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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 <functional>
#include <memory>
#include <tuple>
#include <type_traits>
#include <utility>
#include "base/bind.h"
#include "base/callback_internal.h"
#include "base/compiler_specific.h"
#include "base/memory/raw_scoped_refptr_mismatch_checker.h"
#include "base/memory/weak_ptr.h"
#include "base/template_util.h"
#include "build/build_config.h"
#if defined(OS_MACOSX) && !HAS_FEATURE(objc_arc)
#include "base/mac/scoped_block.h"
#endif
// See base/callback.h for user documentation.
//
//
// CONCEPTS:
// Functor -- A movable type representing something that should be called.
// All function pointers and Callback<> are functors even if the
// invocation syntax differs.
// RunType -- A function type (as opposed to function _pointer_ type) for
// a Callback<>::Run(). Usually just a convenience typedef.
// (Bound)Args -- A set of types that stores the arguments.
//
// Types:
// ForceVoidReturn<> -- Helper class for translating function signatures to
// equivalent forms with a "void" return type.
// FunctorTraits<> -- Type traits used to determine the correct RunType and
// invocation manner for a Functor. This is where function
// signature adapters are applied.
// InvokeHelper<> -- Take a Functor + arguments and actully invokes it.
// Handle the differing syntaxes needed for WeakPtr<>
// support. This is separate from Invoker to avoid creating
// multiple version of Invoker<>.
// Invoker<> -- Unwraps the curried parameters and executes the Functor.
// BindState<> -- Stores the curried parameters, and is the main entry point
// into the Bind() system.
#if defined(OS_WIN)
namespace Microsoft {
namespace WRL {
template <typename>
class ComPtr;
} // namespace WRL
} // namespace Microsoft
#endif
namespace base {
template <typename T>
struct IsWeakReceiver;
template <typename>
struct BindUnwrapTraits;
template <typename Functor, typename BoundArgsTuple, typename SFINAE = void>
struct CallbackCancellationTraits;
namespace internal {
template <typename Functor, typename SFINAE = void>
struct FunctorTraits;
template <typename T>
class UnretainedWrapper {
public:
explicit UnretainedWrapper(T* o) : ptr_(o) {}
T* get() const { return ptr_; }
private:
T* ptr_;
};
template <typename T>
class RetainedRefWrapper {
public:
explicit RetainedRefWrapper(T* o) : ptr_(o) {}
explicit RetainedRefWrapper(scoped_refptr<T> o) : ptr_(std::move(o)) {}
T* get() const { return ptr_.get(); }
private:
scoped_refptr<T> ptr_;
};
template <typename T>
struct IgnoreResultHelper {
explicit IgnoreResultHelper(T functor) : functor_(std::move(functor)) {}
explicit operator bool() const { return !!functor_; }
T functor_;
};
template <typename T, typename Deleter = std::default_delete<T>>
class OwnedWrapper {
public:
explicit OwnedWrapper(T* o) : ptr_(o) {}
explicit OwnedWrapper(std::unique_ptr<T, Deleter>&& ptr)
: ptr_(std::move(ptr)) {}
T* get() const { return ptr_.get(); }
private:
std::unique_ptr<T, Deleter> ptr_;
};
// PassedWrapper is a copyable adapter for a scoper that ignores const.
//
// It is needed to get around the fact that Bind() takes a const reference to
// all its arguments. Because Bind() takes a const reference to avoid
// unnecessary copies, it is incompatible with movable-but-not-copyable
// types; doing a destructive "move" of the type into Bind() would violate
// the const correctness.
//
// This conundrum cannot be solved without either C++11 rvalue references or
// a O(2^n) blowup of Bind() templates to handle each combination of regular
// types and movable-but-not-copyable types. Thus we introduce a wrapper type
// that is copyable to transmit the correct type information down into
// BindState<>. Ignoring const in this type makes sense because it is only
// created when we are explicitly trying to do a destructive move.
//
// Two notes:
// 1) PassedWrapper supports any type that has a move constructor, however
// the type will need to be specifically whitelisted in order for it to be
// bound to a Callback. We guard this explicitly at the call of Passed()
// to make for clear errors. Things not given to Passed() will be forwarded
// and stored by value which will not work for general move-only types.
