EME: Improve promise lifetime

third_party/WebKit/Source/modules/encryptedmedia/ContentDecryptionModuleResultPromise.cpp

 // 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.
 
 #include "modules/encryptedmedia/ContentDecryptionModuleResultPromise.h"
 
 #include "bindings/core/v8/ScriptPromise.h"
 #include "bindings/core/v8/ScriptState.h"
 #include "core/dom/DOMException.h"
 #include "core/dom/ExecutionContext.h"
@@ skipping 48 matching lines @@
 void ContentDecryptionModuleResultPromise::completeWithSession(
     WebContentDecryptionModuleResult::SessionStatus status) {
   NOTREACHED();
   reject(InvalidStateError, "Unexpected completion.");
 }
 
 void ContentDecryptionModuleResultPromise::completeWithError(
     WebContentDecryptionModuleException exceptionCode,
     unsigned long systemCode,
     const WebString& errorMessage) {
+  if (!isValidToFulfillPromise())
+    return;
+
   // Non-zero |systemCode| is appended to the |errorMessage|. If the
   // |errorMessage| is empty, we'll report "Rejected with system code
   // (systemCode)".
   StringBuilder result;
   result.append(errorMessage);
   if (systemCode != 0) {
     if (result.isEmpty())
       result.append("Rejected with system code");
     result.append(" (");
     result.appendNumber(systemCode);
     result.append(')');
   }
   reject(WebCdmExceptionToExceptionCode(exceptionCode), result.toString());
 }
 
 ScriptPromise ContentDecryptionModuleResultPromise::promise() {
   return m_resolver->promise();
 }
 
 void ContentDecryptionModuleResultPromise::reject(ExceptionCode code,
                                                   const String& errorMessage) {
-  // Reject the promise asynchronously. This avoids problems when gc is
-  // destroying objects that result in unfulfilled promises being rejected.
-  // (Resolving promises is still done synchronously as there may be events
-  // already posted that need to happen only after the promise is resolved.)
-  // TODO(jrummell): Make resolving a promise asynchronous as well (including
-  // making sure events still happen after the promise is resolved).
-  if (getExecutionContext()) {
-    getExecutionContext()->postTask(
-        BLINK_FROM_HERE,
-        createSameThreadTask(
-            &ContentDecryptionModuleResultPromise::rejectInternal,
-            wrapPersistent(this), code, errorMessage));
-  }
-}
+  DCHECK(isValidToFulfillPromise());
 
-void ContentDecryptionModuleResultPromise::rejectInternal(
-    ExceptionCode code,
-    const String& errorMessage) {
   m_resolver->reject(DOMException::create(code, errorMessage));
   m_resolver.clear();
 }
 
 ExecutionContext* ContentDecryptionModuleResultPromise::getExecutionContext()
     const {
   return m_resolver->getExecutionContext();
 }
 
+bool ContentDecryptionModuleResultPromise::isValidToFulfillPromise() {
+  // getExecutionContext() is no longer valid once the context is destroyed.
+  return getExecutionContext() &&
+         !getExecutionContext()->activeDOMObjectsAreStopped();

[haraken, 2016/10/14 00:48:41]

Add a comment about why we need to check
getExecutionContext()->activeDOMObjectsAreStopped().

[jrummell, 2016/10/14 02:13:30]

Done.

+}
+
 DEFINE_TRACE(ContentDecryptionModuleResultPromise) {
   visitor->trace(m_resolver);
   ContentDecryptionModuleResult::trace(visitor);
 }
 
 }  // namespace blink