Worklet: Lazily create PaintWorkletGlobalScopes

third_party/WebKit/Source/core/workers/MainThreadWorklet.h

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef MainThreadWorklet_h
 #define MainThreadWorklet_h
 
 #include "core/workers/Worklet.h"
 
 #include "bindings/core/v8/ScriptPromise.h"
 #include "core/CoreExport.h"
 #include "platform/heap/Handle.h"
 
 namespace blink {
 
 class LocalFrame;
 class ScriptPromiseResolver;
+class WorkletGlobalScopeProxy;
 
 // A MainThreadWorklet is a worklet that runs only on the main thread.
 // TODO(nhiroki): This is a temporary class to support module loading for main
 // thread worklets. This and ThreadedWorklet will be merged into the base
 // Worklet class once threaded worklets are ready to use module loading.
 class CORE_EXPORT MainThreadWorklet : public Worklet {
   USING_GARBAGE_COLLECTED_MIXIN(MainThreadWorklet);
   WTF_MAKE_NONCOPYABLE(MainThreadWorklet);
 
  public:
   virtual ~MainThreadWorklet() = default;
 
   // ContextLifecycleObserver
   void ContextDestroyed(ExecutionContext*) final;
 
   DECLARE_VIRTUAL_TRACE();
 
  protected:
   explicit MainThreadWorklet(LocalFrame*);
 
+  // Returns one of available global scopes.
+  WorkletGlobalScopeProxy* FindAvailableGlobalScope() const;
+
+  size_t GetNumberOfGlobalScopes() const { return proxies_.size(); }
+
  private:
   // Worklet.
   void FetchAndInvokeScript(const KURL& module_url_record,
                             const WorkletOptions&,
                             ScriptPromiseResolver*) override;
+
+  // Returns true if there are no global scopes or additional global scopes are
+  // necessary. CreateGlobalScope() will be called in that case. Each worklet
+  // can define how to pool global scopes here.
+  virtual bool NeedsToCreateGlobalScope() = 0;
+  virtual std::unique_ptr<WorkletGlobalScopeProxy> CreateGlobalScope() = 0;
+
+  // "A Worklet has a list of the worklet's WorkletGlobalScopes. Initially this
+  // list is empty; it is populated when the user agent chooses to create its
+  // WorkletGlobalScope."
+  // https://drafts.css-houdini.org/worklets/#worklet-section
+  // TODO(nhiroki): Make (Paint)WorkletGlobalScopeProxy GC-managed object to
+  // avoid that GC graphs are disjointed (https://crbug.com/719775).
+  HashSet<std::unique_ptr<WorkletGlobalScopeProxy>> proxies_;
 };
 
 }  // namespace blink
 
 #endif  // MainThreadWorklet_h