Gate Wallah Study material

Question

Please help with the minimum value. Problem is from the gate wallah study handout.

Comments

Assuming two processes running parallelly in a single processor.

Maximum value is possible when both process run sequentially – 5+5 = 10.

Minimum value is possible when first process read the value of count in the first iteration but pre-empt before incrementing it by 1. Now after the second process completes execution by making count = 5, first process resumes execuition and increments the value of count it read (i.e. 0) by 1. For the next 4 iterations it will increment count by 1 and finally will make the value 5.

Hence, Maximum value is 10, Minimum value is 5.

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Thanks for the reply sir..

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this is wrong . minimum is 2 and maximum is 10 . Refer to the answer provided by me

Answer 1

2 test() calls with 5 iterations for each. For simplicity let's consider 2 test() as processes P1, P2 .

P1: test() call (first iteration): loads '0', increments it by 1, [gets preempted before storing it back]

P2: 4 iterations of test() runs normally and gets preempted. So, now the value of count is 4.

Now,  P1 is starts again from where it left off. It has count value of 1 incremented locally. It stores back 1 and gets preempted.

Now, P2 resumes execution of it's final iteration. It loads the value of count as 1, increments it to 2 and gets preemted.

Now, P1 executes remaining 4 iterations making the value of count as 5.

Finally, P2 executes the 'store' for it's last iteration. It stores back 2 (since it has count value as 2 locally incremented) 

So, minimum turns out to be 2.

The maximum will be 10 (execution happens sequentially)