// 2) is_valid_ is distinct from NULL because it is valid to bind a "NULL"
// scoper to a Callback and allow the Callback to execute once.
template <typename T>
class PassedWrapper {
public:
explicit PassedWrapper(T&& scoper)
: is_valid_(true), scoper_(std::move(scoper)) {}
PassedWrapper(PassedWrapper&& other)
: is_valid_(other.is_valid_), scoper_(std::move(other.scoper_)) {}
T Take() const {
CHECK(is_valid_);
is_valid_ = false;
return std::move(scoper_);
}
private:
mutable bool is_valid_;
mutable T scoper_;
};
template <typename T>
using Unwrapper = BindUnwrapTraits<std::decay_t<T>>;
template <typename T>
decltype(auto) Unwrap(T&& o) {
return Unwrapper<T>::Unwrap(std::forward<T>(o));
}
// IsWeakMethod is a helper that determine if we are binding a WeakPtr<> to a
// method. It is used internally by Bind() to select the correct
// InvokeHelper that will no-op itself in the event the WeakPtr<> for
// the target object is invalidated.
//
// The first argument should be the type of the object that will be received by
// the method.
template <bool is_method, typename... Args>
struct IsWeakMethod : std::false_type {};
template <typename T, typename... Args>
struct IsWeakMethod<true, T, Args...> : IsWeakReceiver<T> {};
// Packs a list of types to hold them in a single type.
template <typename... Types>
struct TypeList {};
// Used for DropTypeListItem implementation.
template <size_t n, typename List>
struct DropTypeListItemImpl;
// Do not use enable_if and SFINAE here to avoid MSVC2013 compile failure.
template <size_t n, typename T, typename... List>
struct DropTypeListItemImpl<n, TypeList<T, List...>>
: DropTypeListItemImpl<n - 1, TypeList<List...>> {};
template <typename T, typename... List>
struct DropTypeListItemImpl<0, TypeList<T, List...>> {
using Type = TypeList<T, List...>;
};
template <>
struct DropTypeListItemImpl<0, TypeList<>> {
using Type = TypeList<>;
};
// A type-level function that drops |n| list item from given TypeList.
template <size_t n, typename List>
using DropTypeListItem = typename DropTypeListItemImpl<n, List>::Type;
// Used for TakeTypeListItem implementation.
template <size_t n, typename List, typename... Accum>
struct TakeTypeListItemImpl;
// Do not use enable_if and SFINAE here to avoid MSVC2013 compile failure.
template <size_t n, typename T, typename... List, typename... Accum>
struct TakeTypeListItemImpl<n, TypeList<T, List...>, Accum...>
: TakeTypeListItemImpl<n - 1, TypeList<List...>, Accum..., T> {};
template <typename T, typename... List, typename... Accum>
struct TakeTypeListItemImpl<0, TypeList<T, List...>, Accum...> {
using Type = TypeList<Accum...>;
};
template <typename... Accum>
struct TakeTypeListItemImpl<0, TypeList<>, Accum...> {
using Type = TypeList<Accum...>;
};
// A type-level function that takes first |n| list item from given TypeList.
// E.g. TakeTypeListItem<3, TypeList<A, B, C, D>> is evaluated to
// TypeList<A, B, C>.
template <size_t n, typename List>
using TakeTypeListItem = typename TakeTypeListItemImpl<n, List>::Type;
// Used for ConcatTypeLists implementation.
template <typename List1, typename List2>
struct ConcatTypeListsImpl;
template <typename... Types1, typename... Types2>
struct ConcatTypeListsImpl<TypeList<Types1...>, TypeList<Types2...>> {
using Type = TypeList<Types1..., Types2...>;
};
// A type-level function that concats two TypeLists.
template <typename List1, typename List2>
using ConcatTypeLists = typename ConcatTypeListsImpl<List1, List2>::Type;
// Used for MakeFunctionType implementation.
template <typename R, typename ArgList>
struct MakeFunctionTypeImpl;
template <typename R, typename... Args>
struct MakeFunctionTypeImpl<R, TypeList<Args...>> {
// MSVC 2013 doesn't support Type Alias of function types.
// Revisit this after we update it to newer version.
typedef R Type(Args...);
};
// A type-level function that constructs a function type that has |R| as its
// return type and has TypeLists items as its arguments.
template <typename R, typename ArgList>
using MakeFunctionType = typename MakeFunctionTypeImpl<R, ArgList>::Type;
// Used for ExtractArgs and ExtractReturnType.
template <typename Signature>
struct ExtractArgsImpl;
template <typename R, typename... Args>
struct ExtractArgsImpl<R(Args...)> {
using ReturnType = R;
using ArgsList = TypeList<Args...>;
};
// A type-level function that extracts function arguments into a TypeList.
// E.g. ExtractArgs<R(A, B, C)> is evaluated to TypeList<A, B, C>.
template <typename Signature>
using ExtractArgs = typename ExtractArgsImpl<Signature>::ArgsList;
// A type-level function that extracts the return type of a function.
