From 8a3c499ffe7e15297dd4c0b446a0b97b4d32108a Mon Sep 17 00:00:00 2001 From: Mark Shannon Date: Wed, 7 Feb 2024 12:38:34 +0000 Subject: [PATCH] GH-108362: Revert "GH-108362: Incremental GC implementation (GH-108038)" (#115132) Revert "GH-108362: Incremental GC implementation (GH-108038)" This reverts commit 36518e69d74607e5f094ce55286188e4545a947d. --- 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, 446 insertions(+), 701 deletions(-) delete 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 c75d4406531..2ac5afa8ce6 100644 --- a/Doc/whatsnew/3.13.rst +++ b/Doc/whatsnew/3.13.rst @@ -92,10 +92,6 @@ 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 ----------------------- @@ -105,13 +101,6 @@ 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 ====================== @@ -257,29 +246,6 @@ 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 aeb07238fc8..8d0bc2a218e 100644 --- a/Include/internal/pycore_gc.h +++ b/Include/internal/pycore_gc.h @@ -88,15 +88,11 @@ static inline void _PyObject_GC_SET_SHARED(PyObject *op) { /* 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 - -/* Bit 0 is set if the object belongs to old space 1 */ -#define _PyGC_NEXT_MASK_OLD_SPACE_1 1 - +#define _PyGC_PREV_MASK_COLLECTING (2) /* 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 */ @@ -122,13 +118,11 @@ 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 & _PyGC_PREV_MASK; + uintptr_t next = gc->_gc_next; return (PyGC_Head*)next; } static inline void _PyGCHead_SET_NEXT(PyGC_Head *gc, PyGC_Head *next) { - uintptr_t unext = (uintptr_t)next; - assert((unext & ~_PyGC_PREV_MASK) == 0); - gc->_gc_next = (gc->_gc_next & ~_PyGC_PREV_MASK) | unext; + gc->_gc_next = (uintptr_t)next; } // Lowest two bits of _gc_prev is used for _PyGC_PREV_MASK_* flags. @@ -136,7 +130,6 @@ 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); @@ -222,13 +215,6 @@ 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 */ @@ -250,8 +236,8 @@ struct _gc_runtime_state { int enabled; int debug; /* linked lists of container objects */ - struct gc_generation young; - struct gc_generation old[2]; + struct gc_generation generations[NUM_GENERATIONS]; + PyGC_Head *generation0; /* a permanent generation which won't be collected */ struct gc_generation permanent_generation; struct gc_generation_stats generation_stats[NUM_GENERATIONS]; @@ -264,20 +250,22 @@ 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; - - Py_ssize_t work_to_do; - /* Which of the old spaces is the visited space */ - int visited_space; + /* 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; }; extern void _PyGC_InitState(struct _gc_runtime_state *); -extern Py_ssize_t _PyGC_Collect(PyThreadState *tstate, int generation, _PyGC_Reason reason); -extern void _PyGC_CollectNoFail(PyThreadState *tstate); +extern Py_ssize_t _PyGC_Collect(PyThreadState *tstate, int generation, + _PyGC_Reason reason); +extern Py_ssize_t _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 efa712c4a0b..34a83ea228e 100644 --- a/Include/internal/pycore_object.h +++ b/Include/internal/pycore_object.h @@ -125,7 +125,19 @@ static inline void _Py_RefcntAdd(PyObject* op, Py_ssize_t n) } #define _Py_RefcntAdd(op, n) _Py_RefcntAdd(_PyObject_CAST(op), n) -extern void _Py_SetImmortal(PyObject *op); +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)) // Makes an immortal object mortal again with the specified refcnt. Should only // be used during runtime finalization. @@ -313,12 +325,11 @@ static inline void _PyObject_GC_TRACK( filename, lineno, __func__); PyInterpreterState *interp = _PyInterpreterState_GET(); - PyGC_Head *generation0 = &interp->gc.young.head; + PyGC_Head *generation0 = interp->gc.generation0; 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 2ad1347ad48..571a7d612c9 100644 --- a/Include/internal/pycore_runtime_init.h +++ b/Include/internal/pycore_runtime_init.h @@ -162,12 +162,12 @@ extern PyTypeObject _PyExc_MemoryError; }, \ .gc = { \ .enabled = 1, \ - .young = { .threshold = 2000, }, \ - .old = { \ + .generations = { \ + /* .head is set in _PyGC_InitState(). */ \ + { .threshold = 700, }, \ + { .threshold = 10, }, \ { .