From 36518e69d74607e5f094ce55286188e4545a947d Mon Sep 17 00:00:00 2001 From: Mark Shannon Date: Mon, 5 Feb 2024 18:28:51 +0000 Subject: [PATCH] GH-108362: Incremental GC implementation (GH-108038) --- Doc/whatsnew/3.13.rst | 34 + Include/internal/pycore_gc.h | 42 +- Include/internal/pycore_object.h | 17 +- Include/internal/pycore_runtime_init.h | 8 +- Lib/test/test_gc.py | 22 +- ...-01-07-04-22-51.gh-issue-108362.oB9Gcf.rst | 13 + Modules/gcmodule.c | 23 +- Objects/object.c | 15 + Objects/structseq.c | 5 +- Python/gc.c | 932 +++++++++++------- Python/gc_free_threading.c | 27 +- Python/import.c | 2 +- Tools/gdb/libpython.py | 7 +- 13 files changed, 701 insertions(+), 446 deletions(-) create mode 100644 Misc/NEWS.d/next/Core and Builtins/2024-01-07-04-22-51.gh-issue-108362.oB9Gcf.rst diff --git a/Doc/whatsnew/3.13.rst b/Doc/whatsnew/3.13.rst index c25d41351c2..0770e28d230 100644 --- a/Doc/whatsnew/3.13.rst +++ b/Doc/whatsnew/3.13.rst @@ -92,6 +92,10 @@ Interpreter improvements: New Features ============ +* The cyclic garbage collector is now incremental. + This means that maximum pause times are reduced, + by an order of magnitude or more for larger heaps. + Improved Error Messages ----------------------- @@ -101,6 +105,13 @@ Improved Error Messages variables. See also :ref:`using-on-controlling-color`. (Contributed by Pablo Galindo Salgado in :gh:`112730`.) +Incremental Garbage Collection +------------------------------ + +* The cycle garbage collector is now incremental. + This means that maximum pause times are reduced + by an order of magnitude or more for larger heaps. + Other Language Changes ====================== @@ -232,6 +243,29 @@ fractions sign handling, minimum width and grouping. (Contributed by Mark Dickinson in :gh:`111320`.) +gc +-- +* The cyclic garbage collector is now incremental, which changes the meanings + of the results of :meth:`gc.get_threshold` and :meth:`gc.get_threshold` as + well as :meth:`gc.get_count` and :meth:`gc.get_stats`. +* :meth:`gc.get_threshold` returns a three-tuple for backwards compatibility, + the first value is the threshold for young collections, as before, the second + value determines the rate at which the old collection is scanned; the + default is 10 and higher values mean that the old collection is scanned more slowly. + The third value is meangless and is always zero. +* :meth:`gc.set_threshold` ignores any items after the second. +* :meth:`gc.get_count` and :meth:`gc.get_stats`. + These functions return the same format of results as before. + The only difference is that instead of the results refering to + the young, aging and old generations, the results refer to the + young generation and the aging and collecting spaces of the old generation. + +In summary, code that attempted to manipulate the behavior of the cycle GC may +not work as well as intended, but it is very unlikely to harmful. +All other code will work just fine. +Uses should avoid calling :meth:`gc.collect` unless their workload is episodic, +but that has always been the case to some extent. + glob ---- diff --git a/Include/internal/pycore_gc.h b/Include/internal/pycore_gc.h index ca1d9fdf525..d2f5c69b45e 100644 --- a/Include/internal/pycore_gc.h +++ b/Include/internal/pycore_gc.h @@ -71,11 +71,15 @@ static inline int _PyObject_GC_MAY_BE_TRACKED(PyObject *obj) { /* Bit flags for _gc_prev */ /* Bit 0 is set when tp_finalize is called */ -#define _PyGC_PREV_MASK_FINALIZED (1) +#define _PyGC_PREV_MASK_FINALIZED 1 /* Bit 1 is set when the object is in generation which is GCed currently. */ -#define _PyGC_PREV_MASK_COLLECTING (2) +#define _PyGC_PREV_MASK_COLLECTING 2 + +/* Bit 0 is set if the object belongs to old space 1 */ +#define _PyGC_NEXT_MASK_OLD_SPACE_1 1 + /* The (N-2) most significant bits contain the real address. */ -#define _PyGC_PREV_SHIFT (2) +#define _PyGC_PREV_SHIFT 2 #define _PyGC_PREV_MASK (((uintptr_t) -1) << _PyGC_PREV_SHIFT) /* set for debugging information */ @@ -101,11 +105,13 @@ typedef enum { // Lowest bit of _gc_next is used for flags only in GC. // But it is always 0 for normal code. static inline PyGC_Head* _PyGCHead_NEXT(PyGC_Head *gc) { - uintptr_t next = gc->_gc_next; + uintptr_t next = gc->_gc_next & _PyGC_PREV_MASK; return (PyGC_Head*)next; } static inline void _PyGCHead_SET_NEXT(PyGC_Head *gc, PyGC_Head *next) { - gc->_gc_next = (uintptr_t)next; + uintptr_t unext = (uintptr_t)next; + assert((unext & ~_PyGC_PREV_MASK) == 0); + gc->_gc_next = (gc->_gc_next & ~_PyGC_PREV_MASK) | unext; } // Lowest two bits of _gc_prev is used for _PyGC_PREV_MASK_* flags. @@ -113,6 +119,7 @@ static inline PyGC_Head* _PyGCHead_PREV(PyGC_Head *gc) { uintptr_t prev = (gc->_gc_prev & _PyGC_PREV_MASK); return (PyGC_Head*)prev; } + static inline void _PyGCHead_SET_PREV(PyGC_Head *gc, PyGC_Head *prev) { uintptr_t uprev = (uintptr_t)prev; assert((uprev & ~_PyGC_PREV_MASK) == 0); @@ -198,6 +205,13 @@ struct gc_generation { generations */ }; +struct gc_collection_stats { + /* number of collected objects */ + Py_ssize_t collected; + /* total number of uncollectable objects (put into gc.garbage) */ + Py_ssize_t uncollectable; +}; + /* Running stats per generation */ struct gc_generation_stats { /* total number of collections */ @@ -219,8 +233,8 @@ struct _gc_runtime_state { int enabled; int debug; /* linked lists of container objects */ - struct gc_generation generations[NUM_GENERATIONS]; - PyGC_Head *generation0; + struct gc_generation young; + struct gc_generation old[2]; /* a permanent generation which won't be collected */ struct gc_generation permanent_generation; struct gc_generation_stats generation_stats[NUM_GENERATIONS]; @@ -233,22 +247,20 @@ struct _gc_runtime_state { /* This is the number of objects that survived the last full collection. It approximates the number of long lived objects tracked by the GC. - (by "full collection", we mean a collection of the oldest generation). */ Py_ssize_t long_lived_total; - /* This is the number of objects that survived all "non-full" - collections, and are awaiting to undergo a full collection for - the first time. */ - Py_ssize_t long_lived_pending; + + Py_ssize_t work_to_do; + /* Which of the old spaces is the visited space */ + int visited_space; }; extern void _PyGC_InitState(struct _gc_runtime_state *); -extern Py_ssize_t _PyGC_Collect(PyThreadState *tstate, int generation, - _PyGC_Reason reason); -extern Py_ssize_t _PyGC_CollectNoFail(PyThreadState *tstate); +extern Py_ssize_t _PyGC_Collect(PyThreadState *tstate, int generation, _PyGC_Reason reason); +extern void _PyGC_CollectNoFail(PyThreadState *tstate); /* Freeze objects tracked by the GC and ignore them in future collections. */ extern void _PyGC_Freeze(PyInterpreterState *interp); diff --git a/Include/internal/pycore_object.h b/Include/internal/pycore_object.h