FrameBuffer2 now has Start/Stop methods.

The Stop method is used to signal any thread that is waiting in the
NextFrame function and will cause it to return immediately.

BUG=webrtc:5514
R=pbos@webrtc.org

Review URL: https://codereview.webrtc.org/2105323002 .

Cr-Commit-Position: refs/heads/master@{#13349}

webrtc/modules/video_coding/frame_buffer2.cc

@@ -47,17 +47,25 @@ FrameBuffer::FrameBuffer(Clock* clock,
       frame_inserted_event_(false, false),
       jitter_estimator_(jitter_estimator),
       timing_(timing),
-      newest_picture_id_(-1) {}
+      newest_picture_id_(-1),
+      stopped_(false) {}
 
 std::unique_ptr<FrameObject> FrameBuffer::NextFrame(int64_t max_wait_time_ms) {
   int64_t latest_return_time = clock_->TimeInMilliseconds() + max_wait_time_ms;
-  while (true) {
   int64_t now = clock_->TimeInMilliseconds();
   int64_t wait_ms = max_wait_time_ms;
-
-    crit_.Enter();
+  while (true) {
+    std::map<FrameKey, std::unique_ptr<FrameObject>, FrameComp>::iterator
+        next_frame;
+    {
+      rtc::CritScope lock(&crit_);
       frame_inserted_event_.Reset();
-    auto next_frame = frames_.end();
+      if (stopped_)
+        return std::unique_ptr<FrameObject>();
+
+      now = clock_->TimeInMilliseconds();
+      wait_ms = max_wait_time_ms;
+      next_frame = frames_.end();
       for (auto frame_it = frames_.begin(); frame_it != frames_.end();
            ++frame_it) {
         const FrameObject& frame = *frame_it->second;
@@ -75,14 +83,14 @@ std::unique_ptr<FrameObject> FrameBuffer::NextFrame(int64_t max_wait_time_ms) {
           break;
         }
       }
-    crit_.Leave();
+    }
 
     // If the timout occures, return. Otherwise a new frame has been inserted
     // and the best frame to decode next will be selected again.
     wait_ms = std::min<int64_t>(wait_ms, latest_return_time - now);
     wait_ms = std::max<int64_t>(wait_ms, 0);
     if (!frame_inserted_event_.Wait(wait_ms)) {
-      crit_.Enter();
+      rtc::CritScope lock(&crit_);
       if (next_frame != frames_.end()) {
         // TODO(philipel): update jitter estimator with correct values.
         jitter_estimator_->UpdateEstimate(100, 100);
@@ -90,16 +98,25 @@ std::unique_ptr<FrameObject> FrameBuffer::NextFrame(int64_t max_wait_time_ms) {
         decoded_frames_.insert(next_frame->first);
         std::unique_ptr<FrameObject> frame = std::move(next_frame->second);
         frames_.erase(frames_.begin(), ++next_frame);
-        crit_.Leave();
         return frame;
       } else {
-        crit_.Leave();
         return std::unique_ptr<FrameObject>();
       }
     }
   }
 }
 
+void FrameBuffer::Start() {
+  rtc::CritScope lock(&crit_);
+  stopped_ = false;
+}
+
+void FrameBuffer::Stop() {
+  rtc::CritScope lock(&crit_);
+  stopped_ = true;
+  frame_inserted_event_.Set();
+}
+
 void FrameBuffer::InsertFrame(std::unique_ptr<FrameObject> frame) {
   rtc::CritScope lock(&crit_);
   if (newest_picture_id_ == -1)

webrtc/modules/video_coding/frame_buffer2.h

@@ -46,6 +46,14 @@ class FrameBuffer {
   // unique ptr if there is no available frame for decoding.
   std::unique_ptr<FrameObject> NextFrame(int64_t max_wait_time_ms);
 
+  // Start the frame buffer, has no effect if the frame buffer is started.
+  // The frame buffer is started upon construction.
+  void Start();
+
+  // Stop the frame buffer, causing any sleeping thread in NextFrame to
+  // return immediately.
+  void Stop();
+
  private:
   // FrameKey is a pair of (picture id, spatial layer).
   using FrameKey = std::pair<uint16_t, uint8_t>;
@@ -73,6 +81,7 @@ class FrameBuffer {
   VCMJitterEstimator* const jitter_estimator_;
   const VCMTiming* const timing_;
   int newest_picture_id_ GUARDED_BY(crit_);
+  bool stopped_ GUARDED_BY(crit_);
 
   RTC_DISALLOW_IMPLICIT_CONSTRUCTORS(FrameBuffer);
 };