// E.g. ExtractReturnType<R(A, B, C)> is evaluated to R.
template <typename Signature>
using ExtractReturnType = typename ExtractArgsImpl<Signature>::ReturnType;
template <typename Callable,
typename Signature = decltype(&Callable::operator())>
struct ExtractCallableRunTypeImpl;
template <typename Callable, typename R, typename... Args>
struct ExtractCallableRunTypeImpl<Callable, R (Callable::*)(Args...)> {
using Type = R(Args...);
};
template <typename Callable, typename R, typename... Args>
struct ExtractCallableRunTypeImpl<Callable, R (Callable::*)(Args...) const> {
using Type = R(Args...);
};
// Evaluated to RunType of the given callable type.
// Example:
// auto f = [](int, char*) { return 0.1; };
// ExtractCallableRunType<decltype(f)>
// is evaluated to
// double(int, char*);
template <typename Callable>
using ExtractCallableRunType =
typename ExtractCallableRunTypeImpl<Callable>::Type;
// IsCallableObject<Functor> is std::true_type if |Functor| has operator().
// Otherwise, it's std::false_type.
// Example:
// IsCallableObject<void(*)()>::value is false.
//
// struct Foo {};
// IsCallableObject<void(Foo::*)()>::value is false.
//
// int i = 0;
// auto f = [i]() {};
// IsCallableObject<decltype(f)>::value is false.
template <typename Functor, typename SFINAE = void>
struct IsCallableObject : std::false_type {};
template <typename Callable>
struct IsCallableObject<Callable, void_t<decltype(&Callable::operator())>>
: std::true_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 : std::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_t<NeedsScopedRefptrButGetsRawPtr<T>::value,
std::true_type,
HasRefCountedTypeAsRawPtr<Args...>> {};
// 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...)> {
using RunType = void(Args...);
};
// FunctorTraits<>
//
// See description at top of file.
template <typename Functor, typename SFINAE>
struct FunctorTraits;
// For empty callable types.
// This specialization is intended to allow binding captureless lambdas, based
// on the fact that captureless lambdas are empty while capturing lambdas are
// not. This also allows any functors as far as it's an empty class.
// Example:
//
// // Captureless lambdas are allowed.
// []() {return 42;};
//
// // Capturing lambdas are *not* allowed.
// int x;
// [x]() {return x;};
//
// // Any empty class with operator() is allowed.
// struct Foo {
// void operator()() const {}
// // No non-static member variable and no virtual functions.
// };
template <typename Functor>
struct FunctorTraits<Functor,
std::enable_if_t<IsCallableObject<Functor>::value &&
std::is_empty<Functor>::value>> {
using RunType = ExtractCallableRunType<Functor>;
static constexpr bool is_method = false;
static constexpr bool is_nullable = false;
template <typename RunFunctor, typename... RunArgs>
static ExtractReturnType<RunType> Invoke(RunFunctor&& functor,
RunArgs&&... args) {
return std::forward<RunFunctor>(functor)(std::forward<RunArgs>(args)...);
}
};
// For functions.
template <typename R, typename... Args>
struct FunctorTraits<R (*)(Args...)> {
using RunType = R(Args...);
static constexpr bool is_method = false;
static constexpr bool is_nullable = true;
template <typename Function, typename... RunArgs>
static R Invoke(Function&& function, RunArgs&&... args) {
return std::forward<Function>(function)(std::forward<RunArgs>(args)...);
}
};
#if defined(OS_WIN) && !defined(ARCH_CPU_64_BITS)
// For functions.
template <typename R, typename... Args>
struct FunctorTraits<R(__stdcall*)(Args...)> {
using RunType = R(Args...);
static constexpr bool is_method = false;
static constexpr bool is_nullable = true;
template <typename... RunArgs>
static R Invoke(R(__stdcall* function)(Args...), RunArgs&&... args) {
return function(std::forward<RunArgs>(args)...);
}
};
// For functions.
template <typename R, typename... Args>
struct FunctorTraits<R(__fastcall*)(Args...)> {
using RunType = R(Args...);
static constexpr bool is_method = false;
static constexpr bool is_nullable = true;
template <typename... RunArgs>
static R Invoke(R(__fastcall* function)(Args...), RunArgs&&... args) {
return function(std::forward<RunArgs>(args)...);
}
};
#endif // defined(OS_WIN) && !defined(ARCH_CPU_64_BITS)
#if defined(OS_MACOSX)
// Support for Objective-C blocks. There are two implementation depending
// on whether Automated Reference Counting (ARC) is enabled. When ARC is
// enabled, then the block itself can be bound as the compiler will ensure
// its lifetime will be correctly managed. Otherwise, require the block to
// be wrapped in a base::mac::ScopedBlock (via base::RetainBlock) that will
// correctly manage the block lifetime.
