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; the list is emptied before sorting
# so other threads may observe an empty list, but they won't see the
# intermediate states of the sort
PyList_Sort:shared:

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

# Creation - pure allocation, no shared state
PyBytes_FromString:atomic:
PyBytes_FromStringAndSize:atomic:
PyBytes_DecodeEscape:atomic:

# Creation from formatting C primitives - pure allocation, no shared state
PyBytes_FromFormat:atomic:
PyBytes_FromFormatV:atomic:

# Creation from object - uses buffer protocol so may call arbitrary code;
# safe as long as the buffer is not mutated by another thread during the operation
PyBytes_FromObject:shared:

# Size - uses atomic load on free-threaded builds
PyBytes_Size:atomic:
PyBytes_GET_SIZE:atomic:

# Raw data - no locking; mutating it is unsafe if the bytes object is shared between threads
PyBytes_AsString:compatible:
PyBytes_AS_STRING:compatible:
PyBytes_AsStringAndSize:compatible:

# Concatenation - uses buffer protocol; safe as long as buffer is not mutated by another thread during the operation
PyBytes_Concat:shared:
PyBytes_ConcatAndDel:shared:
PyBytes_Join:shared:

# Resizing - safe if the object is unique
_PyBytes_Resize:distinct:

# Repr - atomic as bytes are immutable
PyBytes_Repr:atomic:

# Creation from object - may call arbitrary code
PyByteArray_FromObject:shared:

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

# Concatenation - uses buffer protocol; safe as long as buffer is not mutated by another thread during the operation
PyByteArray_Concat:shared:

# Size - uses atomic load on free-threaded builds
PyByteArray_Size:atomic:
PyByteArray_GET_SIZE:atomic:

# Raw data - no locking; mutating it is unsafe if the bytearray object is shared between threads
PyByteArray_AsString:compatible:
PyByteArray_AS_STRING:compatible:

# Capsule objects (Doc/c-api/capsule.rst)

# Type check - read ob_type pointer, always safe
PyCapsule_CheckExact:atomic:

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

# Validation - reads pointer and name fields; safe on distinct objects
PyCapsule_IsValid:distinct:

# Getters - read struct fields; safe on distinct objects but
# concurrent access to the same capsule requires external synchronization
PyCapsule_GetPointer:distinct:
PyCapsule_GetName:distinct:
PyCapsule_GetDestructor:distinct:
PyCapsule_GetContext:distinct:

# Setters - write struct fields; safe on distinct objects but
# concurrent access to the same capsule requires external synchronization
PyCapsule_SetPointer:distinct:
PyCapsule_SetName:distinct:
PyCapsule_SetDestructor:distinct:
PyCapsule_SetContext:distinct:

# Import - looks up a capsule from a module attribute and
# calls PyCapsule_GetPointer; may call arbitrary code
PyCapsule_Import:compatible: