RTCStatsCollector: Utilize network thread to minimize thread hops.

webrtc/p2p/base/transportcontroller.h

Index: webrtc/p2p/base/transportcontroller.h
diff --git a/webrtc/p2p/base/transportcontroller.h b/webrtc/p2p/base/transportcontroller.h
index ea5ec80a901dfc0fd11bcbfb155add02c3e55717..9a456967d3326c017a825bbd693963111833d933 100644
--- a/webrtc/p2p/base/transportcontroller.h
+++ b/webrtc/p2p/base/transportcontroller.h
@@ -83,10 +83,15 @@ class TransportController : public sigslot::has_slots<>,
   bool GetLocalCertificate(
       const std::string& transport_name,
       rtc::scoped_refptr<rtc::RTCCertificate>* certificate) const;
+  bool GetLocalCertificate_n(
+      const std::string& transport_name,
+      rtc::scoped_refptr<rtc::RTCCertificate>* certificate) const;

[Taylor Brandstetter, 2016/12/13 19:47:07]

I'd prefer only leaving the non "_n" methods public. If you're concerned about
the overhead of Thread::Invoke, we can just do:

if (network_thread_->IsCurrent()) {
  DoThingDirectly();
} else {
  network_thread_->Invoke(...);
}

[pthatcher1, 2016/12/13 23:50:19]

I agree.

But I think it would be even better if you could do this:

auto transport = GetTransport(transport_name);
transport->GetCertificate();
transport->GetRemoteSslCertificate();
transport->GetStats();
...

In fact, you almost can except for the current distinction between Transport and
TransportChannel, and maybe between TransportChannel and DtlsTransportChannel. 
But we're currently working on cleaning that up.  And you can probably do close
to that right now.

[hbos, 2016/12/14 14:56:31]

Done : Removing unnecessary "_n" methods, allowing existing methods to be
invoked on any thread with the "if thread is current" logic.

See other comment about not wanting to do too much refactoring here (not doing
GetTransport).

   // Caller owns returned certificate. This method mainly exists for stats
   // reporting.
   std::unique_ptr<rtc::SSLCertificate> GetRemoteSSLCertificate(
       const std::string& transport_name) const;
+  std::unique_ptr<rtc::SSLCertificate> GetRemoteSSLCertificate_n(
+      const std::string& transport_name) const;
   bool SetLocalTransportDescription(const std::string& transport_name,
                                     const TransportDescription& tdesc,
                                     ContentAction action,
@@ -107,6 +112,7 @@ class TransportController : public sigslot::has_slots<>,
   // OpenSSLStreamAdapter,
   // GetSslCipherSuite and GetDtlsSrtpCryptoSuite are not const. Fix this.
   bool GetStats(const std::string& transport_name, TransportStats* stats);
+  bool GetStats_n(const std::string& transport_name, TransportStats* stats);
   void SetMetricsObserver(webrtc::MetricsObserverInterface* metrics_observer);
 
   // Creates a channel if it doesn't exist. Otherwise, increments a reference
@@ -231,11 +237,6 @@ class TransportController : public sigslot::has_slots<>,
                     rtc::SSLRole* role) const;
   bool SetLocalCertificate_n(
       const rtc::scoped_refptr<rtc::RTCCertificate>& certificate);
-  bool GetLocalCertificate_n(
-      const std::string& transport_name,
-      rtc::scoped_refptr<rtc::RTCCertificate>* certificate) const;
-  std::unique_ptr<rtc::SSLCertificate> GetRemoteSSLCertificate_n(
-      const std::string& transport_name) const;
   bool SetLocalTransportDescription_n(const std::string& transport_name,
                                       const TransportDescription& tdesc,
                                       ContentAction action,
@@ -250,7 +251,6 @@ class TransportController : public sigslot::has_slots<>,
                              std::string* err);
   bool RemoveRemoteCandidates_n(const Candidates& candidates, std::string* err);
   bool ReadyForRemoteCandidates_n(const std::string& transport_name) const;
-  bool GetStats_n(const std::string& transport_name, TransportStats* stats);
   void SetMetricsObserver_n(webrtc::MetricsObserverInterface* metrics_observer);
 
   // Handlers for signals from Transport.