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// Copyright (c) 2011 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.
#ifndef BASE_BIND_INTERNAL_H_
#define BASE_BIND_INTERNAL_H_
#include <stddef.h>
#include <type_traits>
#include "base/bind_helpers.h"
#include "base/callback_internal.h"
#include "base/memory/raw_scoped_refptr_mismatch_checker.h"
#include "base/memory/weak_ptr.h"
#include "base/template_util.h"
#include "base/tuple.h"
#include "build/build_config.h"
#if defined(OS_WIN)
#include "base/bind_internal_win.h"
#endif
namespace base {
namespace internal {
// See base/callback.h for user documentation.
//
//
// CONCEPTS:
// Runnable -- A type (really a type class) that has a single Run() method
// and a RunType typedef that corresponds to the type of Run().
// A Runnable can declare that it should treated like a method
// call by including a typedef named IsMethod. The value of
// this typedef is NOT inspected, only the existence. When a
// Runnable declares itself a method, Bind() will enforce special
// refcounting + WeakPtr handling semantics for the first
// parameter which is expected to be an object.
// Functor -- A copyable type representing something that should be called.
// All function pointers, Callback<>, and Runnables are functors
// even if the invocation syntax differs.
// RunType -- A function type (as opposed to function _pointer_ type) for
// a Run() function. Usually just a convenience typedef.
// (Bound)Args -- A set of types that stores the arguments.
//
// Types:
// RunnableAdapter<> -- Wraps the various "function" pointer types into an
// object that adheres to the Runnable interface.
// ForceVoidReturn<> -- Helper class for translating function signatures to
// equivalent forms with a "void" return type.
// FunctorTraits<> -- Type traits used determine the correct RunType and
// RunnableType for a Functor. This is where function
// signature adapters are applied.
// MakeRunnable<> -- Takes a Functor and returns an object in the Runnable
// type class that represents the underlying Functor.
// InvokeHelper<> -- Take a Runnable + arguments and actully invokes it.
// Handle the differing syntaxes needed for WeakPtr<>
// support, and for ignoring return values. This is separate
// from Invoker to avoid creating multiple version of
// Invoker<>.
// Invoker<> -- Unwraps the curried parameters and executes the Runnable.
// BindState<> -- Stores the curried parameters, and is the main entry point
// into the Bind() system, doing most of the type resolution.
// There are ARITY BindState types.
// HasNonConstReferenceParam selects true_type when any of the parameters in
// |Sig| is a non-const reference.
// Implementation note: This non-specialized case handles zero-arity case only.
// Non-zero-arity cases should be handled by the specialization below.
template <typename List>
struct HasNonConstReferenceItem : false_type {};
// Implementation note: Select true_type if the first parameter is a non-const
// reference. Otherwise, skip the first parameter and check rest of parameters
// recursively.
template <typename T, typename... Args>
struct HasNonConstReferenceItem<TypeList<T, Args...>>
: std::conditional<is_non_const_reference<T>::value,
true_type,
HasNonConstReferenceItem<TypeList<Args...>>>::type {};
// HasRefCountedTypeAsRawPtr selects true_type when any of the |Args| is a raw
// pointer to a RefCounted type.
// Implementation note: This non-specialized case handles zero-arity case only.
// Non-zero-arity cases should be handled by the specialization below.
template <typename... Args>
struct HasRefCountedTypeAsRawPtr : false_type {};
// Implementation note: Select true_type if the first parameter is a raw pointer
// to a RefCounted type. Otherwise, skip the first parameter and check rest of
// parameters recursively.
template <typename T, typename... Args>
struct HasRefCountedTypeAsRawPtr<T, Args...>
: std::conditional<NeedsScopedRefptrButGetsRawPtr<T>::value,
true_type,
HasRefCountedTypeAsRawPtr<Args...>>::type {};
// BindsArrayToFirstArg selects true_type when |is_method| is true and the first
// item of |Args| is an array type.
// Implementation note: This non-specialized case handles !is_method case and
// zero-arity case only. Other cases should be handled by the specialization
// below.
template <bool is_method, typename... Args>
struct BindsArrayToFirstArg : false_type {};
template <typename T, typename... Args>
struct BindsArrayToFirstArg<true, T, Args...>
: is_array<typename std::remove_reference<T>::type> {};
// HasRefCountedParamAsRawPtr is the same to HasRefCountedTypeAsRawPtr except
// when |is_method| is true HasRefCountedParamAsRawPtr skips the first argument.
