/* The ma_values pointer is NULL for a combined table
 * or points to an array of PyObject* for a split table
 */
typedef struct {
    PyObject_HEAD
    Py_ssize_t ma_used;
    PyDictKeysObject *ma_keys;
    PyObject **ma_values;
} PyDictObject;
 
struct _dictkeysobject {
    Py_ssize_t dk_refcnt;
    Py_ssize_t dk_size;
    dict_lookup_func dk_lookup;
    Py_ssize_t dk_usable;
    PyDictKeyEntry dk_entries[1];
};
 
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;

static PyObject *
dict_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
{
    PyObject *self;
    PyDictObject *d;
 
    assert(type != NULL && type->tp_alloc != NULL);
    // 申請(qǐng)內(nèi)存空間
    self = type->tp_alloc(type, 0);
    if (self == NULL)
        return NULL;
    d = (PyDictObject *)self;
 
    /* The object has been implicitly tracked by tp_alloc */
    if (type == &PyDict_Type)
        _PyObject_GC_UNTRACK(d);
    // 因?yàn)檫€沒(méi)有增加數(shù)據(jù) 因此哈希表當(dāng)中 ma_used = 0
    d->ma_used = 0;
    // 申請(qǐng)保存鍵值對(duì)的數(shù)組  PyDict_MINSIZE_COMBINED 是一個(gè)宏定義 值為 8 表示哈希表數(shù)組的最小長(zhǎng)度
    d->ma_keys = new_keys_object(PyDict_MINSIZE_COMBINED);
    // 如果申請(qǐng)失敗返回 NULL
    if (d->ma_keys == NULL) {
        Py_DECREF(self);
        return NULL;
    }
    return self;
}
 
// new_keys_object 函數(shù)如下所示
static PyDictKeysObject *new_keys_object(Py_ssize_t size)
{
    PyDictKeysObject *dk;
    Py_ssize_t i;
    PyDictKeyEntry *ep0;
 
    assert(size >= PyDict_MINSIZE_SPLIT);
    assert(IS_POWER_OF_2(size));
    // 這里是申請(qǐng)內(nèi)存的位置真正申請(qǐng)內(nèi)存空間的大小為 PyDictKeysObject 的大小加上 size-1 個(gè)PyDictKeyEntry的大小
    // 這里你可能會(huì)有一位為啥不是 size 個(gè) PyDictKeyEntry 的大小 因?yàn)樵诮Y(jié)構(gòu)體 PyDictKeysObject 當(dāng)中已經(jīng)申請(qǐng)了一個(gè) PyDictKeyEntry 對(duì)象了
    dk = PyMem_MALLOC(sizeof(PyDictKeysObject) +
                      sizeof(PyDictKeyEntry) * (size-1));
    if (dk == NULL) {
        PyErr_NoMemory();
        return NULL;
    }
    // 下面主要是一些初始化的操作 dk_refcnt 設(shè)置成 1 因?yàn)槟壳爸挥幸粋€(gè)字典對(duì)象使用 這個(gè) PyDictKeysObject 對(duì)象
    DK_DEBUG_INCREF dk->dk_refcnt = 1;
    dk->dk_size = size; // 哈希表的大小
    // 下面這行代碼主要是表示哈希表當(dāng)中目前還能存儲(chǔ)多少個(gè)鍵值對(duì) 在 cpython 的實(shí)現(xiàn)當(dāng)中允許有 2/3 的數(shù)組空間去存儲(chǔ)數(shù)據(jù) 超過(guò)這個(gè)數(shù)則需要進(jìn)行擴(kuò)容
    dk->dk_usable = USABLE_FRACTION(size); // #define USABLE_FRACTION(n) ((((n) << 1)+1)/3)
    ep0 = &dk->dk_entries[0];
    /* Hash value of slot 0 is used by popitem, so it must be initialized */
    ep0->me_hash = 0;
    // 將所有的鍵值對(duì)初始化成 NULL
    for (i = 0; i < size; i++) {
        ep0[i].me_key = NULL;
        ep0[i].me_value = NULL;
    }
    dk->dk_lookup = lookdict_unicode_nodummy;
    return dk;
}

