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bpo-33597: Reduce PyGC_Head size (GH-7043)

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INADA Naoki 2018-07-10 17:19:53 +09:00 • committed by GitHub
parent 445f1b35ce
commit 5ac9e6eee5
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4 changed files with 433 additions and 260 deletions
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102
Include/objimpl.h
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@ -251,76 +251,88 @@ PyAPI_FUNC(PyVarObject *) _PyObject_GC_Resize(PyVarObject *, Py_ssize_t);
/* GC information is stored BEFORE the object structure. */
#ifndef Py_LIMITED_API
typedef union _gc_head {
struct {
union _gc_head *gc_next;
union _gc_head *gc_prev;
Py_ssize_t gc_refs;
} gc;
double dummy; /* force worst-case alignment */
typedef struct {
// Pointer to next object in the list.
// 0 means the object is not tracked
uintptr_t _gc_next;
// Pointer to previous object in the list.
// Lowest two bits are used for flags documented later.
uintptr_t _gc_prev;
} PyGC_Head;
extern PyGC_Head *_PyGC_generation0;
#define _Py_AS_GC(o) ((PyGC_Head *)(o)-1)
/* Bit flags for _gc_prev */
/* Bit 0 is set when tp_finalize is called */
#define _PyGC_REFS_MASK_FINALIZED (1 << 0)
/* The (N-1) most significant bits contain the gc state / refcount */
#define _PyGC_REFS_SHIFT (1)
#define _PyGC_REFS_MASK (((size_t) -1) << _PyGC_REFS_SHIFT)
#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)
/* The (N-2) most significant bits contain the real address. */
#define _PyGC_PREV_SHIFT (2)
#define _PyGC_PREV_MASK (((uintptr_t) -1) << _PyGC_PREV_SHIFT)
#define _PyGCHead_REFS(g) ((g)->gc.gc_refs >> _PyGC_REFS_SHIFT)
#define _PyGCHead_SET_REFS(g, v) do { \
(g)->gc.gc_refs = ((g)->gc.gc_refs & ~_PyGC_REFS_MASK) \
| (((size_t)(v)) << _PyGC_REFS_SHIFT); \
} while (0)
#define _PyGCHead_DECREF(g) ((g)->gc.gc_refs -= 1 << _PyGC_REFS_SHIFT)
// Lowest bit of _gc_next is used for flags only in GC.
// But it is always 0 for normal code.
#define _PyGCHead_NEXT(g) ((PyGC_Head*)(g)->_gc_next)
#define _PyGCHead_SET_NEXT(g, p) ((g)->_gc_next = (uintptr_t)(p))
#define _PyGCHead_FINALIZED(g) (((g)->gc.gc_refs & _PyGC_REFS_MASK_FINALIZED) != 0)
#define _PyGCHead_SET_FINALIZED(g, v) do { \
(g)->gc.gc_refs = ((g)->gc.gc_refs & ~_PyGC_REFS_MASK_FINALIZED) \
| (v != 0); \
// Lowest two bits of _gc_prev is used for _PyGC_PREV_MASK_* flags.
#define _PyGCHead_PREV(g) ((PyGC_Head*)((g)->_gc_prev & _PyGC_PREV_MASK))
#define _PyGCHead_SET_PREV(g, p) do { \
assert(((uintptr_t)p & ~_PyGC_PREV_MASK) == 0); \
(g)->_gc_prev = ((g)->_gc_prev & ~_PyGC_PREV_MASK) \
| ((uintptr_t)(p)); \
} while (0)
#define _PyGCHead_FINALIZED(g) (((g)->_gc_prev & _PyGC_PREV_MASK_FINALIZED) != 0)
#define _PyGCHead_SET_FINALIZED(g) ((g)->_gc_prev |= _PyGC_PREV_MASK_FINALIZED)
#define _PyGC_FINALIZED(o) _PyGCHead_FINALIZED(_Py_AS_GC(o))
#define _PyGC_SET_FINALIZED(o, v) _PyGCHead_SET_FINALIZED(_Py_AS_GC(o), v)
#define _PyGC_SET_FINALIZED(o) _PyGCHead_SET_FINALIZED(_Py_AS_GC(o))
#define _PyGC_REFS(o) _PyGCHead_REFS(_Py_AS_GC(o))
#define _PyGC_REFS_UNTRACKED (-2)
#define _PyGC_REFS_REACHABLE (-3)
#define _PyGC_REFS_TENTATIVELY_UNREACHABLE (-4)
/* Tell the GC to track this object. NB: While the object is tracked the
* collector it must be safe to call the ob_traverse method. */
/* Tell the GC to track this object.
