Issue #1442 - Part 12a - Allow idle worker shutdown to begin for an opt-in WorkerHolder mode. https://bugzilla.mozilla.org/show_bug.cgi?id=1362444 Pre-requisite for Part 13.

dom/workers/WorkerHolder.cpp

@@ -8,8 +8,9 @@
 
 BEGIN_WORKERS_NAMESPACE
 
-WorkerHolder::WorkerHolder()
+WorkerHolder::WorkerHolder(Behavior aBehavior)
   : mWorkerPrivate(nullptr)
+  , mBehavior(aBehavior)
 {
 }
 
@@ -44,6 +45,12 @@ WorkerHolder::ReleaseWorker()
   ReleaseWorkerInternal();
 }
 
+WorkerHolder::Behavior
+WorkerHolder::GetBehavior() const
+{
+  return mBehavior;
+}
+
 void
 WorkerHolder::ReleaseWorkerInternal()
 {

dom/workers/WorkerHolder.h

@@ -73,7 +73,12 @@ class WorkerHolder
 public:
   NS_DECL_OWNINGTHREAD
 
-  WorkerHolder();
+  enum Behavior {
+    AllowIdleShutdownStart,
+    PreventIdleShutdownStart,
+  };
+
+  explicit WorkerHolder(Behavior aBehavior = PreventIdleShutdownStart);
   virtual ~WorkerHolder();
 
   bool HoldWorker(WorkerPrivate* aWorkerPrivate, Status aFailStatus);
@@ -81,6 +86,8 @@ public:
 
   virtual bool Notify(Status aStatus) = 0;
 
+  Behavior GetBehavior() const;
+
 protected:
   void ReleaseWorkerInternal();
 
@@ -88,6 +95,8 @@ protected:
 
 private:
   void AssertIsOwningThread() const;
+
+  const Behavior mBehavior;
 };
 
 END_WORKERS_NAMESPACE

dom/workers/WorkerPrivate.cpp

@@ -4154,6 +4154,7 @@ WorkerPrivate::WorkerPrivate(WorkerPrivate* aParent,
   , mDebugger(nullptr)
   , mJSContext(nullptr)
   , mPRThread(nullptr)
+  , mNumHoldersPreventingShutdownStart(0)
   , mDebuggerEventLoopLevel(0)
   , mMainThreadEventTarget(do_GetMainThread())
   , mErrorHandlerRecursionCount(0)
@@ -5382,8 +5383,11 @@ WorkerPrivate::AddHolder(WorkerHolder* aHolder, Status aFailStatus)
 
   MOZ_ASSERT(!mHolders.Contains(aHolder), "Already know about this one!");
 
-  if (mHolders.IsEmpty() && !ModifyBusyCountFromWorker(true)) {
-    return false;
+  if (aHolder->GetBehavior() == WorkerHolder::PreventIdleShutdownStart) {
+    if (!mNumHoldersPreventingShutdownStart && !ModifyBusyCountFromWorker(true)) {
+      return false;
+    }
+    mNumHoldersPreventingShutdownStart += 1;
   }
 
   mHolders.AppendElement(aHolder);
@@ -5398,8 +5402,11 @@ WorkerPrivate::RemoveHolder(WorkerHolder* aHolder)
   MOZ_ASSERT(mHolders.Contains(aHolder), "Didn't know about this one!");
   mHolders.RemoveElement(aHolder);
 
-  if (mHolders.IsEmpty() && !ModifyBusyCountFromWorker(false)) {
-    NS_WARNING("Failed to modify busy count!");
+  if (aHolder->GetBehavior() == WorkerHolder::PreventIdleShutdownStart) {
+    mNumHoldersPreventingShutdownStart -= 1;
+    if (!mNumHoldersPreventingShutdownStart && !ModifyBusyCountFromWorker(false)) {
+      NS_WARNING("Failed to modify busy count!");
+    }
   }
 }
 

dom/workers/WorkerPrivate.h

@@ -980,6 +980,7 @@ class WorkerPrivate : public WorkerPrivateParent<WorkerPrivate>
   RefPtr<WorkerDebuggerGlobalScope> mDebuggerScope;
   nsTArray<ParentType*> mChildWorkers;
   nsTObserverArray<WorkerHolder*> mHolders;
+  uint32_t mNumHoldersPreventingShutdownStart;
   nsTArray<nsAutoPtr<TimeoutInfo>> mTimeouts;
   uint32_t mDebuggerEventLoopLevel;
   RefPtr<ThrottledEventQueue> mMainThreadThrottledEventQueue;