Usual semaphore reference
협의의 세파포어
- S - Integer counter
- P - decrement function - before critical section - wait(S)
- V - increment function - after critical section -signal(S)
- two function should satisfy atomicity - other process cannot change while this function
When shared resource is more than one for preventing Race Condition
Mutex semaphore 인데 공유 자원이 여러개
Semaphore prevent multi-process access to data which are File type integer counter and unlocked by other. supervise many resources
P(S) { S--; if S < 0 // sleep this process } V(S) { S++; if S <= 0 // remove from sleep queue
S
- default value is resources number
- 0 : block