// Copyright (c) 2012 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. // This file contains utility functions and classes that help the // implementation, and management of the Callback objects. #ifndef BASE_CALLBACK_INTERNAL_H_ #define BASE_CALLBACK_INTERNAL_H_ #include #include "base/base_export.h" #include "base/callback_forward.h" #include "base/memory/ref_counted.h" namespace base { struct FakeBindState; namespace internal { class BindStateBase; class FinallyExecutorCommon; class ThenAndCatchExecutorCommon; template class PostTaskExecutor; template struct BindState; class CallbackBase; class CallbackBaseCopyable; struct BindStateBaseRefCountTraits { static void Destruct(const BindStateBase*); }; template using PassingType = std::conditional_t, T, T&&>; // BindStateBase is used to provide an opaque handle that the Callback // class can use to represent a function object with bound arguments. It // behaves as an existential type that is used by a corresponding // DoInvoke function to perform the function execution. This allows // us to shield the Callback class from the types of the bound argument via // "type erasure." // At the base level, the only task is to add reference counting data. Avoid // using or inheriting any virtual functions. Creating a vtable for every // BindState template instantiation results in a lot of bloat. Its only task is // to call the destructor which can be done with a function pointer. class BASE_EXPORT BindStateBase : public RefCountedThreadSafe { public: REQUIRE_ADOPTION_FOR_REFCOUNTED_TYPE(); enum CancellationQueryMode { IS_CANCELLED, MAYBE_VALID, }; using InvokeFuncStorage = void(*)(); BindStateBase(const BindStateBase&) = delete; BindStateBase& operator=(const BindStateBase&) = delete; private: BindStateBase(InvokeFuncStorage polymorphic_invoke, void (*destructor)(const BindStateBase*)); BindStateBase(InvokeFuncStorage polymorphic_invoke, void (*destructor)(const BindStateBase*), bool (*query_cancellation_traits)(const BindStateBase*, CancellationQueryMode mode)); ~BindStateBase() = default; friend struct BindStateBaseRefCountTraits; friend class RefCountedThreadSafe; friend class CallbackBase; friend class CallbackBaseCopyable; // Allowlist subclasses that access the destructor of BindStateBase. template friend struct BindState; friend struct ::base::FakeBindState; bool IsCancelled() const { return query_cancellation_traits_(this, IS_CANCELLED); } bool MaybeValid() const { return query_cancellation_traits_(this, MAYBE_VALID); } // In C++, it is safe to cast function pointers to function pointers of // another type. It is not okay to use void*. We create a InvokeFuncStorage // that that can store our function pointer, and then cast it back to // the original type on usage. InvokeFuncStorage polymorphic_invoke_; // Pointer to a function that will properly destroy |this|. void (*destructor_)(const BindStateBase*); bool (*query_cancellation_traits_)(const BindStateBase*, CancellationQueryMode mode); }; // Holds the Callback methods that don't require specialization to reduce // template bloat. // CallbackBase is a direct base class of MoveOnly callbacks, and // CallbackBase uses CallbackBase for its implementation. class BASE_EXPORT CallbackBase { public: inline CallbackBase(CallbackBase&& c) noexcept; CallbackBase& operator=(CallbackBase&& c) noexcept; explicit CallbackBase(const CallbackBaseCopyable& c); CallbackBase& operator=(const CallbackBaseCopyable& c); explicit CallbackBase(CallbackBaseCopyable&& c) noexcept; CallbackBase& operator=(CallbackBaseCopyable&& c) noexcept; // Returns true if Callback is null (doesn't refer to anything). bool is_null() const { return !bind_state_; } explicit operator bool() const { return !is_null(); } // Returns true if the callback invocation will be nop due to an cancellation. // It's invalid to call this on uninitialized callback. // // Must be called on the Callback's destination sequence. bool IsCancelled() const; // If this returns false, the callback invocation will be a nop due to a // cancellation. This may(!) still return true, even on a cancelled callback. // // This function is thread-safe. bool MaybeValid() const; // Returns the Callback into an uninitialized state. void Reset(); protected: friend class FinallyExecutorCommon; friend class ThenAndCatchExecutorCommon; template friend class PostTaskExecutor; using InvokeFuncStorage = BindStateBase::InvokeFuncStorage; // Returns true if this callback equals |other|. |other| may be null. bool EqualsInternal(const CallbackBase& other) const; inline constexpr CallbackBase(); // Allow initializing of |bind_state_| via the constructor to avoid default // initialization of the scoped_refptr. explicit inline CallbackBase(BindStateBase* bind_state); InvokeFuncStorage polymorphic_invoke() const { return bind_state_->polymorphic_invoke_; } // Force the destructor to be instantiated inside this translation unit so // that our subclasses will not get inlined versions. Avoids more template // bloat. ~CallbackBase(); scoped_refptr bind_state_; }; constexpr CallbackBase::CallbackBase() = default; CallbackBase::CallbackBase(CallbackBase&&) noexcept = default; CallbackBase::CallbackBase(BindStateBase* bind_state) : bind_state_(AdoptRef(bind_state)) {} // CallbackBase is a direct base class of Copyable Callbacks. class BASE_EXPORT CallbackBaseCopyable : public CallbackBase { public: CallbackBaseCopyable(const CallbackBaseCopyable& c); CallbackBaseCopyable(CallbackBaseCopyable&& c) noexcept = default; CallbackBaseCopyable& operator=(const CallbackBaseCopyable& c); CallbackBaseCopyable& operator=(CallbackBaseCopyable&& c) noexcept; protected: constexpr CallbackBaseCopyable() = default; explicit CallbackBaseCopyable(BindStateBase* bind_state) : CallbackBase(bind_state) {} ~CallbackBaseCopyable() = default; }; // Helpers for the `Then()` implementation. template struct ThenHelper; // Specialization when original callback returns `void`. template