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/*
* Copyright (C) 2012 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
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
* OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#ifndef Supplementable_h
#define Supplementable_h
#include "platform/heap/Handle.h"
#include "wtf/Assertions.h"
#include "wtf/HashMap.h"
#include "wtf/Noncopyable.h"
#if DCHECK_IS_ON()
#include "wtf/Threading.h"
#endif
namespace blink {
// What you should know about Supplementable and Supplement
// ========================================================
// Supplementable and Supplement instances are meant to be thread local. They
// should only be accessed from within the thread that created them. The
// 2 classes are not designed for safe access from another thread. Violating
// this design assumption can result in memory corruption and unpredictable
// behavior.
//
// What you should know about the Supplement keys
// ==============================================
// The Supplement is expected to use the same const char* string instance
// as its key. The Supplementable's SupplementMap will use the address of the
// string as the key and not the characters themselves. Hence, 2 strings with
// the same characters will be treated as 2 different keys.
//
// In practice, it is recommended that Supplements implements a static method
// for returning its key to use. For example:
//
// class MyClass : public Supplement<MySupplementable> {
// ...
// static const char* supplementName();
// }
//
// const char* MyClass::supplementName()
// {
// return "MyClass";
// }
//
// An example of the using the key:
//
// MyClass* MyClass::from(MySupplementable* host)
// {
// return static_cast<MyClass*>(
// Supplement<MySupplementable>::from(host, supplementName()));
// }
//
// What you should know about thread checks
// ========================================
// When assertion is enabled this class performs thread-safety check so that
// supplements are provided to and from the same thread.
// If you want to provide some value for Workers, this thread check may be too
// strict, since in you'll be providing the value while worker preparation is
// being done on the main thread, even before the worker thread has started.
// If that's the case you can explicitly call reattachThread() when the
// Supplementable object is passed to the final destination thread (i.e.
// worker thread). This will allow supplements to be accessed on that thread.
// Please be extremely careful to use the method though, as randomly calling
// the method could easily cause racy condition.
//
// Note that reattachThread() does nothing if assertion is not enabled.
//
template <typename T>
class Supplementable;
template <typename T>
class Supplement : public GarbageCollectedMixin {
public:
// TODO(haraken): Remove the default constructor.
// All Supplement objects should be instantiated with m_host.
Supplement() {}
explicit Supplement(T& supplementable) : m_supplementable(&supplementable) {}
// Supplementable and its supplements live and die together.
// Thus supplementable() should never return null (if the default constructor
// is completely removed).
T* supplementable() const { return m_supplementable; }
static void provideTo(Supplementable<T>& supplementable,
const char* key,
Supplement<T>* supplement) {
supplementable.provideSupplement(key, supplement);
}
static Supplement<T>* from(Supplementable<T>& supplementable,
const char* key) {
return supplementable.requireSupplement(key);
}
static Supplement<T>* from(Supplementable<T>* supplementable,
const char* key) {
return supplementable ? supplementable->requireSupplement(key) : 0;
}
DEFINE_INLINE_VIRTUAL_TRACE() { visitor->trace(m_supplementable); }
private:
Member<T> m_supplementable;
};
// Supplementable<T> inherits from GarbageCollectedMixin virtually
// to allow ExecutionContext to derive from two GC mixin classes.
template <typename T>
class Supplementable : public virtual GarbageCollectedMixin {
WTF_MAKE_NONCOPYABLE(Supplementable);
public:
void provideSupplement(const char* key, Supplement<T>* supplement) {
#if DCHECK_IS_ON()
DCHECK_EQ(m_creationThreadId, currentThread());
#endif
this->m_supplements.set(key, supplement);
}
void removeSupplement(const char* key) {
#if DCHECK_IS_ON()
DCHECK_EQ(m_creationThreadId, currentThread());
#endif
this->m_supplements.remove(key);
}
Supplement<T>* requireSupplement(const char* key) {
#if DCHECK_IS_ON()
DCHECK_EQ(m_attachedThreadId, currentThread());
#endif
return this->m_supplements.get(key);
}
void reattachThread() {
#if DCHECK_IS_ON()
m_attachedThreadId = currentThread();
#endif
}
DEFINE_INLINE_VIRTUAL_TRACE() { visitor->trace(m_supplements); }
protected:
using SupplementMap =
HeapHashMap<const char*, Member<Supplement<T>>, PtrHash<const char>>;
SupplementMap m_supplements;
Supplementable()
#if DCHECK_IS_ON()
: m_attachedThreadId(currentThread()),
m_creationThreadId(currentThread())
#endif
{
}
#if DCHECK_IS_ON()
private:
ThreadIdentifier m_attachedThreadId;
ThreadIdentifier m_creationThreadId;
#endif
};
template <typename T>
struct ThreadingTrait<Supplement<T>> {
static const ThreadAffinity Affinity = ThreadingTrait<T>::Affinity;
};
template <typename T>
struct ThreadingTrait<Supplementable<T>> {
static const ThreadAffinity Affinity = ThreadingTrait<T>::Affinity;
};
} // namespace blink
#endif // Supplementable_h
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