index 34a83ea228e..efa712c4a0b 100644 --- a/Include/internal/pycore_object.h +++ b/Include/internal/pycore_object.h @@ -125,19 +125,7 @@ static inline void _Py_RefcntAdd(PyObject* op, Py_ssize_t n) } #define _Py_RefcntAdd(op, n) _Py_RefcntAdd(_PyObject_CAST(op), n) -static inline void _Py_SetImmortal(PyObject *op) -{ - if (op) { -#ifdef Py_GIL_DISABLED - op->ob_tid = _Py_UNOWNED_TID; - op->ob_ref_local = _Py_IMMORTAL_REFCNT_LOCAL; - op->ob_ref_shared = 0; -#else - op->ob_refcnt = _Py_IMMORTAL_REFCNT; -#endif - } -} -#define _Py_SetImmortal(op) _Py_SetImmortal(_PyObject_CAST(op)) +extern void _Py_SetImmortal(PyObject *op); // Makes an immortal object mortal again with the specified refcnt. Should only // be used during runtime finalization. @@ -325,11 +313,12 @@ static inline void _PyObject_GC_TRACK( filename, lineno, __func__); PyInterpreterState *interp = _PyInterpreterState_GET(); - PyGC_Head *generation0 = interp->gc.generation0; + PyGC_Head *generation0 = &interp->gc.young.head; PyGC_Head *last = (PyGC_Head*)(generation0->_gc_prev); _PyGCHead_SET_NEXT(last, gc); _PyGCHead_SET_PREV(gc, last); _PyGCHead_SET_NEXT(gc, generation0); + assert((gc->_gc_next & _PyGC_NEXT_MASK_OLD_SPACE_1) == 0); generation0->_gc_prev = (uintptr_t)gc; #endif } diff --git a/Include/internal/pycore_runtime_init.h b/Include/internal/pycore_runtime_init.h index 0a5c92bb84b..4370ad05bdc 100644 --- a/Include/internal/pycore_runtime_init.h +++ b/Include/internal/pycore_runtime_init.h @@ -160,12 +160,12 @@ extern PyTypeObject _PyExc_MemoryError; }, \ .gc = { \ .enabled = 1, \ - .generations = { \ - /* .head is set in _PyGC_InitState(). */ \ - { .threshold = 700, }, \ - { .threshold = 10, }, \ + .young = { .threshold = 2000, }, \ + .old = { \ { .threshold = 10, }, \ + { .threshold = 0, }, \ }, \ + .work_to_do = -5000, \ }, \ .object_state = _py_object_state_INIT(INTERP), \ .dtoa = _dtoa_state_INIT(&(INTERP)), \ diff --git a/Lib/test/test_gc.py b/Lib/test/test_gc.py index b01f344cb14..0002852fce9 100644 --- a/Lib/test/test_gc.py +++ b/Lib/test/test_gc.py @@ -383,19 +383,11 @@ class GCTests(unittest.TestCase): # each call to collect(N) x = [] gc.collect(0) - # x is now in gen 1 + # x is now in the old gen a, b, c = gc.get_count() - gc.collect(1) - # x is now in gen 2 - d, e, f = gc.get_count() - gc.collect(2) - # x is now in gen 3 - g, h, i = gc.get_count() - # We don't check a, d, g since their exact values depends on + # We don't check a since its exact values depends on # internal implementation details of the interpreter. self.assertEqual((b, c), (1, 0)) - self.assertEqual((e, f), (0, 1)) - self.assertEqual((h, i), (0, 0)) def test_trashcan(self): class Ouch: @@ -846,16 +838,6 @@ class GCTests(unittest.TestCase): self.assertFalse( any(l is element for element in gc.get_objects(generation=2)) ) - gc.collect(generation=1) - self.assertFalse( - any(l is element for element in gc.get_objects(generation=0)) - ) - self.assertFalse( - any(l is element for element in gc.get_objects(generation=1)) - ) - self.assertTrue( - any(l is element for element in gc.get_objects(generation=2)) - ) gc.collect(generation=2) self.assertFalse( any(l is element for element in gc.get_objects(generation=0)) diff --git a/Misc/NEWS.d/next/Core and Builtins/2024-01-07-04-22-51.gh-issue-108362.oB9Gcf.rst b/Misc/NEWS.d/next/Core and Builtins/2024-01-07-04-22-51.gh-issue-108362.oB9Gcf.rst new file mode 100644 index 00000000000..1fe4e0f41e1 --- /dev/null +++ b/Misc/NEWS.d/next/Core and Builtins/2024-01-07-04-22-51.gh-issue-108362.oB9Gcf.rst @@ -0,0 +1,13 @@ +Implements an incremental cyclic garbage collector. By collecting the old +generation in increments, there is no need for a full heap scan. This can +hugely reduce maximum pause time for programs with large heaps. + +Reduces the number of generations from three to two. The old generation is +split into two spaces, "aging" and "collecting". + +Collection happens in two steps:: * First, the young generation is scanned +and the survivors moved to the end of the aging space. * Then objects are +taken from the collecting space, at such a rate that all cycles are +collected eventually. Those objects are then scanned and the survivors +moved to the end of the aging space. When the collecting space becomes +empty, the two spaces are swapped. diff --git a/Modules/gcmodule.c b/Modules/gcmodule.c index ffddef34ecc..3b63dd7a9a8 100644 --- a/Modules/gcmodule.c +++ b/Modules/gcmodule.c @@ -158,17 +158,12 @@ gc_set_threshold_impl(PyObject *module, int threshold0, int group_right_1, { GCState *gcstate = get_gc_state(); - gcstate->generations[0].threshold = threshold0; + gcstate->young.threshold = threshold0; if (group_right_1) { - gcstate->generations[1].threshold = threshold1; + gcstate->old[0].threshold = threshold1; } if (group_right_2) { - gcstate->generations[2].threshold = threshold2; - - /* generations higher than 2 get the same threshold */ - for (int i = 3; i < NUM_GENERATIONS; i++) { - gcstate->generations[i].threshold = gcstate->generations[2].threshold; - } + gcstate->old[1].threshold = threshold2; } Py_RETURN_NONE; } @@ -185,9 +180,9 @@ gc_get_threshold_impl(PyObject *module) { GCState *gcstate = get_gc_state(); return Py_BuildValue("(iii)", - gcstate->generations[0].threshold, - gcstate->generations[1].threshold, - gcstate->generations[2].threshold); + gcstate->young.threshold, + gcstate->old[0].threshold, + 0); } /*[clinic input] @@ -202,9 +197,9 @@ gc_get_count_impl(PyObject *module) { GCState *gcstate = get_gc_state(); return Py_BuildValue("(iii)", - gcstate->generations[0].count, - gcstate->generations[1].count, - gcstate->generations[2].count); + gcstate->young.count, + gcstate->old[gcstate->visited_space].count, + gcstate->old[gcstate->visited_space^1].count); } /*[clinic input] diff --git a/Objects/object.c b/Objects/object.c index bbf7f98ae3d..7247eb21df6 100644 --- a/Objects/object.c +++ b/Objects/object.c @@ -2387,6 +2387,21 @@ _Py_NewReferenceNoTotal(PyObject *op) new_reference(op); } +void +_Py_SetImmortal(PyObject *op) +{ + if (PyObject_IS_GC(op) && _PyObject_GC_IS_TRACKED(op)) { + _PyObject_GC_UNTRACK(op); + } +#ifdef Py_GIL_DISABLED + op->ob_tid = _Py_UNOWNED_TID; + op->ob_ref_local = _Py_IMMORTAL_REFCNT_LOCAL; + op->ob_ref_shared = 0; +#else + op->ob_refcnt = _Py_IMMORTAL_REFCNT; +#endif +} + void _Py_ResurrectReference(PyObject *op) { diff --git a/Objects/structseq.c b/Objects/structseq.c index 581d6ad2408..661d96a968f 100644 --- a/Objects/structseq.c +++ b/Objects/structseq.c @@ -603,6 +603,9 @@ _PyStructSequence_InitBuiltinWithFlags(PyInterpreterState *interp, PyStructSequence_Desc *desc, unsigned long tp_flags) { + if (Py_TYPE(type) == NULL) { + Py_SET_TYPE(type, &PyType_Type); + } Py_ssize_t n_unnamed_members; Py_ssize_t n_members = count_members(desc, &n_unnamed_members); PyMemberDef *members = NULL; @@ -618,7 +621,7 @@ _PyStructSequence_InitBuiltinWithFlags(PyInterpreterState *interp, } initialize_static_fields(type, desc, members, tp_flags); - _Py_SetImmortal(type); + _Py_SetImmortal((PyObject *)type); } #ifndef NDEBUG else { diff --git a/Python/gc.c b/Python/gc.c index 46646760291..cda12ff7fbc 100644 --- a/Python/gc.c +++ b/Python/gc.c @@ -45,7 +45,7 @@ typedef struct _gc_runtime_state GCState; // move_legacy_finalizers() removes this flag instead. // Between them, unreachable list is not normal list and we can not use // most gc_list_* functions for it. -#define NEXT_MASK_UNREACHABLE (1) +#define NEXT_MASK_UNREACHABLE 2 #define AS_GC(op) _Py_AS_GC(op) #define FROM_GC(gc) _Py_FROM_GC(gc) @@ -95,9 +95,48 @@ gc_decref(PyGC_Head *g) g->_gc_prev -= 1 << _PyGC_PREV_SHIFT; } +static inline int +gc_old_space(PyGC_Head *g) +{ + return g->_gc_next & _PyGC_NEXT_MASK_OLD_SPACE_1; +} -#define GEN_HEAD(gcstate, n) (&(gcstate)->generations[n].head) +static inline int +flip_old_space(int space) +{ + assert(space == 0 || space == 1); + return space ^ _PyGC_NEXT_MASK_OLD_SPACE_1; +} +static inline void +gc_flip_old_space(PyGC_Head *g) +{ + g->_gc_next ^= _PyGC_NEXT_MASK_OLD_SPACE_1; +} + +static inline void +gc_set_old_space(PyGC_Head *g, int space) +{ + assert(space == 0 || space == _PyGC_NEXT_MASK_OLD_SPACE_1); + g->_gc_next &= ~_PyGC_NEXT_MASK_OLD_SPACE_1; + g->_gc_next |= space; +} + +static PyGC_Head * +GEN_HEAD(GCState *gcstate, int n) +{ + assert((gcstate->visited_space & (~1)) == 0); + switch(n) { + case 0: + return &gcstate->young.head; + case 1: + return &gcstate->old[gcstate->visited_space].head; + case 2: + return &gcstate->old[gcstate->visited_space^1].head; + default: + Py_UNREACHABLE(); + } +} static GCState * get_gc_state(void) @@ -116,11 +155,12 @@ _PyGC_InitState(GCState *gcstate) GEN.head._gc_prev = (uintptr_t)&GEN.head; \ } while (0) - for (int i = 0; i < NUM_GENERATIONS; i++) { - assert(gcstate->generations[i].count == 0); - INIT_HEAD(gcstate->generations[i]); - }; - gcstate->generation0 = GEN_HEAD(gcstate, 0); + assert(gcstate->young.count == 0); + assert(gcstate->old[0].count == 0); + assert(gcstate->old[1].count == 0); + INIT_HEAD(gcstate->young); + INIT_HEAD(gcstate->old[0]); + INIT_HEAD(gcstate->old[1]); INIT_HEAD(gcstate->permanent_generation); #undef INIT_HEAD @@ -218,6 +258,7 @@ gc_list_is_empty(PyGC_Head *list) static inline void gc_list_append(PyGC_Head *node, PyGC_Head *list) { + assert((list->_gc_prev & ~_PyGC_PREV_MASK) == 0); PyGC_Head *last = (PyGC_Head *)list->_gc_prev; // last <-> node @@ -275,6 +316,8 @@ gc_list_merge(PyGC_Head *from, PyGC_Head *to) PyGC_Head *from_tail = GC_PREV(from); assert(from_head != from); assert(from_tail != from); + assert(gc_list_is_empty(to) || + gc_old_space(to_tail) == gc_old_space(from_tail)); _PyGCHead_SET_NEXT(to_tail, from_head); _PyGCHead_SET_PREV(from_head, to_tail); @@ -343,8 +386,8 @@ enum flagstates {collecting_clear_unreachable_clear, static void validate_list(PyGC_Head *head, enum flagstates flags) { - assert((head->_gc_prev & PREV_MASK_COLLECTING) == 0); - assert((head->_gc_next & NEXT_MASK_UNREACHABLE) == 0); + assert((head->_gc_prev & ~_PyGC_PREV_MASK) == 0); + assert((head->_gc_next & ~_PyGC_PREV_MASK) == 0); uintptr_t prev_value = 0, next_value = 0; switch (flags) { case collecting_clear_unreachable_clear: @@ -366,7 +409,7 @@ validate_list(PyGC_Head *head, enum flagstates flags) PyGC_Head *gc = GC_NEXT(head); while (gc != head) { PyGC_Head *trueprev = GC_PREV(gc); - PyGC_Head *truenext = (PyGC_Head *)(gc->_gc_next & ~NEXT_MASK_UNREACHABLE); + PyGC_Head *truenext = GC_NEXT(gc); assert(truenext != NULL); assert(trueprev == prev); assert((gc->_gc_prev & PREV_MASK_COLLECTING) == prev_value); @@ -376,8 +419,44 @@ validate_list(PyGC_Head *head, enum flagstates flags) } assert(prev == GC_PREV(head)); } + +static void +validate_old(GCState *gcstate) +{ + for (int space = 0; space < 2; space++) { + PyGC_Head *head = &gcstate->old[space].head; + PyGC_Head *gc = GC_NEXT(head); + while (gc != head) { + PyGC_Head *next = GC_NEXT(gc); + assert(gc_old_space(gc) == space); + gc = next; + } + } +} + +static void +validate_consistent_old_space(PyGC_Head *head) +{ + PyGC_Head *prev = head; + PyGC_Head *gc = GC_NEXT(head); + if (gc == head) { + return; + } + int old_space = gc_old_space(gc); + while (gc != head) { + PyGC_Head *truenext = GC_NEXT(gc); + assert(truenext != NULL); + assert(gc_old_space(gc) == old_space); + prev = gc; + gc = truenext; + } + assert(prev == GC_PREV(head)); +} + #else #define validate_list(x, y) do{}while(0) +#define validate_old(g) do{}while(0) +#define validate_consistent_old_space(l) do{}while(0) #endif /*** end of list stuff ***/ @@ -394,15 +473,7 @@ update_refs(PyGC_Head *containers) while (gc != containers) { next = GC_NEXT(gc); - /* Move any object that might have become immortal to the - * permanent generation as the reference count is not accurately - * reflecting the actual number of live references to this object - */ - if (_Py_IsImmortal(FROM_GC(gc))) { - gc_list_move(gc, &get_gc_state()->permanent_generation.head); - gc = next; - continue; - } + assert(!_Py_IsImmortal(FROM_GC(gc))); gc_reset_refs(gc, Py_REFCNT(FROM_GC(gc))); /* Python's cyclic gc should never see an incoming refcount * of 0: if something decref'ed to 0, it should have been @@ -500,12 +571,13 @@ visit_reachable(PyObject *op, void *arg) // Manually unlink gc from unreachable list because the list functions // don't work right in the presence of NEXT_MASK_UNREACHABLE flags. PyGC_Head *prev = GC_PREV(gc); - PyGC_Head *next = (PyGC_Head*)(gc->_gc_next & ~NEXT_MASK_UNREACHABLE); + PyGC_Head *next = GC_NEXT(gc); _PyObject_ASSERT(FROM_GC(prev), prev->_gc_next & NEXT_MASK_UNREACHABLE); _PyObject_ASSERT(FROM_GC(next), next->_gc_next & NEXT_MASK_UNREACHABLE); - prev->_gc_next = gc->_gc_next; // copy NEXT_MASK_UNREACHABLE + prev->_gc_next = gc->_gc_next; // copy flag bits + gc->_gc_next &= ~NEXT_MASK_UNREACHABLE; _PyGCHead_SET_PREV(next, prev); gc_list_append(gc, reachable); @@ -557,6 +629,9 @@ move_unreachable(PyGC_Head *young, PyGC_Head *unreachable) * or to the right have been scanned yet. */ + validate_consistent_old_space(young); + /* Record which old space we are in, and set NEXT_MASK_UNREACHABLE bit for convenience */ + uintptr_t flags = NEXT_MASK_UNREACHABLE | (gc->_gc_next & _PyGC_NEXT_MASK_OLD_SPACE_1); while (gc != young) { if (gc_get_refs(gc)) { /* gc is definitely reachable from outside the @@ -602,17 +677,18 @@ move_unreachable(PyGC_Head *young, PyGC_Head *unreachable) // But this may pollute the unreachable list head's 'next' pointer // too. That's semantically senseless but expedient here - the // damage is repaired when this function ends. - last->_gc_next = (NEXT_MASK_UNREACHABLE | (uintptr_t)gc); + last->_gc_next = flags | (uintptr_t)gc; _PyGCHead_SET_PREV(gc, last); - gc->_gc_next = (NEXT_MASK_UNREACHABLE | (uintptr_t)unreachable); + gc->_gc_next = flags | (uintptr_t)unreachable; unreachable->_gc_prev = (uintptr_t)gc; } - gc = (PyGC_Head*)prev->_gc_next; + gc = _PyGCHead_NEXT(prev); } // young->_gc_prev must be last element remained in the list. young->_gc_prev = (uintptr_t)prev; + young->_gc_next &= _PyGC_PREV_MASK; // don't let the pollution of the list head's next pointer leak - unreachable->_gc_next &= ~NEXT_MASK_UNREACHABLE; + unreachable->_gc_next &= _PyGC_PREV_MASK; } static void @@ -669,8 +745,8 @@ move_legacy_finalizers(PyGC_Head *unreachable, PyGC_Head *finalizers) PyObject *op = FROM_GC(gc); _PyObject_ASSERT(op, gc->_gc_next & NEXT_MASK_UNREACHABLE); + next = GC_NEXT(gc); gc->_gc_next &= ~NEXT_MASK_UNREACHABLE; - next = (PyGC_Head*)gc->_gc_next; if (has_legacy_finalizer(op)) { gc_clear_collecting(gc); @@ -689,8 +765,8 @@ clear_unreachable_mask(PyGC_Head *unreachable) assert((unreachable->_gc_next & NEXT_MASK_UNREACHABLE) == 0); for (gc = GC_NEXT(unreachable); gc != unreachable; gc = next) { _PyObject_ASSERT((PyObject*)FROM_GC(gc), gc->_gc_next & NEXT_MASK_UNREACHABLE); + next = GC_NEXT(gc); gc->_gc_next &= ~NEXT_MASK_UNREACHABLE; - next = (PyGC_Head*)gc->_gc_next; } validate_list(unreachable, collecting_set_unreachable_clear); } @@ -1023,25 +1099,6 @@ delete_garbage(PyThreadState *tstate, GCState *gcstate, } -// Show stats for objects in each generations -static void -show_stats_each_generations(GCState *gcstate) -{ - char buf[100]; - size_t pos = 0; - - for (int i = 0; i < NUM_GENERATIONS && pos < sizeof(buf); i++) { - pos += PyOS_snprintf(buf+pos, sizeof(buf)-pos, - " %zd", - gc_list_size(GEN_HEAD(gcstate, i))); - } - - PySys_FormatStderr( - "gc: objects in each generation:%s\n" - "gc: objects in permanent generation: %zd\n", - buf, gc_list_size(&gcstate->permanent_generation.head)); -} - /* Deduce which objects among "base" are unreachable from outside the list and move them to 'unreachable'. The process consist in the following steps: @@ -1115,7 +1172,6 @@ deduce_unreachable(PyGC_Head *base, PyGC_Head *unreachable) { * the reachable objects instead. But this is a one-time cost, probably not * worth complicating the code to speed just a little. */ - gc_list_init(unreachable); move_unreachable(base, unreachable); // gc_prev is pointer again validate_list(base, collecting_clear_unreachable_clear); validate_list(unreachable, collecting_set_unreachable_set); @@ -1154,21 +1210,340 @@ handle_resurrected_objects(PyGC_Head *unreachable, PyGC_Head* still_unreachable, } +#define UNTRACK_TUPLES 1 +#define UNTRACK_DICTS 2 + +static void +gc_collect_region(PyThreadState *tstate, + PyGC_Head *from, + PyGC_Head *to, + int untrack, + struct gc_collection_stats *stats); + +static inline Py_ssize_t +gc_list_set_space(PyGC_Head *list, int space) +{ + Py_ssize_t size = 0; + PyGC_Head *gc; + for (gc = GC_NEXT(list); gc != list; gc = GC_NEXT(gc)) { + gc_set_old_space(gc, space); + size++; + } + return size; +} + + +static void +add_stats(GCState *gcstate, int gen, struct gc_collection_stats *stats) +{ + gcstate->generation_stats[gen].collected += stats->collected; + gcstate->generation_stats[gen].uncollectable += stats->uncollectable; + gcstate->generation_stats[gen].collections += 1; +} + + +/* Multiply by 4 so that the default incremental threshold of 10 + * scans objects at 40% the rate that the young gen tenures them. */ +#define SCAN_RATE_MULTIPLIER 4 + + +static void +gc_collect_young(PyThreadState *tstate, + struct gc_collection_stats *stats) +{ + GCState *gcstate = &tstate->interp->gc; + PyGC_Head *young = &gcstate->young.head; + PyGC_Head *visited = &gcstate->old[gcstate->visited_space].head; +#ifdef Py_STATS + { + Py_ssize_t count = 0; + PyGC_Head *gc; + for (gc = GC_NEXT(young); gc != young; gc = GC_NEXT(gc)) { + count++; + } + } +#endif + + PyGC_Head survivors; + gc_list_init(&survivors); + gc_collect_region(tstate, young, &survivors, UNTRACK_TUPLES, stats); + Py_ssize_t survivor_count = 0; + if (gcstate->visited_space) { + /* objects in visited space have bit set, so we set it here */ + survivor_count = gc_list_set_space(&survivors, 1); + } + else { + PyGC_Head *gc; + for (gc = GC_NEXT(&survivors); gc != &survivors; gc = GC_NEXT(gc)) { +#ifdef GC_DEBUG + assert(gc_old_space(gc) == 0); +#endif + survivor_count++; + } + } + gc_list_merge(&survivors, visited); + validate_old(gcstate); + gcstate->young.count = 0; + gcstate->old[gcstate->visited_space].count++; + Py_ssize_t scale_factor = gcstate->old[0].threshold; + if (scale_factor < 1) { + scale_factor = 1; + } + gcstate->work_to_do += survivor_count + survivor_count * SCAN_RATE_MULTIPLIER / scale_factor; + add_stats(gcstate, 0, stats); +} + +static inline int +is_in_visited(PyGC_Head *gc, int visited_space) +{ + assert(visited_space == 0 || flip_old_space(visited_space) == 0); + return gc_old_space(gc) == visited_space; +} + +struct container_and_flag { + PyGC_Head *container; + int visited_space; +}; + +/* A traversal callback for adding to container) */ +static int +visit_add_to_container(PyObject *op, void *arg) +{ + OBJECT_STAT_INC(object_visits); + struct container_and_flag *cf = (struct container_and_flag *)arg; + int visited = cf->visited_space; + assert(visited == get_gc_state()->visited_space); + if (_PyObject_IS_GC(op)) { + PyGC_Head *gc = AS_GC(op); + if (_PyObject_GC_IS_TRACKED(op) && + gc_old_space(gc) != visited) { + assert(!_Py_IsImmortal(op)); + gc_flip_old_space(gc); + gc_list_move(gc, cf->container); + } + } + return 0; +} + +static uintptr_t +expand_region_transitively_reachable(PyGC_Head *container, PyGC_Head *gc, GCState *gcstate) +{ + validate_list(container, collecting_clear_unreachable_clear); + struct container_and_flag arg = { + .container = container, + .visited_space = gcstate->visited_space, + }; + uintptr_t size = 0; + assert(GC_NEXT(gc) == container); + while (gc != container) { + /* Survivors will be moved to visited space, so they should + * have been marked as visited */ + assert(is_in_visited(gc, gcstate->visited_space)); + PyObject *op = FROM_GC(gc); + if (_Py_IsImmortal(op)) { + PyGC_Head *next = GC_NEXT(gc); + gc_list_move(gc, &get_gc_state()->permanent_generation.head); + gc = next; + continue; + } + traverseproc traverse = Py_TYPE(op)->tp_traverse; + (void) traverse(op, + visit_add_to_container, + &arg); + gc = GC_NEXT(gc); + size++; + } + return size; +} + +/* Do bookkeeping for a completed GC cycle */ +static void +completed_cycle(GCState *gcstate) +{ + assert(gc_list_is_empty(&gcstate->old[gcstate->visited_space^1].head)); + assert(gc_list_is_empty(&gcstate->young.head)); + gcstate->visited_space = flip_old_space(gcstate->visited_space); + if (gcstate->work_to_do > 0) { + gcstate->work_to_do = 0; + } +} + +static void +gc_collect_increment(PyThreadState *tstate, struct gc_collection_stats *stats) +{ + GCState *gcstate = &tstate->interp->gc; + if (gcstate->work_to_do <= 0) { + /* No work to do */ + return; + } + PyGC_Head *not_visited = &gcstate->old[gcstate->visited_space^1].head; + PyGC_Head *visited = &gcstate->old[gcstate->visited_space].head; + PyGC_Head increment; + gc_list_init(&increment); + if (gc_list_is_empty(not_visited)) { + completed_cycle(gcstate); + return; + } + Py_ssize_t region_size = 0; + while (region_size < gcstate->work_to_do) { + if (gc_list_is_empty(not_visited)) { + break; + } + PyGC_Head *gc = _PyGCHead_NEXT(not_visited); + gc_list_move(gc, &increment); + gc_set_old_space(gc, gcstate->visited_space); + region_size += expand_region_transitively_reachable(&increment, gc, gcstate); + } + assert(region_size == gc_list_size(&increment)); + PyGC_Head survivors; + gc_list_init(&survivors); + gc_collect_region(tstate, &increment, &survivors, UNTRACK_TUPLES, stats); + gc_list_merge(&survivors, visited); + assert(gc_list_is_empty(&increment)); + gcstate->work_to_do -= region_size; + validate_old(gcstate); + add_stats(gcstate, 1, stats); + if (gc_list_is_empty(not_visited)) { + completed_cycle(gcstate); + } +} + + +static void +gc_collect_full(PyThreadState *tstate, + struct gc_collection_stats *stats) +{ + GCState *gcstate = &tstate->interp->gc; + validate_old(gcstate); + PyGC_Head *young = &gcstate->young.head; + PyGC_Head *old0 = &gcstate->old[0].head; + PyGC_Head *old1 = &gcstate->old[1].head; + /* merge all generations into old0 */ + gc_list_merge(young, old0); + gcstate->young.count = 0; + PyGC_Head *gc = GC_NEXT(old1); + while (gc != old1) { + PyGC_Head *next = GC_NEXT(gc); + gc_set_old_space(gc, 0); + gc = next; + } + gc_list_merge(old1, old0); + + gc_collect_region(tstate, old0, old0, + UNTRACK_TUPLES | UNTRACK_DICTS, + stats); + gcstate->visited_space = 1; + gcstate->young.count = 0; + gcstate->old[0].count = 0; + gcstate->old[1].count = 0; + + gcstate->work_to_do = - gcstate->young.threshold * 2; + + _PyGC_ClearAllFreeLists(tstate->interp); + validate_old(gcstate); + add_stats(gcstate, 2, stats); +} + +/* This is the main function. Read this to understand how the + * collection process works. */ +static void +gc_collect_region(PyThreadState *tstate, + PyGC_Head *from, + PyGC_Head *to, + int untrack, + struct gc_collection_stats *stats) +{ + PyGC_Head unreachable; /* non-problematic unreachable trash */ + PyGC_Head finalizers; /* objects with, & reachable from, __del__ */ + PyGC_Head *gc; /* initialize to prevent a compiler warning */ + GCState *gcstate = &tstate->interp->gc; + + assert(gcstate->garbage != NULL); + assert(!_PyErr_Occurred(tstate)); + + gc_list_init(&unreachable); + deduce_unreachable(from, &unreachable); + validate_consistent_old_space(from); + if (untrack & UNTRACK_TUPLES) { + untrack_tuples(from); + } + if (untrack & UNTRACK_DICTS) { + untrack_dicts(from); + } + validate_consistent_old_space(to); + if (from != to) { + gc_list_merge(from, to); + } + validate_consistent_old_space(to); + /* Move reachable objects to next generation. */ + + /* All objects in unreachable are trash, but objects reachable from + * legacy finalizers (e.g. tp_del) can't safely be deleted. + */ + gc_list_init(&finalizers); + // NEXT_MASK_UNREACHABLE is cleared here. + // After move_legacy_finalizers(), unreachable is normal list. + move_legacy_finalizers(&unreachable, &finalizers); + /* finalizers contains the unreachable objects with a legacy finalizer; + * unreachable objects reachable *from* those are also uncollectable, + * and we move those into the finalizers list too. + */ + move_legacy_finalizer_reachable(&finalizers); + validate_list(&finalizers, collecting_clear_unreachable_clear); + validate_list(&unreachable, collecting_set_unreachable_clear); + /* Print debugging information. */ + if (gcstate->debug & _PyGC_DEBUG_COLLECTABLE) { + for (gc = GC_NEXT(&unreachable); gc != &unreachable; gc = GC_NEXT(gc)) { + debug_cycle("collectable", FROM_GC(gc)); + } + } + + /* Clear weakrefs and invoke callbacks as necessary. */ + stats->collected += handle_weakrefs(&unreachable, to); + validate_list(to, collecting_clear_unreachable_clear); + validate_list(&unreachable, collecting_set_unreachable_clear); + + /* Call tp_finalize on objects which have one. */ + finalize_garbage(tstate, &unreachable); + /* Handle any objects that may have resurrected after the call + * to 'finalize_garbage' and continue the collection with the + * objects that are still unreachable */ + PyGC_Head final_unreachable; + gc_list_init(&final_unreachable); + handle_resurrected_objects(&unreachable, &final_unreachable, to); + + /* Call tp_clear on objects in the final_unreachable set. This will cause + * the reference cycles to be broken. It may also cause some objects + * in finalizers to be freed. + */ + stats->collected += gc_list_size(&final_unreachable); + delete_garbage(tstate, gcstate, &final_unreachable, to); + + /* Collect statistics on uncollectable objects found and print + * debugging information. */ + Py_ssize_t n = 0; + for (gc = GC_NEXT(&finalizers); gc != &finalizers; gc = GC_NEXT(gc)) { + n++; + if (gcstate->debug & _PyGC_DEBUG_UNCOLLECTABLE) + debug_cycle("uncollectable", FROM_GC(gc)); + } + stats->uncollectable = n; + /* Append instances in the uncollectable set to a Python + * reachable list of garbage. The programmer has to deal with + * this if they insist on creating this type of structure. + */ + handle_legacy_finalizers(tstate, gcstate, &finalizers, to); + validate_list(to, collecting_clear_unreachable_clear); +} + /* Invoke progress callbacks to notify clients that garbage collection * is starting or stopping */ static void -invoke_gc_callback(PyThreadState *tstate, const char *phase, - int generation, Py_ssize_t collected, - Py_ssize_t uncollectable) +do_gc_callback(GCState *gcstate, const char *phase, + int generation, struct gc_collection_stats *stats) { - assert(!_PyErr_Occurred(tstate)); - - /* we may get called very early */ - GCState *gcstate = &tstate->interp->gc; - if (gcstate->callbacks == NULL) { - return; - } + assert(!PyErr_Occurred()); /* The local variable cannot be rebound, check it for sanity */ assert(PyList_CheckExact(gcstate->callbacks)); @@ -1176,8 +1551,8 @@ invoke_gc_callback(PyThreadState *tstate, const char *phase, if (PyList_GET_SIZE(gcstate->callbacks) != 0) { info = Py_BuildValue("{sisnsn}", "generation", generation, - "collected", collected, - "uncollectable", uncollectable); + "collected", stats->collected, + "uncollectable", stats->uncollectable); if (info == NULL) { PyErr_FormatUnraisable("Exception ignored on invoking gc callbacks"); return; @@ -1206,275 +1581,17 @@ invoke_gc_callback(PyThreadState *tstate, const char *phase, } Py_DECREF(phase_obj); Py_XDECREF(info); - assert(!