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

[nageru] / mux.h

diff --git a/mux.h b/mux.h
index c6c442100c58b18c481754747693b54c8571bcbc..5bf3e413014e7f0de6caf1e992e2747dc573fe98 100644 (file)
--- a/mux.h
+++ b/mux.h
@@ -10,10 +10,12 @@ extern "C" {
 
 #include <sys/types.h>
 #include <atomic>
+#include <condition_variable>
 #include <functional>
 #include <mutex>
 #include <string>
 #include <utility>
+#include <thread>
 #include <vector>
 
 struct MuxMetrics {
@@ -39,13 +41,24 @@ public:
                CODEC_H264,
                CODEC_NV12,  // Uncompressed 4:2:0.
        };
+       enum WriteStrategy {
+               // add_packet() will write the packet immediately, unless plugged.
+               WRITE_FOREGROUND,
+
+               // All writes will happen on a separate thread, so add_packet()
+               // won't block. Use this if writing to a file and you might be
+               // holding a mutex (because blocking I/O with a mutex held is
+               // not good). Note that this will clone every packet, so it has
+               // higher overhead.
+               WRITE_BACKGROUND,
+       };
 
        // Takes ownership of avctx. <write_callback> will be called every time
        // a write has been made to the video stream (id 0), with the pts of
        // the just-written frame. (write_callback can be nullptr.)
        // Does not take ownership of <metrics>; elements in there, if any,
        // will be added to.
-       Mux(AVFormatContext *avctx, int width, int height, Codec video_codec, const std::string &video_extradata, const AVCodecParameters *audio_codecpar, int time_base, std::function<void(int64_t)> write_callback, const std::vector<MuxMetrics *> &metrics);
+       Mux(AVFormatContext *avctx, int width, int height, Codec video_codec, const std::string &video_extradata, const AVCodecParameters *audio_codecpar, int time_base, std::function<void(int64_t)> write_callback, WriteStrategy write_strategy, const std::vector<MuxMetrics *> &metrics);
        ~Mux();
        void add_packet(const AVPacket &pkt, int64_t pts, int64_t dts);
 
@@ -61,17 +74,36 @@ public:
        void unplug();
 
 private:
-       void write_packet_or_die(const AVPacket &pkt);  // Must be called with <mu> held.
+       // If write_strategy == WRITE_FOREGORUND, Must be called with <mu> held.
+       void write_packet_or_die(const AVPacket &pkt, int64_t unscaled_pts);
+       void thread_func();
+
+       WriteStrategy write_strategy;
 
        std::mutex mu;
-       AVFormatContext *avctx;  // Protected by <mu>.
+
+       // These are only in use if write_strategy == WRITE_BACKGROUND.
+       std::atomic<bool> writer_thread_should_quit{false};
+       std::thread writer_thread;
+
+       AVFormatContext *avctx;  // Protected by <mu>, iff write_strategy == WRITE_BACKGROUND.
        int plug_count = 0;  // Protected by <mu>.
-       std::vector<AVPacket *> plugged_packets;  // Protected by <mu>.
+
+       // Protected by <mu>. If write_strategy == WRITE_FOREGROUND,
+       // this is only in use when plugging.
+       struct QueuedPacket {
+               AVPacket *pkt;
+               int64_t unscaled_pts;
+       };
+       std::vector<QueuedPacket> packet_queue;
+       std::condition_variable packet_queue_ready;
 
        AVStream *avstream_video, *avstream_audio;
 
        std::function<void(int64_t)> write_callback;
        std::vector<MuxMetrics *> metrics;
+
+       friend struct PacketBefore;
 };
 
 #endif  // !defined(_MUX_H)