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       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                 : 2564317865 : static inline PyGC_Head* _Py_AS_GC(PyObject *op) {
      23                 : 2564317865 :     return (_Py_CAST(PyGC_Head*, op) - 1);
      24                 :            : }
      25                 :            : #define _PyGC_Head_UNUSED PyGC_Head
      26                 :            : 
      27                 :            : /* True if the object is currently tracked by the GC. */
      28                 : 1170426733 : static inline int _PyObject_GC_IS_TRACKED(PyObject *op) {
      29                 : 1170426733 :     PyGC_Head *gc = _Py_AS_GC(op);
      30                 : 1170426733 :     return (gc->_gc_next != 0);
      31                 :            : }
      32                 :            : #define _PyObject_GC_IS_TRACKED(op) _PyObject_GC_IS_TRACKED(_Py_CAST(PyObject*, op))
      33                 :            : 
      34                 :            : /* True if the object may be tracked by the GC in the future, or already is.
      35                 :            :    This can be useful to implement some optimizations. */
      36                 :  461127744 : static inline int _PyObject_GC_MAY_BE_TRACKED(PyObject *obj) {
      37         [ +  + ]:  461127744 :     if (!PyObject_IS_GC(obj)) {
      38                 :  362327101 :         return 0;
      39                 :            :     }
      40         [ +  + ]:   98800643 :     if (PyTuple_CheckExact(obj)) {
      41                 :   11414995 :         return _PyObject_GC_IS_TRACKED(obj);
      42                 :            :     }
      43                 :   87385648 :     return 1;
      44                 :            : }
      45                 :            : 
      46                 :            : 
      47                 :            : /* Bit flags for _gc_prev */
      48                 :            : /* Bit 0 is set when tp_finalize is called */
      49                 :            : #define _PyGC_PREV_MASK_FINALIZED  (1)
      50                 :            : /* Bit 1 is set when the object is in generation which is GCed currently. */
      51                 :            : #define _PyGC_PREV_MASK_COLLECTING (2)
      52                 :            : /* The (N-2) most significant bits contain the real address. */
      53                 :            : #define _PyGC_PREV_SHIFT           (2)
      54                 :            : #define _PyGC_PREV_MASK            (((uintptr_t) -1) << _PyGC_PREV_SHIFT)
      55                 :            : 
      56                 :            : // Lowest bit of _gc_next is used for flags only in GC.
      57                 :            : // But it is always 0 for normal code.
      58                 : 3316727227 : static inline PyGC_Head* _PyGCHead_NEXT(PyGC_Head *gc) {
      59                 : 3316727227 :     uintptr_t next = gc->_gc_next;
      60                 : 3316727227 :     return _Py_CAST(PyGC_Head*, next);
      61                 :            : }
      62                 : 2259749464 : static inline void _PyGCHead_SET_NEXT(PyGC_Head *gc, PyGC_Head *next) {
      63                 : 2259749464 :     gc->_gc_next = _Py_CAST(uintptr_t, next);
      64                 : 2259749464 : }
      65                 :            : 
      66                 :            : // Lowest two bits of _gc_prev is used for _PyGC_PREV_MASK_* flags.
      67                 :  905046473 : static inline PyGC_Head* _PyGCHead_PREV(PyGC_Head *gc) {
      68                 :  905046473 :     uintptr_t prev = (gc->_gc_prev & _PyGC_PREV_MASK);
      69                 :  905046473 :     return _Py_CAST(PyGC_Head*, prev);
      70                 :            : }
      71                 : 2214724981 : static inline void _PyGCHead_SET_PREV(PyGC_Head *gc, PyGC_Head *prev) {
      72                 : 2214724981 :     uintptr_t uprev = _Py_CAST(uintptr_t, prev);
      73                 :            :     assert((uprev & ~_PyGC_PREV_MASK) == 0);
      74                 : 2214724981 :     gc->_gc_prev = ((gc->_gc_prev & ~_PyGC_PREV_MASK) | uprev);
      75                 : 2214724981 : }
      76                 :            : 
      77                 :   45057092 : static inline int _PyGCHead_FINALIZED(PyGC_Head *gc) {
      78                 :   45057092 :     return ((gc->_gc_prev & _PyGC_PREV_MASK_FINALIZED) != 0);
      79                 :            : }
      80                 :   22214642 : static inline void _PyGCHead_SET_FINALIZED(PyGC_Head *gc) {
      81                 :   22214642 :     gc->_gc_prev |= _PyGC_PREV_MASK_FINALIZED;
      82                 :   22214642 : }
      83                 :            : 
      84                 :   22416443 : static inline int _PyGC_FINALIZED(PyObject *op) {
      85                 :   22416443 :     PyGC_Head *gc = _Py_AS_GC(op);
      86                 :   22416443 :     return _PyGCHead_FINALIZED(gc);
      87                 :            : }
      88                 :   22190732 : static inline void _PyGC_SET_FINALIZED(PyObject *op) {
      89                 :   22190732 :     PyGC_Head *gc = _Py_AS_GC(op);
      90                 :   22190732 :     _PyGCHead_SET_FINALIZED(gc);
      91                 :   22190732 : }
      92                 :            : 
      93                 :            : 
      94                 :            : /* GC runtime state */
      95                 :            : 
      96                 :            : /* If we change this, we need to change the default value in the
      97                 :            :    signature of gc.collect. */
      98                 :            : #define NUM_GENERATIONS 3
      99                 :            : /*
     100                 :            :    NOTE: about untracking of mutable objects.
     101                 :            : 
     102                 :            :    Certain types of container cannot participate in a reference cycle, and
     103                 :            :    so do not need to be tracked by the garbage collector. Untracking these
     104                 :            :    objects reduces the cost of garbage collections. However, determining
     105                 :            :    which objects may be untracked is not free, and the costs must be
     106                 :            :    weighed against the benefits for garbage collection.
