Function async_seek

libavformat/async.c:392–473

}

static int64_t async_seek(URLContext *h, int64_t pos, int whence)
{
    AsyncContext *c    = h->priv_data;
    RingBuffer   *ring = &c->ring;
    int64_t       ret;
    int64_t       new_logical_pos;
    int fifo_size;
    int fifo_size_of_read_back;

    if (whence == AVSEEK_SIZE) {
        av_log(h, AV_LOG_TRACE, "async_seek: AVSEEK_SIZE: %"PRId64"\n", (int64_t)c->logical_size);
        return c->logical_size;
    } else if (whence == SEEK_CUR) {
        av_log(h, AV_LOG_TRACE, "async_seek: %"PRId64"\n", pos);
        new_logical_pos = pos + c->logical_pos;
    } else if (whence == SEEK_SET){
        av_log(h, AV_LOG_TRACE, "async_seek: %"PRId64"\n", pos);
        new_logical_pos = pos;
    } else {
        return AVERROR(EINVAL);
    }
    if (new_logical_pos < 0)
        return AVERROR(EINVAL);

    fifo_size = ring_size(ring);
    fifo_size_of_read_back = ring_size_of_read_back(ring);
    if (new_logical_pos == c->logical_pos) {
        /* current position */
        return c->logical_pos;
    } else if ((new_logical_pos >= (c->logical_pos - fifo_size_of_read_back)) &&
               (new_logical_pos < (c->logical_pos + fifo_size + SHORT_SEEK_THRESHOLD))) {
        int pos_delta = (int)(new_logical_pos - c->logical_pos);
        /* fast seek */
        av_log(h, AV_LOG_TRACE, "async_seek: fask_seek %"PRId64" from %d dist:%d/%d\n",
                new_logical_pos, (int)c->logical_pos,
                (int)(new_logical_pos - c->logical_pos), fifo_size);

        if (pos_delta > 0) {
            // fast seek forwards
            async_read_internal(h, NULL, pos_delta);
        } else {
            // fast seek backwards
            ring_drain(ring, pos_delta);
            c->logical_pos = new_logical_pos;
        }

        return c->logical_pos;
    } else if (c->logical_size <= 0) {
        /* can not seek */
        return AVERROR(EINVAL);
    } else if (new_logical_pos > c->logical_size) {
        /* beyond end */
        return AVERROR(EINVAL);
    }

    pthread_mutex_lock(&c->mutex);

    c->seek_request   = 1;