//
// The two implementation ensure that the One Definition Rule (ODR) is not
// broken (it is not possible to write a template base::RetainBlock that would
// work correctly both with ARC enabled and disabled).
#if HAS_FEATURE(objc_arc)
template <typename R, typename... Args>
struct FunctorTraits<R (^)(Args...)> {
using RunType = R(Args...);
static constexpr bool is_method = false;
static constexpr bool is_nullable = true;
template <typename BlockType, typename... RunArgs>
static R Invoke(BlockType&& block, RunArgs&&... args) {
// According to LLVM documentation (§ 6.3), "local variables of automatic
// storage duration do not have precise lifetime." Use objc_precise_lifetime
// to ensure that the Objective-C block is not deallocated until it has
// finished executing even if the Callback<> is destroyed during the block
// execution.
__attribute__((objc_precise_lifetime)) R (^scoped_block)(Args...) = block;
return scoped_block(std::forward<RunArgs>(args)...);
}
};
#else // HAS_FEATURE(objc_arc)
template <typename R, typename... Args>
struct FunctorTraits<base::mac::ScopedBlock<R (^)(Args...)>> {
using RunType = R(Args...);
static constexpr bool is_method = false;
static constexpr bool is_nullable = true;
template <typename BlockType, typename... RunArgs>
static R Invoke(BlockType&& block, RunArgs&&... args) {
// Copy the block to ensure that the Objective-C block is not deallocated
// until it has finished executing even if the Callback<> is destroyed
// during the block execution.
base::mac::ScopedBlock<R (^)(Args...)> scoped_block(block);
return scoped_block.get()(std::forward<RunArgs>(args)...);
}
};
#endif // HAS_FEATURE(objc_arc)
#endif // defined(OS_MACOSX)
// For methods.
template <typename R, typename Receiver, typename... Args>
struct FunctorTraits<R (Receiver::*)(Args...)> {
using RunType = R(Receiver*, Args...);
static constexpr bool is_method = true;
static constexpr bool is_nullable = true;
template <typename Method, typename ReceiverPtr, typename... RunArgs>
static R Invoke(Method method,
ReceiverPtr&& receiver_ptr,
RunArgs&&... args) {
return ((*receiver_ptr).*method)(std::forward<RunArgs>(args)...);
}
};
// For const methods.
template <typename R, typename Receiver, typename... Args>
struct FunctorTraits<R (Receiver::*)(Args...) const> {
using RunType = R(const Receiver*, Args...);
static constexpr bool is_method = true;
static constexpr bool is_nullable = true;
template <typename Method, typename ReceiverPtr, typename... RunArgs>
static R Invoke(Method method,
ReceiverPtr&& receiver_ptr,
RunArgs&&... args) {
return ((*receiver_ptr).*method)(std::forward<RunArgs>(args)...);
}
};
#ifdef __cpp_noexcept_function_type
// noexcept makes a distinct function type in C++17.
// I.e. `void(*)()` and `void(*)() noexcept` are same in pre-C++17, and
// different in C++17.
template <typename R, typename... Args>
struct FunctorTraits<R (*)(Args...) noexcept> : FunctorTraits<R (*)(Args...)> {
};
template <typename R, typename Receiver, typename... Args>
struct FunctorTraits<R (Receiver::*)(Args...) noexcept>
: FunctorTraits<R (Receiver::*)(Args...)> {};
template <typename R, typename Receiver, typename... Args>
struct FunctorTraits<R (Receiver::*)(Args...) const noexcept>
: FunctorTraits<R (Receiver::*)(Args...) const> {};
#endif
// For IgnoreResults.
template <typename T>
struct FunctorTraits<IgnoreResultHelper<T>> : FunctorTraits<T> {
using RunType =
typename ForceVoidReturn<typename FunctorTraits<T>::RunType>::RunType;
template <typename IgnoreResultType, typename... RunArgs>
static void Invoke(IgnoreResultType&& ignore_result_helper,
RunArgs&&... args) {
FunctorTraits<T>::Invoke(
std::forward<IgnoreResultType>(ignore_result_helper).functor_,
std::forward<RunArgs>(args)...);
}
};
// For OnceCallbacks.
template <typename R, typename... Args>
struct FunctorTraits<OnceCallback<R(Args...)>> {
using RunType = R(Args...);
static constexpr bool is_method = false;
static constexpr bool is_nullable = true;
template <typename CallbackType, typename... RunArgs>
static R Invoke(CallbackType&& callback, RunArgs&&... args) {
DCHECK(!callback.is_null());
return std::forward<CallbackType>(callback).Run(
std::forward<RunArgs>(args)...);
}
};
// For RepeatingCallbacks.
