Why is the while (*lock != 0); used here? Wouldn't the code be the same if the while and if were replaced with a short circuit and such as if (*lock == 0 && test_and_set(*lock) == 0) or just two nested if statements?

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@sss: Because we don't want to call test and set ( which actually modifies the memory location ) until we actually think thats the case. Till then we spin and wait to see if its worth calling test and set and only then call it.

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I think a short-circuit would do the same thing there though. We're spinning anyway in the while(1), so if you keep checking on the condition if lock == 0 && test_and_set(*lock) == 0, if the lock value were set to 1 then it would short-circuit and you wouldn't actually perform the test_and_set in that case either. I'm not sure what the answer to the original query is though, except I guess it's one way of doing it.

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I agree with @arsenal, using the if (*lock == 0 && test_and_set(*lock) == 0) condition would behave the same way, because the test_and_set will still only get called if the lock is 0.

I can't think of any scenarios where they would perform differently, I believe these are just two different ways of implementing the test_and_test_and_set lock.

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@everyone: Your understanding is correct.

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