*
* NB: While the object is tracked by the collector, it must be safe to call the
* ob_traverse method.
*
* Internal note: _PyGC_generation0->_gc_prev doesn't have any bit flags
* because it's not object header. So we don't use _PyGCHead_PREV() and
* _PyGCHead_SET_PREV() for it to avoid unnecessary bitwise operations.
*/
#define _PyObject_GC_TRACK(o) do { \
PyGC_Head *g = _Py_AS_GC(o); \
if (_PyGCHead_REFS(g) != _PyGC_REFS_UNTRACKED) \
if (g->_gc_next != 0) { \
Py_FatalError("GC object already tracked"); \
_PyGCHead_SET_REFS(g, _PyGC_REFS_REACHABLE); \
g->gc.gc_next = _PyGC_generation0; \
g->gc.gc_prev = _PyGC_generation0->gc.gc_prev; \
g->gc.gc_prev->gc.gc_next = g; \
_PyGC_generation0->gc.gc_prev = g; \
} \
assert((g->_gc_prev & _PyGC_PREV_MASK_COLLECTING) == 0); \
PyGC_Head *last = (PyGC_Head*)(_PyGC_generation0->_gc_prev); \
_PyGCHead_SET_NEXT(last, g); \
_PyGCHead_SET_PREV(g, last); \
_PyGCHead_SET_NEXT(g, _PyGC_generation0); \
_PyGC_generation0->_gc_prev = (uintptr_t)g; \
} while (0);
/* Tell the GC to stop tracking this object.
* gc_next doesn't need to be set to NULL, but doing so is a good
* way to provoke memory errors if calling code is confused.
*
* Internal note: This may be called while GC. So _PyGC_PREV_MASK_COLLECTING must
* be cleared. But _PyGC_PREV_MASK_FINALIZED bit is kept.
*/
#define _PyObject_GC_UNTRACK(o) do { \
PyGC_Head *g = _Py_AS_GC(o); \
assert(_PyGCHead_REFS(g) != _PyGC_REFS_UNTRACKED); \
_PyGCHead_SET_REFS(g, _PyGC_REFS_UNTRACKED); \
g->gc.gc_prev->gc.gc_next = g->gc.gc_next; \
g->gc.gc_next->gc.gc_prev = g->gc.gc_prev; \
g->gc.gc_next = NULL; \
PyGC_Head *prev = _PyGCHead_PREV(g); \
PyGC_Head *next = _PyGCHead_NEXT(g); \
assert(next != NULL); \
_PyGCHead_SET_NEXT(prev, next); \
_PyGCHead_SET_PREV(next, prev); \
g->_gc_next = 0; \
g->_gc_prev &= _PyGC_PREV_MASK_FINALIZED; \
} while (0);
/* True if the object is currently tracked by the GC. */
#define _PyObject_GC_IS_TRACKED(o) \
(_PyGC_REFS(o) != _PyGC_REFS_UNTRACKED)
#define _PyObject_GC_IS_TRACKED(o) (_Py_AS_GC(o)->_gc_next != 0)
/* True if the object may be tracked by the GC in the future, or already is.
This can be useful to implement some optimizations. */