135 lines
4.4 KiB
C++
135 lines
4.4 KiB
C++
/*
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* Copyright (C) 2012 Google, Inc. All Rights Reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
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* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR
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* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
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* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
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* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
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* OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#ifndef Supplementable_h
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#define Supplementable_h
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#include <wtf/Assertions.h>
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#include <wtf/HashMap.h>
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#include <wtf/MainThread.h>
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#if ASSERT_ENABLED
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#include <wtf/Threading.h>
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#endif
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namespace WebCore {
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// What you should know about Supplementable and Supplement
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// ========================================================
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// Supplementable and Supplement instances are meant to be thread local. They
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// should only be accessed from within the thread that created them. The
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// 2 classes are not designed for safe access from another thread. Violating
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// this design assumption can result in memory corruption and unpredictable
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// behavior.
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//
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// What you should know about the Supplement keys
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// ==============================================
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// The Supplement is expected to use the same const char* string instance
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// as its key. The Supplementable's SupplementMap will use the address of the
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// string as the key and not the characters themselves. Hence, 2 strings with
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// the same characters will be treated as 2 different keys.
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//
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// In practice, it is recommended that Supplements implements a static method
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// for returning its key to use. For example:
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//
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// class MyClass : public Supplement<MySupplementable> {
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// ...
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// static const char* supplementName();
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// }
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//
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// const char* MyClass::supplementName()
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// {
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// return "MyClass";
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// }
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//
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// An example of the using the key:
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//
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// MyClass* MyClass::from(MySupplementable* host)
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// {
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// return reinterpret_cast<MyClass*>(Supplement<MySupplementable>::from(host, supplementName()));
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// }
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template<typename T>
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class Supplementable;
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template<typename T>
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class Supplement {
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public:
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virtual ~Supplement() = default;
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#if ASSERT_ENABLED || ENABLE(SECURITY_ASSERTIONS)
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virtual bool isRefCountedWrapper() const { return false; }
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#endif
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static void provideTo(Supplementable<T>* host, const char* key, std::unique_ptr<Supplement<T>> supplement)
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{
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host->provideSupplement(key, WTFMove(supplement));
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}
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static Supplement<T>* from(Supplementable<T>* host, const char* key)
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{
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return host ? host->requireSupplement(key) : 0;
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}
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};
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template<typename T>
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class Supplementable {
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public:
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void provideSupplement(const char* key, std::unique_ptr<Supplement<T>> supplement)
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{
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ASSERT(canCurrentThreadAccessThreadLocalData(m_thread));
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ASSERT(!m_supplements.get(key));
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m_supplements.set(key, WTFMove(supplement));
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}
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void removeSupplement(const char* key)
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{
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ASSERT(canCurrentThreadAccessThreadLocalData(m_thread));
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m_supplements.remove(key);
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}
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Supplement<T>* requireSupplement(const char* key)
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{
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ASSERT(canCurrentThreadAccessThreadLocalData(m_thread));
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return m_supplements.get(key);
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}
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#if ASSERT_ENABLED
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protected:
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Supplementable() = default;
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#endif
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private:
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typedef HashMap<const char*, std::unique_ptr<Supplement<T>>, PtrHash<const char*>> SupplementMap;
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SupplementMap m_supplements;
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#if ASSERT_ENABLED
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Ref<Thread> m_thread { Thread::current() };
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#endif
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};
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} // namespace WebCore
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#endif // Supplementable_h
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