1 #ifndef Py_INTERNAL_GC_H 2 #define Py_INTERNAL_GC_H 3 #ifdef __cplusplus 4 extern "C" { 5 #endif 6 7 #ifndef Py_BUILD_CORE 8 # error "this header requires Py_BUILD_CORE define" 9 #endif 10 11 /* GC information is stored BEFORE the object structure. */ 12 typedef struct { 13 // Pointer to next object in the list. 14 // 0 means the object is not tracked 15 uintptr_t _gc_next; 16 17 // Pointer to previous object in the list. 18 // Lowest two bits are used for flags documented later. 19 uintptr_t _gc_prev; 20 } PyGC_Head; 21 22 #define _Py_AS_GC(o) ((PyGC_Head *)(o)-1) 23 24 /* True if the object is currently tracked by the GC. */ 25 #define _PyObject_GC_IS_TRACKED(o) (_Py_AS_GC(o)->_gc_next != 0) 26 27 /* True if the object may be tracked by the GC in the future, or already is. 28 This can be useful to implement some optimizations. */ 29 #define _PyObject_GC_MAY_BE_TRACKED(obj) \ 30 (PyObject_IS_GC(obj) && \ 31 (!PyTuple_CheckExact(obj) || _PyObject_GC_IS_TRACKED(obj))) 32 33 34 /* Bit flags for _gc_prev */ 35 /* Bit 0 is set when tp_finalize is called */ 36 #define _PyGC_PREV_MASK_FINALIZED (1) 37 /* Bit 1 is set when the object is in generation which is GCed currently. */ 38 #define _PyGC_PREV_MASK_COLLECTING (2) 39 /* The (N-2) most significant bits contain the real address. */ 40 #define _PyGC_PREV_SHIFT (2) 41 #define _PyGC_PREV_MASK (((uintptr_t) -1) << _PyGC_PREV_SHIFT) 42 43 // Lowest bit of _gc_next is used for flags only in GC. 44 // But it is always 0 for normal code. 45 #define _PyGCHead_NEXT(g) ((PyGC_Head*)(g)->_gc_next) 46 #define _PyGCHead_SET_NEXT(g, p) ((g)->_gc_next = (uintptr_t)(p)) 47 48 // Lowest two bits of _gc_prev is used for _PyGC_PREV_MASK_* flags. 49 #define _PyGCHead_PREV(g) ((PyGC_Head*)((g)->_gc_prev & _PyGC_PREV_MASK)) 50 #define _PyGCHead_SET_PREV(g, p) do { \ 51 assert(((uintptr_t)p & ~_PyGC_PREV_MASK) == 0); \ 52 (g)->_gc_prev = ((g)->_gc_prev & ~_PyGC_PREV_MASK) \ 53 | ((uintptr_t)(p)); \ 54 } while (0) 55 56 #define _PyGCHead_FINALIZED(g) \ 57 (((g)->_gc_prev & _PyGC_PREV_MASK_FINALIZED) != 0) 58 #define _PyGCHead_SET_FINALIZED(g) \ 59 ((g)->_gc_prev |= _PyGC_PREV_MASK_FINALIZED) 60 61 #define _PyGC_FINALIZED(o) \ 62 _PyGCHead_FINALIZED(_Py_AS_GC(o)) 63 #define _PyGC_SET_FINALIZED(o) \ 64 _PyGCHead_SET_FINALIZED(_Py_AS_GC(o)) 65 66 67 /* GC runtime state */ 68 69 /* If we change this, we need to change the default value in the 70 signature of gc.collect. */ 71 #define NUM_GENERATIONS 3 72 /* 73 NOTE: about untracking of mutable objects. 74 75 Certain types of container cannot participate in a reference cycle, and 76 so do not need to be tracked by the garbage collector. Untracking these 77 objects reduces the cost of garbage collections. However, determining 78 which objects may be untracked is not free, and the costs must be 79 weighed against the benefits for garbage collection. 80 81 There are two possible strategies for when to untrack a container: 82 83 i) When the container is created. 84 ii) When the container is examined by the garbage collector. 85 86 Tuples containing only immutable objects (integers, strings etc, and 87 recursively, tuples of immutable objects) do not need to be tracked. 88 The interpreter creates a large number of tuples, many of which will 89 not survive until garbage collection. It is therefore not worthwhile 90 to untrack eligible tuples at creation time. 91 92 Instead, all tuples except the empty tuple are tracked when created. 