Worklet: Lazily create PaintWorkletGlobalScopes

third_party/WebKit/Source/core/workers/WorkletGlobalScopeManager.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 WorkletGlobalScopeManager_h
+#define WorkletGlobalScopeManager_h
+
+#include <memory>
+#include "core/CoreExport.h"
+#include "core/workers/WorkletGlobalScopeProxy.h"
+#include "platform/heap/GarbageCollected.h"
+#include "public/platform/WebURLRequest.h"
+
+namespace blink {
+
+class WorkletPendingTasks;
+
+// Manages proxies to worklet global scopes on the main thread. Owned by the
+// Worklet class.
+class CORE_EXPORT WorkletGlobalScopeManager
+    : public GarbageCollectedFinalized<WorkletGlobalScopeManager> {
+  WTF_MAKE_NONCOPYABLE(WorkletGlobalScopeManager);
+
+ public:
+  WorkletGlobalScopeManager() = default;
+  virtual ~WorkletGlobalScopeManager() = default;
+
+  // Adds a global scope to the managed set.
+  void AddGlobalScope(std::unique_ptr<WorkletGlobalScopeProxy>);

[kinuko, 2017/05/24 06:53:40]

nit: it looks we can remove 'GlobalScope' part from the method names here and
below

[nhiroki, 2017/05/24 08:11:22]

The latest patchset removed this and other functions in this class.

+
+  // Returns one of available global scopes.
+  WorkletGlobalScopeProxy* FindAvailableGlobalScope() const;
+
+  // Fetches and evaluates module scripts on all global scopes.
+  void AddModuleToGlobalScopes(const KURL& module_url_record,
+                               WebURLRequest::FetchCredentialsMode,
+                               WorkletPendingTasks*);
+
+  // Terminates all global scopes.
+  void TerminateGlobalScopes();
+
+  size_t GetNumberOfGlobalScopes() const { return proxies_.size(); }

[kinuko, 2017/05/24 06:53:39]

It looks we can also simply let MainThreadWorklet hold the HashSet proxies_, but
only expose 'GetNumberOfGlobalScopes()' and 'FindAvailableGlobalScope()' methods
to subclasses as protected, without introducing this wrapper class?  (To be
clear, I did want to clarify the interface to proxies, while was neutral on
introducing a wrapper class)

(Either works for me, but in the current code having both 'CreateGlobalScope'
and 'AddGlobalScope' exposed to subclasses feels a bit less tight to me.  With
the anyone can add whatever global scope to the proxies without implementing
CreateGlobalScope.  If we'll have a plan to further extend this class / add more
code in this class I'm fine with having this wrapper class)

[nhiroki, 2017/05/24 08:11:22]

Done.
I don't have a strong opinion whether to introduce the wrapper class and also
don't have an extension plan of that. The latest patchset re-merges the wrapper
class into MainThreadWorklet and reduces # of public/protected functions around
the proxy collection.

+
+  DEFINE_INLINE_TRACE() {}
+
+ private:
+  // "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).
+  WTF::HashSet<std::unique_ptr<WorkletGlobalScopeProxy>> proxies_;
+};
+
+}  // namespace blink
+
+#endif  // WorkletGlobalScopeManager_h