关于rt_ringbuffer_put_force的问题讨论

发布于 2018-05-24 14:16:35 浏览：2419 订阅该版

* 本帖最后由 geniusgogo 于 2018-5-24 14:18 编辑 *

最近要用到ringbuffer功能，所以review了一下rt_ringbuffer的实现，发现rt_ringbuffer_put_force的实现存在问题。
先看其实现：
```/**
 * put a block of data into ring buffer
 *
 * When the buffer is full, it will discard the old data.
 */
rt_size_t rt_ringbuffer_put_force(struct rt_ringbuffer *rb,
                            const rt_uint8_t     *ptr,
                            rt_uint16_t           length)
{
    rt_uint16_t space_length;

RT_ASSERT(rb != RT_NULL);

space_length = rt_ringbuffer_space_len(rb);

if (length > space_length)
        length = rb->buffer_size;

if (rb->buffer_size - rb->write_index > length)
    {
        /* read_index - write_index = empty space */
        memcpy(&rb->buffer_ptr[rb->write_index], ptr, length);
        /* this should not cause overflow because there is enough space for
         * length of data in current mirror */
        rb->write_index += length;

if (length > space_length)
            rb->read_index = rb->write_index;

return length;
    }

memcpy(&rb->buffer_ptr[rb->write_index],
           &ptr[0],
           rb->buffer_size - rb->write_index);
    memcpy(&rb->buffer_ptr[0],
           &ptr[rb->buffer_size - rb->write_index],
           length - (rb->buffer_size - rb->write_index));

/* we are going into the other side of the mirror */
    rb->write_mirror = ~rb->write_mirror;
    rb->write_index = length - (rb->buffer_size - rb->write_index);

if (length > space_length)
    {
        rb->read_mirror = ~rb->read_mirror;
        rb->read_index = rb->write_index;
    }

return length;
}
RTM_EXPORT(rt_ringbuffer_put_force);```
按理说如果put的数据大于ringbuffer的size或者剩余空间时，将会丢弃最老的数据。
而这里的实现首先将put的length给截短了，这就导致put的数据被丢弃了后面的，只
put进最前面的那段数据，而其实是尽可能put进后面那段数据。
举例：假如ringbuff的buffer size是5。put_force是1 2 3 4 5 6 7 8 9 10这10个数据。
那么应该是put 6 7 8 9 10而不是put 1 2 3 4 5.