Python源码学习之初始化(三)-PyDictObject的初始化

先来看它的定义

typedef struct _dictobject PyDictObject;

struct _dictobject {

    PyObject_HEAD

    Py_ssize_t ma_fill;  /* # Active + # Dummy */

    Py_ssize_t ma_used;  /* # Active */



    /* The table contains ma_mask + 1 slots, and that's a power of 2.

     * We store the mask instead of the size because the mask is more

     * frequently needed.

     */

    Py_ssize_t ma_mask;



    /* ma_table points to ma_smalltable for small tables, else to

     * additional malloc'ed memory.  ma_table is never NULL!  This rule

     * saves repeated runtime null-tests in the workhorse getitem and

     * setitem calls.

     */

    PyDictEntry *ma_table;

    PyDictEntry *(*ma_lookup)(PyDictObject *mp, PyObject *key, Py_hash_t hash);

    PyDictEntry ma_smalltable[PyDict_MINSIZE];

};



在PyObject *PyDict_New(void)中,调用了宏定义EMPTY_TO_MINSIZE



#define INIT_NONZERO_DICT_SLOTS(mp) do {                                \

    (mp)->ma_table = (mp)->ma_smalltable;                               \

    (mp)->ma_mask = PyDict_MINSIZE - 1;                                 \

    } while(0)



#define EMPTY_TO_MINSIZE(mp) do {                                       \

    memset((mp)->ma_smalltable, 0, sizeof((mp)->ma_smalltable));        \

    (mp)->ma_used = (mp)->ma_fill = 0;                                  \

    INIT_NONZERO_DICT_SLOTS(mp);                                        \

    } while(0)

	

可以看出ma_table开始是指向ma_smalltable的,这和代码的注释一致



mp->ma_lookup = lookdict_unicode; 给函数指针赋值,dict的搜索函数



随着int PyDict_SetItem(register PyObject *op, PyObject *key, PyObject *value)的不断调用

该函数会在最后判断

    if (!(mp->ma_used > n_used && mp->ma_fill*3 >= (mp->ma_mask+1)*2))

        return 0;

    return dictresize(mp, (mp->ma_used > 50000 ? 2 : 4) * mp->ma_used);

可见在ma_fill = 6 && ma_mask=7 的时候,走到了dictresize

会重新申请新的内存, ma_table就不再指向ma_smalltable, 而是新的内存,

然后把原来老的内容拷贝到新的内存里面.by calling insertdict_clean

之后 ma_fill = ma_used = 6, ma_mask = 31



    /* Get space for a new table. */

    oldtable = mp->ma_table;

    assert(oldtable != NULL);

    is_oldtable_malloced = oldtable != mp->ma_smalltable;

	    if (is_oldtable_malloced)

        PyMem_DEL(oldtable);

		

最后看老的内存是否应该释放

如果老的是ma_smalltable, 就不管了