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