python (3.11.7)
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 #define _PyGC_Head_UNUSED PyGC_Head
24
25 /* True if the object is currently tracked by the GC. */
26 #define _PyObject_GC_IS_TRACKED(o) (_Py_AS_GC(o)->_gc_next != 0)
27
28 /* True if the object may be tracked by the GC in the future, or already is.
29 This can be useful to implement some optimizations. */
30 #define _PyObject_GC_MAY_BE_TRACKED(obj) \
31 (PyObject_IS_GC(obj) && \
32 (!PyTuple_CheckExact(obj) || _PyObject_GC_IS_TRACKED(obj)))
33
34
35 /* Bit flags for _gc_prev */
36 /* Bit 0 is set when tp_finalize is called */
37 #define _PyGC_PREV_MASK_FINALIZED (1)
38 /* Bit 1 is set when the object is in generation which is GCed currently. */
39 #define _PyGC_PREV_MASK_COLLECTING (2)
40 /* The (N-2) most significant bits contain the real address. */
41 #define _PyGC_PREV_SHIFT (2)
42 #define _PyGC_PREV_MASK (((uintptr_t) -1) << _PyGC_PREV_SHIFT)
43
44 // Lowest bit of _gc_next is used for flags only in GC.
45 // But it is always 0 for normal code.
46 #define _PyGCHead_NEXT(g) ((PyGC_Head*)(g)->_gc_next)
47 #define _PyGCHead_SET_NEXT(g, p) _Py_RVALUE((g)->_gc_next = (uintptr_t)(p))
48
49 // Lowest two bits of _gc_prev is used for _PyGC_PREV_MASK_* flags.
50 #define _PyGCHead_PREV(g) ((PyGC_Head*)((g)->_gc_prev & _PyGC_PREV_MASK))
51 #define _PyGCHead_SET_PREV(g, p) do { \
52 assert(((uintptr_t)p & ~_PyGC_PREV_MASK) == 0); \
53 (g)->_gc_prev = ((g)->_gc_prev & ~_PyGC_PREV_MASK) \
54 | ((uintptr_t)(p)); \
55 } while (0)
56
57 #define _PyGCHead_FINALIZED(g) \
58 (((g)->_gc_prev & _PyGC_PREV_MASK_FINALIZED) != 0)
59 #define _PyGCHead_SET_FINALIZED(g) \
60 _Py_RVALUE((g)->_gc_prev |= _PyGC_PREV_MASK_FINALIZED)
61
62 #define _PyGC_FINALIZED(o) \
63 _PyGCHead_FINALIZED(_Py_AS_GC(o))
64 #define _PyGC_SET_FINALIZED(o) \
65 _PyGCHead_SET_FINALIZED(_Py_AS_GC(o))
66
67
68 /* GC runtime state */
69
70 /* If we change this, we need to change the default value in the
71 signature of gc.collect. */
72 #define NUM_GENERATIONS 3
73 /*
74 NOTE: about untracking of mutable objects.
75
76 Certain types of container cannot participate in a reference cycle, and
77 so do not need to be tracked by the garbage collector. Untracking these
78 objects reduces the cost of garbage collections. However, determining
79 which objects may be untracked is not free, and the costs must be
80 weighed against the benefits for garbage collection.
81
82 There are two possible strategies for when to untrack a container:
83
84 i) When the container is created.
85 ii) When the container is examined by the garbage collector.
86
87 Tuples containing only immutable objects (integers, strings etc, and
88 recursively, tuples of immutable objects) do not need to be tracked.
89 The interpreter creates a large number of tuples, many of which will
90 not survive until garbage collection. It is therefore not worthwhile
91 to untrack eligible tuples at creation time.
92
93 Instead, all tuples except the empty tuple are tracked when created.
94 During garbage collection it is determined whether any surviving tuples
95 can be untracked. A tuple can be untracked if all of its contents are
96 already not tracked. Tuples are examined for untracking in all garbage
97 collection cycles. It may take more than one cycle to untrack a tuple.
98
99 Dictionaries containing only immutable objects also do not need to be
100 tracked. Dictionaries are untracked when created. If a tracked item is
101 inserted into a dictionary (either as a key or value), the dictionary
102 becomes tracked. During a full garbage collection (all generations),
103 the collector will untrack any dictionaries whose contents are not
104 tracked.
105
106 The module provides the python function is_tracked(obj), which returns
107 the CURRENT tracking status of the object. Subsequent garbage
108 collections may change the tracking status of the object.
109
110 Untracking of certain containers was introduced in issue #4688, and
111 the algorithm was refined in response to issue #14775.
112 */
113
114 struct gc_generation {
115 PyGC_Head head;
116 int threshold; /* collection threshold */
117 int count; /* count of allocations or collections of younger
118 generations */
119 };
120
121 /* Running stats per generation */
122 struct gc_generation_stats {
123 /* total number of collections */
124 Py_ssize_t collections;
125 /* total number of collected objects */
126 Py_ssize_t collected;
127 /* total number of uncollectable objects (put into gc.garbage) */
128 Py_ssize_t uncollectable;
129 };
130
131 struct _gc_runtime_state {
132 /* List of objects that still need to be cleaned up, singly linked
133 * via their gc headers' gc_prev pointers. */
134 PyObject *trash_delete_later;
135 /* Current call-stack depth of tp_dealloc calls. */
136 int trash_delete_nesting;
137
138 /* Is automatic collection enabled? */
139 int enabled;
140 int debug;
141 /* linked lists of container objects */
142 struct gc_generation generations[NUM_GENERATIONS];
143 PyGC_Head *generation0;
144 /* a permanent generation which won't be collected */
145 struct gc_generation permanent_generation;
146 struct gc_generation_stats generation_stats[NUM_GENERATIONS];
147 /* true if we are currently running the collector */
148 int collecting;
149 /* list of uncollectable objects */
150 PyObject *garbage;
151 /* a list of callbacks to be invoked when collection is performed */
152 PyObject *callbacks;
153 /* This is the number of objects that survived the last full
154 collection. It approximates the number of long lived objects
155 tracked by the GC.
156
157 (by "full collection", we mean a collection of the oldest
158 generation). */
159 Py_ssize_t long_lived_total;
160 /* This is the number of objects that survived all "non-full"
161 collections, and are awaiting to undergo a full collection for
162 the first time. */
163 Py_ssize_t long_lived_pending;
164 };
165
166
167 extern void _PyGC_InitState(struct _gc_runtime_state *);
168
169 extern Py_ssize_t _PyGC_CollectNoFail(PyThreadState *tstate);
170
171
172 // Functions to clear types free lists
173 extern void _PyTuple_ClearFreeList(PyInterpreterState *interp);
174 extern void _PyFloat_ClearFreeList(PyInterpreterState *interp);
175 extern void _PyList_ClearFreeList(PyInterpreterState *interp);
176 extern void _PyDict_ClearFreeList(PyInterpreterState *interp);
177 extern void _PyAsyncGen_ClearFreeLists(PyInterpreterState *interp);
178 extern void _PyContext_ClearFreeList(PyInterpreterState *interp);
179
180 #ifdef __cplusplus
181 }
182 #endif
183 #endif /* !Py_INTERNAL_GC_H */
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