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A shared variable x, initialized to zero, is operated on by four concurrent processes W, X, Y, Z as follows. Each of the processes W and X reads x from memory, increments by one, stores it to memory, and then terminates. Each of the processes Y and Z reads x from memory, decrements by two, stores it to memory, and then terminates. Each process before reading x invokes the P operation (i.e., wait) on a counting semaphore S and invokes the V operation (i.e., signal) on the semaphore S after storing x to memory. Semaphore S is initialized to two. What is the maximum possible value of x after all processes complete execution?
- a)-2
- b)-1
- c)1
- d)2
Correct answer is option 'D'. Can you explain this answer?
Verified Answer
A shared variable x, initialized to zero, is operated on by four concu...
Since initial value of semaphore is 2, two processes can enter critical section at a time- this is bad and we can see why.
Say, X and Y be the processes.X increments x by 1 and Z decrements x by 2. Now, Z stores back and after this X stores back. So, final value of x is 1 and not -1 and two Signal operations make the semaphore value 2 again. So, now W and Z can also execute like this and the value of x can be 2 which is the maximum possible in any order of execution of the processes. (If the semaphore is initialized to 1, processed would execute correctly and we get the final
value of x as -2.)
Option (D) is the correct answer.
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Most Upvoted Answer
A shared variable x, initialized to zero, is operated on by four concu...
Solution:
Given:
- Shared variable x is initialized to zero.
- Four concurrent processes W, X, Y, Z operate on x.
- Processes W and X increment x by one.
- Processes Y and Z decrement x by two.
- Each process invokes P operation on semaphore S before reading x and V operation on semaphore S after writing x to memory.
- Semaphore S is initialized to two.
Let's consider the possible scenarios where maximum value of x can be achieved:
1. W and X execute first followed by Y and Z
- W and X both increment x by 1 each. So, x becomes 2.
- Y and Z both decrement x by 2 each. So, x becomes -2.
2. Y and Z execute first followed by W and X
- Y and Z both decrement x by 2 each. So, x becomes -4.
- W and X both increment x by 1 each. So, x becomes -2.
3. W executes first followed by X, Y, and Z
- W increments x by 1. So, x becomes 1.
- X increments x by 1. So, x becomes 2.
- Y decrements x by 2. So, x becomes 0.
- Z decrements x by 2. So, x becomes -2.
4. X executes first followed by W, Y, and Z
- X increments x by 1. So, x becomes 1.
- W increments x by 1. So, x becomes 2.
- Y decrements x by 2. So, x becomes 0.
- Z decrements x by 2. So, x becomes -2.
From the above scenarios, we can see that the maximum possible value of x is 2.
Therefore, option D is the correct answer.
Given:
- Shared variable x is initialized to zero.
- Four concurrent processes W, X, Y, Z operate on x.
- Processes W and X increment x by one.
- Processes Y and Z decrement x by two.
- Each process invokes P operation on semaphore S before reading x and V operation on semaphore S after writing x to memory.
- Semaphore S is initialized to two.
Let's consider the possible scenarios where maximum value of x can be achieved:
1. W and X execute first followed by Y and Z
- W and X both increment x by 1 each. So, x becomes 2.
- Y and Z both decrement x by 2 each. So, x becomes -2.
2. Y and Z execute first followed by W and X
- Y and Z both decrement x by 2 each. So, x becomes -4.
- W and X both increment x by 1 each. So, x becomes -2.
3. W executes first followed by X, Y, and Z
- W increments x by 1. So, x becomes 1.
- X increments x by 1. So, x becomes 2.
- Y decrements x by 2. So, x becomes 0.
- Z decrements x by 2. So, x becomes -2.
4. X executes first followed by W, Y, and Z
- X increments x by 1. So, x becomes 1.
- W increments x by 1. So, x becomes 2.
- Y decrements x by 2. So, x becomes 0.
- Z decrements x by 2. So, x becomes -2.
From the above scenarios, we can see that the maximum possible value of x is 2.
Therefore, option D is the correct answer.
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A shared variable x, initialized to zero, is operated on by four concurrent processes W, X, Y, Z as follows. Each of the processes W and X reads x from memory, increments by one, stores it to memory, and then terminates. Each of the processes Y and Z reads x from memory, decrements by two, stores it to memory, and then terminates. Each process before reading x invokes the P operation (i.e., wait) on a counting semaphore S and invokes the V operation (i.e., signal) on the semaphore S after storing x to memory. Semaphore S is initialized to two. What is the maximum possible value of x after all processes complete execution?a)-2b)-1c)1d)2Correct answer is option 'D'. Can you explain this answer?
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A shared variable x, initialized to zero, is operated on by four concurrent processes W, X, Y, Z as follows. Each of the processes W and X reads x from memory, increments by one, stores it to memory, and then terminates. Each of the processes Y and Z reads x from memory, decrements by two, stores it to memory, and then terminates. Each process before reading x invokes the P operation (i.e., wait) on a counting semaphore S and invokes the V operation (i.e., signal) on the semaphore S after storing x to memory. Semaphore S is initialized to two. What is the maximum possible value of x after all processes complete execution?a)-2b)-1c)1d)2Correct answer is option 'D'. Can you explain this answer? for Computer Science Engineering (CSE) 2024 is part of Computer Science Engineering (CSE) preparation. The Question and answers have been prepared according to the Computer Science Engineering (CSE) exam syllabus. Information about A shared variable x, initialized to zero, is operated on by four concurrent processes W, X, Y, Z as follows. Each of the processes W and X reads x from memory, increments by one, stores it to memory, and then terminates. Each of the processes Y and Z reads x from memory, decrements by two, stores it to memory, and then terminates. Each process before reading x invokes the P operation (i.e., wait) on a counting semaphore S and invokes the V operation (i.e., signal) on the semaphore S after storing x to memory. Semaphore S is initialized to two. What is the maximum possible value of x after all processes complete execution?a)-2b)-1c)1d)2Correct answer is option 'D'. Can you explain this answer? covers all topics & solutions for Computer Science Engineering (CSE) 2024 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for A shared variable x, initialized to zero, is operated on by four concurrent processes W, X, Y, Z as follows. Each of the processes W and X reads x from memory, increments by one, stores it to memory, and then terminates. Each of the processes Y and Z reads x from memory, decrements by two, stores it to memory, and then terminates. Each process before reading x invokes the P operation (i.e., wait) on a counting semaphore S and invokes the V operation (i.e., signal) on the semaphore S after storing x to memory. Semaphore S is initialized to two. What is the maximum possible value of x after all processes complete execution?a)-2b)-1c)1d)2Correct answer is option 'D'. Can you explain this answer?.
