FFmepg 多线程解码历程 - 6：frame_thread_init

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#FFmpeg多线程

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本文详细介绍了FFmpeg中frame_thread_init函数的工作原理，包括如何根据设备性能自动配置线程数量、初始化线程所需的资源及环境、创建并启动线程等过程。

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//ff_thread_init选择帧线程初始化，就会进入frame_thread_init

static int frame_thread_init(AVCodecContext *avctx)

{
    int thread_count = avctx->thread_count;
    const AVCodec *codec = avctx->codec;
    AVCodecContext *src = avctx;
    FrameThreadContext *fctx;
    int i, err = 0;
//如果我们在初始化codec的时候没有设置thread_count或者设置为0，则就会自动根据手机设备来获取
    if (!thread_count) {
        int nb_cpus = ff_get_logical_cpus(avctx);
        if ((avctx->debug & (FF_DEBUG_VIS_QP | FF_DEBUG_VIS_MB_TYPE)) || avctx->debug_mv)
            nb_cpus = 1;
        // use number of cores + 1 as thread count if there is more than one
        if (nb_cpus > 1)
            thread_count = avctx->thread_count = FFMIN(nb_cpus + 1, MAX_AUTO_THREADS); //#define FFMIN(a,b) ((a) > (b) ? (b) : (a))
        else
            thread_count = avctx->thread_count = 1;
    }

    if (thread_count <= 1) { //如果thread_count <= 1那么即使进入帧级线程初始化，在解码的时候也不会调用帧级解码函数的
        avctx->active_thread_type = 0;
        return 0;
    }

    avctx->thread_opaque = fctx = av_mallocz(sizeof(FrameThreadContext));

    fctx->threads = av_mallocz(sizeof(PerThreadContext) * thread_count); //相当与初始化线程池，个数就是thread_count
    pthread_mutex_init(&fctx->buffer_mutex, NULL);
    fctx->delaying = 1;

    for (i = 0; i < thread_count; i++) {
        AVCodecContext *copy = av_malloc(sizeof(AVCodecContext));
        PerThreadContext *p = &fctx->threads[i];

        pthread_mutex_init(&p->mutex, NULL);
        pthread_mutex_init(&p->progress_mutex, NULL);
        pthread_cond_init(&p->input_cond, NULL);
        pthread_cond_init(&p->progress_cond, NULL);
        pthread_cond_init(&p->output_cond, NULL);

        p->parent = fctx;
        p->avctx = copy;

        if (!copy) {
            err = AVERROR(ENOMEM);
            goto error;
        }

        *copy = *src;
        copy->thread_opaque = p;
        copy->pkt = &p->avpkt;

        if (!i) {
            src = copy;

            if (codec->init)
                err = codec->init(copy);
       //更新下一个线程的AVCodecContext参考线程的上下文中的值
            update_context_from_thread(avctx, copy, 1);
        } else {
            copy->priv_data = av_malloc(codec->priv_data_size);
            if (!copy->priv_data) {
                err = AVERROR(ENOMEM);
                goto error;
            }
            memcpy(copy->priv_data, src->priv_data, codec->priv_data_size);
            copy->internal = av_malloc(sizeof(AVCodecInternal));
            if (!copy->internal) {
                err = AVERROR(ENOMEM);
                goto error;
            }
            *copy->internal = *src->internal;
            copy->internal->is_copy = 1;

            if (codec->init_thread_copy)
                err = codec->init_thread_copy(copy);
        }

        if (err) goto error;
///下面出创建线程，调用frame_worker_thread
        err = AVERROR(pthread_create(&p->thread, NULL, frame_worker_thread, p));
        p->thread_init= !err;
        if(!p->thread_init)
            goto error;
    }

    return 0;

error:
    frame_thread_free(avctx, i+1);

    return err;
}