Write video to disk on a background thread; reduces mutex contention a fair bit when...

[nageru] / mux.cpp

diff --git a/mux.cpp b/mux.cpp
index d01c18038a893cfec7152d35d8e3b0f1131ed0fb..5c6a150edd80e80e1e2825e6ab1d012f1a33253f 100644 (file)
--- a/mux.cpp
+++ b/mux.cpp
@@ -31,7 +31,9 @@ using namespace std;
 struct PacketBefore {
        PacketBefore(const AVFormatContext *ctx) : ctx(ctx) {}
 
-       bool operator() (const AVPacket *a, const AVPacket *b) const {
+       bool operator() (const Mux::QueuedPacket &a_qp, const Mux::QueuedPacket &b_qp) const {
+               const AVPacket *a = a_qp.pkt;
+               const AVPacket *b = b_qp.pkt;
                int64_t a_dts = (a->dts == AV_NOPTS_VALUE ? a->pts : a->dts);
                int64_t b_dts = (b->dts == AV_NOPTS_VALUE ? b->pts : b->dts);
                AVRational a_timebase = ctx->streams[a->stream_index]->time_base;
@@ -46,8 +48,8 @@ struct PacketBefore {
        const AVFormatContext * const ctx;
 };
 
-Mux::Mux(AVFormatContext *avctx, int width, int height, Codec video_codec, const string &video_extradata, const AVCodecParameters *audio_codecpar, int time_base, std::function<void(int64_t)> write_callback, const vector<MuxMetrics *> &metrics)
-       : avctx(avctx), write_callback(write_callback), metrics(metrics)
+Mux::Mux(AVFormatContext *avctx, int width, int height, Codec video_codec, const string &video_extradata, const AVCodecParameters *audio_codecpar, int time_base, std::function<void(int64_t)> write_callback, WriteStrategy write_strategy, const vector<MuxMetrics *> &metrics)
+       : write_strategy(write_strategy), avctx(avctx), write_callback(write_callback), metrics(metrics)
 {
        avstream_video = avformat_new_stream(avctx, nullptr);
        if (avstream_video == nullptr) {
@@ -116,10 +118,20 @@ Mux::Mux(AVFormatContext *avctx, int width, int height, Codec video_codec, const
 
        // Make sure the header is written before the constructor exits.
        avio_flush(avctx->pb);
+
+       if (write_strategy == WRITE_BACKGROUND) {
+               writer_thread = thread(&Mux::thread_func, this);
+       }
 }
 
 Mux::~Mux()
 {
+       assert(plug_count == 0);
+       if (write_strategy == WRITE_BACKGROUND) {
+               writer_thread_should_quit = true;
+               packet_queue_ready.notify_all();
+               writer_thread.join();
+       }
        int64_t old_pos = avctx->pb->pos;
        av_write_trailer(avctx);
        for (MuxMetrics *metric : metrics) {
@@ -154,25 +166,20 @@ void Mux::add_packet(const AVPacket &pkt, int64_t pts, int64_t dts)
 
        {
                lock_guard<mutex> lock(mu);
-               if (plug_count > 0) {
-                       plugged_packets.push_back(av_packet_clone(&pkt_copy));
+               if (write_strategy == WriteStrategy::WRITE_BACKGROUND) {
+                       packet_queue.push_back(QueuedPacket{ av_packet_clone(&pkt_copy), pts });
+                       if (plug_count == 0) packet_queue_ready.notify_all();
+               } else if (plug_count > 0) {
+                       packet_queue.push_back(QueuedPacket{ av_packet_clone(&pkt_copy), pts });
                } else {
-                       write_packet_or_die(pkt_copy);
+                       write_packet_or_die(pkt_copy, pts);
                }
        }
 
        av_packet_unref(&pkt_copy);
-
-       // Note: This will be wrong in the case of plugged packets, but that only happens
-       // for network streams, not for files, and write callbacks are only really relevant
-       // for files. (We don't want to do this from write_packet_or_die, as it only has
-       // the rescaled pts, which is unsuitable for callback.)
-       if (pkt.stream_index == 0 && write_callback != nullptr) {
-               write_callback(pts);
-       }
 }
 
-void Mux::write_packet_or_die(const AVPacket &pkt)
+void Mux::write_packet_or_die(const AVPacket &pkt, int64_t unscaled_pts)
 {
        for (MuxMetrics *metric : metrics) {
                if (pkt.stream_index == 0) {
@@ -192,6 +199,10 @@ void Mux::write_packet_or_die(const AVPacket &pkt)
        for (MuxMetrics *metric : metrics) {
                metric->metric_written_bytes += avctx->pb->pos - old_pos;
        }
+
+       if (pkt.stream_index == 0 && write_callback != nullptr) {
+               write_callback(unscaled_pts);
+       }
 }
 
 void Mux::plug()
@@ -208,13 +219,42 @@ void Mux::unplug()
        }
        assert(plug_count >= 0);
 
-       sort(plugged_packets.begin(), plugged_packets.end(), PacketBefore(avctx));
+       sort(packet_queue.begin(), packet_queue.end(), PacketBefore(avctx));
 
-       for (AVPacket *pkt : plugged_packets) {
-               write_packet_or_die(*pkt);
-               av_packet_free(&pkt);
+       if (write_strategy == WRITE_BACKGROUND) {
+               packet_queue_ready.notify_all();
+       } else {
+               for (QueuedPacket &qp : packet_queue) {
+                       write_packet_or_die(*qp.pkt, qp.unscaled_pts);
+                       av_packet_free(&qp.pkt);
+               }
+               packet_queue.clear();
+       }
+}
+
+void Mux::thread_func()
+{
+       unique_lock<mutex> lock(mu);
+       for ( ;; ) {
+               packet_queue_ready.wait(lock, [this]() {
+                       return writer_thread_should_quit || (!packet_queue.empty() && plug_count == 0);
+               });
+               if (writer_thread_should_quit && packet_queue.empty()) {
+                       // All done.
+                       break;
+               }
+
+               assert(!packet_queue.empty() && plug_count == 0);
+               vector<QueuedPacket> packets;
+               swap(packets, packet_queue);
+
+               lock.unlock();
+               for (QueuedPacket &qp : packets) {
+                       write_packet_or_die(*qp.pkt, qp.unscaled_pts);
+                       av_packet_free(&qp.pkt);
+               }
+               lock.lock();
        }
-       plugged_packets.clear();
 }
 
 void MuxMetrics::init(const vector<pair<string, string>> &labels)