gh-113743: Make the MRO cache thread-safe in free-threaded builds (#1… · python/cpython@ae460d4 · GitHub
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gh-113743: Make the MRO cache thread-safe in free-threaded builds (#113930)
Makes _PyType_Lookup thread safe, including: Thread safety of the underlying cache. Make mutation of mro and type members thread safe Also _PyType_GetMRO and _PyType_GetBases are currently returning borrowed references which aren't safe.
1 parent e74fa29 commit ae460d4

11 files changed

Lines changed: 500 additions & 80 deletions

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‎Include/cpython/pyatomic.h‎

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‎Include/cpython/pyatomic_gcc.h‎

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@@ -495,6 +495,9 @@ static inline int
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_Py_atomic_load_int_acquire(const int *obj)
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{ return __atomic_load_n(obj, __ATOMIC_ACQUIRE); }
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static inline uint32_t
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_Py_atomic_load_uint32_acquire(const uint32_t *obj)
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{ return __atomic_load_n(obj, __ATOMIC_ACQUIRE); }
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// --- _Py_atomic_fence ------------------------------------------------------
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‎Include/cpython/pyatomic_msc.h‎

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@@ -938,6 +938,17 @@ _Py_atomic_load_int_acquire(const int *obj)
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#endif
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}
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static inline uint32_t
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_Py_atomic_load_uint32_acquire(const uint32_t *obj)
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{
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#if defined(_M_X64) || defined(_M_IX86)
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return *(uint32_t volatile *)obj;
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#elif defined(_M_ARM64)
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return (int)__ldar32((uint32_t volatile *)obj);
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#else
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# error "no implementation of _Py_atomic_load_uint32_acquire"
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#endif
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}
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// --- _Py_atomic_fence ------------------------------------------------------
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‎Include/cpython/pyatomic_std.h‎

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@@ -870,6 +870,13 @@ _Py_atomic_load_int_acquire(const int *obj)
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memory_order_acquire);
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}
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static inline uint32_t
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_Py_atomic_load_uint32_acquire(const uint32_t *obj)
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{
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_Py_USING_STD;
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return atomic_load_explicit((const _Atomic(uint32_t)*)obj,
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memory_order_acquire);
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}
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// --- _Py_atomic_fence ------------------------------------------------------

‎Include/internal/pycore_critical_section.h‎

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@@ -293,7 +293,8 @@ _PyCriticalSection_SuspendAll(PyThreadState *tstate);
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#ifdef Py_GIL_DISABLED
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static inline void
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_PyCriticalSection_AssertHeld(PyMutex *mutex) {
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_PyCriticalSection_AssertHeld(PyMutex *mutex)
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{
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#ifdef Py_DEBUG
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PyThreadState *tstate = _PyThreadState_GET();
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uintptr_t prev = tstate->critical_section;

‎Include/internal/pycore_lock.h‎

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@@ -251,6 +251,39 @@ PyAPI_FUNC(void) _PyRWMutex_RUnlock(_PyRWMutex *rwmutex);
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PyAPI_FUNC(void) _PyRWMutex_Lock(_PyRWMutex *rwmutex);
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PyAPI_FUNC(void) _PyRWMutex_Unlock(_PyRWMutex *rwmutex);
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// Similar to linux seqlock: https://en.wikipedia.org/wiki/Seqlock
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// We use a sequence number to lock the writer, an even sequence means we're unlocked, an odd
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// sequence means we're locked. Readers will read the sequence before attempting to read the
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// underlying data and then read the sequence number again after reading the data. If the
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// sequence has not changed the data is valid.
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//
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// Differs a little bit in that we use CAS on sequence as the lock, instead of a seperate spin lock.
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// The writer can also detect that the undelering data has not changed and abandon the write
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// and restore the previous sequence.
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typedef struct {
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uint32_t sequence;
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} _PySeqLock;
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// Lock the sequence lock for the writer
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PyAPI_FUNC(void) _PySeqLock_LockWrite(_PySeqLock *seqlock);
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// Unlock the sequence lock and move to the next sequence number.
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PyAPI_FUNC(void) _PySeqLock_UnlockWrite(_PySeqLock *seqlock);
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// Abandon the current update indicating that no mutations have occured
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// and restore the previous sequence value.
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PyAPI_FUNC(void) _PySeqLock_AbandonWrite(_PySeqLock *seqlock);
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// Begin a read operation and return the current sequence number.
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PyAPI_FUNC(uint32_t) _PySeqLock_BeginRead(_PySeqLock *seqlock);
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// End the read operation and confirm that the sequence number has not changed.
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// Returns 1 if the read was successful or 0 if the read should be re-tried.
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PyAPI_FUNC(uint32_t) _PySeqLock_EndRead(_PySeqLock *seqlock, uint32_t previous);
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// Check if the lock was held during a fork and clear the lock. Returns 1
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// if the lock was held and any associated datat should be cleared.
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PyAPI_FUNC(uint32_t) _PySeqLock_AfterFork(_PySeqLock *seqlock);
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#ifdef __cplusplus
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}

‎Include/internal/pycore_typeobject.h‎

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@@ -9,6 +9,7 @@ extern "C" {
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#endif
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#include "pycore_moduleobject.h" // PyModuleObject
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#include "pycore_lock.h" // PyMutex
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/* state */
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// bpo-42745: next_version_tag remains shared by all interpreters
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// because of static types.
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unsigned int next_version_tag;
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PyMutex type_mutex;
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};
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// Type attribute lookup cache: speed up attribute and method lookups,
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// see _PyType_Lookup().
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struct type_cache_entry {
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unsigned int version; // initialized from type->tp_version_tag
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#ifdef Py_GIL_DISABLED
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_PySeqLock sequence;
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#endif
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PyObject *name; // reference to exactly a str or None
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PyObject *value; // borrowed reference or NULL
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};
@@ -74,7 +79,7 @@ struct types_state {
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extern PyStatus _PyTypes_InitTypes(PyInterpreterState *);
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extern void _PyTypes_FiniTypes(PyInterpreterState *);
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extern void _PyTypes_Fini(PyInterpreterState *);
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extern void _PyTypes_AfterFork(void);
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/* other API */
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‎Modules/_abc.c‎

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