Week 5

Programming Assignment 2

Semaphores

Two operations:
- wait(s)
  - Traditional: P(s)
    - originally: from the Dutch word, passeren (“to pass”)
    - later: prolagen—formed from the Dutch words proberen (“to try”) and verlagen (“to decrease”)
  - Definition:
```
 < await (s > 0) s = s - 1; > 
```
- signal(s)
  - Traditional: V(s)
    - originally: from the Dutch word, vrijgeven (“to release”)
    - later: verhogen (“to increase”)
  - Definition:
```
 < s = s + 1; > 
```
wait(s) and signal(s) work the same for binary and counting (general) semaphores
- binary semaphore: value is always either 1 or 0
- general semaphore: value is nonnegative

Class exercises