Record asynchronously

The record file was written from the stream thread. As a consequence,
any blocking I/O to write the file delayed the decoder.

For maximum performance even when recording is enabled, send
(refcounted) packets to a separate recording thread.

app/src/recorder.c

@@ -5,6 +5,7 @@
 
 #include "compat.h"
 #include "config.h"
+#include "lock_util.h"
 #include "log.h"
 
 static const AVRational SCRCPY_TIME_BASE = {1, 1000000}; // timestamps in us
@@ -26,6 +27,82 @@ find_muxer(const char *name) {
     return oformat;
 }
 
+static struct record_packet *
+record_packet_new(const AVPacket *packet) {
+    struct record_packet *rec = SDL_malloc(sizeof(*rec));
+    if (!rec) {
+        return NULL;
+    }
+    if (av_packet_ref(&rec->packet, packet)) {
+        SDL_free(rec);
+        return NULL;
+    }
+    rec->next = NULL;
+    return rec;
+}
+
+static void
+record_packet_delete(struct record_packet *rec) {
+    av_packet_unref(&rec->packet);
+    SDL_free(rec);
+}
+
+static void
+recorder_queue_init(struct recorder_queue *queue) {
+    queue->first = NULL;
+    // queue->last is undefined if queue->first == NULL
+}
+
+static inline bool
+recorder_queue_is_empty(struct recorder_queue *queue) {
+    return !queue->first;
+}
+
+static bool
+recorder_queue_push(struct recorder_queue *queue, const AVPacket *packet) {
+    struct record_packet *rec = record_packet_new(packet);
+    if (!rec) {
+        LOGC("Could not allocate record packet");
+        return false;
+    }
+    rec->next = NULL;
+
+    if (recorder_queue_is_empty(queue)) {
+        queue->first = queue->last = rec;
+    } else {
+        // chain rec after the (current) last packet
+        queue->last->next = rec;
+        // the last packet is now rec
+        queue->last = rec;
+    }
+    return true;
+}
+
+static inline struct record_packet *
+recorder_queue_take(struct recorder_queue *queue) {
+    SDL_assert(!recorder_queue_is_empty(queue));
+
+    struct record_packet *rec = queue->first;
+    SDL_assert(rec);
+
+    queue->first = rec->next;
+    // no need to update queue->last if the queue is left empty:
+    // queue->last is undefined if queue->first == NULL
+
+    return rec;
+}
+
+static void
+recorder_queue_clear(struct recorder_queue *queue) {
+    struct record_packet *rec = queue->first;
+    while (rec) {
+        struct record_packet *current = rec;
+        rec = rec->next;
+        record_packet_delete(current);
+    }
+    queue->first = NULL;
+}
+
 bool
 recorder_init(struct recorder *recorder,
               const char *filename,
@@ -37,6 +114,24 @@ recorder_init(struct recorder *recorder,
         return false;
     }
 
+    recorder->mutex = SDL_CreateMutex();
+    if (!recorder->mutex) {
+        LOGC("Could not create mutex");
+        SDL_free(recorder->filename);
+        return false;
+    }
+
+    recorder->queue_cond = SDL_CreateCond();
+    if (!recorder->queue_cond) {
+        LOGC("Could not create cond");
+        SDL_DestroyMutex(recorder->mutex);
+        SDL_free(recorder->filename);
+        return false;
+    }
+
+    recorder_queue_init(&recorder->queue);
+    recorder->stopped = false;
+    recorder->failed = false;
     recorder->format = format;
     recorder->declared_frame_size = declared_frame_size;
     recorder->header_written = false;
@@ -46,6 +141,8 @@ recorder_init(struct recorder *recorder,
 
 void
 recorder_destroy(struct recorder *recorder) {
+    SDL_DestroyCond(recorder->queue_cond);
+    SDL_DestroyMutex(recorder->mutex);
     SDL_free(recorder->filename);
 }
 
@@ -186,3 +283,90 @@ recorder_write(struct recorder *recorder, AVPacket *packet) {
     recorder_rescale_packet(recorder, packet);
     return av_write_frame(recorder->ctx, packet) >= 0;
 }
+
+static int
+run_recorder(void *data) {
+    struct recorder *recorder = data;
+
+    for (;;) {
+        mutex_lock(recorder->mutex);
+
+        while (!recorder->stopped &&
+                recorder_queue_is_empty(&recorder->queue)) {
+            cond_wait(recorder->queue_cond, recorder->mutex);
+        }
+
+        // if stopped is set, continue to process the remaining events (to
+        // finish the recording) before actually stopping
+
+        if (recorder->stopped && recorder_queue_is_empty(&recorder->queue)) {
+            mutex_unlock(recorder->mutex);
+            break;
+        }
+
+        struct record_packet *rec = recorder_queue_take(&recorder->queue);
+
+        mutex_unlock(recorder->mutex);
+
+        bool ok = recorder_write(recorder, &rec->packet);
+        record_packet_delete(rec);
+        if (!ok) {
+            LOGE("Could not record packet");
+
+            mutex_lock(recorder->mutex);
+            recorder->failed = true;
+            // discard pending packets
+            recorder_queue_clear(&recorder->queue);
+            mutex_unlock(recorder->mutex);
+            break;
+        }
+
+    }
+
+    LOGD("Recorder thread ended");
+
+    return 0;
+}
+
+bool
+recorder_start(struct recorder *recorder) {
+    LOGD("Starting recorder thread");
+
+    recorder->thread = SDL_CreateThread(run_recorder, "recorder", recorder);
+    if (!recorder->thread) {
+        LOGC("Could not start recorder thread");
+        return false;
+    }
+
+    return true;
+}
+
+void
+recorder_stop(struct recorder *recorder) {
+    mutex_lock(recorder->mutex);
+    recorder->stopped = true;
+    cond_signal(recorder->queue_cond);
+    mutex_unlock(recorder->mutex);
+}
+
+void
+recorder_join(struct recorder *recorder) {
+    SDL_WaitThread(recorder->thread, NULL);
+}
+
+bool
+recorder_push(struct recorder *recorder, const AVPacket *packet) {
+    mutex_lock(recorder->mutex);
+    SDL_assert(!recorder->stopped);
+
+    if (recorder->failed) {
+        // reject any new packet (this will stop the stream)
+        return false;
+    }
+
+    bool ok = recorder_queue_push(&recorder->queue, packet);
+    cond_signal(recorder->queue_cond);
+
+    mutex_unlock(recorder->mutex);
+    return ok;
+}

app/src/recorder.h

@@ -3,6 +3,8 @@
 
 #include <stdbool.h>
 #include <libavformat/avformat.h>
+#include <SDL2/SDL_mutex.h>
+#include <SDL2/SDL_thread.h>
 
 #include "common.h"
 
@@ -11,12 +13,29 @@ enum recorder_format {
     RECORDER_FORMAT_MKV,
 };
 
+struct record_packet {
+    AVPacket packet;
+    struct record_packet *next;
+};
+
+struct recorder_queue {
+    struct record_packet *first;
+    struct record_packet *last; // undefined if first is NULL
+};
+
 struct recorder {
     char *filename;
     enum recorder_format format;
     AVFormatContext *ctx;
     struct size declared_frame_size;
     bool header_written;
+
+    SDL_Thread *thread;
+    SDL_mutex *mutex;
+    SDL_cond *queue_cond;
+    bool stopped; // set on recorder_stop() by the stream reader
+    bool failed; // set on packet write failure
+    struct recorder_queue queue;
 };
 
 bool
@@ -33,6 +52,15 @@ void
 recorder_close(struct recorder *recorder);
 
 bool
-recorder_write(struct recorder *recorder, AVPacket *packet);
+recorder_start(struct recorder *recorder);
+
+void
+recorder_stop(struct recorder *recorder);
+
+void
+recorder_join(struct recorder *recorder);
+
+bool
+recorder_push(struct recorder *recorder, const AVPacket *packet);
 
 #endif

app/src/stream.c

@@ -71,7 +71,7 @@ notify_stopped(void) {
 
 static bool
 process_config_packet(struct stream *stream, AVPacket *packet) {
-    if (stream->recorder && !recorder_write(stream->recorder, packet)) {
+    if (stream->recorder && !recorder_push(stream->recorder, packet)) {
         LOGE("Could not send config packet to recorder");
         return false;
     }
@@ -87,8 +87,8 @@ process_frame(struct stream *stream, AVPacket *packet) {
     if (stream->recorder) {
         packet->dts = packet->pts;
 
-        if (!recorder_write(stream->recorder, packet)) {
-            LOGE("Could not write frame to output file");
+        if (!recorder_push(stream->recorder, packet)) {
+            LOGE("Could not send packet to recorder");
             return false;
         }
     }
@@ -201,15 +201,22 @@ run_stream(void *data) {
         goto finally_free_codec_ctx;
     }
 
-    if (stream->recorder && !recorder_open(stream->recorder, codec)) {
+    if (stream->recorder) {
+        if (!recorder_open(stream->recorder, codec)) {
             LOGE("Could not open recorder");
             goto finally_close_decoder;
         }
 
+        if (!recorder_start(stream->recorder)) {
+            LOGE("Could not start recorder");
+            goto finally_close_recorder;
+        }
+    }
+
     stream->parser = av_parser_init(AV_CODEC_ID_H264);
     if (!stream->parser) {
         LOGE("Could not initialize parser");
-        goto finally_close_recorder;
+        goto finally_stop_and_join_recorder;
     }
 
     // We must only pass complete frames to av_parser_parse2()!
@@ -239,6 +246,12 @@ run_stream(void *data) {
     }
 
     av_parser_close(stream->parser);
+finally_stop_and_join_recorder:
+    if (stream->recorder) {
+        recorder_stop(stream->recorder);
+        LOGI("Finishing recording...");
+        recorder_join(stream->recorder);
+    }
 finally_close_recorder:
     if (stream->recorder) {
         recorder_close(stream->recorder);