question from interview

Andrew

17y8.2kC#

Hi all
it's my first time here and here's a question that I was asked yesterday
it's kind of pseudocode

____________________________________________
int globalVar = 0;
void Func() {
for (int i = 0; i < 10; i++)
globalVar = globalVar + 1;
}

void main() {
Thread x = new Thread(Func); x.Start();
Thread y = new Thread(Func); y.Start();
x.Join();
y.Join();

Write(globalVar);
}
____________________________________________

the final globalVar has values from 1 to 20.
I understand how it can be from 10 to 20, but
can you explain how can it be less than 10?

thanks

2 Replies

Know the answer? Post it — somebody with the same question will find it here.

Andrew17y ago
Kirtan , thanks for your reply

The question was about thread concurrency.
Two threads run the same code, that increments global variable 10 times each.

If both threads enter the critical section at the same time then final result would be 10 (instead of 20), but it can be even less than 10.
But I don't see how it can be so.
Kirtan Patel17y ago
Iterate through Loop from 0 to <5

public void Func()
        {
            for (int i = 0; i <5; i++)
            {
                Globalvar += 1;

            }
        }

and

void main()
{
Thread x = new Thread(Func);
            Thread y = new Thread(Func);

            x.Start();
            x.Join();
            y.Start();

          Write(Globalvar);
}

thats it :)