CPython 源码阅读 - dict

// dictobject.h
typedef struct _dictkeysobject PyDictKeysObject;

typedef struct {
    PyObject_HEAD

    /* Number of items in the dictionary */
    Py_ssize_t ma_used;

    /* Dictionary version: globally unique, value change each time
       the dictionary is modified */
    uint64_t ma_version_tag;

    PyDictKeysObject *ma_keys;

    /* If ma_values is NULL, the table is "combined": keys and values
       are stored in ma_keys.
       If ma_values is not NULL, the table is splitted:
       keys are stored in ma_keys and values are stored in ma_values */
    PyObject **ma_values;
} PyDictObject;

// dict-common.h
struct _dictkeysobject {
    Py_ssize_t dk_refcnt;

    /* Size of the hash table (dk_indices). It must be a power of 2. */
    Py_ssize_t dk_size;

    /* Function to lookup in the hash table (dk_indices)
       lookdict() / lookdict_unicode() / lookdict_unicode_nodummy() / lookdict_split() */
    dict_lookup_func dk_lookup;

    /* Number of usable entries in dk_entries. */
    Py_ssize_t dk_usable;

    /* Number of used entries in dk_entries. */
    Py_ssize_t dk_nentries;

    /* Actual hash table of dk_size entries. It holds indices in dk_entries,
       or DKIX_EMPTY(-1) or DKIX_DUMMY(-2).
       Indices must be: 0 <= indice < USABLE_FRACTION(dk_size).
       The size in bytes of an indice depends on dk_size:
       - 1 byte if dk_size <= 0xff (char*)
       - 2 bytes if dk_size <= 0xffff (int16_t*)
       - 4 bytes if dk_size <= 0xffffffff (int32_t*)
       - 8 bytes otherwise (int64_t*)
       Dynamically sized, 8 is minimum. */
    union {
        int8_t as_1[8];
        int16_t as_2[4];
        int32_t as_4[2];
#if SIZEOF_VOID_P > 4
        int64_t as_8[1];
#endif
    } dk_indices;

    /* "PyDictKeyEntry dk_entries[dk_usable];" array follows:
       see the DK_ENTRIES() macro */
};

// dict-common.h
#define DKIX_EMPTY (-1)
#define DKIX_DUMMY (-2)  /* Used internally */
#define DKIX_ERROR (-3)

// dictobject.c
#define DK_SIZE(dk) ((dk)->dk_size)
#if SIZEOF_VOID_P > 4
#define DK_IXSIZE(dk)                          \
    (DK_SIZE(dk) <= 0xff ?                     \
        1 : DK_SIZE(dk) <= 0xffff ?            \
            2 : DK_SIZE(dk) <= 0xffffffff ?    \
                4 : sizeof(int64_t))
#else
#define DK_IXSIZE(dk)                          \
    (DK_SIZE(dk) <= 0xff ?                     \
        1 : DK_SIZE(dk) <= 0xffff ?            \
            2 : sizeof(int32_t))
#endif
#define DK_ENTRIES(dk) \
    ((PyDictKeyEntry*)(&(dk)->dk_indices.as_1[DK_SIZE(dk) * DK_IXSIZE(dk)]))

typedef struct {
    /* Cached hash code of me_key. */
    Py_hash_t me_hash;
    PyObject *me_key;
    PyObject *me_value; /* This field is only meaningful for combined tables */
} PyDictKeyEntry;

// dictobject.c
PyObject *
PyDict_New(void)
{
    PyDictKeysObject *keys = new_keys_object(PyDict_MINSIZE);  // PyDict_MINSIZE == 8
    if (keys == NULL)
        return NULL;
    return new_dict(keys, NULL);
}

// dictobject.c
static PyDictKeysObject *new_keys_object(Py_ssize_t size)
{
    PyDictKeysObject *dk;
    Py_ssize_t es, usable;

    assert(size >= PyDict_MINSIZE);
    assert(IS_POWER_OF_2(size));

    // [1]
    usable = USABLE_FRACTION(size);
    if (size <= 0xff) {
        es = 1;
    }
    else if (size <= 0xffff) {
        es = 2;
    }
#if SIZEOF_VOID_P > 4
    else if (size <= 0xffffffff) {
        es = 4;
    }
#endif
    else {
        es = sizeof(Py_ssize_t);
    }

    if (size == PyDict_MINSIZE && numfreekeys > 0) {
        // [2]
        dk = keys_free_list[--numfreekeys];
    }
    else {
        // [3]
        dk = PyObject_MALLOC(sizeof(PyDictKeysObject)
                             - Py_MEMBER_SIZE(PyDictKeysObject, dk_indices)
                             + es * size
                             + sizeof(PyDictKeyEntry) * usable);
        if (dk == NULL) {
            PyErr_NoMemory();
            return NULL;
        }
    }
    DK_DEBUG_INCREF dk->dk_refcnt = 1;
    dk->dk_size = size;
    dk->dk_usable = usable;
    dk->dk_lookup = lookdict_unicode_nodummy;
    dk->dk_nentries = 0;
    // 置为默认状态
    memset(&dk->dk_indices.as_1[0], 0xff, es * size);
    memset(DK_ENTRIES(dk), 0, sizeof(PyDictKeyEntry) * usable);
    return dk;
}

// dictobject.c
#define USABLE_FRACTION(n) (((n) << 1)/3)

// 结构体大小 + dk_indices 大小 + dk_entries 大小
sizeof(PyDictKeysObject) - Py_MEMBER_SIZE(PyDictKeysObject, dk_indices) + \
es * size + sizeof(PyDictKeyEntry) * usable

// dictobject.c
static PyObject *
new_dict(PyDictKeysObject *keys, PyObject **values)
{
    PyDictObject *mp;
    assert(keys != NULL);
    if (numfree) {
        mp = free_list[--numfree];
        assert (mp != NULL);
        assert (Py_TYPE(mp) == &PyDict_Type);
        _Py_NewReference((PyObject *)mp);
    }
    else {
        mp = PyObject_GC_New(PyDictObject, &PyDict_Type);
        if (mp == NULL) {
            DK_DECREF(keys);
            free_values(values);
            return NULL;
        }
    }
    mp->ma_keys = keys;
    mp->ma_values = values;
    mp->ma_used = 0;
    mp->ma_version_tag = DICT_NEXT_VERSION();
    assert(_PyDict_CheckConsistency(mp));
    return (PyObject *)mp;
}