RTCStatsCollector collecting stats on multiple threads.

webrtc/stats/rtcstatscollector.h

Index: webrtc/stats/rtcstatscollector.h
diff --git a/webrtc/stats/rtcstatscollector.h b/webrtc/stats/rtcstatscollector.h
index 735421d5410533e0b642125c3b27262aed30062a..ee59a100225489f57495064638c6b072aa2f66c5 100644
--- a/webrtc/stats/rtcstatscollector.h
+++ b/webrtc/stats/rtcstatscollector.h
@@ -12,9 +12,12 @@
 #define WEBRTC_STATS_RTCSTATSCOLLECTOR_H_
 
 #include <memory>
+#include <vector>
 
 #include "webrtc/api/rtcstats_objects.h"
 #include "webrtc/api/rtcstatsreport.h"
+#include "webrtc/base/asyncinvoker.h"
+#include "webrtc/base/refcount.h"
 #include "webrtc/base/scoped_ref_ptr.h"
 #include "webrtc/base/timeutils.h"
 
@@ -22,11 +25,21 @@ namespace webrtc {
 
 class PeerConnection;
 
-// All calls to the collector and gathering of stats is performed on the
-// signaling thread. A stats report is cached for |cache_lifetime_| ms.
-class RTCStatsCollector {
+class RTCStatsCollectorCallback : public virtual rtc::RefCountInterface {
  public:
-  explicit RTCStatsCollector(
+  virtual ~RTCStatsCollectorCallback() {}
+
+  virtual void OnStatsDelivered(
+      const rtc::scoped_refptr<const RTCStatsReport>& report) = 0;
+};
+
+// All public methods of the collector are to be called on the signaling thread.
+// Stats are gathered on the signaling, worker and network threads
+// asynchronously. The callback is invoked on the signaling thread. Resulting
+// reports are cached for |cache_lifetime_| ms.
+class RTCStatsCollector : public virtual rtc::RefCountInterface {
+ public:
+  static rtc::scoped_refptr<RTCStatsCollector> Create(
       PeerConnection* pc,
       int64_t cache_lifetime_us = 50 * rtc::kNumMicrosecsPerMillisec);
 
@@ -34,18 +47,42 @@ class RTCStatsCollector {
   // it is returned, otherwise new stats are gathered and returned. A report is
   // considered fresh for |cache_lifetime_| ms. const RTCStatsReports are safe
   // to use across multiple threads and may be destructed on any thread.
-  rtc::scoped_refptr<const RTCStatsReport> GetStatsReport();
+  void GetStatsReport(rtc::scoped_refptr<RTCStatsCollectorCallback> callback);
   // Clears the cache's reference to the most recent stats report. Subsequently
   // calling |GetStatsReport| guarantees fresh stats.
   void ClearCachedStatsReport();
 
+ protected:
+  RTCStatsCollector(PeerConnection* pc, int64_t cache_lifetime_us);
+
+  // Stats gathering on a particular thread. Calls |AddPartialResults| before
+  // returning. Virtual for the sake of testing.
+  virtual void ProducePartialResultsOnSignalingThread(int64_t timestamp_us);
+  virtual void ProducePartialResultsOnWorkerThread(int64_t timestamp_us);
+  virtual void ProducePartialResultsOnNetworkThread(int64_t timestamp_us);
+
+  // Can be called on any thread.
+  void AddPartialResults(
+      const rtc::scoped_refptr<RTCStatsReport>& partial_report);
+
  private:
-  bool IsOnSignalingThread() const;
+  void AddPartialResults_s(rtc::scoped_refptr<RTCStatsReport> partial_report);
+  void DeliverCachedReport();
 
-  std::unique_ptr<RTCPeerConnectionStats> ProducePeerConnectionStats(
+  std::unique_ptr<RTCPeerConnectionStats> ProducePeerConnectionStats_s(
       int64_t timestamp_us) const;
 
   PeerConnection* const pc_;
+  rtc::Thread* const signaling_thread_;
+  rtc::Thread* const worker_thread_;
+  rtc::Thread* const network_thread_;
+  rtc::AsyncInvoker invoker_;
+
+  int num_pending_partial_reports_;
+  int64_t partial_report_timestamp_us_;
+  rtc::scoped_refptr<RTCStatsReport> partial_report_;
+  std::vector<rtc::scoped_refptr<RTCStatsCollectorCallback>> callbacks_;
+
   // A timestamp, in microseconds, that is based on a timer that is
   // monotonically increasing. That is, even if the system clock is modified the
   // difference between the timer and this timestamp is how fresh the cached