[FFmpeg-devel] [PATCH v3 2/3] lavf/dashdec: Multithreaded DASH initialization
Andreas Rheinhardt
andreas.rheinhardt at outlook.com
Wed Aug 31 05:54:12 EEST 2022
Lukas Fellechner:
> This patch adds an "init-threads" option, specifying the max
> number of threads to use. Multiple worker threads are spun up
> to massively bring down init times.
> ---
> libavformat/dashdec.c | 351 +++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 350 insertions(+), 1 deletion(-)
>
> diff --git a/libavformat/dashdec.c b/libavformat/dashdec.c
> index e82da45e43..20f2557ea3 100644
> --- a/libavformat/dashdec.c
> +++ b/libavformat/dashdec.c
> @@ -24,6 +24,7 @@
> #include "libavutil/opt.h"
> #include "libavutil/time.h"
> #include "libavutil/parseutils.h"
> +#include "libavutil/thread.h"
> #include "internal.h"
> #include "avio_internal.h"
> #include "dash.h"
> @@ -152,6 +153,8 @@ typedef struct DASHContext {
> int max_url_size;
> char *cenc_decryption_key;
>
> + int init_threads;
> +
> /* Flags for init section*/
> int is_init_section_common_video;
> int is_init_section_common_audio;
> @@ -2033,6 +2036,331 @@ static void move_metadata(AVStream *st, const char *key, char **value)
> }
> }
>
> +#if HAVE_THREADS
> +
> +struct work_pool_data
> +{
> + AVFormatContext *ctx;
> + struct representation *pls;
> + struct representation *common_pls;
> + pthread_mutex_t *common_mutex;
> + pthread_cond_t *common_condition;
> + int is_common;
> + int is_started;
> + int result;
> +};
> +
> +struct thread_data
This is against our naming conventions: CamelCase for struct tags and
typedefs, lowercase names with underscore for variable names.
> +{
> + pthread_t thread;
> + pthread_mutex_t *mutex;
> + struct work_pool_data *work_pool;
> + int work_pool_size;
> + int is_started;
> + int has_error;
> +};
> +
> +static void *worker_thread(void *ptr)
> +{
> + int ret = 0;
> + int i;
> + struct thread_data *thread_data = (struct thread_data*)ptr;
> + struct work_pool_data *work_pool = NULL;
> + struct work_pool_data *data = NULL;
> + for (;;) {
> +
> + // get next work item unless there was an error
> + pthread_mutex_lock(thread_data->mutex);
> + data = NULL;
> + if (!thread_data->has_error) {
> + work_pool = thread_data->work_pool;
> + for (i = 0; i < thread_data->work_pool_size; i++) {
> + if (!work_pool->is_started) {
> + data = work_pool;
> + data->is_started = 1;
> + break;
> + }
> + work_pool++;
> + }
> + }
> + pthread_mutex_unlock(thread_data->mutex);
> +
> + if (!data) {
> + // no more work to do
> + return NULL;
> + }
> +
> + // if we are common section provider, init and signal
> + if (data->is_common) {
> + data->pls->parent = data->ctx;
> + ret = update_init_section(data->pls);
> + if (ret < 0) {
> + pthread_cond_signal(data->common_condition);
> + goto end;
> + }
> + else
> + ret = AVERROR(pthread_cond_signal(data->common_condition));
> + }
> +
> + // if we depend on common section provider, wait for signal and copy
> + if (data->common_pls) {
> + ret = AVERROR(pthread_cond_wait(data->common_condition, data->common_mutex));
> + if (ret < 0)
> + goto end;
> +
> + if (!data->common_pls->init_sec_buf) {
> + goto end;
> + ret = AVERROR(EFAULT);
> + }
> +
> + ret = copy_init_section(data->pls, data->common_pls);
> + if (ret < 0)
> + goto end;
> + }
> +
> + ret = begin_open_demux_for_component(data->ctx, data->pls);
> + if (ret < 0)
> + goto end;
> +
> + end:
> + data->result = ret;
> +
> + // notify error to other threads and exit
> + if (ret < 0) {
> + pthread_mutex_lock(thread_data->mutex);
> + thread_data->has_error = 1;
> + pthread_mutex_unlock(thread_data->mutex);
> + return NULL;
> + }
> + }
> +
> +
> + return NULL;
> +}
> +
> +static void create_work_pool_data(AVFormatContext *ctx, int stream_index,
> + struct representation *pls, struct representation *common_pls,
> + struct work_pool_data *init_data, pthread_mutex_t *common_mutex,
> + pthread_cond_t *common_condition)
> +{
> + init_data->ctx = ctx;
> + init_data->pls = pls;
> + init_data->pls->stream_index = stream_index;
> + init_data->common_condition = common_condition;
> + init_data->common_mutex = common_mutex;
> + init_data->result = -1;
> +
> + if (pls == common_pls) {
> + init_data->is_common = 1;
> + }
> + else if (common_pls) {
> + init_data->common_pls = common_pls;
> + }
> +}
> +
> +static int start_thread(struct thread_data *thread_data,
> + struct work_pool_data *work_pool, int work_pool_size, pthread_mutex_t *mutex)
> +{
> + int ret;
> +
> + thread_data->mutex = mutex;
> + thread_data->work_pool = work_pool;
> + thread_data->work_pool_size = work_pool_size;
> +
> + ret = AVERROR(pthread_create(&thread_data->thread, NULL, worker_thread, (void*)thread_data));
> + if (ret == 0)
> + thread_data->is_started = 1;
> +
> + return ret;
> +}
> +
> +static int init_streams_multithreaded(AVFormatContext *s, int nstreams, int threads)
> +{
> + DASHContext *c = s->priv_data;
> + int ret = 0;
> + int stream_index = 0;
> + int i;
We allow "for (int i = 0;"
> +
> + // alloc data
> + struct work_pool_data *init_data = (struct work_pool_data*)av_mallocz(sizeof(struct work_pool_data) * nstreams);
> + if (!init_data)
> + return AVERROR(ENOMEM);
> +
> + struct thread_data *thread_data = (struct thread_data*)av_mallocz(sizeof(struct thread_data) * threads);
> + if (!thread_data)
> + return AVERROR(ENOMEM);
1. init_data leaks here on error.
