Python源码学习十一 一个常用的内存分配函数

void *

_PyObject_DebugMallocApi(char id, size_t nbytes)

{

    uchar *p;           /* base address of malloc'ed block */

    uchar *tail;        /* p + 2*SST + nbytes == pointer to tail pad bytes */

    size_t total;       /* nbytes + 4*SST */



    bumpserialno();

    total = nbytes + 4*SST;

    if (total < nbytes)

        /* overflow:  can't represent total as a size_t */

        return NULL;



    p = (uchar *)PyObject_Malloc(total);

    if (p == NULL)

        return NULL;



    /* at p, write size (SST bytes), id (1 byte), pad (SST-1 bytes) */

    write_size_t(p, nbytes);

    p[SST] = (uchar)id;

    memset(p + SST + 1 , FORBIDDENBYTE, SST-1);



    if (nbytes > 0)

        memset(p + 2*SST, CLEANBYTE, nbytes);



    /* at tail, write pad (SST bytes) and serialno (SST bytes) */

    tail = p + 2*SST + nbytes;

    memset(tail, FORBIDDENBYTE, SST);

    write_size_t(tail + SST, serialno);



    return p + 2*SST;

}



SST是宏定义 4

执行的实际作用是把nbytes的值(360 in this case)写在内存区的前四个字节,然后是一个uchar型的id , 'o' in this case

接着是nbytes个浩浩荡荡的0xcb

然后是4个oxfb, 和hex形式的serialno

(PyFrameObject*)op0x00b25528
(*((PyFrameObject*)op)).f_localsplus0x00b25668


我们看到f_localsplus的值正是 op + offset

offset is the f_localsplus offset in PyFrameObject definition