Bug 1447744 - don't implement nsINamed for mozilla::Runnable when it's unused; r=erahm

We only use nsINamed on runnables for certain kinds of telemetry, and
those kinds of telemetry aren't being gathered on RELEASE_OR_BETA
builds.  We effectively make nsINamed::GetName a no-op when we're not
collecting said telemetry.  But implementing nsINamed does have a cost:
the vtable of every runnable (and we have hundreds of subclasses of
mozilla::Runnable) will contain pointers for GetName (and extra pointers
for QueryInterface/AddRef/Release), and all those pointers times all
those subclasses adds up quickly.  Let's not implement nsINamed when
nsINamed isn't going to be used.

This change saves ~100K of binary size on x86-64 Linux; the savings
should be similar on other 64-bit systems, and ~50K on 32-bit systems.

xpcom/tests/gtest/TestThreadUtils.cpp

@@ -170,11 +170,9 @@ static void Expect(const char* aContext, int aCounter, int aMaxExpected)
 
 static void ExpectRunnableName(Runnable* aRunnable, const char* aExpectedName)
 {
+#ifdef MOZ_COLLECTING_RUNNABLE_TELEMETRY
   nsAutoCString name;
   EXPECT_TRUE(NS_SUCCEEDED(aRunnable->GetName(name))) << "Runnable::GetName()";
-#ifdef RELEASE_OR_BETA
-  EXPECT_TRUE(name.IsEmpty()) << "Runnable name shall be empty in RELEASE or BETA!";
-#else
   EXPECT_TRUE(name.EqualsASCII(aExpectedName)) << "Verify Runnable name";
 #endif
 }

xpcom/threads/AbstractThread.cpp

@@ -173,6 +173,7 @@ private:
       return rv;
     }
 
+#ifdef MOZ_COLLECTING_RUNNABLE_TELEMETRY
     NS_IMETHOD GetName(nsACString& aName) override
     {
       aName.AssignLiteral("AbstractThread::Runner");
@@ -186,6 +187,7 @@ private:
       }
       return NS_OK;
     }
+#endif
 
   private:
     RefPtr<EventTargetWrapper> mThread;

xpcom/threads/SchedulerGroup.cpp

@@ -384,6 +384,7 @@ SchedulerGroup::Runnable::DocGroup() const
   return mDocGroup;
 }
 
+#ifdef MOZ_COLLECTING_RUNNABLE_TELEMETRY
 NS_IMETHODIMP
 SchedulerGroup::Runnable::GetName(nsACString& aName)
 {
@@ -398,6 +399,7 @@ SchedulerGroup::Runnable::GetName(nsACString& aName)
 
   return NS_OK;
 }
+#endif
 
 NS_IMETHODIMP
 SchedulerGroup::Runnable::Run()

xpcom/threads/SchedulerGroup.h

@@ -122,7 +122,9 @@ public:
     SchedulerGroup* Group() const { return mGroup; }
     dom::DocGroup* DocGroup() const;
 
+#ifdef MOZ_COLLECTING_RUNNABLE_TELEMETRY
     NS_IMETHOD GetName(nsACString& aName) override;
+#endif
 
     bool IsBackground() const { return mGroup->IsBackground(); }
 

xpcom/threads/ThrottledEventQueue.cpp

@@ -80,11 +80,13 @@ class ThrottledEventQueue::Inner final : public nsIObserver
       return NS_OK;
     }
 
+#ifdef MOZ_COLLECTING_RUNNABLE_TELEMETRY
     NS_IMETHODIMP
     GetName(nsACString& aName) override
     {
       return mInner->CurrentName(aName);
     }
+#endif
   };
 
   mutable Mutex mMutex;

xpcom/threads/TimerThread.cpp

@@ -145,7 +145,9 @@ public:
     return NS_OK;
   }
 
+#ifdef MOZ_COLLECTING_RUNNABLE_TELEMETRY
   NS_IMETHOD GetName(nsACString& aName) override;
+#endif
 
   nsTimerEvent()
     : mozilla::CancelableRunnable("nsTimerEvent")
@@ -263,6 +265,7 @@ nsTimerEvent::DeleteAllocatorIfNeeded()
   }
 }
 
+#ifdef MOZ_COLLECTING_RUNNABLE_TELEMETRY
 NS_IMETHODIMP
 nsTimerEvent::GetName(nsACString& aName)
 {
@@ -272,6 +275,7 @@ nsTimerEvent::GetName(nsACString& aName)
   mTimer->GetName(aName);
   return NS_OK;
 }
+#endif
 
 NS_IMETHODIMP
 nsTimerEvent::Run()

xpcom/threads/nsProxyRelease.h

@@ -44,19 +44,17 @@ public:
     return Run();
   }
 
+#ifdef MOZ_COLLECTING_RUNNABLE_TELEMETRY
   NS_IMETHOD GetName(nsACString& aName) override
   {
-#ifdef RELEASE_OR_BETA
-    aName.Truncate();
-#else
     if (mName) {
       aName.Append(nsPrintfCString("ProxyReleaseEvent for %s", mName));
     } else {
       aName.AssignLiteral("ProxyReleaseEvent");
     }
-#endif
     return NS_OK;
   }
+#endif
 
 private:
   T* MOZ_OWNING_REF mDoomed;

xpcom/threads/nsThread.cpp

@@ -900,7 +900,7 @@ void canary_alarm_handler(int signum)
     }                                                                          \
   } while(0)
 
