CP, Semaphores | chuahou.dev

[12.2] Basic operations
- down/P/wait/acquire
- up/V/signal/release
[12.3] CSO implementation
- BooleanSemaphore(initiallyAvailable: Boolean)
- MutexSemaphore = BooleanSemaphore(true)
- SignallingSemaphore = BooleanSemaphore(false)
- [12.39] CountingSemaphore(available: Int)
  - Internal value = # permits for downs.
- [12.38] ...Semaphore(fair = true) to provide fairness to waiters.
[12.7] Easy to deadlock when acquiring multiple semaphores.
[12.11] Multiple ups before down means subsequent signals are lost.
- [12.12] Ensure \(\texttt{up}_1 \prec \texttt{down}_1 \prec \texttt{up}_2\).
[12.16] Passing the baton. First thread downs mutex, signals to second thread, second thread ups mutex.
- Waiting thread must lift mutex before waiting (otherwise deadlock).
[12.27] Ephemeral semaphores can be used like ephemeral reply channels.