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 0002852fce9..b01f344cb14 100644 --- a/Lib/test/test_gc.py +++ b/Lib/test/test_gc.py @@ -383,11 +383,19 @@ class GCTests(unittest.TestCase): # each call to collect(N) x = [] gc.collect(0) - # x is now in the old gen + # x is now in gen 1 a, b, c = gc.get_count() - # We don't check a since its exact values depends on + 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 # 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: @@ -838,6 +846,16 @@ 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 deleted file mode 100644 index 1fe4e0f41e1..00000000000 --- a/Misc/NEWS.d/next/Core and Builtins/2024-01-07-04-22-51.gh-issue-108362.oB9Gcf.rst +++ /dev/null @@ -1,13 +0,0 @@ -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 3a42654b41b..a2b66b9b78c 100644 --- a/Modules/gcmodule.c +++ b/Modules/gcmodule.c @@ -158,12 +158,17 @@ gc_set_threshold_impl(PyObject *module, int threshold0, int group_right_1, { GCState *gcstate = get_gc_state(); - gcstate->young.threshold = threshold0; + gcstate->generations[0].threshold = threshold0; if (group_right_1) { - gcstate->old[0].threshold = threshold1; + gcstate->generations[1].threshold = threshold1; } if (group_right_2) { - gcstate->old[1].threshold = threshold2; + 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; + } } Py_RETURN_NONE; } @@ -180,9 +185,9 @@ gc_get_threshold_impl(PyObject *module) { GCState *gcstate = get_gc_state(); return Py_BuildValue("(iii)", - gcstate->young.threshold, - gcstate->old[0].threshold, - 0); + gcstate->generations[0].threshold, + gcstate->generations[1].threshold, + gcstate->generations[2].threshold); } /*[clinic input] @@ -197,9 +202,9 @@ gc_get_count_impl(PyObject *module) { GCState *gcstate = get_gc_state(); return Py_BuildValue("(iii)", - gcstate->young.count, - gcstate->old[gcstate->visited_space].count, - gcstate->old[gcstate->visited_space^1].count); + gcstate->generations[0].count, + gcstate->generations[1].count, + gcstate->generations[2].count); } /*[clinic input] diff --git a/Objects/object.c b/Objects/object.c index 7247eb21df6..bbf7f98ae3d 100644 --- a/Objects/object.c +++ b/Objects/object.c @@ -2387,21 +2387,6 @@ _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 661d96a968f..581d6ad2408 100644 --- a/Objects/structseq.c +++ b/Objects/structseq.c @@ -603,9 +603,6 @@ _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; @@ -621,7 +618,7 @@ _PyStructSequence_InitBuiltinWithFlags(PyInterpreterState *interp, } initialize_static_fields(type, desc, members, tp_flags); - _Py_SetImmortal((PyObject *)type); + _Py_SetImmortal(type); } #ifndef NDEBUG else { diff --git a/Python/gc.c b/Python/gc.c index cda12ff7fbc..46646760291 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 2 +#define NEXT_MASK_UNREACHABLE (1) #define AS_GC(op) _Py_AS_GC(op) #define FROM_GC(gc) _Py_FROM_GC(gc) @@ -95,48 +95,9 @@ 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; -} -static inline int -flip_old_space(int space) -{ - assert(space == 0 || space == 1); - return space ^ _PyGC_NEXT_MASK_OLD_SPACE_1; -} +#define