A shared variable x, initialized to zero, is operated on by four concurrent processes W, X, Y, Z as follows. Each of the processes W and X reads x from memory, increments by one, stores it to memory, and then terminates. Each of the processes Y and Z reads x from memory, decrements by two, stores it to memory, and then terminates. Each process before reading x invokes the P operation (i.e., wait) on a counting semaphore S and invokes the V operation (i.e., signal) on the semaphore S after storing x to memory. Semaphore S is initialized to two. What is the maximum possible value of x after all processes complete execution?a)-2b)-1c)1d)2Correct answer is option 'D'. Can you explain this answer? for Computer Science Engineering (CSE) 2024 is part of Computer Science Engineering (CSE) preparation. The Question and answers have been prepared according to the Computer Science Engineering (CSE) exam syllabus. Information about A shared variable x, initialized to zero, is operated on by four concurrent processes W, X, Y, Z as follows. Each of the processes W and X reads x from memory, increments by one, stores it to memory, and then terminates. Each of the processes Y and Z reads x from memory, decrements by two, stores it to memory, and then terminates. Each process before reading x invokes the P operation (i.e., wait) on a counting semaphore S and invokes the V operation (i.e., signal) on the semaphore S after storing x to memory. Semaphore S is initialized to two. What is the maximum possible value of x after all processes complete execution?a)-2b)-1c)1d)2Correct answer is option 'D'. Can you explain this answer? covers all topics & solutions for Computer Science Engineering (CSE) 2024 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for A shared variable x, initialized to zero, is operated on by four concurrent processes W, X, Y, Z as follows. Each of the processes W and X reads x from memory, increments by one, stores it to memory, and then terminates. Each of the processes Y and Z reads x from memory, decrements by two, stores it to memory, and then terminates. Each process before reading x invokes the P operation (i.e., wait) on a counting semaphore S and invokes the V operation (i.e., signal) on the semaphore S after storing x to memory. Semaphore S is initialized to two. What is the maximum possible value of x after all processes complete execution?a)-2b)-1c)1d)2Correct answer is option 'D'. Can you explain this answer?.
Solutions for A shared variable x, initialized to zero, is operated on by four concurrent processes W, X, Y, Z as follows. Each of the processes W and X reads x from memory, increments by one, stores it to memory, and then terminates. Each of the processes Y and Z reads x from memory, decrements by two, stores it to memory, and then terminates. Each process before reading x invokes the P operation (i.e., wait) on a counting semaphore S and invokes the V operation (i.e., signal) on the semaphore S after storing x to memory. Semaphore S is initialized to two. What is the maximum possible value of x after all processes complete execution?a)-2b)-1c)1d)2Correct answer is option 'D'. Can you explain this answer? in English & in Hindi are available as part of our courses for Computer Science Engineering (CSE).
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A shared variable x, initialized to zero, is operated on by four concurrent processes W, X, Y, Z as follows. Each of the processes W and X reads x from memory, increments by one, stores it to memory, and then terminates. Each of the processes Y and Z reads x from memory, decrements by two, stores it to memory, and then terminates. Each process before reading x invokes the P operation (i.e., wait) on a counting semaphore S and invokes the V operation (i.e., signal) on the semaphore S after storing x to memory. Semaphore S is initialized to two. What is the maximum possible value of x after all processes complete execution?a)-2b)-1c)1d)2Correct answer is option 'D'. Can you explain this answer?, a detailed solution for A shared variable x, initialized to zero, is operated on by four concurrent processes W, X, Y, Z as follows. Each of the processes W and X reads x from memory, increments by one, stores it to memory, and then terminates. Each of the processes Y and Z reads x from memory, decrements by two, stores it to memory, and then terminates. Each process before reading x invokes the P operation (i.e., wait) on a counting semaphore S and invokes the V operation (i.e., signal) on the semaphore S after storing x to memory. Semaphore S is initialized to two. What is the maximum possible value of x after all processes complete execution?a)-2b)-1c)1d)2Correct answer is option 'D'. Can you explain this answer? has been provided alongside types of A shared variable x, initialized to zero, is operated on by four concurrent processes W, X, Y, Z as follows. Each of the processes W and X reads x from memory, increments by one, stores it to memory, and then terminates. Each of the processes Y and Z reads x from memory, decrements by two, stores it to memory, and then terminates. Each process before reading x invokes the P operation (i.e., wait) on a counting semaphore S and invokes the V operation (i.e., signal) on the semaphore S after storing x to memory. Semaphore S is initialized to two. What is the maximum possible value of x after all processes complete execution?a)-2b)-1c)1d)2Correct answer is option 'D'. Can you explain this answer? theory, EduRev gives you an
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