2. In fact, it seems to me that both init_data and thread_data are
nowhere freed.
> +
> + // alloc mutex and conditions
> + pthread_mutex_t work_pool_mutex;
> +
> + pthread_mutex_t common_video_mutex;
> + pthread_cond_t common_video_cond;
> +
> + pthread_mutex_t common_audio_mutex;
> + pthread_cond_t common_audio_cond;
> +
> + pthread_mutex_t common_subtitle_mutex;
> + pthread_cond_t common_subtitle_cond;
> +
> + // init mutex and conditions
> + ret = AVERROR(pthread_mutex_init(&work_pool_mutex, NULL));
> + if (ret < 0)
> + goto cleanup;
> +
> + if (c->is_init_section_common_video) {
> + ret = AVERROR(pthread_mutex_init(&common_video_mutex, NULL));
> + if (ret < 0)
> + goto cleanup;
> +
> + ret = AVERROR(pthread_cond_init(&common_video_cond, NULL));
> + if (ret < 0)
> + goto cleanup;
> + }
> +
> + if (c->is_init_section_common_audio) {
> + ret = AVERROR(pthread_mutex_init(&common_audio_mutex, NULL));
> + if (ret < 0)
> + goto cleanup;
> +
> + ret = AVERROR(pthread_cond_init(&common_audio_cond, NULL));
> + if (ret < 0)
> + goto cleanup;
> + }
> +
> + if (c->is_init_section_common_subtitle) {
> + ret = AVERROR(pthread_mutex_init(&common_subtitle_mutex, NULL));
> + if (ret < 0)
> + goto cleanup;
> +
> + ret = AVERROR(pthread_cond_init(&common_subtitle_cond, NULL));
> + if (ret < 0)
> + goto cleanup;
> + }
> +
> + // init work pool data
> + struct work_pool_data* current_data = init_data;
> +
> + for (i = 0; i < c->n_videos; i++) {
> + create_work_pool_data(s, stream_index, c->videos[i],
> + c->is_init_section_common_video ? c->videos[0] : NULL,
> + current_data, &common_video_mutex, &common_video_cond);
> +
> + stream_index++;
> + current_data++;
> + }
> +
> + for (i = 0; i < c->n_audios; i++) {
> + create_work_pool_data(s, stream_index, c->audios[i],
> + c->is_init_section_common_audio ? c->audios[0] : NULL,
> + current_data, &common_audio_mutex, &common_audio_cond);
> +
> + stream_index++;
> + current_data++;
> + }
> +
> + for (i = 0; i < c->n_subtitles; i++) {
> + create_work_pool_data(s, stream_index, c->subtitles[i],
> + c->is_init_section_common_subtitle ? c->subtitles[0] : NULL,
> + current_data, &common_subtitle_mutex, &common_subtitle_cond);
> +
> + stream_index++;
> + current_data++;
> + }
This is very repetitive.