template <typename R, typename... Args>
struct FunctorTraits<RepeatingCallback<R(Args...)>> {
using RunType = R(Args...);
static constexpr bool is_method = false;
static constexpr bool is_nullable = true;
template <typename CallbackType, typename... RunArgs>
static R Invoke(CallbackType&& callback, RunArgs&&... args) {
DCHECK(!callback.is_null());
return std::forward<CallbackType>(callback).Run(
std::forward<RunArgs>(args)...);
}
};
template <typename Functor>
using MakeFunctorTraits = FunctorTraits<std::decay_t<Functor>>;
// InvokeHelper<>
//
// There are 2 logical InvokeHelper<> specializations: normal, WeakCalls.
//
// The normal type just calls the underlying runnable.
//
// WeakCalls need special syntax that is applied to the first argument to check
// if they should no-op themselves.
template <bool is_weak_call, typename ReturnType>
struct InvokeHelper;
template <typename ReturnType>
struct InvokeHelper<false, ReturnType> {
template <typename Functor, typename... RunArgs>
static inline ReturnType MakeItSo(Functor&& functor, RunArgs&&... args) {
using Traits = MakeFunctorTraits<Functor>;
return Traits::Invoke(std::forward<Functor>(functor),
std::forward<RunArgs>(args)...);
}
};
template <typename ReturnType>
struct InvokeHelper<true, ReturnType> {
// 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(std::is_void<ReturnType>::value,
"weak_ptrs can only bind to methods without return values");
template <typename Functor, typename BoundWeakPtr, typename... RunArgs>
static inline void MakeItSo(Functor&& functor,
BoundWeakPtr&& weak_ptr,
RunArgs&&... args) {
if (!weak_ptr)
return;
using Traits = MakeFunctorTraits<Functor>;
Traits::Invoke(std::forward<Functor>(functor),
std::forward<BoundWeakPtr>(weak_ptr),
std::forward<RunArgs>(args)...);
}
};
// Invoker<>
//
// See description at the top of the file.
template <typename StorageType, typename UnboundRunType>
struct Invoker;
template <typename StorageType, typename R, typename... UnboundArgs>
struct Invoker<StorageType, R(UnboundArgs...)> {
static R RunOnce(BindStateBase* base,
PassingType<UnboundArgs>... unbound_args) {
// 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.
StorageType* storage = static_cast<StorageType*>(base);
static constexpr size_t num_bound_args =
std::tuple_size<decltype(storage->bound_args_)>::value;
return RunImpl(std::move(storage->functor_),
std::move(storage->bound_args_),
std::make_index_sequence<num_bound_args>(),
std::forward<UnboundArgs>(unbound_args)...);
}
static R Run(BindStateBase* base, PassingType<UnboundArgs>... unbound_args) {
// 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.
const StorageType* storage = static_cast<StorageType*>(base);
static constexpr size_t num_bound_args =
std::tuple_size<decltype(storage->bound_args_)>::value;
return RunImpl(storage->functor_, storage->bound_args_,
std::make_index_sequence<num_bound_args>(),
std::forward<UnboundArgs>(unbound_args)...);
}
private:
template <typename Functor, typename BoundArgsTuple, size_t... indices>
static inline R RunImpl(Functor&& functor,
BoundArgsTuple&& bound,
std::index_sequence<indices...>,
UnboundArgs&&... unbound_args) {
static constexpr bool is_method = MakeFunctorTraits<Functor>::is_method;
using DecayedArgsTuple = std::decay_t<BoundArgsTuple>;
static constexpr bool is_weak_call =
IsWeakMethod<is_method,
std::tuple_element_t<indices, DecayedArgsTuple>...>();
return InvokeHelper<is_weak_call, R>::MakeItSo(
std::forward<Functor>(functor),
Unwrap(std::get<indices>(std::forward<BoundArgsTuple>(bound)))...,
std::forward<UnboundArgs>(unbound_args)...);
}
};
// Extracts necessary type info from Functor and BoundArgs.
