FFmepg 多線程解碼曆程 – 7：submit_packet

//在ff_thread_decode_frame中會調用submit_packet將碼流交給對應的解碼線程，來實現線程狀態的改變，具體的流程圖見下面圖

static int submit_packet(PerThreadContext *p, AVPacket *avpkt)

{
    FrameThreadContext *fctx = p->parent;
    PerThreadContext *prev_thread = fctx->prev_thread;
    const AVCodec *codec = p->avctx->codec;

    if (!avpkt->size && !(codec->capabilities & CODEC_CAP_DELAY)) return 0;

    pthread_mutex_lock(&p->mutex);

    release_delayed_buffers(p);

    if (prev_thread) {
        int err;
        if (prev_thread->state == STATE_SETTING_UP) {
            pthread_mutex_lock(&prev_thread->progress_mutex);
            while (prev_thread->state == STATE_SETTING_UP)  //判斷之前的線程狀態為STATE_SETTING_UP的時候，進行線程的等待，
                pthread_cond_wait(&prev_thread->progress_cond, &prev_thread->progress_mutex);
            pthread_mutex_unlock(&prev_thread->progress_mutex);
        }

        err = update_context_from_thread(p->avctx, prev_thread->avctx, 0);//如果之前的線程狀態變為STATE_SETUP_FINISHED，然後從線程中哦功能更新內容
        if (err) {
            pthread_mutex_unlock(&p->mutex);
            return err;
        }
    }

    av_buffer_unref(&p->avpkt.buf);
    p->avpkt = *avpkt;
    if (avpkt->buf)
        p->avpkt.buf = av_buffer_ref(avpkt->buf);
    else {
        av_fast_malloc(&p->buf, &p->allocated_buf_size, avpkt->size + FF_INPUT_BUFFER_PADDING_SIZE);
        p->avpkt.data = p->buf;
        memcpy(p->buf, avpkt->data, avpkt->size);
        memset(p->buf + avpkt->size, 0, FF_INPUT_BUFFER_PADDING_SIZE);
    }

    p->state = STATE_SETTING_UP;
    pthread_cond_signal(&p->input_cond);//發送碼流輸入準備好的訊號給解碼線程pthread_cond_waite(&p->input_cond),讓解碼線程
    pthread_mutex_unlock(&p->mutex);

    /*
     * If the client doesn't have a thread-safe get_buffer(),
     * then decoding threads call back to the main thread,
     * and it calls back to the client here.
     */

    if (!p->avctx->thread_safe_callbacks && (
#if FF_API_GET_BUFFER
         p->avctx->get_buffer ||
#endif
         p->avctx->get_buffer2 != avcodec_default_get_buffer2)) {
        while (p->state != STATE_SETUP_FINISHED && p->state != STATE_INPUT_READY) {
            pthread_mutex_lock(&p->progress_mutex);
            while (p->state == STATE_SETTING_UP)
                pthread_cond_wait(&p->progress_cond, &p->progress_mutex);

            if (p->state == STATE_GET_BUFFER) {
                p->result = ff_get_buffer(p->avctx, p->requested_frame, p->requested_flags);
                p->state  = STATE_SETTING_UP;
                pthread_cond_signal(&p->progress_cond);
            }
            pthread_mutex_unlock(&p->progress_mutex);
        }
    }

    fctx->prev_thread = p;
    fctx->next_decoding++;

    return 0;

}

主線程接收資料，準備完畢後發出pthread_cond_signal(&p->input_cond)訊號，然後解碼線程接收到以後，設定線程狀態為finish_setup，發送廣播p->process_cond，進行解碼，

解碼線程解完以後，發送p->progress_cond訊號，主線程回調，從解碼線程中擷取get_buffer，解碼之後的資料，然後發送p->progress_cond訊號給解碼線程，然後解碼線程發出p->output_cond訊號給主線程，主線程輸出解碼之後的frame給使用者

注釋1：