GEN_HEAD(gcstate, n) (&(gcstate)->generations[n].head) -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) @@ -155,12 +116,11 @@ _PyGC_InitState(GCState *gcstate) GEN.head._gc_prev = (uintptr_t)&GEN.head; \ } while (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]); + 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); INIT_HEAD(gcstate->permanent_generation); #undef INIT_HEAD @@ -258,7 +218,6 @@ 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 @@ -316,8 +275,6 @@ 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); @@ -386,8 +343,8 @@ enum flagstates {collecting_clear_unreachable_clear, static void validate_list(PyGC_Head *head, enum flagstates flags) { - assert((head->_gc_prev & ~_PyGC_PREV_MASK) == 0); - assert((head->_gc_next & ~_PyGC_PREV_MASK) == 0); + assert((head->_gc_prev & PREV_MASK_COLLECTING) == 0); + assert((head->_gc_next & NEXT_MASK_UNREACHABLE) == 0); uintptr_t prev_value = 0, next_value = 0; switch (flags) { case collecting_clear_unreachable_clear: @@ -409,7 +366,7 @@ 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 = GC_NEXT(gc); + PyGC_Head *truenext = (PyGC_Head *)(gc->_gc_next & ~NEXT_MASK_UNREACHABLE); assert(truenext != NULL); assert(trueprev == prev); assert((gc->_gc_prev & PREV_MASK_COLLECTING) == prev_value); @@ -419,44 +376,8 @@ 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 ***/ @@ -473,7 +394,15 @@ update_refs(PyGC_Head *containers) while (gc != containers) { next = GC_NEXT(gc); - assert(!_Py_IsImmortal(FROM_GC(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; + } 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 @@ -571,13 +500,12 @@ 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 = GC_NEXT(gc); + PyGC_Head *next = (PyGC_Head*)(gc->_gc_next & ~NEXT_MASK_UNREACHABLE); _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 flag bits - gc->_gc_next &= ~NEXT_MASK_UNREACHABLE; + prev->_gc_next = gc->_gc_next; // copy NEXT_MASK_UNREACHABLE _PyGCHead_SET_PREV(next, prev); gc_list_append(gc, reachable); @@ -629,9 +557,6 @@ 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 @@ -677,18 +602,17 @@ 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 = flags | (uintptr_t)gc; + last->_gc_next = (NEXT_MASK_UNREACHABLE | (uintptr_t)gc); _PyGCHead_SET_PREV(gc, last); - gc->_gc_next = flags | (uintptr_t)unreachable; + gc->_gc_next = (NEXT_MASK_UNREACHABLE | (uintptr_t)unreachable); unreachable->_gc_prev = (uintptr_t)gc; } - gc = _PyGCHead_NEXT(prev); + gc = (PyGC_Head*)prev->_gc_next; } // 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 &= _PyGC_PREV_MASK; + unreachable->_gc_next &= ~NEXT_MASK_UNREACHABLE; } static void @@ -745,8 +669,8 @@ 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); @@ -765,8 +689,8 @@ 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); } @@ -1099,6 +1023,25 @@ 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: @@ -1172,6 +1115,7 @@ 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); @@ -1210,340 +1154,21 @@ 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 -do_gc_callback(GCState *gcstate, const char *phase, - int generation, struct gc_collection_stats *stats) +invoke_gc_callback(PyThreadState *tstate, const char *phase, + int generation, Py_ssize_t collected, + Py_ssize_t uncollectable) { - assert(!PyErr_Occurred()); + assert(!