// Used to implement MakeUnboundRunType, BindOnce and BindRepeating.
template <typename Functor, typename... BoundArgs>
struct BindTypeHelper {
static constexpr size_t num_bounds = sizeof...(BoundArgs);
using FunctorTraits = MakeFunctorTraits<Functor>;
// Example:
// When Functor is `double (Foo::*)(int, const std::string&)`, and BoundArgs
// is a template pack of `Foo*` and `int16_t`:
// - RunType is `double(Foo*, int, const std::string&)`,
// - ReturnType is `double`,
// - RunParamsList is `TypeList<Foo*, int, const std::string&>`,
// - BoundParamsList is `TypeList<Foo*, int>`,
// - UnboundParamsList is `TypeList<const std::string&>`,
// - BoundArgsList is `TypeList<Foo*, int16_t>`,
// - UnboundRunType is `double(const std::string&)`.
using RunType = typename FunctorTraits::RunType;
using ReturnType = ExtractReturnType<RunType>;
using RunParamsList = ExtractArgs<RunType>;
using BoundParamsList = TakeTypeListItem<num_bounds, RunParamsList>;
using UnboundParamsList = DropTypeListItem<num_bounds, RunParamsList>;
using BoundArgsList = TypeList<BoundArgs...>;
using UnboundRunType = MakeFunctionType<ReturnType, UnboundParamsList>;
};
template <typename Functor>
std::enable_if_t<FunctorTraits<Functor>::is_nullable, bool> IsNull(
const Functor& functor) {
return !functor;
}
template <typename Functor>
std::enable_if_t<!FunctorTraits<Functor>::is_nullable, bool> IsNull(
const Functor&) {
return false;
}
// Used by QueryCancellationTraits below.
template <typename Functor, typename BoundArgsTuple, size_t... indices>
bool QueryCancellationTraitsImpl(BindStateBase::CancellationQueryMode mode,
const Functor& functor,
const BoundArgsTuple& bound_args,
std::index_sequence<indices...>) {
switch (mode) {
case BindStateBase::IS_CANCELLED:
return CallbackCancellationTraits<Functor, BoundArgsTuple>::IsCancelled(
functor, std::get<indices>(bound_args)...);
case BindStateBase::MAYBE_VALID:
return CallbackCancellationTraits<Functor, BoundArgsTuple>::MaybeValid(
functor, std::get<indices>(bound_args)...);
}
NOTREACHED();
}
// Relays |base| to corresponding CallbackCancellationTraits<>::Run(). Returns
// true if the callback |base| represents is canceled.
template <typename BindStateType>
bool QueryCancellationTraits(const BindStateBase* base,
BindStateBase::CancellationQueryMode mode) {
const BindStateType* storage = static_cast<const BindStateType*>(base);
static constexpr size_t num_bound_args =
std::tuple_size<decltype(storage->bound_args_)>::value;
return QueryCancellationTraitsImpl(
mode, storage->functor_, storage->bound_args_,
std::make_index_sequence<num_bound_args>());
}
// The base case of BanUnconstructedRefCountedReceiver that checks nothing.
template <typename Functor, typename Receiver, typename... Unused>
std::enable_if_t<
!(MakeFunctorTraits<Functor>::is_method &&
std::is_pointer<std::decay_t<Receiver>>::value &&
IsRefCountedType<std::remove_pointer_t<std::decay_t<Receiver>>>::value)>
BanUnconstructedRefCountedReceiver(const Receiver& receiver, Unused&&...) {}
template <typename Functor>
void BanUnconstructedRefCountedReceiver() {}
// Asserts that Callback is not the first owner of a ref-counted receiver.
template <typename Functor, typename Receiver, typename... Unused>
std::enable_if_t<
MakeFunctorTraits<Functor>::is_method &&
std::is_pointer<std::decay_t<Receiver>>::value &&
IsRefCountedType<std::remove_pointer_t<std::decay_t<Receiver>>>::value>
BanUnconstructedRefCountedReceiver(const Receiver& receiver, Unused&&...) {
DCHECK(receiver);
// It's error prone to make the implicit first reference to ref-counted types.
// In the example below, base::BindOnce() makes the implicit first reference
// to the ref-counted Foo. If PostTask() failed or the posted task ran fast
// enough, the newly created instance can be destroyed before |oo| makes
// another reference.
// Foo::Foo() {
// base::PostTask(FROM_HERE, base::BindOnce(&Foo::Bar, this));
// }
//
// scoped_refptr<Foo> oo = new Foo();
//
// Instead of doing like above, please consider adding a static constructor,
// and keep the first reference alive explicitly.