_PyErr_Occurred(tstate)); + assert(!PyErr_Occurred()); } - -/* Find the oldest generation (highest numbered) where the count - * exceeds the threshold. Objects in the that generation and - * generations younger than it will be collected. */ -static int -gc_select_generation(GCState *gcstate) +static void +invoke_gc_callback(GCState *gcstate, const char *phase, + int generation, struct gc_collection_stats *stats) { - for (int i = NUM_GENERATIONS-1; i >= 0; i--) { - if (gcstate->generations[i].count > gcstate->generations[i].threshold) { - /* Avoid quadratic performance degradation in number - of tracked objects (see also issue #4074): - - To limit the cost of garbage collection, there are two strategies; - - make each collection faster, e.g. by scanning fewer objects - - do less collections - This heuristic is about the latter strategy. - - In addition to the various configurable thresholds, we only trigger a - full collection if the ratio - - long_lived_pending / long_lived_total - - is above a given value (hardwired to 25%). - - The reason is that, while "non-full" collections (i.e., collections of - the young and middle generations) will always examine roughly the same - number of objects -- determined by the aforementioned thresholds --, - the cost of a full collection is proportional to the total number of - long-lived objects, which is virtually unbounded. - - Indeed, it has been remarked that doing a full collection every - of object creations entails a dramatic performance - degradation in workloads which consist in creating and storing lots of - long-lived objects (e.g. building a large list of GC-tracked objects would - show quadratic performance, instead of linear as expected: see issue #4074). - - Using the above ratio, instead, yields amortized linear performance in - the total number of objects (the effect of which can be summarized - thusly: "each full garbage collection is more and more costly as the - number of objects grows, but we do fewer and fewer of them"). - - This heuristic was suggested by Martin von Löwis on python-dev in - June 2008. His original analysis and proposal can be found at: - http://mail.python.org/pipermail/python-dev/2008-June/080579.html - */ - if (i == NUM_GENERATIONS - 1 - && gcstate->long_lived_pending < gcstate->long_lived_total / 4) - { - continue; - } - return i; - } + if (gcstate->callbacks == NULL) { + return; } - return -1; -} - - -/* This is the main function. Read this to understand how the - * collection process works. */ -static Py_ssize_t -gc_collect_main(PyThreadState *tstate, int generation, _PyGC_Reason reason) -{ - int i; - Py_ssize_t m = 0; /* # objects collected */ - Py_ssize_t n = 0; /* # unreachable objects that couldn't be collected */ - PyGC_Head *young; /* the generation we are examining */ - PyGC_Head *old; /* next older generation */ - PyGC_Head unreachable; /* non-problematic unreachable trash */ - PyGC_Head finalizers; /* objects with, & reachable from, __del__ */ - PyGC_Head *gc; - _PyTime_t t1 = 0; /* initialize to prevent a compiler warning */ - GCState *gcstate = &tstate->interp->gc; - - // gc_collect_main() must not be called before _PyGC_Init - // or after _PyGC_Fini() - assert(gcstate->garbage != NULL); - assert(!_PyErr_Occurred(tstate)); - - int expected = 0; - if (!_Py_atomic_compare_exchange_int(&gcstate->collecting, &expected, 1)) { - // Don't start a garbage collection if one is already in progress. - return 0; - } - - if (generation == GENERATION_AUTO) { - // Select the oldest generation that needs collecting. We will collect - // objects from that generation and all generations younger than it. - generation = gc_select_generation(gcstate); - if (generation < 0) { - // No generation needs to be collected. - _Py_atomic_store_int(&gcstate->collecting, 0); - return 0; - } - } - - assert(generation >= 0 && generation < NUM_GENERATIONS); - -#ifdef Py_STATS - if (_Py_stats) { - _Py_stats->object_stats.object_visits = 0; - } -#endif - GC_STAT_ADD(generation, collections, 1); - - if (reason != _Py_GC_REASON_SHUTDOWN) { - invoke_gc_callback(tstate, "start", generation, 0, 0); - } - - if (gcstate->debug & _PyGC_DEBUG_STATS) { - PySys_WriteStderr("gc: collecting generation %d...\n", generation); - show_stats_each_generations(gcstate); - t1 = _PyTime_GetPerfCounter(); - } - - if (PyDTrace_GC_START_ENABLED()) { - PyDTrace_GC_START(generation); - } - - /* update collection and allocation counters */ - if (generation+1 < NUM_GENERATIONS) { - gcstate->generations[generation+1].count += 1; - } - for (i = 0; i <= generation; i++) { - gcstate->generations[i].count = 0; - } - - /* merge younger generations with one we are currently collecting */ - for (i = 0; i < generation; i++) { - gc_list_merge(GEN_HEAD(gcstate, i), GEN_HEAD(gcstate, generation)); - } - - /* handy references */ - young = GEN_HEAD(gcstate, generation); - if (generation < NUM_GENERATIONS-1) { - old = GEN_HEAD(gcstate, generation+1); - } - else { - old = young; - } - validate_list(old, collecting_clear_unreachable_clear); - - deduce_unreachable(young, &unreachable); - - untrack_tuples(young); - /* Move reachable objects to next generation. */ - if (young != old) { - if (generation == NUM_GENERATIONS - 2) { - gcstate->long_lived_pending += gc_list_size(young); - } - gc_list_merge(young, old); - } - else { - /* We only un-track dicts in full collections, to avoid quadratic - dict build-up. See issue #14775. */ - untrack_dicts(young); - gcstate->long_lived_pending = 0; - gcstate->long_lived_total = gc_list_size(young); - } - - /* All objects in unreachable are trash, but objects reachable from - * legacy finalizers (e.g. tp_del) can't safely be deleted. - */ - gc_list_init(&finalizers); - // NEXT_MASK_UNREACHABLE is cleared here. - // After move_legacy_finalizers(), unreachable is normal list. - move_legacy_finalizers(&unreachable, &finalizers); - /* finalizers contains the unreachable objects with a legacy finalizer; - * unreachable objects reachable *from* those are also uncollectable, - * and we move those into the finalizers list too. - */ - move_legacy_finalizer_reachable(&finalizers); - - validate_list(&finalizers, collecting_clear_unreachable_clear); - validate_list(&unreachable, collecting_set_unreachable_clear); - - /* Print debugging information. */ - if (gcstate->debug & _PyGC_DEBUG_COLLECTABLE) { - for (gc = GC_NEXT(&unreachable); gc != &unreachable; gc = GC_NEXT(gc)) { - debug_cycle("collectable", FROM_GC(gc)); - } - } - - /* Clear weakrefs and invoke callbacks as necessary. */ - m += handle_weakrefs(&unreachable, old); - - validate_list(old, collecting_clear_unreachable_clear); - validate_list(&unreachable, collecting_set_unreachable_clear); - - /* Call