五、从PyIntObject出发

来源：互联网发布：sql distinct一个字段编辑：程序博客网时间：2024/05/17 07:45

1.初识PyIntObject

本节要说的内容是“整数”，我们来看看这个PyInt_Type变量，这个变量里面大量的元信息是我们要关注的。它描述了一个整数对象。

[intobject.c]PyTypeObject PyInt_Type = {    PyVarObject_HEAD_INIT(&PyType_Type, 0)    "int",    sizeof(PyIntObject),  //对象占用内存大小    0,    (destructor)int_dealloc,                    /* tp_dealloc */ //对象析构    (printfunc)int_print,                       /* tp_print */  //打印PyIntObject对象    0,                                          /* tp_getattr */    0,                                          /* tp_setattr */    (cmpfunc)int_compare,                       /* tp_compare */  //比较操作    (reprfunc)int_to_decimal_string,            /* tp_repr */    &int_as_number,                             /* tp_as_number */  //一个函数域，描述作为一个number该有的行为    0,                                          /* tp_as_sequence */    0,                                          /* tp_as_mapping */    (hashfunc)int_hash,                         /* tp_hash */ //获得HASH值    0,                                          /* tp_call */    (reprfunc)int_to_decimal_string,            /* tp_str */    PyObject_GenericGetAttr,                    /* tp_getattro */    0,                                          /* tp_setattro */    0,                                          /* tp_as_buffer */    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_CHECKTYPES |        Py_TPFLAGS_BASETYPE | Py_TPFLAGS_INT_SUBCLASS,          /* 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 */    int_getset,                                 /* 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 */};

各个函数的实现都在intobject.c中，可自行查看。

如：加法代码：

[intobject.h]#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);    /* casts in the line below avoid undefined behaviour on overflow */    x = (long)((unsigned long)a + b);    //溢出检查    if ((x^a) >= 0 || (x^b) >= 0)        return PyInt_FromLong(x);    return PyLong_Type.tp_as_number->nb_add((PyObject *)v, (PyObject *)w);}

2.PyIntObject的创建和维护

对象创建三种途径：

[intobject.h]PyAPI_FUNC(PyObject *) PyInt_FromLong(long);PyAPI_FUNC(PyObject *) PyInt_FromSize_t(size_t); //实际上调用的是PyInt_FromFloatPyAPI_FUNC(PyObject *) PyInt_FromSsize_t(Py_ssize_t);//实际上调用的是PyInt_FromFloat

我们主要讨论：PyInt_FromLong

------------------------------------割，以下讨论整数的存储形式，及方案------------------------------------

小整数对象使用对象池技术：Python直接将这些整数对应的PyIntObject缓存在内存中，其指针放在small_ints中

[intobject.c]#ifndef NSMALLPOSINTS#define NSMALLPOSINTS           257#endif#ifndef NSMALLNEGINTS#define NSMALLNEGINTS           5#endif#if NSMALLNEGINTS + NSMALLPOSINTS > 0/* References to small integers are saved in this array so that they   can 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

大整数对象Python运行环境将提供一块内存空间，这些内存空间由这些大整数轮流使用。

[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;

通用整数对象池的创建：

[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));//申请一块block的内存    if (p == NULL)        return (PyIntObject *) PyErr_NoMemory();    ((PyIntBlock *)p)->next = block_list;//连接到已有的block_list中，大家非常熟悉的头接法    block_list = (PyIntBlock *)p; //重新把block_list置为头部    /* Link the int objects together, from rear to front, then return       the address of the last int object in the block. */    p = &((PyIntBlock *)p)->objects[0];    q = p + N_INTOBJECTS;    while (--q > p)        Py_TYPE(q) = (struct _typeobject *)(q-1);    Py_TYPE(q) = NULL;    return p + N_INTOBJECTS - 1;}[ctypes.h]#define Py_TYPE(ob) (((PyObject*)(ob))->ob_type)

效果如图：

通用整数对象池的使用：

[intobject.c]static voidint_dealloc(PyIntObject *v){    if (PyInt_CheckExact(v)) {        Py_TYPE(v) = (struct _typeobject *)free_list;        free_list = v;    }    else        Py_TYPE(v)->tp_free((PyObject *)v);}

小整数对象池的创建：

[intobject.c]int_PyInt_Init(void){    PyIntObject *v;    int ival;#if NSMALLNEGINTS + NSMALLPOSINTS > 0    for (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 *)Py_TYPE(v);        PyObject_INIT(v, &PyInt_Type);        v->ob_ival = ival;        small_ints[ival + NSMALLNEGINTS] = v;    }#endif    return 1;}

创建后效果如图：事实上，小整数对象也是生存在block_list所维护的内存上

------------------------------------割，以上讨论整数的存储形式，及方案------------------------------------

现在存储有了，让我们来看看PyInt_FromLong，具体如何创建一个PyIntObject

[intobject.c]PyObject *PyInt_FromLong(long ival){    register PyIntObject *v;#if NSMALLNEGINTS + NSMALLPOSINTS > 0//如果小整数对象池被激活，尝试使用小整形对象池  if (-NSMALLNEGINTS <= ival && ival < NSMALLPOSINTS) {        v = small_ints[ival + NSMALLNEGINTS];        Py_INCREF(v);#ifdef COUNT_ALLOCS        if (ival >= 0)            quick_int_allocs++;        else            quick_neg_int_allocs++;#endif        return (PyObject *) v;    }#endif//木有办法了，大整形，只好用通用的整数对象池了//对象池木有空间，新申请    if (free_list == NULL) {        if ((free_list = fill_free_list()) == NULL)            return NULL;    }    /* Inline PyObject_New */    v = free_list;    free_list = (PyIntObject *)Py_TYPE(v);    PyObject_INIT(v, &PyInt_Type);    v->ob_ival = ival;    return (PyObject *) v;}