Expose `threading.Semaphore._value`

Feature or enhancement

It would be useful to be able to access the value of threading.Semaphore._value as part of the public API of Semaphore, say via a get_value method.

Pitch

The value is useful for debugging and testing, helping users to understand the state and invariants of their code. There is also educational value in allowing users to see the internal state of a Semaphore, seeing as how it's an important concurrency primitive.

https://cs.github.com/?scopeName=All+repos&scope=&q=semaphore._value+language%3Apython# finds 68 uses of the exact phrase "semaphore._value" on Github, so I'm not alone in wanting access to this (although several of these are asyncio.locks.Semaphore).

Previous discussion

asyncio.locks.Semaphore has a locked method that exposes whether the value of the Semaphore is zero. It does appear that many of the uses are comparing the value to zero, so adding a locked method to threading.Semaphore would be sufficient for a lot of usage.

While writing this issue, I noticed that in 3.11, threading.Semaphore has its value printed in __repr__ (changed in #20534, the bpo mentions "expose their public states" as the rationale)

It looks like multiprocesing.Semaphore has an undocumented get_value method (although there is an issue about potentially removing it https://github.com/python/cpython/issues/84974 )

從 threading.Semaphore 及其目前的 repr 行為開始，然後比較 asyncio.locks.Semaphore.locked 與 multiprocessing.Semaphore.get_value。判斷公開 API 是否應公開該值，還是只公開其為零的狀態，並在為所選介面定義測試和文件之前，考量現有的討論與理由。