Introduce KeepAliveWhilePending to ScriptPromiseResolverWithContext.

Source/core/dom/AsyncInitializerResolver.h

+// Copyright 2014 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 AsyncInitializerResolver_h
+#define AsyncInitializerResolver_h
+
+#include "bindings/v8/ScriptPromiseResolverWithContext.h"
+#include "core/dom/ContextLifecycleObserver.h"
+#include "core/dom/ExecutionContext.h"
+#include "platform/heap/Heap.h"
+#include "wtf/OwnPtr.h"
+#include "wtf/RefPtr.h"
+#include "wtf/WeakPtr.h"
+
+namespace WebCore {
+
+// AsyncInitializerResolver is a helper class of asynchronous initialization
+// using Promises. Once AsyncInitializerResolver<T> is created, the resolver
+// will live until one of the following conditions is met:
+//  - the associated promise is resolved
+//  - the associated promise is rejected
+//  - the associated execution context is destroyed
+//
+// AsyncInitializerResolver<Initializer> takes an actual initializer.
+// It is guaranteed the resolver stays alive while the initializer is alive
+// after start() is called,
+// i.e. You can access the resolver pointer set by start() in the initializer
+// If you want to access the resolver outside of the initializer,
+// use a weak pointer.
+//
+template<typename T>
+class AsyncInitializerResolver : public ContextLifecycleObserver {
+public:
+    typedef T Initializer;
+
+    static WeakPtr<AsyncInitializerResolver<T> > create(ScriptState* scriptState)
+    {
+        AsyncInitializerResolver* resolver = new AsyncInitializerResolver(scriptState);
+        return resolver->weakPtr();
+    }
+
+    void start(PassOwnPtr<Initializer> initializer)
+    {
+        ASSERT(!m_initializer);
+        m_initializer = initializer;
+        m_initializer->start(this);
+    }
+
+    static ScriptPromise createAndStart(ScriptState* scriptState, PassOwnPtr<T> initializer)
+    {
+        AsyncInitializerResolver* resolver = new AsyncInitializerResolver(scriptState);
+        ScriptPromise promise = resolver->promise();
+        resolver->start(initializer);
+        return promise;
+    }
+
+    virtual ~AsyncInitializerResolver() { }
+
+    ScriptPromise promise() { return m_resolver->promise(); }
+    ScriptState* scriptState() const { return m_resolver->scriptState(); }
+    template<typename U> void resolve(U u)
+    {
+        m_resolver->resolve(u);
+        m_protect.clear();
+    }
+    template<typename U> void reject(U u)
+    {
+        m_resolver->reject(u);
+        m_protect.clear();
+    }
+
+    // LifecycleObserver implementation.
+    // Because the lifecycle context is held in the associated execution
+    // context, this function is called when the execution context is
+    // destroyed.
+    virtual void contextDestroyed() OVERRIDE
+    {
+        ContextLifecycleObserver::contextDestroyed();
+        m_initializer->contextDestroyed();
+        // |this| will be deleted in the next Oilpan GC.
+        m_protect.clear();
+    }
+
+    WeakPtr<AsyncInitializerResolver<Initializer> > weakPtr() { return m_factory.createWeakPtr(); }
+
+private:
+    class Holder : public GarbageCollectedFinalized<Holder> {
+    public:
+        Holder(PassOwnPtr<AsyncInitializerResolver<T> > target) : m_protect(target) { }
+        virtual void trace(Visitor*) { }
+
+    private:
+        OwnPtr<AsyncInitializerResolver<T> > m_protect;
+    };
+
+    AsyncInitializerResolver(ScriptState* scriptState)
+        : ContextLifecycleObserver(scriptState->executionContext())
+        , m_resolver(ScriptPromiseResolverWithContext::create(scriptState))
+        , m_factory(this)
+        , m_protect(new Holder(adoptPtr(this)))
+    {
+    }
+
+    RefPtr<ScriptPromiseResolverWithContext> m_resolver;
+    OwnPtr<Initializer> m_initializer;
+    WeakPtrFactory<AsyncInitializerResolver<Initializer> > m_factory;
+    // In order to keep alive self until one of the termination conditions
+    // is met, AsyncInitizlierResolver has an OwnPtr referencing self.
+    // Clearing it means deleting it.
+    Persistent<Holder> m_protect;

[kouhei (in TOK), 2014/06/05 07:54:47]

Why don't we make AsyncInitializerResolver GarbageCollectedFinalized. Then we
can remove Holder. :)

[yhirano, 2014/06/05 09:09:19]

My compiler complains at having Persistent in GarbageCollectedFinalized, like
this:
../../third_party/WebKit/Source/core/dom/AsyncInitializerResolver.h:33:1: error:
[blink-gc] Class 'AsyncInitializerResolver<WebCore::MIDIAccessInitializer>'
contains GC root in field 'm_protect'.
class AsyncInitializerResolver FINAL : public
GarbageCollectedFinalized<AsyncInitializerResolver<T> >, public
ContextLifecycleObserver {
^
../../third_party/WebKit/Source/core/dom/AsyncInitializerResolver.h:103:5: note:
[blink-gc] Field 'm_protect' defining a GC root declared here:
    Persistent<AsyncInitializerResolver<Initializer> > m_protect;

+};
+
+} // namespace WebCore
+
+#endif // #ifndef AsyncInitializerResolver_h