Issue #1442 - Part 12b - Allow idle worker shutdown while Cache/CacheStorage DOM objects exist, but block it during Cache operation. https://bugzilla.mozilla.org/show_bug.cgi?id=1362444 Pre-requisite for Part 13.

dom/cache/CacheOpChild.cpp

@@ -74,7 +74,11 @@ CacheOpChild::CacheOpChild(CacheWorkerHolder* aWorkerHolder,
   MOZ_DIAGNOSTIC_ASSERT(mPromise);
 
   MOZ_ASSERT_IF(!NS_IsMainThread(), aWorkerHolder);
-  SetWorkerHolder(aWorkerHolder);
+  RefPtr<CacheWorkerHolder> workerHolder =
+    CacheWorkerHolder::PreferBehavior(aWorkerHolder,
+                                      CacheWorkerHolder::PreventIdleShutdownStart);
+
+  SetWorkerHolder(workerHolder);
 }
 
 CacheOpChild::~CacheOpChild()
@@ -165,7 +169,11 @@ CacheOpChild::Recv__delete__(const ErrorResult& aRv,
         break;
       }
 
-      actor->SetWorkerHolder(GetWorkerHolder());
+      RefPtr<CacheWorkerHolder> workerHolder =
+        CacheWorkerHolder::PreferBehavior(GetWorkerHolder(),
+                                          CacheWorkerHolder::AllowIdleShutdownStart);
+
+      actor->SetWorkerHolder(workerHolder);
       RefPtr<Cache> cache = new Cache(mGlobal, actor);
       mPromise->MaybeResolve(cache);
       break;

dom/cache/CacheStorage.cpp

@@ -204,7 +204,8 @@ CacheStorage::CreateOnWorker(Namespace aNamespace, nsIGlobalObject* aGlobal,
   }
 
   RefPtr<CacheWorkerHolder> workerHolder =
-    CacheWorkerHolder::Create(aWorkerPrivate);
+    CacheWorkerHolder::Create(aWorkerPrivate,
+                              CacheWorkerHolder::AllowIdleShutdownStart);
   if (!workerHolder) {
     NS_WARNING("Worker thread is shutting down.");
     aRv.Throw(NS_ERROR_FAILURE);

dom/cache/CacheWorkerHolder.cpp

@@ -18,11 +18,11 @@ using mozilla::dom::workers::WorkerPrivate;
 
 // static
 already_AddRefed<CacheWorkerHolder>
-CacheWorkerHolder::Create(WorkerPrivate* aWorkerPrivate)
+CacheWorkerHolder::Create(WorkerPrivate* aWorkerPrivate, Behavior aBehavior)
 {
   MOZ_DIAGNOSTIC_ASSERT(aWorkerPrivate);
 
-  RefPtr<CacheWorkerHolder> workerHolder = new CacheWorkerHolder();
+  RefPtr<CacheWorkerHolder> workerHolder = new CacheWorkerHolder(aBehavior);
   if (NS_WARN_IF(!workerHolder->HoldWorker(aWorkerPrivate, Terminating))) {
     return nullptr;
   }
@@ -30,6 +30,28 @@ CacheWorkerHolder::Create(WorkerPrivate* aWorkerPrivate)
   return workerHolder.forget();
 }
 
+// static
+already_AddRefed<CacheWorkerHolder>
+CacheWorkerHolder::PreferBehavior(CacheWorkerHolder* aCurrentHolder,
+                                  Behavior aBehavior)
+{
+  if (!aCurrentHolder) {
+    return nullptr;
+  }
+
+  RefPtr<CacheWorkerHolder> orig = aCurrentHolder;
+  if (orig->GetBehavior() == aBehavior) {
+    return orig.forget();
+  }
+
+  RefPtr<CacheWorkerHolder> replace = Create(orig->mWorkerPrivate, aBehavior);
+  if (!replace) {
+    return orig.forget();
+  }
+
+  return replace.forget();
+}
+
 void
 CacheWorkerHolder::AddActor(ActorChild* aActor)
 {
@@ -88,8 +110,9 @@ CacheWorkerHolder::Notify(Status aStatus)
   return true;
 }
 
-CacheWorkerHolder::CacheWorkerHolder()
+CacheWorkerHolder::CacheWorkerHolder(Behavior aBehavior)
-  : mNotified(false)
+  : WorkerHolder(aBehavior)
+  , mNotified(false)
 {
 }
 

dom/cache/CacheWorkerHolder.h

@@ -25,7 +25,11 @@ class CacheWorkerHolder final : public workers::WorkerHolder
 {
 public:
   static already_AddRefed<CacheWorkerHolder>
-  Create(workers::WorkerPrivate* aWorkerPrivate);
+  Create(workers::WorkerPrivate* aWorkerPrivate,
+         Behavior aBehavior);
+
+  static already_AddRefed<CacheWorkerHolder>
+  PreferBehavior(CacheWorkerHolder* aCurrentHolder, Behavior aBehavior);
 
   void AddActor(ActorChild* aActor);
   void RemoveActor(ActorChild* aActor);
@@ -36,7 +40,7 @@ public:
   virtual bool Notify(workers::Status aStatus) override;
 
 private:
-  CacheWorkerHolder();
+  explicit CacheWorkerHolder(Behavior aBehavior);
   ~CacheWorkerHolder();
 
   nsTArray<ActorChild*> mActorList;