From e99f159be4f70cf9e40865d638e79fa426968827 Mon Sep 17 00:00:00 2001 From: mpage Date: Tue, 8 Oct 2024 07:04:35 -0700 Subject: [PATCH] gh-115999: Stop the world when invalidating function versions (#124997) Stop the world when invalidating function versions The tier1 interpreter specializes `CALL` instructions based on the values of certain function attributes (e.g. `__code__`, `__defaults__`). The tier1 interpreter uses function versions to verify that the attributes of a function during execution of a specialization match those seen during specialization. A function's version is initialized in `MAKE_FUNCTION` and is invalidated when any of the critical function attributes are changed. The tier1 interpreter stores the function version in the inline cache during specialization. A guard is used by the specialized instruction to verify that the version of the function on the operand stack matches the cached version (and therefore has all of the expected attributes). It is assumed that once the guard passes, all attributes will remain unchanged while executing the rest of the specialized instruction. Stopping the world when invalidating function versions ensures that all critical function attributes will remain unchanged after the function version guard passes in free-threaded builds. It's important to note that this is only true if the remainder of the specialized instruction does not enter and exit a stop-the-world point. We will stop the world the first time any of the following function attributes are mutated: - defaults - vectorcall - kwdefaults - closure - code This should happen rarely and only happens once per function, so the performance impact on majority of code should be minimal. Additionally, refactor the API for manipulating function versions to more clearly match the stated semantics. --- Include/internal/pycore_function.h | 10 +++ Include/internal/pycore_runtime_init.h | 3 +- Objects/funcobject.c | 89 ++++++++++++++++---------- Python/specialize.c | 8 +-- 4 files changed, 72 insertions(+), 38 deletions(-) diff --git a/Include/internal/pycore_function.h b/Include/internal/pycore_function.h index 6d44e933e8a8cb..c45d281125febb 100644 --- a/Include/internal/pycore_function.h +++ b/Include/internal/pycore_function.h @@ -18,6 +18,10 @@ extern PyObject* _PyFunction_Vectorcall( #define FUNC_MAX_WATCHERS 8 +#define FUNC_VERSION_UNSET 0 +#define FUNC_VERSION_CLEARED 1 +#define FUNC_VERSION_FIRST_VALID 2 + #define FUNC_VERSION_CACHE_SIZE (1<<12) /* Must be a power of 2 */ struct _func_version_cache_item { @@ -41,6 +45,12 @@ struct _py_func_state { extern PyFunctionObject* _PyFunction_FromConstructor(PyFrameConstructor *constr); +static inline int +_PyFunction_IsVersionValid(uint32_t version) +{ + return version >= FUNC_VERSION_FIRST_VALID; +} + extern uint32_t _PyFunction_GetVersionForCurrentState(PyFunctionObject *func); PyAPI_FUNC(void) _PyFunction_SetVersion(PyFunctionObject *func, uint32_t version); void _PyFunction_ClearCodeByVersion(uint32_t version); diff --git a/Include/internal/pycore_runtime_init.h b/Include/internal/pycore_runtime_init.h index e6adb98eb19130..a17ba46966daa1 100644 --- a/Include/internal/pycore_runtime_init.h +++ b/Include/internal/pycore_runtime_init.h @@ -11,6 +11,7 @@ extern "C" { #include "pycore_ceval_state.h" // _PyEval_RUNTIME_PERF_INIT #include "pycore_faulthandler.h" // _faulthandler_runtime_state_INIT #include "pycore_floatobject.h" // _py_float_format_unknown +#include "pycore_function.h" #include "pycore_object.h" // _PyObject_HEAD_INIT #include "pycore_obmalloc_init.h" // _obmalloc_global_state_INIT #include "pycore_parser.h" // _parser_runtime_state_INIT @@ -243,7 +244,7 @@ extern PyTypeObject _PyExc_MemoryError; .dict_state = _dict_state_INIT, \ .mem_free_queue = _Py_mem_free_queue_INIT(INTERP.mem_free_queue), \ .func_state = { \ - .next_version = 1, \ + .next_version = FUNC_VERSION_FIRST_VALID, \ }, \ .types = { \ .next_version_tag = _Py_TYPE_BASE_VERSION_TAG, \ diff --git a/Objects/funcobject.c b/Objects/funcobject.c index 