// // static
// scoped_refptr<Foo> Foo::Create() {
// auto foo = base::WrapRefCounted(new Foo());
// base::PostTask(FROM_HERE, base::BindOnce(&Foo::Bar, foo));
// return foo;
// }
//
// Foo::Foo() {}
//
// scoped_refptr<Foo> oo = Foo::Create();
DCHECK(receiver->HasAtLeastOneRef())
<< "base::Bind{Once,Repeating}() refuses to create the first reference "
"to ref-counted objects. That typically happens around PostTask() in "
"their constructor, and such objects can be destroyed before `new` "
"returns if the task resolves fast enough.";
}
// BindState<>
//
// This stores all the state passed into Bind().
template <typename Functor, typename... BoundArgs>
struct BindState final : BindStateBase {
using IsCancellable = std::integral_constant<
bool,
CallbackCancellationTraits<Functor,
std::tuple<BoundArgs...>>::is_cancellable>;
template <typename ForwardFunctor, typename... ForwardBoundArgs>
static BindState* Create(BindStateBase::InvokeFuncStorage invoke_func,
ForwardFunctor&& functor,
ForwardBoundArgs&&... bound_args) {
// Ban ref counted receivers that were not yet fully constructed to avoid
// a common pattern of racy situation.
BanUnconstructedRefCountedReceiver<ForwardFunctor>(bound_args...);
// IsCancellable is std::false_type if
// CallbackCancellationTraits<>::IsCancelled returns always false.
// Otherwise, it's std::true_type.
return new BindState(IsCancellable{}, invoke_func,
std::forward<ForwardFunctor>(functor),
std::forward<ForwardBoundArgs>(bound_args)...);
}
Functor functor_;
std::tuple<BoundArgs...> bound_args_;
private:
template <typename ForwardFunctor, typename... ForwardBoundArgs>
explicit BindState(std::true_type,
BindStateBase::InvokeFuncStorage invoke_func,
ForwardFunctor&& functor,
ForwardBoundArgs&&... bound_args)
: BindStateBase(invoke_func,
&Destroy,
&QueryCancellationTraits<BindState>),
functor_(std::forward<ForwardFunctor>(functor)),
bound_args_(std::forward<ForwardBoundArgs>(bound_args)...) {
DCHECK(!IsNull(functor_));
}
template <typename ForwardFunctor, typename... ForwardBoundArgs>
explicit BindState(std::false_type,
BindStateBase::InvokeFuncStorage invoke_func,
ForwardFunctor&& functor,
ForwardBoundArgs&&... bound_args)
: BindStateBase(invoke_func, &Destroy),
functor_(std::forward<ForwardFunctor>(functor)),
bound_args_(std::forward<ForwardBoundArgs>(bound_args)...) {
DCHECK(!IsNull(functor_));
}
~BindState() = default;
static void Destroy(const BindStateBase* self) {
delete static_cast<const BindState*>(self);
}
};
// Used to implement MakeBindStateType.
template <bool is_method, typename Functor, typename... BoundArgs>
struct MakeBindStateTypeImpl;
template <typename Functor, typename... BoundArgs>
struct MakeBindStateTypeImpl<false, Functor, BoundArgs...> {
static_assert(!HasRefCountedTypeAsRawPtr<std::decay_t<BoundArgs>...>::value,
"A parameter is a refcounted type and needs scoped_refptr.");
using Type = BindState<std::decay_t<Functor>, std::decay_t<BoundArgs>...>;
};
template <typename Functor>
struct MakeBindStateTypeImpl<true, Functor> {
using Type = BindState<std::decay_t<Functor>>;
};
template <typename Functor, typename Receiver, typename... BoundArgs>
struct MakeBindStateTypeImpl<true, Functor, Receiver, BoundArgs...> {
private:
using DecayedReceiver = std::decay_t<Receiver>;
static_assert(!std::is_array<std::remove_reference_t<Receiver>>::value,
"First bound argument to a method cannot be an array.");
static_assert(
!std::is_pointer<DecayedReceiver>::value ||
IsRefCountedType<std::remove_pointer_t<DecayedReceiver>>::value,
"Receivers may not be raw pointers. If using a raw pointer here is safe"
" and has no lifetime concerns, use base::Unretained() and document why"
" it's safe.");
static_assert(!HasRefCountedTypeAsRawPtr<std::decay_t<BoundArgs>...>::value,
"A parameter is a refcounted type and needs scoped_refptr.");
public:
using Type = BindState<
std::decay_t<Functor>,
std::conditional_t<std::is_pointer<DecayedReceiver>::value,
scoped_refptr<std::remove_pointer_t<DecayedReceiver>>,
DecayedReceiver>,
std::decay_t<BoundArgs>...>;
};
template <typename Functor, typename... BoundArgs>
using MakeBindStateType =
typename MakeBindStateTypeImpl<MakeFunctorTraits<Functor>::is_method,
Functor,
BoundArgs...>::Type;
} // namespace internal
// An injection point to control |this| pointer behavior on a method invocation.