tp_finalize on objects which have one. */ - finalize_garbage(tstate, &unreachable); - - /* Handle any objects that may have resurrected after the call - * to 'finalize_garbage' and continue the collection with the - * objects that are still unreachable */ - PyGC_Head final_unreachable; - handle_resurrected_objects(&unreachable, &final_unreachable, old); - - /* Call tp_clear on objects in the final_unreachable set. This will cause - * the reference cycles to be broken. It may also cause some objects - * in finalizers to be freed. - */ - m += gc_list_size(&final_unreachable); - delete_garbage(tstate, gcstate, &final_unreachable, old); - - /* Collect statistics on uncollectable objects found and print - * debugging information. */ - for (gc = GC_NEXT(&finalizers); gc != &finalizers; gc = GC_NEXT(gc)) { - n++; - if (gcstate->debug & _PyGC_DEBUG_UNCOLLECTABLE) - debug_cycle("uncollectable", FROM_GC(gc)); - } - if (gcstate->debug & _PyGC_DEBUG_STATS) { - double d = _PyTime_AsSecondsDouble(_PyTime_GetPerfCounter() - t1); - PySys_WriteStderr( - "gc: done, %zd unreachable, %zd uncollectable, %.4fs elapsed\n", - n+m, n, d); - } - - /* Append instances in the uncollectable set to a Python - * reachable list of garbage. The programmer has to deal with - * this if they insist on creating this type of structure. - */ - handle_legacy_finalizers(tstate, gcstate, &finalizers, old); - validate_list(old, collecting_clear_unreachable_clear); - - /* Clear free list only during the collection of the highest - * generation */ - if (generation == NUM_GENERATIONS-1) { - _PyGC_ClearAllFreeLists(tstate->interp); - } - - if (_PyErr_Occurred(tstate)) { - if (reason == _Py_GC_REASON_SHUTDOWN) { - _PyErr_Clear(tstate); - } - else { - PyErr_FormatUnraisable("Exception ignored in garbage collection"); - } - } - - /* Update stats */ - struct gc_generation_stats *stats = &gcstate->generation_stats[generation]; - stats->collections++; - stats->collected += m; - stats->uncollectable += n; - - GC_STAT_ADD(generation, objects_collected, m); -#ifdef Py_STATS - if (_Py_stats) { - GC_STAT_ADD(generation, object_visits, - _Py_stats->object_stats.object_visits); - _Py_stats->object_stats.object_visits = 0; - } -#endif - - if (PyDTrace_GC_DONE_ENABLED()) { - PyDTrace_GC_DONE(n + m); - } - - if (reason != _Py_GC_REASON_SHUTDOWN) { - invoke_gc_callback(tstate, "stop", generation, m, n); - } - - assert(!_PyErr_Occurred(tstate)); - _Py_atomic_store_int(&gcstate->collecting, 0); - return n + m; + do_gc_callback(gcstate, phase, generation, stats); } static int @@ -1549,7 +1666,7 @@ _PyGC_GetObjects(PyInterpreterState *interp, Py_ssize_t generation) } } else { - if (append_objects(result, GEN_HEAD(gcstate, generation))) { + if (append_objects(result, GEN_HEAD(gcstate, (int)generation))) { goto error; } } @@ -1564,10 +1681,16 @@ void _PyGC_Freeze(PyInterpreterState *interp) { GCState *gcstate = &interp->gc; - for (int i = 0; i < NUM_GENERATIONS; ++i) { - gc_list_merge(GEN_HEAD(gcstate, i), &gcstate->permanent_generation.head); - gcstate->generations[i].count = 0; - } + gc_list_merge(&gcstate->young.head, &gcstate->permanent_generation.head); + gcstate->young.count = 0; + PyGC_Head*old0 = &gcstate->old[0].head; + PyGC_Head*old1 = &gcstate->old[1].head; + gc_list_merge(old0, &gcstate->permanent_generation.head); + gcstate->old[0].count = 0; + gc_list_set_space(old1, 0); + gc_list_merge(old1, &gcstate->permanent_generation.head); + gcstate->old[1].count = 0; + validate_old(gcstate); } void @@ -1575,7 +1698,8 @@ _PyGC_Unfreeze(PyInterpreterState *interp) { GCState *gcstate = &interp->gc; gc_list_merge(&gcstate->permanent_generation.head, - GEN_HEAD(gcstate, NUM_GENERATIONS-1)); + &gcstate->old[0].head); + validate_old(gcstate); } Py_ssize_t @@ -1611,32 +1735,100 @@ PyGC_IsEnabled(void) return gcstate->enabled; } -/* Public API to invoke gc.collect() from C */ -Py_ssize_t -PyGC_Collect(void) +// Show stats for objects in each generations +static void +show_stats_each_generations(GCState *gcstate) { - PyThreadState *tstate = _PyThreadState_GET(); - GCState *gcstate = &tstate->interp->gc; + char buf[100]; + size_t pos = 0; - if (!gcstate->enabled) { - return 0; + for (int i = 0; i < NUM_GENERATIONS && pos < sizeof(buf); i++) { + pos += PyOS_snprintf(buf+pos, sizeof(buf)-pos, + " %zd", + gc_list_size(GEN_HEAD(gcstate, i))); } - Py_ssize_t n; - PyObject *exc = _PyErr_GetRaisedException(tstate); - n = gc_collect_main(tstate, NUM_GENERATIONS - 1, _Py_GC_REASON_MANUAL); - _PyErr_SetRaisedException(tstate, exc); - - return n; + PySys_FormatStderr( + "gc: objects in each generation:%s\n" + "gc: objects in permanent generation: %zd\n", + buf, gc_list_size(&gcstate->permanent_generation.head)); } Py_ssize_t _PyGC_Collect(PyThreadState *tstate, int generation, _PyGC_Reason reason) { - return gc_collect_main(tstate, generation, reason); + GCState *gcstate = &tstate->interp->gc; + + int expected = 0; + if (!_Py_atomic_compare_exchange_int(&gcstate->collecting, &expected, 1)) { + // Don't start a garbage collection if one is already in progress. + return 0; + } + + struct gc_collection_stats stats = { 0 }; + if (reason != _Py_GC_REASON_SHUTDOWN) { + invoke_gc_callback(gcstate, "start", generation, &stats); + } + _PyTime_t t1 = 0; /* initialize to prevent a compiler warning */ + if (gcstate->debug & _PyGC_DEBUG_STATS) { + PySys_WriteStderr("gc: collecting generation %d...\n", generation); + show_stats_each_generations(gcstate); + t1 = _PyTime_GetPerfCounter(); + } + if (PyDTrace_GC_START_ENABLED()) { + PyDTrace_GC_START(generation); + } + GC_STAT_ADD(generation, collections, 1); + PyObject *exc = _PyErr_GetRaisedException(tstate); + switch(generation) { + case 0: + gc_collect_young(tstate, &stats); + break; + case 1: + gc_collect_young(tstate, &stats); + gc_collect_increment(tstate, &stats); + break; + case 2: + gc_collect_full(tstate, &stats); + break; + default: + Py_UNREACHABLE(); + } + if (PyDTrace_GC_DONE_ENABLED()) { + PyDTrace_GC_DONE(stats.uncollectable + stats.collected); + } + if (reason != _Py_GC_REASON_SHUTDOWN) { + invoke_gc_callback(gcstate, "stop", generation, &stats); + } + _PyErr_SetRaisedException(tstate, exc); + GC_STAT_ADD(generation, objects_collected, stats.collected); +#ifdef Py_STATS + if (_Py_stats) { + GC_STAT_ADD(generation, object_visits, + _Py_stats->object_stats.object_visits); + _Py_stats->object_stats.object_visits = 0; + } +#endif + validate_old(gcstate); + if (gcstate->debug & _PyGC_DEBUG_STATS) { + double d = _PyTime_AsSecondsDouble(_PyTime_GetPerfCounter() - t1); + PySys_WriteStderr( + "gc: done, %zd collected, %zd uncollectable, %.4fs elapsed\n", + stats.collected, stats.uncollectable, d); + } + + _Py_atomic_store_int(&gcstate->collecting, 0); + return