Python 源码剖析（二）【整数对象】
二、整数对象
1、PyIntObject
2、PyIntObject 对象的创建和维护
3、Hack PyIntObject
1、PyIntObject
PyIntObject的定义：
[intobject.h]
typedef struct {
PyObject_HEAD
long ob_ival;
} PyIntObject;
其类型对象为PyInt_Type：
[intobject.c]
PyTypeObject PyInt_Type = {
PyObject_HEAD_INIT(&PyType_Type)
0,
"int",
sizeof(PyIntObject),
0,
(destructor)int_dealloc, /* tp_dealloc */
(printfunc)int_print, /* tp_print */
0, /* tp_getattr */
0, /* tp_setattr */
(cmpfunc)int_compare, /* tp_compare */
(reprfunc)int_repr, /* tp_repr */
&int_as_number, /* tp_as_number */
0, /* tp_as_sequence */
0, /* tp_as_mapping */
(hashfunc)int_hash, /* tp_hash */
0, /* tp_call */
(reprfunc)int_repr, /* tp_str */
PyObject_GenericGetAttr, /* tp_getattro */
0, /* tp_setattro */
0, /* tp_as_buffer */
Py_TPFLAGS_DEFAULT | Py_TPFLAGS_CHECKTYPES | Py_TPFLAGS_BASETYPE, /* tp_flags */
int_doc, /* tp_doc */
0, /* tp_traverse */
0, /* tp_clear */
0, /* tp_richcompare */
0, /* tp_weaklistoffset */
0, /* tp_iter */
0, /* tp_iternext */
int_methods, /* tp_methods */
0, /* tp_members */
0, /* tp_getset */
0, /* tp_base */
0, /* tp_dict */
0, /* tp_descr_get */
0, /* tp_descr_set */
0, /* tp_dictoffset */
0, /* tp_init */
0, /* tp_alloc */
int_new, /* tp_new */
(freefunc)int_free, /* tp_free */
};
可见PyInt_Type保存着PyIntObject的元信息，包括这些操作：
|
int_dealloc |
删除PyIntObject对象 |
|
int_free |
删除PyIntObject对象 |
|
int_repr |
转化成PyString对象 |
|
int_hash |
获得HASH值 |
|
int_print |
打印PyIntObject对象 |
|
int_compare |
比较操作 |
|
int_as_number |
数值操作 |
|
int_methods |
成员函数 |
比较操作代码，其实就是将包装的long进行比较：
[intobject.c]
static int int_compare(PyIntObject *v, PyIntObject *w)
{
register long i = v->ob_ival;
register long j = w->ob_ival;
return (i < j) ? -1 : (i > j) ? 1 : 0;
}
注意int_as_number，其实是一个PyNumberMethods结构体：
[intobject.c]
static PyNumberMethods int_as_number = {
(binaryfunc)int_add, /*nb_add*/
(binaryfunc)int_sub, /*nb_subtract*/
(binaryfunc)int_mul, /*nb_multiply*/
……
(binaryfunc)int_div, /* nb_floor_divide */
int_true_divide, /* nb_true_divide */
0, /* nb_inplace_floor_divide */
0, /* nb_inplace_true_divide */
};
PyNumberMethods定义了38个数值操作，如加法：
[intobject.h]
/* Macro, trading safety for speed */
#define PyInt_AS_LONG(op) (((PyIntObject *)(op))->ob_ival)
[intobject.c]
#define CONVERT_TO_LONG(obj, lng) \
if (PyInt_Check(obj)) { \
lng = PyInt_AS_LONG(obj); \
} \
else { \
Py_INCREF(Py_NotImplemented); \
return Py_NotImplemented; \
}
static PyObject *
int_add(PyIntObject *v, PyIntObject *w)
{
register long a, b, x;
CONVERT_TO_LONG(v, a);
CONVERT_TO_LONG(w, b);
x = a + b;
if ((x^a) >= 0 || (x^b) >= 0)
return PyInt_FromLong(x);
return PyLong_Type.tp_as_number->nb_add((PyObject *)v, (PyObject *)w);
}
如果没有溢出，就返回一个新的PyIntObject，否则返回一个PyLongObject。
2、PyIntObject 对象的创建和维护
2.1、Python创建的途径
有三种途径可获得一个PyIntObject对象：
PyObject *PyInt_FromLong(long ival)PyObject* PyInt_FromString(char *s, char **pend, int base)#ifdef Py_USING_UNICODEPyObject*PyInt_FromUnicode(Py_UNICODE *s, int length, int base)#endif
其中PyInt_FromString时先转成浮点数再调用PyInt_FromLong：
[intobject.c]PyObject* PyInt_FromString(char *s, char **pend, int base){char *end;long x;．．．．．．//convert string to longif (base == 0 && s[0] == '0'){x = (long) PyOS_strtoul(s, &end, base);}elsex = PyOS_strtol(s, &end, base);．．．．．．return PyInt_FromLong(x);}
2.2、小整数对象
频繁申请、释放空间会降低运行效率、产生系统堆内存碎片，影响python性能。因此对于经常使用的整数，python使用对象池技术，并将小整数（对象池保存范围）定位[-5,100)：
[intobject.c]