// Implementation note: This non-specialized case handles !is_method case and
// zero-arity case only. Other cases should be handled by the specialization
// below.
template <bool is_method, typename... Args>
struct HasRefCountedParamAsRawPtr : HasRefCountedTypeAsRawPtr<Args...> {};
template <typename T, typename... Args>
struct HasRefCountedParamAsRawPtr<true, T, Args...>
: HasRefCountedTypeAsRawPtr<Args...> {};
// RunnableAdapter<>
//
// The RunnableAdapter<> templates provide a uniform interface for invoking
// a function pointer, method pointer, or const method pointer. The adapter
// exposes a Run() method with an appropriate signature. Using this wrapper
// allows for writing code that supports all three pointer types without
// undue repetition. Without it, a lot of code would need to be repeated 3
// times.
//
// For method pointers and const method pointers the first argument to Run()
// is considered to be the received of the method. This is similar to STL's
// mem_fun().
//
// This class also exposes a RunType typedef that is the function type of the
// Run() function.
//
// If and only if the wrapper contains a method or const method pointer, an
// IsMethod typedef is exposed. The existence of this typedef (NOT the value)
// marks that the wrapper should be considered a method wrapper.
template <typename Functor>
class RunnableAdapter;
// Function.
template <typename R, typename... Args>
class RunnableAdapter<R(*)(Args...)> {
public:
// MSVC 2013 doesn't support Type Alias of function types.
// Revisit this after we update it to newer version.
typedef R RunType(Args...);
explicit RunnableAdapter(R(*function)(Args...))
: function_(function) {
}
template <typename... RunArgs>
R Run(RunArgs&&... args) {
return function_(std::forward<RunArgs>(args)...);
}
private:
R (*function_)(Args...);
};
// Method.
template <typename R, typename T, typename... Args>
class RunnableAdapter<R(T::*)(Args...)> {
public:
// MSVC 2013 doesn't support Type Alias of function types.
// Revisit this after we update it to newer version.
typedef R RunType(T*, Args...);
using IsMethod = true_type;
explicit RunnableAdapter(R(T::*method)(Args...))
: method_(method) {
}
template <typename... RunArgs>
R Run(T* object, RunArgs&&... args) {
return (object->*method_)(std::forward<RunArgs>(args)...);
}
private:
R (T::*method_)(Args...);
};
// Const Method.
template <typename R, typename T, typename... Args>
class RunnableAdapter<R(T::*)(Args...) const> {
public:
using RunType = R(const T*, Args...);
using IsMethod = true_type;
explicit RunnableAdapter(R(T::*method)(Args...) const)
: method_(method) {
}
template <typename... RunArgs>
R Run(const T* object, RunArgs&&... args) {
return (object->*method_)(std::forward<RunArgs>(args)...);
}
private:
R (T::*method_)(Args...) const;
};
// ForceVoidReturn<>
//
// Set of templates that support forcing the function return type to void.
template <typename Sig>
struct ForceVoidReturn;
template <typename R, typename... Args>
struct ForceVoidReturn<R(Args...)> {
// MSVC 2013 doesn't support Type Alias of function types.
// Revisit this after we update it to newer version.
typedef void RunType(Args...);
};
// FunctorTraits<>
//
// See description at top of file.
template <typename T>
struct FunctorTraits {
using RunnableType = RunnableAdapter<T>;
using RunType = typename RunnableType::RunType;
};
template <typename T>
struct FunctorTraits<IgnoreResultHelper<T>> {
using RunnableType = typename FunctorTraits<T>::RunnableType;
using RunType =
typename ForceVoidReturn<typename RunnableType::RunType>::RunType;
};
template <typename T>
struct FunctorTraits<Callback<T>> {
using RunnableType = Callback<T> ;
using RunType = typename Callback<T>::RunType;
};
// MakeRunnable<>
//
// Converts a passed in functor to a RunnableType using type inference.
template <typename T>
typename FunctorTraits<T>::RunnableType MakeRunnable(const T& t) {
return RunnableAdapter<T>(t);
}
template <typename T>
typename FunctorTraits<T>::RunnableType
MakeRunnable(const IgnoreResultHelper<T>& t) {
return MakeRunnable(t.functor_);
}
template <typename T>
const typename FunctorTraits<Callback<T>>::RunnableType&
MakeRunnable(const Callback<T>& t) {
DCHECK(!t.is_null());
return t;
}
// InvokeHelper<>
//
// There are 3 logical InvokeHelper<> specializations: normal, void-return,
// WeakCalls.
//
// The normal type just calls the underlying runnable.
//
// We need a InvokeHelper to handle void return types in order to support
// IgnoreResult(). Normally, if the Runnable's RunType had a void return,
// the template system would just accept "return functor.Run()" ignoring
// the fact that a void function is being used with return. This piece of
// sugar breaks though when the Runnable's RunType is not void. Thus, we
// need a partial specialization to change the syntax to drop the "return"
// from the invocation call.