> +
> + // start threads
> + struct thread_data *current_thread = thread_data;
> + for (i = 0; i < threads; i++) {
> + ret = start_thread(current_thread, init_data, nstreams, &work_pool_mutex);
> + if (ret < 0)
> + goto cleanup;
> +
> + current_thread++;
> + }
> +
> +cleanup:
> + // we need to cleanup even in case of errors, so we need to store results of init, run and cleanup
> + int initResult = ret;
> + int runResult = 0;
> + int cleanupResult = 0;
> +
> + // join threads
> + current_thread = thread_data;
> + for (i = 0; i < threads; i++) {
> + if (current_thread->is_started) {
> + ret = AVERROR(pthread_join(current_thread->thread, NULL));
> + if (ret < 0)
> + cleanupResult = ret;
> + }
> + current_thread++;
> + }
> +
> + // finalize streams and collect results
> + current_data = init_data;
> + for (i = 0; i < nstreams; i++) {
> + if (current_data->result < 0) {
> + // thread ran into error: collect result and break
> + runResult = current_data->result;
> + break;
> + }
> + else {
> + // thread success: create streams on AVFormatContext
> + ret = end_open_demux_for_component(s, current_data->pls);
> + if (ret < 0)
> + runResult = ret;
> + }
> + current_data++;
> + }
> +
> + // cleanup mutex and conditions
> + ret = AVERROR(pthread_mutex_destroy(&work_pool_mutex));
> + if (ret < 0)
> + cleanupResult = ret;
> +
> + if (c->is_init_section_common_video) {
> + ret = AVERROR(pthread_mutex_destroy(&common_video_mutex));
> + if (ret < 0)
> + cleanupResult = ret;
> +
> + ret = AVERROR(pthread_cond_destroy(&common_video_cond));
> + if (ret < 0)
> + cleanupResult = ret;
> + }
> +
> + if (c->is_init_section_common_audio) {
> + ret = AVERROR(pthread_mutex_destroy(&common_audio_mutex));
> + if (ret < 0)
> + cleanupResult = ret;
> +
> + ret = AVERROR(pthread_cond_destroy(&common_audio_cond));
> + if (ret < 0)
> + cleanupResult = ret;
> + }
> +
> + if (c->is_init_section_common_subtitle) {
> + ret = AVERROR(pthread_mutex_destroy(&common_subtitle_mutex));
> + if (ret < 0)
> + cleanupResult = ret;
> +
> + ret = AVERROR(pthread_cond_destroy(&common_subtitle_cond));
> + if (ret < 0)
> + cleanupResult = ret;
> + }
> +
> + // return results if errors have occured in one of the phases
> + if (initResult < 0)
> + return initResult;
> +
> + if (runResult < 0)
> + return runResult;
> +
> + if (cleanupResult < 0)
> + return cleanupResult;
> +
> + return 0;
> +}
> +
> +#endif
> +
> static int dash_read_header(AVFormatContext *s)
> {
> DASHContext *c = s->priv_data;
> @@ -2067,6 +2395,23 @@ static int dash_read_header(AVFormatContext *s)
> if (c->n_subtitles)
> c->is_init_section_common_subtitle = is_common_init_section_exist(c->subtitles, c->n_subtitles);
>
> + int threads = 0;
> + int nstreams = c->n_videos + c->n_audios + c->n_subtitles;
> +
> +#if HAVE_THREADS
> + threads = FFMIN(nstreams, c->init_threads);
> +#endif
> +
> + if (threads > 1)
> + {
> +#if HAVE_THREADS
> + ret = init_streams_multithreaded(s, nstreams, threads);
> + if (ret < 0)
> + return ret;
> +#endif
> + }
> + else
> + {
> /* Open the demuxer for video and audio components if available */
> for (i = 0; i < c->n_videos; i++) {
> rep = c->videos[i];
> @@ -2115,6 +2460,7 @@ static int dash_read_header(AVFormatContext *s)
>
> if (!stream_index)
> return AVERROR_INVALIDDATA;
> + }
>
> /* Create a program */
> program = av_new_program(s, 0);
> @@ -2366,7 +2712,10 @@ static const AVOption dash_options[] = {
> OFFSET(allowed_extensions), AV_OPT_TYPE_STRING,
> {.str = "aac,m4a,m4s,m4v,mov,mp4,webm,ts"},
> INT_MIN, INT_MAX, FLAGS},
> - { "cenc_decryption_key", "Media decryption key (hex)", OFFSET(cenc_decryption_key), AV_OPT_TYPE_STRING, {.str = NULL}, INT_MIN, INT_MAX, .flags = FLAGS },
> + { "cenc_decryption_key", "Media decryption key (hex)", OFFSET(cenc_decryption_key),
> + AV_OPT_TYPE_STRING, {.str = NULL}, INT_MIN, INT_MAX, .flags = FLAGS },
> + { "init_threads", "Number of threads to use for initializing the DASH stream",
> + OFFSET(init_threads), AV_OPT_TYPE_INT, {.i64 = 0}, 0, 64, FLAGS },
> {NULL}
> };
>
> --
> 2.31.1.windows.1
>
1. We actually have an API to process multiple tasks by different
threads: Look at libavutil/slicethread.h. Why can't you reuse that?
2. In case initialization of one of the conditions/mutexes fails, you
are nevertheless destroying them; you are even destroying completely
uninitialized mutexes. This is undefined behaviour. Checking the result
of it does not fix this.
- Andreas
More information about the ffmpeg-devel
mailing list