_PyErr_Occurred(tstate)); + + /* we may get called very early */ + GCState *gcstate = &tstate->interp->gc; + if (gcstate->callbacks == NULL) { + return; + } /* The local variable cannot be rebound, check it for sanity */ assert(PyList_CheckExact(gcstate->callbacks)); @@ -1551,8 +1176,8 @@ do_gc_callback(GCState *gcstate, const char *phase, if (PyList_GET_SIZE(gcstate->callbacks) != 0) { info = Py_BuildValue("{sisnsn}", "generation", generation, - "collected", stats->collected, - "uncollectable", stats->uncollectable); + "collected", collected, + "uncollectable", uncollectable); if (info == NULL) { PyErr_FormatUnraisable("Exception ignored on invoking gc callbacks"); return; @@ -1581,17 +1206,275 @@ do_gc_callback(GCState *gcstate, const char *phase, } Py_DECREF(phase_obj); Py_XDECREF(info); - assert(!PyErr_Occurred()); + assert(!_PyErr_Occurred(tstate)); } -static void -invoke_gc_callback(GCState *gcstate, const char *phase, - int generation, struct gc_collection_stats *stats) + +/* 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) { - if (gcstate->callbacks == NULL) { - return; + 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; + } } - do_gc_callback(gcstate, phase, generation, stats); + 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; } static int @@ -1666,7 +1549,7 @@ _PyGC_GetObjects(PyInterpreterState *interp, Py_ssize_t generation) } } else { - if (append_objects(result, GEN_HEAD(gcstate, (int)generation))) { + if (append_objects(result, GEN_HEAD(gcstate, generation))) { goto error; } } @@ -1681,16 +1564,10 @@ void _PyGC_Freeze(PyInterpreterState *interp) { GCState *gcstate = &interp->gc; - 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); + for (int i = 0; i < NUM_GENERATIONS; ++i) { + gc_list_merge(GEN_HEAD(gcstate, i), &gcstate->permanent_generation.head); + gcstate->generations[i].count = 0; + } } void @@ -1698,8 +1575,7 @@ _PyGC_Unfreeze(PyInterpreterState *interp) { GCState *gcstate = &interp->gc; gc_list_merge(&gcstate->permanent_generation.head, - &gcstate->old[0].head); - validate_old(gcstate); + GEN_HEAD(gcstate, NUM_GENERATIONS-1)); } Py_ssize_t @@ -1735,100 +1611,32 @@ PyGC_IsEnabled(void) return gcstate->enabled; } -// Show stats for objects in each generations -static void -show_stats_each_generations(GCState *gcstate) +/* Public API to invoke gc.collect() from C */ +Py_ssize_t +PyGC_Collect(void) { - char buf[100]; - size_t pos = 0; + PyThreadState *tstate = _PyThreadState_GET(); + GCState *gcstate = &tstate->interp->gc; - 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))); + if (!gcstate->enabled) { + return 0; } - 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 n; + PyObject *exc = _PyErr_GetRaisedException(tstate); + n = gc_collect_main(tstate, NUM_GENERATIONS - 1, _Py_GC_REASON_MANUAL); + _PyErr_SetRaisedException(tstate, exc); + + return n; } Py_ssize_t _PyGC_Collect(PyThreadState *tstate, int generation, _PyGC_Reason 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; + return gc_collect_main(tstate, generation, reason); } -/* 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, @@ -1837,7 +1645,7 @@ _PyGC_CollectNoFail(PyThreadState *tstate) during interpreter shutdown (and then never finish it). See http://bugs.python.org/issue8713#msg195178 for an example. */ - _PyGC_Collect(_PyThreadState_GET(), 2, _Py_GC_REASON_SHUTDOWN); + return gc_collect_main(tstate, NUM_GENERATIONS - 1, _Py_GC_REASON_SHUTDOWN); } void @@ -1972,10 +1780,10 @@ _PyObject_GC_Link(PyObject *op) GCState *gcstate = &tstate->interp->gc; g->_gc_next = 0; g->_gc_prev = 0; - gcstate->young.count++; /* number of allocated GC objects */ - if (gcstate->young.count > gcstate->young.threshold && + gcstate->generations[0].count++; /* number of allocated GC objects */ + if (gcstate->generations[0].count > gcstate->generations[0].threshold && gcstate->enabled && - gcstate->young.threshold && + gcstate->generations[0].threshold && !_Py_atomic_load_int_relaxed(&gcstate->collecting) && !