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