commit c6b919f3f421fd3156b8a305c7eb8eded4ed9bf3
author Ravago Jones <ravagojones@gmail.com> Sun Jan 01 21:34:12 2023 -0800
committer Ravago Jones <ravagojones@gmail.com> Tue Jan 31 20:43:37 2023 -0800
tree d21d0f5b7ee59898ecb083a7cd2f5d04fa1cc722
parent dd9db205452a1cbe6787a8e8ce468f098943471c

Defer requeuing buffers in v4l2 reader

Enqueuing buffers takes a long time, so we want to move it out of the
way of images being sent.

Requeue the buffers in a worker thread that's running at a lower
priority.

Signed-off-by: Ravago Jones <ravagojones@gmail.com>
Change-Id: I3887bca9099916b1864ff88893b940d6a31f7edf

frc971/vision/v4l2_reader.h

diff --git a/frc971/vision/v4l2_reader.h b/frc971/vision/v4l2_reader.h
index 669c157..31c0888 100644
--- a/frc971/vision/v4l2_reader.h
+++ b/frc971/vision/v4l2_reader.h
@@ -5,10 +5,13 @@
 #include <string>
 
 #include "absl/types/span.h"
+#include "aos/containers/ring_buffer.h"
 #include "aos/events/epoll.h"
 #include "aos/events/event_loop.h"
 #include "aos/ftrace.h"
+#include "aos/realtime.h"
 #include "aos/scoped/scoped_fd.h"
+#include "aos/util/threaded_consumer.h"
 #include "frc971/vision/vision_generated.h"
 #include "glog/logging.h"
 
@@ -57,6 +60,23 @@
   void StreamOff();
   void StreamOn();
 
+  // Enqueues a buffer for v4l2 to stream into (expensive).
+  void EnqueueBuffer(int buffer_index);
+
+  // Initializations that need to happen in the main thread.
+  //
+  // Implementations of MarkBufferToBeEnqueued should call this before calling
+  // EnqueueBuffer.
+  void ReinitializeBuffer(int buffer_index) {
+    CHECK_GE(buffer_index, 0);
+    CHECK_LT(buffer_index, static_cast<int>(buffers_.size()));
+    buffers_[buffer_index].InitializeMessage(ImageSize());
+  }
+
+  // Submits a buffer to be enqueued later in a lower priority thread.
+  // Legacy V4L2Reader still does this in the main thread.
+  virtual void MarkBufferToBeEnqueued(int buffer_index);
+
   int Ioctl(unsigned long number, void *arg);
 
   bool multiplanar() const { return multiplanar_; }
@@ -70,9 +90,9 @@
 
   const aos::ScopedFD &fd() { return fd_; };
 
- private:
   static constexpr int kNumberBuffers = 4;
 
+ private:
   struct Buffer {
     void InitializeMessage(size_t max_image_size);
 
@@ -113,8 +133,6 @@
   // buffer, or BufferInfo() if there wasn't a frame to dequeue.
   BufferInfo DequeueBuffer();
 
-  void EnqueueBuffer(int buffer);
-
   // The mmaped V4L2 buffers.
   std::array<Buffer, kNumberBuffers> buffers_;
 
@@ -159,11 +177,15 @@
  private:
   void OnImageReady();
 
+  void MarkBufferToBeEnqueued(int buffer) override;
+
   int ImageSensorIoctl(unsigned long number, void *arg);
 
   aos::internal::EPoll *epoll_;
 
   aos::ScopedFD image_sensor_fd_;
+
+  aos::util::ThreadedConsumer<int, kNumberBuffers> buffer_requeuer_;
 };
 
 }  // namespace vision