EME: Improve promise lifetime

third_party/WebKit/Source/modules/encryptedmedia/ContentDecryptionModuleResultPromise.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 ContentDecryptionModuleResultPromise_h
 #define ContentDecryptionModuleResultPromise_h
 
 #include "bindings/core/v8/ScriptPromiseResolver.h"
+#include "core/dom/ContextLifecycleObserver.h"
 #include "core/dom/ExceptionCode.h"
 #include "platform/ContentDecryptionModuleResult.h"
 
 namespace blink {
 
 ExceptionCode WebCdmExceptionToExceptionCode(
     WebContentDecryptionModuleException);
 
 // This class wraps the promise resolver to simplify creation of
 // ContentDecryptionModuleResult objects. The default implementations of the
 // complete(), completeWithSession(), etc. methods will reject the promise
 // with an error. It needs to be subclassed and the appropriate complete()
 // method overridden to resolve the promise as needed.
 class ContentDecryptionModuleResultPromise
-    : public ContentDecryptionModuleResult {
+    : public ContentDecryptionModuleResult,
+      public ContextLifecycleObserver {
+  USING_GARBAGE_COLLECTED_MIXIN(ContentDecryptionModuleResultPromise);
+
  public:
   ~ContentDecryptionModuleResultPromise() override;
 
   // ContentDecryptionModuleResult implementation.
   void complete() override;
   void completeWithContentDecryptionModule(
       WebContentDecryptionModule*) override;
   void completeWithSession(
       WebContentDecryptionModuleResult::SessionStatus) override;
   void completeWithError(WebContentDecryptionModuleException,
                          unsigned long systemCode,
                          const WebString&) override;
 
+  // ContextLifecycleObserver implementation.
+  void contextDestroyed() override;
+
   // It is only valid to call this before completion.
   ScriptPromise promise();
 
   DECLARE_VIRTUAL_TRACE();
 
  protected:
   explicit ContentDecryptionModuleResultPromise(ScriptState*);
 
   // Resolves the promise with |value|. Used by subclasses to resolve the
   // promise.
   template <typename... T>
   void resolve(T... value) {
+    if (m_contextDestroyed ||
+        getExecutionContext()->activeDOMObjectsAreStopped()) {

[jrummell, 2016/10/10 21:06:15]

I included activeDOMObjectsAreStopped() since contextDestroyed() may not be
called before it is called on MediaKeys/MediaKeySession. This appears to be the
way to determine if blink is in the process of calling contextDestroyed() on all
affected objects. Let me know if there's a better way to do this.

+      m_resolver.clear();
+      return;
+    }
+
     m_resolver->resolve(value...);
     m_resolver.clear();
   }
 
   // Rejects the promise with a DOMException. This will post a task to
   // actually reject the promise later on.
   void reject(ExceptionCode, const String& errorMessage);
 
-  ExecutionContext* getExecutionContext() const;
+ private:
+  Member<ScriptPromiseResolver> m_resolver;
 
- private:
-  // Rejects the promise with a DOMException.
-  void rejectInternal(ExceptionCode, const String& errorMessage);
-
-  Member<ScriptPromiseResolver> m_resolver;
+  // Set once the Context is destroyed.
+  bool m_contextDestroyed;
 };
 
 }  // namespace blink
 
 #endif  // ContentDecryptionModuleResultPromise_h