stats.uncollectable + stats.collected; } +/* Public API to invoke gc.collect() from C */ Py_ssize_t +PyGC_Collect(void) +{ + return _PyGC_Collect(_PyThreadState_GET(), 2, _Py_GC_REASON_MANUAL); +} + +void _PyGC_CollectNoFail(PyThreadState *tstate) { /* Ideally, this function is only called on interpreter shutdown, @@ -1645,7 +1837,7 @@ _PyGC_CollectNoFail(PyThreadState *tstate) during interpreter shutdown (and then never finish it). See http://bugs.python.org/issue8713#msg195178 for an example. */ - return gc_collect_main(tstate, NUM_GENERATIONS - 1, _Py_GC_REASON_SHUTDOWN); + _PyGC_Collect(_PyThreadState_GET(), 2, _Py_GC_REASON_SHUTDOWN); } void @@ -1780,10 +1972,10 @@ _PyObject_GC_Link(PyObject *op) GCState *gcstate = &tstate->interp->gc; g->_gc_next = 0; g->_gc_prev = 0; - gcstate->generations[0].count++; /* number of allocated GC objects */ - if (gcstate->generations[0].count > gcstate->generations[0].threshold && + gcstate->young.count++; /* number of allocated GC objects */ + if (gcstate->young.count > gcstate->young.threshold && gcstate->enabled && - gcstate->generations[0].threshold && + gcstate->young.threshold && !_Py_atomic_load_int_relaxed(&gcstate->collecting) && !_PyErr_Occurred(tstate)) { @@ -1794,7 +1986,9 @@ _PyObject_GC_Link(PyObject *op) void _Py_RunGC(PyThreadState *tstate) { - gc_collect_main(tstate, GENERATION_AUTO, _Py_GC_REASON_HEAP); + if (tstate->interp->gc.enabled) { + _PyGC_Collect(tstate, 1, _Py_GC_REASON_HEAP); + } } static PyObject * @@ -1897,8 +2091,8 @@ PyObject_GC_Del(void *op) #endif } GCState *gcstate = get_gc_state(); - if (gcstate->generations[0].count > 0) { - gcstate->generations[0].count--; + if (gcstate->young.count > 0) { + gcstate->young.count--; } PyObject_Free(((char *)op)-presize); } @@ -1921,26 +2115,36 @@ PyObject_GC_IsFinalized(PyObject *obj) return 0; } +static int +visit_generation(gcvisitobjects_t callback, void *arg, struct gc_generation *gen) +{ + PyGC_Head *gc_list, *gc; + gc_list = &gen->head; + for (gc = GC_NEXT(gc_list); gc != gc_list; gc = GC_NEXT(gc)) { + PyObject *op = FROM_GC(gc); + Py_INCREF(op); + int res = callback(op, arg); + Py_DECREF(op); + if (!res) { + return -1; + } + } + return 0; +} + void PyUnstable_GC_VisitObjects(gcvisitobjects_t callback, void *arg) { - size_t i; GCState *gcstate = get_gc_state(); int origenstate = gcstate->enabled; gcstate->enabled = 0; - for (i = 0; i < NUM_GENERATIONS; i++) { - PyGC_Head *gc_list, *gc; - gc_list = GEN_HEAD(gcstate, i); - for (gc = GC_NEXT(gc_list); gc != gc_list; gc = GC_NEXT(gc)) { - PyObject *op = FROM_GC(gc); - Py_INCREF(op); - int res = callback(op, arg); - Py_DECREF(op); - if (!res) { - goto done; - } - } + if (visit_generation(callback, arg, &gcstate->young)) { + goto done; } + if (visit_generation(callback, arg, &gcstate->old[0])) { + goto done; + } + visit_generation(callback, arg, &gcstate->old[1]); done: gcstate->enabled = origenstate; } diff --git a/Python/gc_free_threading.c b/Python/gc_free_threading.c index 8fbcdb15109..1c4da726866 100644 --- a/Python/gc_free_threading.c +++ b/Python/gc_free_threading.c @@ -616,7 +616,7 @@ void _PyGC_InitState(GCState *gcstate) { // TODO: move to pycore_runtime_init.h once the incremental GC lands. - gcstate->generations[0].threshold = 2000; + gcstate->young.threshold = 2000; } @@ -911,8 +911,8 @@ cleanup_worklist(struct worklist *worklist) static bool gc_should_collect(GCState *gcstate) { - int count = _Py_atomic_load_int_relaxed(&gcstate->generations[0].count); - int threshold = gcstate->generations[0].threshold; + int count = _Py_atomic_load_int_relaxed(&gcstate->young.count); + int threshold = gcstate->young.threshold; if (count <= threshold || threshold == 0 || !gcstate->enabled) { return false; } @@ -920,7 +920,7 @@ gc_should_collect(GCState *gcstate) // objects. A few tests rely on immediate scheduling of the GC so we ignore // the scaled threshold if generations[1].threshold is set to zero. return (count > gcstate->long_lived_total / 4 || - gcstate->generations[1].threshold == 0); + gcstate->old[0].threshold == 0); } static void @@ -1031,10 +1031,15 @@ gc_collect_main(PyThreadState *tstate, int generation, _PyGC_Reason reason) /* update collection and allocation counters */ if (generation+1 < NUM_GENERATIONS) { - gcstate->generations[generation+1].count += 1; + gcstate->old[generation].count += 1; } for (i = 0; i <= generation; i++) { - gcstate->generations[i].count = 0; + if (i == 0) { + gcstate->young.count = 0; + } + else { + gcstate->old[i-1].count = 0; + } } PyInterpreterState *interp = tstate->interp; @@ -1357,7 +1362,7 @@ _PyGC_Collect(PyThreadState *tstate, int generation, _PyGC_Reason reason) return gc_collect_main(tstate, generation, reason); } -Py_ssize_t +void _PyGC_CollectNoFail(PyThreadState *tstate) { /* Ideally, this function is only called on interpreter shutdown, @@ -1366,7 +1371,7 @@ _PyGC_CollectNoFail(PyThreadState *tstate) during interpreter shutdown (and then never finish it). See http://bugs.python.org/issue8713#msg195178 for an example. */ - return gc_collect_main(tstate, NUM_GENERATIONS - 1, _Py_GC_REASON_SHUTDOWN); + gc_collect_main(tstate, NUM_GENERATIONS - 1, _Py_GC_REASON_SHUTDOWN); } void @@ -1490,7 +1495,7 @@ _PyObject_GC_Link(PyObject *op) { PyThreadState *tstate = _PyThreadState_GET(); GCState *gcstate = &tstate->interp->gc; - gcstate->generations[0].count++; + gcstate->young.count++; if (gc_should_collect(gcstate) && !_Py_atomic_load_int_relaxed(&gcstate->collecting)) @@ -1605,8 +1610,8 @@ PyObject_GC_Del(void *op) #endif } GCState *gcstate = get_gc_state(); - if (gcstate->generations[0].count > 0) { - gcstate->generations[0].count--; + if (gcstate->young.count > 0) { + gcstate->young.count--; } PyObject_Free(((char *)op)-presize); } diff --git a/Python/import.c b/Python/import.c index 2fd0c08a6bb..dfc5ec1f2f2 100644 --- a/Python/import.c +++ b/Python/import.c @@ -1030,7 +1030,7 @@ _extensions_cache_set(PyObject *filename, PyObject *name, PyModuleDef *def) if (!already_set) { /* We assume that all module defs are statically allocated and will never be freed. Otherwise, we would incref here. */ - _Py_SetImmortal(def); + _Py_SetImmortal((PyObject *)def); } res = 0; diff --git a/Tools/gdb/libpython.py b/Tools/gdb/libpython.py index 483f28b46df..96b891481d9 100755 --- a/Tools/gdb/libpython.py +++ b/Tools/gdb/libpython.py @@ -1753,8 +1753,11 @@ class Frame(object): return (name == 'take_gil') def is_gc_collect(self): - '''Is this frame gc_collect_main() within the garbage-collector?''' - return self._gdbframe.name() in ('collect', 'gc_collect_main') + '''Is this frame a collector within the garbage-collector?''' + return self._gdbframe.name() in ( + 'collect', 'gc_collect_full', 'gc_collect_main', + 'gc_collect_young', 'gc_collect_increment' + ) def get_pyop(self): try: