Bug 1375412: Strengthen ownership of a11y::LazyInstantiator when posting runnable back to main thread; r=eeejay

MozReview-Commit-ID: A0IdEfAs4q9

accessible/windows/msaa/LazyInstantiator.cpp

@@ -10,7 +10,6 @@
 #include "mozilla/a11y/Accessible.h"
 #include "mozilla/Assertions.h"
 #include "mozilla/mscom/MainThreadRuntime.h"
-#include "mozilla/mscom/Ptr.h"
 #include "mozilla/mscom/Registration.h"
 #include "mozilla/UniquePtr.h"
 #include "nsAccessibilityService.h"
@@ -264,9 +263,11 @@ LazyInstantiator::ShouldInstantiate(const DWORD aClientTid)
     // Call GatherTelemetry on a background thread because it does I/O on
     // the executable file to retrieve version information.
     nsCOMPtr<nsIRunnable> runnable(
-        NewRunnableMethod<nsCOMPtr<nsIFile>>(this,
+        NewRunnableMethod<nsCOMPtr<nsIFile>, RefPtr<AccumulateRunnable>>(
+                                             this,
                                              &LazyInstantiator::GatherTelemetry,
-                                             clientExe));
+                                             clientExe,
+                                             new AccumulateRunnable(this)));
     NS_NewThread(getter_AddRefs(mTelemetryThread), runnable);
   }
 #endif // defined(MOZ_TELEMETRY_REPORTING)
@@ -328,7 +329,8 @@ LazyInstantiator::AppendVersionInfo(nsIFile* aClientExe,
 }
 
 void
-LazyInstantiator::GatherTelemetry(nsIFile* aClientExe)
+LazyInstantiator::GatherTelemetry(nsIFile* aClientExe,
+                                  AccumulateRunnable* aRunnable)
 {
   MOZ_ASSERT(!NS_IsMainThread());
 
@@ -338,10 +340,11 @@ LazyInstantiator::GatherTelemetry(nsIFile* aClientExe)
     AppendVersionInfo(aClientExe, value);
   }
 
+  aRunnable->SetData(value);
+
   // Now that we've (possibly) obtained version info, send the resulting
   // string back to the main thread to accumulate in telemetry.
-  NS_DispatchToMainThread(NewNonOwningRunnableMethod<nsString>(this,
-        &LazyInstantiator::AccumulateTelemetry, value));
+  NS_DispatchToMainThread(aRunnable);
 }
 
 void

accessible/windows/msaa/LazyInstantiator.h

@@ -8,6 +8,7 @@
 #define mozilla_a11y_LazyInstantiator_h
 
 #include "IUnknownImpl.h"
+#include "mozilla/mscom/Ptr.h"
 #include "mozilla/RefPtr.h"
 #include "nsString.h"
 #if defined(MOZ_TELEMETRY_REPORTING)
@@ -86,8 +87,37 @@ private:
 
   bool GetClientExecutableName(const DWORD aClientTid, nsIFile** aOutClientExe);
 #if defined(MOZ_TELEMETRY_REPORTING)
+  class AccumulateRunnable final : public Runnable
+  {
+  public:
+    explicit AccumulateRunnable(LazyInstantiator* aObj)
+      : Runnable("mozilla::a11y::LazyInstantiator::AccumulateRunnable")
+      , mObj(aObj)
+    {
+      MOZ_ASSERT(NS_IsMainThread());
+      aObj->AddRef();
+    }
+
+    void SetData(const nsAString& aData)
+    {
+      mData = aData;
+    }
+
+    NS_IMETHOD Run() override
+    {
+      mObj->AccumulateTelemetry(mData);
+      return NS_OK;
+    }
+
+  private:
+    mscom::STAUniquePtr<LazyInstantiator> mObj;
+    nsString                              mData;
+  };
+
+  friend class AccumulateRunnable;
+
   void AppendVersionInfo(nsIFile* aClientExe, nsAString& aStrToAppend);
-  void GatherTelemetry(nsIFile* aClientExe);
+  void GatherTelemetry(nsIFile* aClientExe, AccumulateRunnable* aRunnable);
   void AccumulateTelemetry(const nsString& aValue);
 #endif // defined(MOZ_TELEMETRY_REPORTING)