     107                 :            : 
     108                 :            :    There are two possible strategies for when to untrack a container:
     109                 :            : 
     110                 :            :    i) When the container is created.
     111                 :            :    ii) When the container is examined by the garbage collector.
     112                 :            : 
     113                 :            :    Tuples containing only immutable objects (integers, strings etc, and
     114                 :            :    recursively, tuples of immutable objects) do not need to be tracked.
     115                 :            :    The interpreter creates a large number of tuples, many of which will
     116                 :            :    not survive until garbage collection. It is therefore not worthwhile
     117                 :            :    to untrack eligible tuples at creation time.
     118                 :            : 
     119                 :            :    Instead, all tuples except the empty tuple are tracked when created.
     120                 :            :    During garbage collection it is determined whether any surviving tuples
     121                 :            :    can be untracked. A tuple can be untracked if all of its contents are
     122                 :            :    already not tracked. Tuples are examined for untracking in all garbage
     123                 :            :    collection cycles. It may take more than one cycle to untrack a tuple.
     124                 :            : 
     125                 :            :    Dictionaries containing only immutable objects also do not need to be
     126                 :            :    tracked. Dictionaries are untracked when created. If a tracked item is
     127                 :            :    inserted into a dictionary (either as a key or value), the dictionary
     128                 :            :    becomes tracked. During a full garbage collection (all generations),
     129                 :            :    the collector will untrack any dictionaries whose contents are not
     130                 :            :    tracked.
     131                 :            : 
     132                 :            :    The module provides the python function is_tracked(obj), which returns
     133                 :            :    the CURRENT tracking status of the object. Subsequent garbage
     134                 :            :    collections may change the tracking status of the object.
     135                 :            : 
     136                 :            :    Untracking of certain containers was introduced in issue #4688, and
     137                 :            :    the algorithm was refined in response to issue #14775.
     138                 :            : */
     139                 :            : 
     140                 :            : struct gc_generation {
     141                 :            :     PyGC_Head head;
     142                 :            :     int threshold; /* collection threshold */
     143                 :            :     int count; /* count of allocations or collections of younger
     144                 :            :                   generations */
     145                 :            : };
     146                 :            : 
     147                 :            : /* Running stats per generation */
     148                 :            : struct gc_generation_stats {
     149                 :            :     /* total number of collections */
     150                 :            :     Py_ssize_t collections;
     151                 :            :     /* total number of collected objects */
     152                 :            :     Py_ssize_t collected;
     153                 :            :     /* total number of uncollectable objects (put into gc.garbage) */
     154                 :            :     Py_ssize_t uncollectable;
     155                 :            : };
     156                 :            : 
     157                 :            : struct _gc_runtime_state {
     158                 :            :     /* List of objects that still need to be cleaned up, singly linked
     159                 :            :      * via their gc headers' gc_prev pointers.  */
     160                 :            :     PyObject *trash_delete_later;
     161                 :            :     /* Current call-stack depth of tp_dealloc calls. */
     162                 :            :     int trash_delete_nesting;
     163                 :            : 
     164                 :            :     /* Is automatic collection enabled? */
     165                 :            :     int enabled;
     166                 :            :     int debug;
     167                 :            :     /* linked lists of container objects */
     168                 :            :     struct gc_generation generations[NUM_GENERATIONS];
     169                 :            :     PyGC_Head *generation0;
     170                 :            :     /* a permanent generation which won't be collected */
     171                 :            :     struct gc_generation permanent_generation;
     172                 :            :     struct gc_generation_stats generation_stats[NUM_GENERATIONS];
     173                 :            :     /* true if we are currently running the collector */
     174                 :            :     int collecting;
     175                 :            :     /* list of uncollectable objects */
     176                 :            :     PyObject *garbage;
     177                 :            :     /* a list of callbacks to be invoked when collection is performed */
     178                 :            :     PyObject *callbacks;
     179                 :            :     /* This is the number of objects that survived the last full
     180                 :            :        collection. It approximates the number of long lived objects
     181                 :            :        tracked by the GC.
     182                 :            : 
     183                 :            :        (by "full collection", we mean a collection of the oldest
     184                 :            :        generation). */
     185                 :            :     Py_ssize_t long_lived_total;
     186                 :            :     /* This is the number of objects that survived all "non-full"
     187                 :            :        collections, and are awaiting to undergo a full collection for
     188                 :            :        the first time. */
     189                 :            :     Py_ssize_t long_lived_pending;
     190                 :            : };
     191                 :            : 
     192                 :            : 
     193                 :            : extern void _PyGC_InitState(struct _gc_runtime_state *);
     194                 :            : 
     195                 :            : extern Py_ssize_t _PyGC_CollectNoFail(PyThreadState *tstate);
     196                 :            : 
     197                 :            : 
     198                 :            : // Functions to clear types free lists
     199                 :            : extern void _PyTuple_ClearFreeList(PyInterpreterState *interp);
     200                 :            : extern void _PyFloat_ClearFreeList(PyInterpreterState *interp);
     201                 :            : extern void _PyList_ClearFreeList(PyInterpreterState *interp);
     202                 :            : extern void _PyDict_ClearFreeList(PyInterpreterState *interp);
     203                 :            : extern void _PyAsyncGen_ClearFreeLists(PyInterpreterState *interp);
     204                 :            : extern void _PyContext_ClearFreeList(PyInterpreterState *interp);
     205                 :            : 
     206                 :            : #ifdef __cplusplus
     207                 :            : }
     208                 :            : #endif
     209                 :            : #endif /* !Py_INTERNAL_GC_H */