98e6766d0ca0d8..855d1a2eeca819 100644 --- a/Objects/funcobject.c +++ b/Objects/funcobject.c @@ -128,7 +128,7 @@ _PyFunction_FromConstructor(PyFrameConstructor *constr) op->func_annotate = NULL; op->func_typeparams = NULL; op->vectorcall = _PyFunction_Vectorcall; - op->func_version = 0; + op->func_version = FUNC_VERSION_UNSET; // NOTE: functions created via FrameConstructor do not use deferred // reference counting because they are typically not part of cycles // nor accessed by multiple threads. @@ -207,7 +207,7 @@ PyFunction_NewWithQualName(PyObject *code, PyObject *globals, PyObject *qualname op->func_annotate = NULL; op->func_typeparams = NULL; op->vectorcall = _PyFunction_Vectorcall; - op->func_version = 0; + op->func_version = FUNC_VERSION_UNSET; if ((code_obj->co_flags & CO_NESTED) == 0) { // Use deferred reference counting for top-level functions, but not // nested functions because they are more likely to capture variables, @@ -287,31 +287,59 @@ functions is running. */ +static inline struct _func_version_cache_item * +get_cache_item(PyInterpreterState *interp, uint32_t version) +{ + return interp->func_state.func_version_cache + + (version % FUNC_VERSION_CACHE_SIZE); +} + void _PyFunction_SetVersion(PyFunctionObject *func, uint32_t version) { + assert(func->func_version == FUNC_VERSION_UNSET); + assert(version >= FUNC_VERSION_FIRST_VALID); + // This should only be called from MAKE_FUNCTION. No code is specialized + // based on the version, so we do not need to stop the world to set it. + func->func_version = version; #ifndef Py_GIL_DISABLED PyInterpreterState *interp = _PyInterpreterState_GET(); - if (func->func_version != 0) { - struct _func_version_cache_item *slot = - interp->func_state.func_version_cache - + (func->func_version % FUNC_VERSION_CACHE_SIZE); - if (slot->func == func) { - slot->func = NULL; - // Leave slot->code alone, there may be use for it. - } - } + struct _func_version_cache_item *slot = get_cache_item(interp, version); + slot->func = func; + slot->code = func->func_code; #endif - func->func_version = version; +} + +static void +func_clear_version(PyInterpreterState *interp, PyFunctionObject *func) +{ + if (func->func_version < FUNC_VERSION_FIRST_VALID) { + // Version was never set or has already been cleared. + return; + } #ifndef Py_GIL_DISABLED - if (version != 0) { - struct _func_version_cache_item *slot = - interp->func_state.func_version_cache - + (version % FUNC_VERSION_CACHE_SIZE); - slot->func = func; - slot->code = func->func_code; + struct _func_version_cache_item *slot = + get_cache_item(interp, func->func_version); + if (slot->func == func) { + slot->func = NULL; + // Leave slot->code alone, there may be use for it. } #endif + func->func_version = FUNC_VERSION_CLEARED; +} + +// Called when any of the critical function attributes are changed +static void +_PyFunction_ClearVersion(PyFunctionObject *func) +{ + if (func->func_version < FUNC_VERSION_FIRST_VALID) { + // Version was never set or has already been cleared. + return; + } + PyInterpreterState *interp = _PyInterpreterState_GET(); + _PyEval_StopTheWorld(interp); + func_clear_version(interp, func); + _PyEval_StartTheWorld(interp); } void @@ -319,9 +347,7 @@ _PyFunction_ClearCodeByVersion(uint32_t version) { #ifndef Py_GIL_DISABLED PyInterpreterState *interp = _PyInterpreterState_GET(); - struct _func_version_cache_item *slot = - interp->func_state.func_version_cache - + (version % FUNC_VERSION_CACHE_SIZE); + struct _func_version_cache_item *slot = get_cache_item(interp, version); if (slot->code) { assert(PyCode_Check(slot->code)); PyCodeObject *code = (PyCodeObject *)slot->code; @@ -340,9 +366,7 @@ _PyFunction_LookupByVersion(uint32_t version, PyObject **p_code) return NULL; #else PyInterpreterState *interp = _PyInterpreterState_GET(); - struct _func_version_cache_item *slot = - interp->func_state.func_version_cache - + (version % FUNC_VERSION_CACHE_SIZE); + struct _func_version_cache_item *slot = get_cache_item(interp, version); if (slot->code) { assert(PyCode_Check(slot->code)); PyCodeObject *code = (PyCodeObject *)slot->code; @@ -431,7 +455,7 @@ PyFunction_SetDefaults(PyObject *op, PyObject *defaults) } handle_func_event(PyFunction_EVENT_MODIFY_DEFAULTS, (PyFunctionObject *) op, defaults); - _PyFunction_SetVersion((PyFunctionObject *)op, 0); + _PyFunction_ClearVersion((PyFunctionObject *)op); Py_XSETREF(((PyFunctionObject *)op)->func_defaults, defaults); return 0; } @@ -440,7 +464,7 @@ void PyFunction_SetVectorcall(PyFunctionObject *func, vectorcallfunc vectorcall) { assert(func != NULL); - _PyFunction_SetVersion(func, 0); + _PyFunction_ClearVersion(func); func->vectorcall = vectorcall; } @@ -473,7 +497,7 @@ PyFunction_SetKwDefaults(PyObject *op, PyObject *defaults) } handle_func_event(PyFunction_EVENT_MODIFY_KWDEFAULTS, (PyFunctionObject *) op, defaults); - _PyFunction_SetVersion((PyFunctionObject *)op, 0); + _PyFunction_ClearVersion((PyFunctionObject *)op); Py_XSETREF(((PyFunctionObject *)op)->func_kwdefaults, defaults); return 0; } @@ -506,7 +530,7 @@ PyFunction_SetClosure(PyObject *op, PyObject *closure) Py_TYPE(closure)->tp_name); return -1; } - _PyFunction_SetVersion((PyFunctionObject *)op, 0); + _PyFunction_ClearVersion((PyFunctionObject *)op); Py_XSETREF(((PyFunctionObject *)op)->func_closure, closure); return 0; } @@ -658,7 +682,7 @@ func_set_code(PyObject *self, PyObject *value, void *Py_UNUSED(ignored)) } handle_func_event(PyFunction_EVENT_MODIFY_CODE, op, value); - _PyFunction_SetVersion(op, 0); + _PyFunction_ClearVersion(op); Py_XSETREF(op->func_code, Py_NewRef(value)); return 0; } @@ -744,7 +768,7 @@ func_set_defaults(PyObject *self, PyObject *value, void *Py_UNUSED(ignored)) } handle_func_event(PyFunction_EVENT_MODIFY_DEFAULTS, op, value); - _PyFunction_SetVersion(op, 0); + _PyFunction_ClearVersion(op); Py_XSETREF(op->func_defaults, Py_XNewRef(value)); return 0; } @@ -787,7 +811,7 @@ func_set_kwdefaults(PyObject *self, PyObject *value, void *Py_UNUSED(ignored)) } handle_func_event(PyFunction_EVENT_MODIFY_KWDEFAULTS, op, value); - _PyFunction_SetVersion(op, 0); + _PyFunction_ClearVersion(op); Py_XSETREF(op->func_kwdefaults, Py_XNewRef(value)); return 0; } @@ -1030,7 +1054,7 @@ static int func_clear(PyObject *self) { PyFunctionObject *op = _PyFunction_CAST(self); - _PyFunction_SetVersion(op, 0); + func_clear_version(_PyInterpreterState_GET(), op); Py_CLEAR(op->func_globals); Py_CLEAR(op->func_builtins); Py_CLEAR(op->func_module); @@ -1068,7 +1092,6 @@ func_dealloc(PyObject *self) if (op->func_weakreflist != NULL) { PyObject_ClearWeakRefs((PyObject *) op); } - _PyFunction_SetVersion(op, 0); (void)func_clear((PyObject*)op); // These aren't cleared by func_clear(). Py_DECREF(op->func_code); diff --git a/Python/specialize.c b/Python/specialize.c index d8bff39511cf12..4b33a468733d6b 100644 --- a/Python/specialize.c +++ b/Python/specialize.c @@ -1599,7 +1599,7 @@ function_get_version(PyObject *o, int opcode) assert(Py_IS_TYPE(o, &PyFunction_Type)); PyFunctionObject *func = (PyFunctionObject *)o; uint32_t version = _PyFunction_GetVersionForCurrentState(func); - if (version == 0) { + if (!_PyFunction_IsVersionValid(version)) { SPECIALIZATION_FAIL(opcode, SPEC_FAIL_OUT_OF_VERSIONS); return 0; } @@ -1692,7 +1692,7 @@ _Py_Specialize_BinarySubscr( goto fail; } uint32_t version = _PyFunction_GetVersionForCurrentState(func); - if (version == 0) { + if (!_PyFunction_IsVersionValid(version)) { SPECIALIZATION_FAIL(BINARY_SUBSCR, SPEC_FAIL_OUT_OF_VERSIONS); goto fail; } @@ -1977,7 +1977,7 @@ specialize_py_call(PyFunctionObject *func, _Py_CODEUNIT *instr, int nargs, argcount = code->co_argcount; } int version = _PyFunction_GetVersionForCurrentState(func); - if (version == 0) { + if (!_PyFunction_IsVersionValid(version)) { SPECIALIZATION_FAIL(CALL, SPEC_FAIL_OUT_OF_VERSIONS); return -1; } @@ -2009,7 +2009,7 @@ specialize_py_call_kw(PyFunctionObject *func, _Py_CODEUNIT *instr, int nargs, return -1; } int version = _PyFunction_GetVersionForCurrentState(func); - if (version == 0) { + if (!_PyFunction_IsVersionValid(version)) { SPECIALIZATION_FAIL(CALL, SPEC_FAIL_OUT_OF_VERSIONS); return -1; }