//
// WeakCalls similarly need special syntax that is applied to the first
// argument to check if they should no-op themselves.
template <bool IsWeakCall, typename ReturnType, typename Runnable>
struct InvokeHelper;
template <typename ReturnType, typename Runnable>
struct InvokeHelper<false, ReturnType, Runnable> {
template <typename... RunArgs>
static ReturnType MakeItSo(Runnable runnable, RunArgs&&... args) {
return runnable.Run(std::forward<RunArgs>(args)...);
}
};
template <typename Runnable>
struct InvokeHelper<false, void, Runnable> {
template <typename... RunArgs>
static void MakeItSo(Runnable runnable, RunArgs&&... args) {
runnable.Run(std::forward<RunArgs>(args)...);
}
};
template <typename Runnable>
struct InvokeHelper<true, void, Runnable> {
template <typename BoundWeakPtr, typename... RunArgs>
static void MakeItSo(Runnable runnable,
BoundWeakPtr weak_ptr,
RunArgs&&... args) {
if (!weak_ptr.get()) {
return;
}
runnable.Run(weak_ptr.get(), std::forward<RunArgs>(args)...);
}
};
#if !defined(_MSC_VER)
template <typename ReturnType, typename Runnable>
struct InvokeHelper<true, ReturnType, Runnable> {
// WeakCalls are only supported for functions with a void return type.
// Otherwise, the function result would be undefined if the the WeakPtr<>
// is invalidated.
static_assert(is_void<ReturnType>::value,
"weak_ptrs can only bind to methods without return values");
};
#endif
// Invoker<>
//
// See description at the top of the file.
template <typename BoundIndices,
typename StorageType, typename Unwrappers,
typename InvokeHelperType, typename UnboundForwardRunType>
struct Invoker;
template <size_t... bound_indices,
typename StorageType,
typename... Unwrappers,
typename InvokeHelperType,
typename R,
typename... UnboundForwardArgs>
struct Invoker<IndexSequence<bound_indices...>,
StorageType, TypeList<Unwrappers...>,
InvokeHelperType, R(UnboundForwardArgs...)> {
static R Run(BindStateBase* base,
UnboundForwardArgs... unbound_args) {
StorageType* storage = static_cast<StorageType*>(base);
// Local references to make debugger stepping easier. If in a debugger,
// you really want to warp ahead and step through the
// InvokeHelper<>::MakeItSo() call below.
return InvokeHelperType::MakeItSo(
storage->runnable_,
Unwrappers::Unwrap(get<bound_indices>(storage->bound_args_))...,
CallbackForward(unbound_args)...);
}
};
// BindState<>
//
// This stores all the state passed into Bind() and is also where most
// of the template resolution magic occurs.
//
// Runnable is the functor we are binding arguments to.
// RunType is type of the Run() function that the Invoker<> should use.
// Normally, this is the same as the RunType of the Runnable, but it can
// be different if an adapter like IgnoreResult() has been used.
//
// BoundArgs contains the storage type for all the bound arguments.
template <typename Runnable, typename RunType, typename... BoundArgs>
struct BindState;
template <typename Runnable,
typename R,
typename... Args,
typename... BoundArgs>
struct BindState<Runnable, R(Args...), BoundArgs...> final
: public BindStateBase {
private:
using StorageType = BindState<Runnable, R(Args...), BoundArgs...>;
using RunnableType = Runnable;
// true_type if Runnable is a method invocation and the first bound argument
// is a WeakPtr.
using IsWeakCall =
IsWeakMethod<HasIsMethodTag<Runnable>::value, BoundArgs...>;
using BoundIndices = MakeIndexSequence<sizeof...(BoundArgs)>;
using Unwrappers = TypeList<UnwrapTraits<BoundArgs>...>;
using UnboundForwardArgs = DropTypeListItem<
sizeof...(BoundArgs),
TypeList<typename CallbackParamTraits<Args>::ForwardType...>>;
using UnboundForwardRunType = MakeFunctionType<R, UnboundForwardArgs>;
using InvokeHelperType = InvokeHelper<IsWeakCall::value, R, Runnable>;
using UnboundArgs = DropTypeListItem<sizeof...(BoundArgs), TypeList<Args...>>;
public:
using InvokerType = Invoker<BoundIndices, StorageType, Unwrappers,
InvokeHelperType, UnboundForwardRunType>;
using UnboundRunType = MakeFunctionType<R, UnboundArgs>;
template <typename... ForwardArgs>
BindState(const Runnable& runnable, ForwardArgs&&... bound_args)
: BindStateBase(&Destroy),
runnable_(runnable),
ref_(bound_args...),
bound_args_(std::forward<ForwardArgs>(bound_args)...) {}
RunnableType runnable_;
MaybeScopedRefPtr<HasIsMethodTag<Runnable>::value, BoundArgs...> ref_;
Tuple<BoundArgs...> bound_args_;
private:
~BindState() {}
static void Destroy(BindStateBase* self) {
delete static_cast<BindState*>(self);
}
};
} // namespace internal
} // namespace base
#endif // BASE_BIND_INTERNAL_H_