-#ifndef RELEASE_OR_BETA
+#ifdef MOZ_COLLECTING_RUNNABLE_TELEMETRY
 static bool
 GetLabeledRunnableName(nsIRunnable* aEvent,
                        nsACString& aName,
@@ -1011,7 +1011,7 @@ nsThread::ProcessNextEvent(bool aMayWait, bool* aResult)
         HangMonitor::NotifyActivity();
       }
 
-#ifndef RELEASE_OR_BETA
+#ifdef MOZ_COLLECTING_RUNNABLE_TELEMETRY
       bool schedulerLoggingEnabled = GetSchedulerLoggingEnabled();
       if (schedulerLoggingEnabled
           && mNestedEventLoopDepth > mCurrentEventLoopDepth

xpcom/threads/nsThreadUtils.cpp

@@ -43,8 +43,8 @@ IdlePeriod::GetIdlePeriodHint(TimeStamp* aIdleDeadline)
 // NS_IMPL_NAMED_* relies on the mName field, which is not present on
 // release or beta. Instead, fall back to using "Runnable" for all
 // runnables.
-#ifdef RELEASE_OR_BETA
-NS_IMPL_ISUPPORTS(Runnable, nsIRunnable, nsINamed)
+#ifndef MOZ_COLLECTING_RUNNABLE_TELEMETRY
+NS_IMPL_ISUPPORTS(Runnable, nsIRunnable)
 #else
 NS_IMPL_NAMED_ADDREF(Runnable, mName)
 NS_IMPL_NAMED_RELEASE(Runnable, mName)
@@ -58,20 +58,18 @@ Runnable::Run()
   return NS_OK;
 }
 
+#ifdef MOZ_COLLECTING_RUNNABLE_TELEMETRY
 NS_IMETHODIMP
 Runnable::GetName(nsACString& aName)
 {
-#ifdef RELEASE_OR_BETA
-  aName.Truncate();
-#else
   if (mName) {
     aName.AssignASCII(mName);
   } else {
     aName.Truncate();
   }
-#endif
   return NS_OK;
 }
+#endif
 
 NS_IMPL_ISUPPORTS_INHERITED(CancelableRunnable, Runnable,
                             nsICancelableRunnable)
@@ -102,6 +100,7 @@ PrioritizableRunnable::PrioritizableRunnable(already_AddRefed<nsIRunnable>&& aRu
 #endif
 }
 
+#ifdef MOZ_COLLECTING_RUNNABLE_TELEMETRY
 NS_IMETHODIMP
 PrioritizableRunnable::GetName(nsACString& aName)
 {
@@ -112,6 +111,7 @@ PrioritizableRunnable::GetName(nsACString& aName)
   }
   return NS_OK;
 }
+#endif
 
 NS_IMETHODIMP
 PrioritizableRunnable::Run()
@@ -364,6 +364,7 @@ public:
                                 aTarget);
   }
 
+#ifdef MOZ_COLLECTING_RUNNABLE_TELEMETRY
   NS_IMETHOD GetName(nsACString& aName) override
   {
     aName.AssignLiteral("IdleRunnableWrapper");
@@ -377,6 +378,7 @@ public:
     }
     return NS_OK;
   }
+#endif
 
 private:
   ~IdleRunnableWrapper()

xpcom/threads/nsThreadUtils.h

@@ -425,26 +425,39 @@ enum RunnableKind
   IdleWithTimer
 };
 
+// Implementing nsINamed on Runnable bloats vtables for the hundreds of
+// Runnable subclasses that we have, so we want to avoid that overhead
+// when we're not using nsINamed for anything.
+#ifndef RELEASE_OR_BETA
+#define MOZ_COLLECTING_RUNNABLE_TELEMETRY
+#endif
+
 // This class is designed to be subclassed.
-class Runnable : public nsIRunnable, public nsINamed
+class Runnable
+  : public nsIRunnable
+#ifdef MOZ_COLLECTING_RUNNABLE_TELEMETRY
+  , public nsINamed
+#endif
 {
 public:
   NS_DECL_THREADSAFE_ISUPPORTS
   NS_DECL_NSIRUNNABLE
+#ifdef MOZ_COLLECTING_RUNNABLE_TELEMETRY
   NS_DECL_NSINAMED
+#endif
 
   Runnable() = delete;
 
-#ifdef RELEASE_OR_BETA
-  explicit Runnable(const char* aName) {}
-#else
+#ifdef MOZ_COLLECTING_RUNNABLE_TELEMETRY
   explicit Runnable(const char* aName) : mName(aName) {}
+#else
+  explicit Runnable(const char* aName) {}
 #endif
 
 protected:
   virtual ~Runnable() {}
 
-#ifndef RELEASE_OR_BETA
+#ifdef MOZ_COLLECTING_RUNNABLE_TELEMETRY
   const char* mName = nullptr;
 #endif
 
@@ -503,7 +516,9 @@ public:
   PrioritizableRunnable(already_AddRefed<nsIRunnable>&& aRunnable,
                         uint32_t aPriority);
 
+#ifdef MOZ_COLLECTING_RUNNABLE_TELEMETRY
   NS_IMETHOD GetName(nsACString& aName) override;
+#endif
 
   NS_DECL_ISUPPORTS_INHERITED
   NS_DECL_NSIRUNNABLE