How does semaphore work?

Question

Can the semaphore be lower than 0? I mean, say I have a semaphore with N=3 and I call \"down\" 4 times, then N will remain 0 but one process will be blocked?

And same th

Answer 1

Just see N as the counter that counts your limited resource. Since you can not have a negative number of resources, N remains >= 0. If the number of your available resources changes, the maximum N has to be changed, too. I wouln't consider it good style to increment n without decrementing it first in any other case.