93 During garbage collection it is determined whether any surviving tuples 94 can be untracked. A tuple can be untracked if all of its contents are 95 already not tracked. Tuples are examined for untracking in all garbage 96 collection cycles. It may take more than one cycle to untrack a tuple. 97 98 Dictionaries containing only immutable objects also do not need to be 99 tracked. Dictionaries are untracked when created. If a tracked item is 100 inserted into a dictionary (either as a key or value), the dictionary 101 becomes tracked. During a full garbage collection (all generations), 102 the collector will untrack any dictionaries whose contents are not 103 tracked. 104 105 The module provides the python function is_tracked(obj), which returns 106 the CURRENT tracking status of the object. Subsequent garbage 107 collections may change the tracking status of the object. 108 109 Untracking of certain containers was introduced in issue #4688, and 110 the algorithm was refined in response to issue #14775. 111 */ 112 113 struct gc_generation { 114 PyGC_Head head; 115 int threshold; /* collection threshold */ 116 int count; /* count of allocations or collections of younger 117 generations */ 118 }; 119 120 /* Running stats per generation */ 121 struct gc_generation_stats { 122 /* total number of collections */ 123 Py_ssize_t collections; 124 /* total number of collected objects */ 125 Py_ssize_t collected; 126 /* total number of uncollectable objects (put into gc.garbage) */ 127 Py_ssize_t uncollectable; 128 }; 129 130 struct _gc_runtime_state { 131 /* List of objects that still need to be cleaned up, singly linked 132 * via their gc headers' gc_prev pointers. */ 133 PyObject *trash_delete_later; 134 /* Current call-stack depth of tp_dealloc calls. */ 135 int trash_delete_nesting; 136 137 int enabled; 138 int debug; 139 /* linked lists of container objects */ 140 struct gc_generation generations[NUM_GENERATIONS]; 141 PyGC_Head *generation0; 142 /* a permanent generation which won't be collected */ 143 struct gc_generation permanent_generation; 144 struct gc_generation_stats generation_stats[NUM_GENERATIONS]; 145 /* true if we are currently running the collector */ 146 int collecting; 147 /* list of uncollectable objects */ 148 PyObject *garbage; 149 /* a list of callbacks to be invoked when collection is performed */ 150 PyObject *callbacks; 151 /* This is the number of objects that survived the last full 152 collection. It approximates the number of long lived objects 153 tracked by the GC. 154 155 (by "full collection", we mean a collection of the oldest 156 generation). */ 157 Py_ssize_t long_lived_total; 158 /* This is the number of objects that survived all "non-full" 159 collections, and are awaiting to undergo a full collection for 160 the first time. */ 161 Py_ssize_t long_lived_pending; 162 }; 163 164 extern void _PyGC_InitState(struct _gc_runtime_state *); 165 166 extern Py_ssize_t _PyGC_CollectNoFail(PyThreadState *tstate); 167 168 169 // Functions to clear types free lists 170 extern void _PyFrame_ClearFreeList(PyInterpreterState *interp); 171 extern void _PyTuple_ClearFreeList(PyInterpreterState *interp); 172 extern void _PyFloat_ClearFreeList(PyInterpreterState *interp); 173 extern void _PyList_ClearFreeList(PyInterpreterState *interp); 174 extern void _PyDict_ClearFreeList(PyInterpreterState *interp); 175 extern void _PyAsyncGen_ClearFreeLists(PyInterpreterState *interp); 176 extern void _PyContext_ClearFreeList(PyInterpreterState *interp); 177 178 #ifdef __cplusplus 179 } 180 #endif 181 #endif /* !Py_INTERNAL_GC_H */ 182