Bug 1514908 - Reduce deep copies of the closures passed to this function. r=baku

By taking an rvalue reference and using std::move more aggressively, we can
avoid at least two copies of these closures, which avoids a bit of atomic
refcounting.

Differential Revision: https://phabricator.services.mozilla.com/D14807

--HG--
extra : moz-landing-system : lando

dom/workers/WorkerRef.cpp

@@ -89,8 +89,8 @@ void WorkerRef::Notify() {
     return;
   }
 
-  std::function<void()> callback = mCallback;
-  mCallback = nullptr;
+  std::function<void()> callback = std::move(mCallback);
+  MOZ_ASSERT(!mCallback);
 
   callback();
 }
@@ -99,7 +99,7 @@ void WorkerRef::Notify() {
 // WeakWorkerRef
 
 /* static */ already_AddRefed<WeakWorkerRef> WeakWorkerRef::Create(
-    WorkerPrivate* aWorkerPrivate, const std::function<void()>& aCallback) {
+    WorkerPrivate* aWorkerPrivate, std::function<void()>&& aCallback) {
   MOZ_ASSERT(aWorkerPrivate);
   aWorkerPrivate->AssertIsOnWorkerThread();
 
@@ -113,7 +113,7 @@ void WorkerRef::Notify() {
   }
 
   ref->mHolder = std::move(holder);
-  ref->mCallback = aCallback;
+  ref->mCallback = std::move(aCallback);
 
   return ref.forget();
 }
@@ -144,7 +144,7 @@ WorkerPrivate* WeakWorkerRef::GetUnsafePrivate() const {
 
 /* static */ already_AddRefed<StrongWorkerRef> StrongWorkerRef::Create(
     WorkerPrivate* aWorkerPrivate, const char* aName,
-    const std::function<void()>& aCallback) {
+    std::function<void()>&& aCallback) {
   MOZ_ASSERT(aWorkerPrivate);
   MOZ_ASSERT(aName);
 
@@ -158,7 +158,7 @@ WorkerPrivate* WeakWorkerRef::GetUnsafePrivate() const {
   }
 
   ref->mHolder = std::move(holder);
-  ref->mCallback = aCallback;
+  ref->mCallback = std::move(aCallback);
 
   return ref.forget();
 }

dom/workers/WorkerRef.h

@@ -108,7 +108,7 @@ class WeakWorkerRef final : public WorkerRef {
  public:
   static already_AddRefed<WeakWorkerRef> Create(
       WorkerPrivate* aWorkerPrivate,
-      const std::function<void()>& aCallback = nullptr);
+      std::function<void()>&& aCallback = nullptr);
 
   WorkerPrivate* GetPrivate() const;
 
@@ -127,7 +127,7 @@ class StrongWorkerRef final : public WorkerRef {
  public:
   static already_AddRefed<StrongWorkerRef> Create(
       WorkerPrivate* aWorkerPrivate, const char* aName,
-      const std::function<void()>& aCallback = nullptr);
+      std::function<void()>&& aCallback = nullptr);
 
   WorkerPrivate* Private() const;