#ifndef NSMALLPOSINTS#define NSMALLPOSINTS 100#endif#ifndef NSMALLNEGINTS#define NSMALLNEGINTS 5#endif#if NSMALLNEGINTS + NSMALLPOSINTS > 0/* References to small integers are saved in this array so that theycan be shared.The integers that are saved are those in the range-NSMALLNEGINTS (inclusive) to NSMALLPOSINTS (not inclusive).*/static PyIntObject *small_ints[NSMALLNEGINTS + NSMALLPOSINTS];#endif
2.3、大整数对象
对于大整数，pyhton则是使用内存池，提供一个free_list保存，谁需要保存谁：
[intobject.c]
#define BLOCK_SIZE 1000 /* 1K less typical malloc overhead */#define BHEAD_SIZE 8 /* Enough for a 64-bit pointer */#define N_INTOBJECTS ((BLOCK_SIZE - BHEAD_SIZE) / sizeof(PyIntObject))
struct _intblock {struct _intblock *next;PyIntObject objects[N_INTOBJECTS];};
typedef struct _intblock PyIntBlock;
static PyIntBlock *block_list = NULL;static PyIntObject *free_list = NULL;
PyIntBlock的单向列表通过block_list维护，而这些block中的PyIntObject的列表中可以被使用的内存通过free_list来维护（一个block可放82个PyIntObject）。
2.4、添加和删除
看一下产生PyIntObject：
[intobject.c]PyObject* PyInt_FromLong(long ival){register PyIntObject *v;#if NSMALLNEGINTS + NSMALLPOSINTS > 0if (-NSMALLNEGINTS <= ival && ival < NSMALLPOSINTS) {v = small_ints[ival + NSMALLNEGINTS];Py_INCREF(v);#ifdef COUNT_ALLOCSif (ival >= 0)quick_int_allocs++;elsequick_neg_int_allocs++;#endifreturn (PyObject *) v;}#endifif (free_list == NULL) {if ((free_list = fill_free_list()) == NULL)return NULL;}/* Inline PyObject_New */v = free_list;free_list = (PyIntObject *)v->ob_type;PyObject_INIT(v, &PyInt_Type);v->ob_ival = ival;return (PyObject *) v;}
先判断是否为小整数，是的话返回对象池中的小整数；否则转向block_list，调用fill_free_list：
[intobject.c]static PyIntObject* fill_free_list(void){PyIntObject *p, *q;/* Python's object allocator isn't appropriate for large blocks. */p = (PyIntObject *) PyMem_MALLOC(sizeof(PyIntBlock));if (p == NULL)return (PyIntObject *) PyErr_NoMemory();((PyIntBlock *)p)->next = block_list;block_list = (PyIntBlock *)p;/* Link the int objects together, from rear to front, then returnthe address of the last int object in the block. */p = &((PyIntBlock *)p)->objects[0];q = p + N_INTOBJECTS;while (--q > p)q->ob_type = (struct _typeobject *)(q-1);q->ob_type = NULL;return p + N_INTOBJECTS - 1;}
当一个block没被填满时，不会再调用fill_free_list申请新空间，free_list指向可用空间，block_list指向最新创建的PyIntBlock对象。
注意，但某个对象被删除时，free_list会指向该空间，不会造成空间浪费：
[intobject.c]static void int_dealloc(PyIntObject *v){if (PyInt_CheckExact(v)) {v->ob_type = (struct _typeobject *)free_list;free_list = v;}elsev->ob_type->tp_free((PyObject *)v);}
2.5、小整数对象池的初始化
小整数对象池small_ints初始化 _PyInt_Init：
[intobject.c]int _PyInt_Init(void){PyIntObject *v;int ival;#if NSMALLNEGINTS + NSMALLPOSINTS > 0for (ival = -NSMALLNEGINTS; ival < NSMALLPOSINTS; ival++){if (!free_list && (free_list = fill_free_list()) == NULL)return 0;/* PyObject_New is inlined */v = free_list;free_list = (PyIntObject *)v->ob_type;PyObject_INIT(v, &PyInt_Type);v->ob_ival = ival;small_ints[ival + NSMALLNEGINTS] = v;}#endifreturn 1;}
3、Hack PyIntObject
修改int_print源码查看block_list、free_list、小整数缓冲池信息：
static int int_print(PyIntObject *v, FILE *fp, int flags)
{
PyIntObject* intObjectPtr;
PyIntBlock *p = block_list;
PyIntBlock *last = NULL;
int count = 0;
int i;
while(p != NULL)
{
++count;
last = p;
p = p->next;
}
intObjectPtr = last->objects;
intObjectPtr += N_INTOBJECTS - 1;
printf("address @%p\n", v);
printf("********** value\trefCount **********\n");
for(i = 0; i < 10; ++i, --intObjectPtr)
{
printf("%d\t\t%d\n", intObjectPtr->ob_ival, intObjectPtr->ob_refcnt);
}
printf("block_list count : %d\n", count);
printf("free_list : %p\n\n", free_list);
return 0;
}
有兴趣的可以试一下。
