函数lock_rec_create

/*********************************************************************//**
Creates a new record lock and inserts it to the lock queue. Does NOT check
for deadlocks or lock compatibility!
@return    created lock */
static
lock_t*
lock_rec_create(
/*============*/
    ulint               type_mode,/*!< in: lock mode and wait flag, type is ignored and replaced by LOCK_REC */
    const buf_block_t*  block,    /*!< in: buffer block containing the record */
    ulint               heap_no,  /*!< in: heap number of the record */
    dict_index_t*       index,    /*!< in: index of record */
    trx_t*              trx)      /*!< in: transaction */
{
    lock_t*        lock;
    ulint        page_no;
    ulint        space;
    ulint        n_bits;
    ulint        n_bytes;
    const page_t*    page;

    ut_ad(mutex_own(&kernel_mutex));

    space = buf_block_get_space(block);
    page_no    = buf_block_get_page_no(block);
    page = block->frame;

    /* If rec is the supremum record, then we reset the gap and
    LOCK_REC_NOT_GAP bits, as all locks on the supremum are
    automatically of the gap type */

    if (UNIV_UNLIKELY(heap_no == PAGE_HEAP_NO_SUPREMUM)) {
        ut_ad(!(type_mode & LOCK_REC_NOT_GAP));

        type_mode = type_mode & ~(LOCK_GAP | LOCK_REC_NOT_GAP);
    }

    /* Make lock bitmap bigger by a safety margin */
    n_bits = page_dir_get_n_heap(page) + LOCK_PAGE_BITMAP_MARGIN; //函数详见 即page页中包含记录个数+64
    n_bytes =  + n_bits / ; //转化为所需的字节,注意这里要加1,例如 5bits 进行运算后,要分配一个字节

    lock = mem_heap_alloc(trx->lock_heap, sizeof(lock_t) + n_bytes); //为锁分配内存

    UT_LIST_ADD_LAST(trx_locks, trx->trx_locks, lock);

    lock->trx = trx;

    lock->type_mode = (type_mode & ~LOCK_TYPE_MASK) | LOCK_REC;
    lock->index = index;

    lock->un_member.rec_lock.space = space;
    lock->un_member.rec_lock.page_no = page_no;
    lock->un_member.rec_lock.n_bits = n_bytes * ; //bitmap的容量

    /* Reset to zero the bitmap which resides immediately after the
    lock struct */

    lock_rec_bitmap_reset(lock); //清0，详见/* Set the bit corresponding to rec */
    lock_rec_set_nth_bit(lock, heap_no); //详见

    HASH_INSERT(lock_t, hash, lock_sys->rec_hash,
            lock_rec_fold(space, page_no), lock);
    if (lock_is_wait_not_by_other(type_mode)) {

        lock_set_lock_and_trx_wait(lock, trx);
    }

    return(lock);
}