Thread-safe atomic counters

Feature or enhancement

Python doesn't currently have a thread-safe atomic counter. CPython currently internally uses a few different patterns to implement thread-safe counters. For example, some test code uses appends to a shared list because the implementation of list.append() is atomic.

We should provide a counter that is explicitly thread-safe so that people don't have to rely on other idioms. The minimum initial API should provide:

• atomic increment
• get value (i.e., inspect)

The threading module may be a good place for it.

cc @rhettinger

先檢視 threading 模組，以及 issue 中描述的現有執行緒安全計數器模式。定義並測試用於原子遞增和值檢查的最小 API，包括並行存取時的行為。