118 lines
4.2 KiB
C++
118 lines
4.2 KiB
C++
// Copyright (c) 2012 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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// This file contains utility functions and classes that help the
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// implementation, and management of the Callback objects.
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#ifndef BASE_CALLBACK_INTERNAL_H_
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#define BASE_CALLBACK_INTERNAL_H_
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#include "base/atomic_ref_count.h"
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#include "base/base_export.h"
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#include "base/callback_forward.h"
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#include "base/macros.h"
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#include "base/memory/ref_counted.h"
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namespace base {
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namespace internal {
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template <CopyMode copy_mode>
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class CallbackBase;
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// BindStateBase is used to provide an opaque handle that the Callback
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// class can use to represent a function object with bound arguments. It
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// behaves as an existential type that is used by a corresponding
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// DoInvoke function to perform the function execution. This allows
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// us to shield the Callback class from the types of the bound argument via
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// "type erasure."
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// At the base level, the only task is to add reference counting data. Don't use
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// RefCountedThreadSafe since it requires the destructor to be a virtual method.
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// Creating a vtable for every BindState template instantiation results in a lot
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// of bloat. Its only task is to call the destructor which can be done with a
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// function pointer.
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class BindStateBase {
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protected:
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explicit BindStateBase(void (*destructor)(BindStateBase*))
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: ref_count_(0), destructor_(destructor) {}
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~BindStateBase() = default;
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private:
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friend class scoped_refptr<BindStateBase>;
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template <CopyMode copy_mode>
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friend class CallbackBase;
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void AddRef();
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void Release();
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AtomicRefCount ref_count_;
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// Pointer to a function that will properly destroy |this|.
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void (*destructor_)(BindStateBase*);
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DISALLOW_COPY_AND_ASSIGN(BindStateBase);
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};
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// Holds the Callback methods that don't require specialization to reduce
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// template bloat.
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// CallbackBase<MoveOnly> is a direct base class of MoveOnly callbacks, and
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// CallbackBase<Copyable> uses CallbackBase<MoveOnly> for its implementation.
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template <>
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class BASE_EXPORT CallbackBase<CopyMode::MoveOnly> {
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public:
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CallbackBase(CallbackBase&& c);
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CallbackBase& operator=(CallbackBase&& c);
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// Returns true if Callback is null (doesn't refer to anything).
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bool is_null() const { return bind_state_.get() == NULL; }
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explicit operator bool() const { return !is_null(); }
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// Returns the Callback into an uninitialized state.
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void Reset();
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protected:
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// In C++, it is safe to cast function pointers to function pointers of
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// another type. It is not okay to use void*. We create a InvokeFuncStorage
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// that that can store our function pointer, and then cast it back to
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// the original type on usage.
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using InvokeFuncStorage = void(*)();
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// Returns true if this callback equals |other|. |other| may be null.
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bool EqualsInternal(const CallbackBase& other) const;
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// Allow initializing of |bind_state_| via the constructor to avoid default
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// initialization of the scoped_refptr. We do not also initialize
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// |polymorphic_invoke_| here because doing a normal assignment in the
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// derived Callback templates makes for much nicer compiler errors.
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explicit CallbackBase(BindStateBase* bind_state);
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// Force the destructor to be instantiated inside this translation unit so
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// that our subclasses will not get inlined versions. Avoids more template
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// bloat.
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~CallbackBase();
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scoped_refptr<BindStateBase> bind_state_;
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InvokeFuncStorage polymorphic_invoke_ = nullptr;
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};
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// CallbackBase<Copyable> is a direct base class of Copyable Callbacks.
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template <>
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class BASE_EXPORT CallbackBase<CopyMode::Copyable>
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: public CallbackBase<CopyMode::MoveOnly> {
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public:
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CallbackBase(const CallbackBase& c);
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CallbackBase(CallbackBase&& c);
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CallbackBase& operator=(const CallbackBase& c);
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CallbackBase& operator=(CallbackBase&& c);
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protected:
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explicit CallbackBase(BindStateBase* bind_state)
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: CallbackBase<CopyMode::MoveOnly>(bind_state) {}
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~CallbackBase() {}
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};
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extern template class CallbackBase<CopyMode::MoveOnly>;
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extern template class CallbackBase<CopyMode::Copyable>;
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} // namespace internal
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} // namespace base
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#endif // BASE_CALLBACK_INTERNAL_H_
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