed from the Semaphore suspended queue?Is it implementation dependent or is it FIFO always?If not FIFO then how starvation will be handled.I got this doubt while reading following ... Priority based/SJf..etc ,then it will neither be strong semaphore nor weak semaphore?# Please clarify

rahul sharma 5 asked in Operating System Dec 4, 2016

by rahul sharma 5

3.3k views

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Recent questions tagged semaphore