#define GROWTH_RATE(d) (((d)->ma_used*2)+((d)->ma_keys->dk_size>>1))

static int
insertion_resize(PyDictObject *mp)
{
    return dictresize(mp, GROWTH_RATE(mp));
}
 
static int
dictresize(PyDictObject *mp, Py_ssize_t minused)
{
    Py_ssize_t newsize;
    PyDictKeysObject *oldkeys;
    PyObject **oldvalues;
    Py_ssize_t i, oldsize;
    // 下面的代碼的主要作用就是計(jì)算得到能夠大于等于 minused 最小的 2 的整數(shù)次冪
/* Find the smallest table size > minused. */
    for (newsize = PyDict_MINSIZE_COMBINED;
         newsize <= minused && newsize > 0;
         newsize <<= 1)
        ;
    if (newsize <= 0) {
        PyErr_NoMemory();
        return -1;
    }
    oldkeys = mp->ma_keys;
    oldvalues = mp->ma_values;
    /* Allocate a new table. */
   // 創(chuàng)建新的數(shù)組
    mp->ma_keys = new_keys_object(newsize);
    if (mp->ma_keys == NULL) {
        mp->ma_keys = oldkeys;
        return -1;
    }
    if (oldkeys->dk_lookup == lookdict)
        mp->ma_keys->dk_lookup = lookdict;
    oldsize = DK_SIZE(oldkeys);
    mp->ma_values = NULL;
    /* If empty then nothing to copy so just return */
    if (oldsize == 1) {
        assert(oldkeys == Py_EMPTY_KEYS);
        DK_DECREF(oldkeys);
        return 0;
    }
    /* Main loop below assumes we can transfer refcount to new keys
     * and that value is stored in me_value.
     * Increment ref-counts and copy values here to compensate
     * This (resizing a split table) should be relatively rare */
    if (oldvalues != NULL) {
        for (i = 0; i < oldsize; i++) {
            if (oldvalues[i] != NULL) {
                Py_INCREF(oldkeys->dk_entries[i].me_key);
                oldkeys->dk_entries[i].me_value = oldvalues[i];
            }
        }
    }
    /* Main loop */
    // 將原來(lái)數(shù)組當(dāng)中的元素加入到新的數(shù)組當(dāng)中
    for (i = 0; i < oldsize; i++) {
        PyDictKeyEntry *ep = &oldkeys->dk_entries[i];
        if (ep->me_value != NULL) {
            assert(ep->me_key != dummy);
            insertdict_clean(mp, ep->me_key, ep->me_hash, ep->me_value);
        }
    }
    // 更新一下當(dāng)前哈希表當(dāng)中能夠插入多少數(shù)據(jù)
    mp->ma_keys->dk_usable -= mp->ma_used;
    if (oldvalues != NULL) {
        /* NULL out me_value slot in oldkeys, in case it was shared */
        for (i = 0; i < oldsize; i++)
            oldkeys->dk_entries[i].me_value = NULL;
        assert(oldvalues != empty_values);
        free_values(oldvalues);
        DK_DECREF(oldkeys);
    }
    else {
        assert(oldkeys->dk_lookup != lookdict_split);
        if (oldkeys->dk_lookup != lookdict_unicode_nodummy) {
            PyDictKeyEntry *ep0 = &oldkeys->dk_entries[0];
            for (i = 0; i < oldsize; i++) {
                if (ep0[i].me_key == dummy)
                    Py_DECREF(dummy);
            }
        }
        assert(oldkeys->dk_refcnt == 1);
        DK_DEBUG_DECREF PyMem_FREE(oldkeys);
    }
    return 0;
}

static void
insertdict_clean(PyDictObject *mp, PyObject *key, Py_hash_t hash,
                 PyObject *value)
{
    size_t i;
    size_t perturb;
    PyDictKeysObject *k = mp->ma_keys;
    // 首先得到 mask 的值
    size_t mask = (size_t)DK_SIZE(k)-1;
    PyDictKeyEntry *ep0 = &k->dk_entries[0];
    PyDictKeyEntry *ep;
  
    i = hash & mask;
    ep = &ep0[i];
    for (perturb = hash; ep->me_key != NULL; perturb >>= PERTURB_SHIFT) {
        // 下面便是遇到哈希沖突時(shí)的處理辦法
        i = (i << 2) + i + perturb + 1;
        ep = &ep0[i & mask];
    }
    assert(ep->me_value == NULL);
    ep->me_key = key;
    ep->me_hash = hash;
    ep->me_value = value;
}