cpython/Doc/data/threadsafety.dat

# Thread safety annotations for C API functions.
#
# Each line has the form:
#   function_name : level
#
# Where level is one of:
#   incompatible -- not safe even with external locking
#   compatible   -- safe if the caller serializes all access with external locks
#   distinct     -- safe on distinct objects without external synchronization
#   shared       -- safe for concurrent use on the same object
#   atomic       -- atomic
#
# Lines beginning with '#' are ignored.
# The function name must match the C domain identifier used in the documentation.

# Synchronization primitives (Doc/c-api/synchronization.rst)
PyMutex_Lock:shared:
PyMutex_Unlock:shared:
PyMutex_IsLocked:atomic:

# List objects (Doc/c-api/list.rst)

# Type checks - read ob_type pointer, always safe
PyList_Check:atomic:
PyList_CheckExact:atomic:

# Creation - pure allocation, no shared state
PyList_New:atomic:

# Size - uses atomic load on free-threaded builds
PyList_Size:atomic:
PyList_GET_SIZE:atomic:

# Strong-reference lookup - lock-free with atomic ops
PyList_GetItemRef:atomic:

# Borrowed-reference lookups - no locking; returned borrowed
# reference is unsafe in free-threaded builds without
# external synchronization
PyList_GetItem:compatible:
PyList_GET_ITEM:compatible:

# Single-item mutations - hold per-object lock for duration;
# appear atomic to lock-free readers
PyList_SetItem:atomic:
PyList_Append:atomic:

# Insert - protected by per-object critical section; shifts
# elements so lock-free readers may observe intermediate states
PyList_Insert:shared:

# Initialization macro - no synchronization; normally only used
# to fill in new lists where there is no previous content
PyList_SET_ITEM:compatible:

# Bulk operations - hold per-object lock for duration
PyList_GetSlice:atomic:
PyList_AsTuple:atomic:
PyList_Clear:atomic:

# Reverse - protected by per-object critical section; swaps
# elements so lock-free readers may observe intermediate states
PyList_Reverse:shared:

# Slice assignment - lock target list; also lock source when it
# is a list
PyList_SetSlice:shared:

# Sort - per-object lock held; comparison callbacks may execute
# arbitrary Python code
PyList_Sort:shared:

# Extend - lock target list; also lock source when it is a
# list, set, or dict
PyList_Extend:shared: