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:atomic:
PyMutex_Unlock:atomic:
PyMutex_IsLocked:atomic:


# Dictionary objects (Doc/c-api/dict.rst)

# Type checks - read ob_type pointer, always safe
PyDict_Check:atomic:
PyDict_CheckExact:atomic:

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

# Lock-free lookups - use _Py_dict_lookup_threadsafe(), no locking.
# Atomic with simple types.
PyDict_Contains:shared:
PyDict_ContainsString:atomic:
PyDict_GetItemRef:shared:
PyDict_GetItemStringRef:atomic:
PyDict_Size:atomic:
PyDict_GET_SIZE:atomic:

# Borrowed-reference lookups - lock-free dict access but returned
# borrowed reference is unsafe in free-threaded builds without
# external synchronization
PyDict_GetItem:compatible:
PyDict_GetItemWithError:compatible:
PyDict_GetItemString:compatible:
PyDict_SetDefault:compatible:

# Iteration - no locking; returns borrowed refs
PyDict_Next:compatible:

# Single-item mutations - protected by per-object critical section
PyDict_SetItem:shared:
PyDict_SetItemString:atomic:
PyDict_DelItem:shared:
PyDict_DelItemString:atomic:
PyDict_SetDefaultRef:shared:
PyDict_Pop:shared:
PyDict_PopString:atomic:

# Bulk reads - hold per-object lock for duration
PyDict_Clear:atomic:
PyDict_Copy:atomic:
PyDict_Keys:atomic:
PyDict_Values:atomic:
PyDict_Items:atomic:

# Merge/update - lock target dict; also lock source when it is a dict
PyDict_Update:shared:
PyDict_Merge:shared:
PyDict_MergeFromSeq2:shared:

# Watcher registration - no synchronization on interpreter state
PyDict_AddWatcher:compatible:
PyDict_ClearWatcher:compatible:

# Per-dict watcher tags - non-atomic RMW on _ma_watcher_tag;
# safe on distinct dicts only
PyDict_Watch:distinct:
PyDict_Unwatch:distinct:


# 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:

# Creation - may iterate the iterable argument, calling arbitrary code.
# Atomic for sets, frozensets, dicts, and frozendicts.
PySet_New:shared:
PyFrozenSet_New:shared:

# Size - uses atomic load on free-threaded builds
PySet_Size:atomic:
PySet_GET_SIZE:atomic:

# Contains - lock-free, atomic with simple types
PySet_Contains:shared:

# Mutations - hold per-object lock for duration
# atomic with simple types
PySet_Add:shared:
PySet_Discard:shared:

# Pop - hold per-object lock for duration
PySet_Pop:atomic:

# Clear - empties the set before clearing
PySet_Clear:atomic:

# 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:

# Tuple objects

# Creation - pure allocation, no shared state
PyTuple_New:atomic:
PyTuple_FromArray:atomic:
PyTuple_Pack:atomic:

# Size - tuples are immutable so size never changes
PyTuple_Size:atomic:
PyTuple_GET_SIZE:atomic:

# Borrowed-reference lookups - tuples are immutable so items
# never change, however the tuple must be kept alive while using the borrowed reference
PyTuple_GetItem:compatible:
PyTuple_GET_ITEM:compatible:

# Slice - creates a new tuple from an existing tuple
PyTuple_GetSlice:atomic:

# SetItem - only usable on tuples with refcount 1
PyTuple_SetItem:compatible:
PyTuple_SET_ITEM:compatible:

# Resize - only usable on tuples with refcount 1
_PyTuple_Resize:compatible:

# Struct Sequence objects

# Creation
PyStructSequence_NewType:atomic:
PyStructSequence_New:atomic:

# Initialization - modifies the type object in place
PyStructSequence_InitType:distinct:
PyStructSequence_InitType2:distinct:

# Borrowed-reference lookups - same as tuple items
PyStructSequence_GetItem:compatible:
PyStructSequence_GET_ITEM:compatible:

# SetItem - only for filling in brand new instances
PyStructSequence_SetItem:compatible:
PyStructSequence_SET_ITEM:compatible: