@@ -2299,12 +2299,20 @@ per-object locks for :term:`free-threaded <free threading>` CPython. They are
22992299intended to replace reliance on the :term:`global interpreter lock`, and are
23002300no-ops in versions of Python with the global interpreter lock.
23012301
2302+ Critical sections are intended to be used for custom types implemented
2303+ in C-API extensions. They should generally not be used with built-in types like
2304+ :class:`list` and :class:`dict` because their public C-APIs
2305+ already use critical sections internally, with the notable
2306+ exception of :c:func:`PyDict_Next`, which requires critical section
2307+ to be acquired externally.
2308+
23022309Critical sections avoid deadlocks by implicitly suspending active critical
2303- sections and releasing the locks during calls to :c:func:`PyEval_SaveThread`.
2304- When :c:func:`PyEval_RestoreThread` is called, the most recent critical section
2305- is resumed, and its locks reacquired. This means the critical section API
2306- provides weaker guarantees than traditional locks -- they are useful because
2307- their behavior is similar to the :term:`GIL`.
2310+ sections, hence, they do not provide exclusive access such as provided by
2311+ traditional locks like :c:type:`PyMutex`. When a critical section is started,
2312+ the per-object lock for the object is acquired. If the code executed inside the
2313+ critical section calls C-API functions then it can suspend the critical section thereby
2314+ releasing the per-object lock, so other threads can acquire the per-object lock
2315+ for the same object.
23082316
23092317Variants that accept :c:type:`PyMutex` pointers rather than Python objects are also
23102318available. Use these variants to start a critical section in a situation where
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