_PyErr_Occurred(tstate)) { @@ -1986,9 +1794,7 @@ _PyObject_GC_Link(PyObject *op) void _Py_RunGC(PyThreadState *tstate) { - if (tstate->interp->gc.enabled) { - _PyGC_Collect(tstate, 1, _Py_GC_REASON_HEAP); - } + gc_collect_main(tstate, GENERATION_AUTO, _Py_GC_REASON_HEAP); } static PyObject * @@ -2091,8 +1897,8 @@ PyObject_GC_Del(void *op) #endif } GCState *gcstate = get_gc_state(); - if (gcstate->young.count > 0) { - gcstate->young.count--; + if (gcstate->generations[0].count > 0) { + gcstate->generations[0].count--; } PyObject_Free(((char *)op)-presize); } @@ -2115,36 +1921,26 @@ 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; - if (visit_generation(callback, arg, &gcstate->young)) { - goto done; + 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->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 1c4da726866..8fbcdb15109 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->young.threshold = 2000; + gcstate->generations[0].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->young.count); - int threshold = gcstate->young.threshold; + int count = _Py_atomic_load_int_relaxed(&gcstate->generations[0].count); + int threshold = gcstate->generations[0].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->old[0].threshold == 0); + gcstate->generations[1].threshold == 0); } static void @@ -1031,15 +1031,10 @@ gc_collect_main(PyThreadState *tstate, int generation, _PyGC_Reason reason) /* update collection and allocation counters */ if (generation+1 < NUM_GENERATIONS) { - gcstate->old[generation].count += 1; + gcstate->generations[generation+1].count += 1; } for (i = 0; i <= generation; i++) { - if (i == 0) { - gcstate->young.count = 0; - } - else { - gcstate->old[i-1].count = 0; - } + gcstate->generations[i].count = 0; } PyInterpreterState *interp = tstate->interp; @@ -1362,7 +1357,7 @@ _PyGC_Collect(PyThreadState *tstate, int generation, _PyGC_Reason reason) return gc_collect_main(tstate, generation, reason); } -void +Py_ssize_t _PyGC_CollectNoFail(PyThreadState *tstate) { /* Ideally, this function is only called on interpreter shutdown, @@ -1371,7 +1366,7 @@ _PyGC_CollectNoFail(PyThreadState *tstate) during interpreter shutdown (and then never finish it). See http://bugs.python.org/issue8713#msg195178 for an example. */ - gc_collect_main(tstate, NUM_GENERATIONS - 1, _Py_GC_REASON_SHUTDOWN); + return gc_collect_main(tstate, NUM_GENERATIONS - 1, _Py_GC_REASON_SHUTDOWN); } void @@ -1495,7 +1490,7 @@ _PyObject_GC_Link(PyObject *op) { PyThreadState *tstate = _PyThreadState_GET(); GCState *gcstate = &tstate->interp->gc; - gcstate->young.count++; + gcstate->generations[0].count++; if (gc_should_collect(gcstate) && !_Py_atomic_load_int_relaxed(&gcstate->collecting)) @@ -1610,8 +1605,8 @@ PyObject_GC_Del(void *op) #endif } GCState *gcstate = get_gc_state(); - if (gcstate->young.count > 0) { - gcstate->young.count--; + if (gcstate->generations[0].count > 0) { + gcstate->generations[0].count--; } PyObject_Free(((char *)op)-presize); } diff --git a/Python/import.c b/Python/import.c index dfc5ec1f2f2..2fd0c08a6bb 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((PyObject *)def); + _Py_SetImmortal(def); } res = 0; diff --git a/Tools/gdb/libpython.py b/Tools/gdb/libpython.py index 96b891481d9..483f28b46df 100755 --- a/Tools/gdb/libpython.py +++ b/Tools/gdb/libpython.py @@ -1753,11 +1753,8 @@ class Frame(object): return (name == 'take_gil') def is_gc_collect(self): - '''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' - ) + '''Is this frame gc_collect_main() within the garbage-collector?''' + return self._gdbframe.name() in ('collect', 'gc_collect_main') def get_pyop(self): try: