Bug 962044 - Forward event loop lag messages via an observer. r=ted

toolkit/xre/EventTracer.cpp

@@ -64,6 +64,12 @@
 #include <prthread.h>
 #include <prtime.h>
 
+#ifdef MOZ_WIDGET_GONK
+#include "nsThreadUtils.h"
+#include "nsIObserverService.h"
+#include "mozilla/Services.h"
+#endif
+
 using mozilla::TimeDuration;
 using mozilla::TimeStamp;
 using mozilla::FireAndWaitForTracerEvent;
@@ -77,6 +83,31 @@ struct TracerStartClosure {
   bool mLogTracing;
 };
 
+#ifdef MOZ_WIDGET_GONK
+class EventLoopLagDispatcher : public nsRunnable
+{
+  public:
+    explicit EventLoopLagDispatcher(int aLag)
+      : mLag(aLag) {}
+
+    NS_IMETHODIMP Run()
+    {
+      nsCOMPtr<nsIObserverService> obsService =
+        mozilla::services::GetObserverService();
+      if (!obsService) {
+        return NS_ERROR_FAILURE;
+      }
+
+      nsAutoString value;
+      value.AppendInt(mLag);
+      return obsService->NotifyObservers(nullptr, "event-loop-lag", value.get());
+    }
+
+  private:
+    int mLag;
+};
+#endif
+
 /*
  * The tracer thread fires events at the native event loop roughly
  * every kMeasureInterval. It will sleep to attempt not to send them
@@ -146,6 +177,10 @@ void TracerThread(void *arg)
         fprintf(log, "MOZ_EVENT_TRACE sample %llu %lf\n",
                 now,
                 duration.ToMilliseconds());
+#ifdef MOZ_WIDGET_GONK
+        NS_DispatchToMainThread(
+         new EventLoopLagDispatcher(int(duration.ToSecondsSigDigits() * 1000)));
+#endif
       }
 
       if (next_sleep > duration.ToMilliseconds()) {