// If IsWeakReceiver<> is true_type for |T| and |T| is used for a receiver of a
// method, base::Bind cancels the method invocation if the receiver is tested as
// false.
// E.g. Foo::bar() is not called:
// struct Foo : base::SupportsWeakPtr<Foo> {
// void bar() {}
// };
//
// WeakPtr<Foo> oo = nullptr;
// base::BindOnce(&Foo::bar, oo).Run();
template <typename T>
struct IsWeakReceiver : std::false_type {};
template <typename T>
struct IsWeakReceiver<std::reference_wrapper<T>> : IsWeakReceiver<T> {};
template <typename T>
struct IsWeakReceiver<WeakPtr<T>> : std::true_type {};
// An injection point to control how bound objects passed to the target
// function. BindUnwrapTraits<>::Unwrap() is called for each bound objects right
// before the target function is invoked.
template <typename>
struct BindUnwrapTraits {
template <typename T>
static T&& Unwrap(T&& o) {
return std::forward<T>(o);
}
};
template <typename T>
struct BindUnwrapTraits<internal::UnretainedWrapper<T>> {
static T* Unwrap(const internal::UnretainedWrapper<T>& o) { return o.get(); }
};
template <typename T>
struct BindUnwrapTraits<std::reference_wrapper<T>> {
static T& Unwrap(std::reference_wrapper<T> o) { return o.get(); }
};
template <typename T>
struct BindUnwrapTraits<internal::RetainedRefWrapper<T>> {
static T* Unwrap(const internal::RetainedRefWrapper<T>& o) { return o.get(); }
};
template <typename T, typename Deleter>
struct BindUnwrapTraits<internal::OwnedWrapper<T, Deleter>> {
static T* Unwrap(const internal::OwnedWrapper<T, Deleter>& o) {
return o.get();
}
};
template <typename T>
struct BindUnwrapTraits<internal::PassedWrapper<T>> {
static T Unwrap(const internal::PassedWrapper<T>& o) { return o.Take(); }
};
#if defined(OS_WIN)
template <typename T>
struct BindUnwrapTraits<Microsoft::WRL::ComPtr<T>> {
static T* Unwrap(const Microsoft::WRL::ComPtr<T>& ptr) { return ptr.Get(); }
};
#endif
// CallbackCancellationTraits allows customization of Callback's cancellation
// semantics. By default, callbacks are not cancellable. A specialization should
// set is_cancellable = true and implement an IsCancelled() that returns if the
// callback should be cancelled.
template <typename Functor, typename BoundArgsTuple, typename SFINAE>
struct CallbackCancellationTraits {
static constexpr bool is_cancellable = false;
};
// Specialization for method bound to weak pointer receiver.
template <typename Functor, typename... BoundArgs>
struct CallbackCancellationTraits<
Functor,
std::tuple<BoundArgs...>,
std::enable_if_t<
internal::IsWeakMethod<internal::FunctorTraits<Functor>::is_method,
BoundArgs...>::value>> {
static constexpr bool is_cancellable = true;
template <typename Receiver, typename... Args>
static bool IsCancelled(const Functor&,
const Receiver& receiver,
const Args&...) {
return !receiver;
}
template <typename Receiver, typename... Args>
static bool MaybeValid(const Functor&,
const Receiver& receiver,
const Args&...) {
return receiver.MaybeValid();
}
};
// Specialization for a nested bind.
template <typename Signature, typename... BoundArgs>
struct CallbackCancellationTraits<OnceCallback<Signature>,
std::tuple<BoundArgs...>> {
static constexpr bool is_cancellable = true;
template <typename Functor>
static bool IsCancelled(const Functor& functor, const BoundArgs&...) {
return functor.IsCancelled();
}
template <typename Functor>
static bool MaybeValid(const Functor& functor, const BoundArgs&...) {
return functor.MaybeValid();
}
};
template <typename Signature, typename... BoundArgs>
struct CallbackCancellationTraits<RepeatingCallback<Signature>,
std::tuple<BoundArgs...>> {
static constexpr bool is_cancellable = true;
template <typename Functor>
static bool IsCancelled(const Functor& functor, const BoundArgs&...) {
return functor.IsCancelled();
}
template <typename Functor>
static bool MaybeValid(const Functor& functor, const BoundArgs&...) {
return functor.MaybeValid();
}
};
// Returns a RunType of bound functor.
// E.g. MakeUnboundRunType<R(A, B, C), A, B> is evaluated to R(C).
template <typename Functor, typename... BoundArgs>
using MakeUnboundRunType =
typename internal::BindTypeHelper<Functor, BoundArgs...>::UnboundRunType;
} // namespace base
#endif // BASE_BIND_INTERNAL_H_