Manage WebSQL callbacks with OwnPtr instead of refcounting

Source/modules/webdatabase/SQLCallbackWrapper.h

 /*
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 24 matching lines @@
 namespace WebCore {
 
 // A helper class to safely dereference the callback objects held by
 // SQLStatement and SQLTransaction on the proper thread. The 'wrapped'
 // callback is dereferenced:
 // - by destructing the enclosing wrapper - on any thread
 // - by calling clear() - on any thread
 // - by unwrapping and then dereferencing normally - on context thread only
 template<typename T> class SQLCallbackWrapper {
 public:
-    SQLCallbackWrapper(PassRefPtr<T> callback, ExecutionContext* executionContext)
+    SQLCallbackWrapper(PassOwnPtr<T> callback, ExecutionContext* executionContext)
         : m_callback(callback)
         , m_executionContext(m_callback ? executionContext : 0)
     {
         ASSERT(!m_callback || (m_executionContext.get() && m_executionContext->isContextThread()));
     }
 
     ~SQLCallbackWrapper()
     {
         clear();
     }
 
     void clear()
     {
         ExecutionContext* context;
-        T* callback;
+        OwnPtr<T> callback;
         {
             MutexLocker locker(m_mutex);
             if (!m_callback) {
                 ASSERT(!m_executionContext);
                 return;
             }
             if (m_executionContext->isContextThread()) {
                 m_callback = 0;
                 m_executionContext = 0;
                 return;
             }
             context = m_executionContext.release().leakRef();
-            callback = m_callback.release().leakRef();
+            callback = m_callback.release();
         }
-        context->postTask(SafeReleaseTask::create(callback));
+        context->postTask(SafeReleaseTask::create(callback.release()));
     }
 
-    PassRefPtr<T> unwrap()
+    PassOwnPtr<T> unwrap()

[abarth-chromium, 2013/12/04 01:55:50]

release() ?

[adamk, 2013/12/04 02:08:26]

Don't want to touch this in this change; unwrap() is mentioned in comments.

     {
         MutexLocker locker(m_mutex);
         ASSERT(!m_callback || m_executionContext->isContextThread());
         m_executionContext = 0;
         return m_callback.release();
     }
 
     // Useful for optimizations only, please test the return value of unwrap to be sure.
     bool hasCallback() const { return m_callback; }

[abarth-chromium, 2013/12/04 01:55:50]

No mutex?  This function is kind of scary!

[adamk, 2013/12/04 02:08:26]

Yeah, don't quite get what this is for, especially considering the comment.
Anyway, I didn't make it any worse!

 
 private:
     class SafeReleaseTask : public ExecutionContextTask {
     public:
-        static PassOwnPtr<SafeReleaseTask> create(T* callbackToRelease)
+        static PassOwnPtr<SafeReleaseTask> create(PassOwnPtr<T> callbackToRelease)
         {
             return adoptPtr(new SafeReleaseTask(callbackToRelease));
         }
 
         virtual void performTask(ExecutionContext* context)
         {
             ASSERT(m_callbackToRelease && context && context->isContextThread());
-            m_callbackToRelease->deref();
+            m_callbackToRelease.clear();
             context->deref();
         }
 
         virtual bool isCleanupTask() const { return true; }
 
     private:
-        explicit SafeReleaseTask(T* callbackToRelease)
+        explicit SafeReleaseTask(PassOwnPtr<T> callbackToRelease)
             : m_callbackToRelease(callbackToRelease)
         {
         }
 
-        T* m_callbackToRelease;
+        OwnPtr<T> m_callbackToRelease;
     };
 
     Mutex m_mutex;
-    RefPtr<T> m_callback;
+    OwnPtr<T> m_callback;
     RefPtr<ExecutionContext> m_executionContext;
 };
 
 } // namespace WebCore
 
 #endif // SQLCallbackWrapper_h