[Design] Multithreading Async Increment Problem

Question

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If two threads are incrementing a variable 100 times each without synchronization, what would be the possible min and maximum value.

Solution

Well, max is init+200, and min is init+2. Suggested by the top answer:

1. P1 & P2 copy var
2. P1 increments 99 times. so var becomes var + 99
3. P2 increments once. so var becomes var + 1
4. P1 copies var (value is var + 1)
5. P2 increments 99 times. so var becomes var + 100
6. P1 increments once. so var becomes var + 2