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Diffstat (limited to 'security/sandbox/chromium/base/bind_helpers.h')
| -rw-r--r-- | security/sandbox/chromium/base/bind_helpers.h | 658 |
1 files changed, 658 insertions, 0 deletions
diff --git a/security/sandbox/chromium/base/bind_helpers.h b/security/sandbox/chromium/base/bind_helpers.h new file mode 100644 index 000000000..2add755b4 --- /dev/null +++ b/security/sandbox/chromium/base/bind_helpers.h @@ -0,0 +1,658 @@ +// 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. + +// This defines a set of argument wrappers and related factory methods that +// can be used specify the refcounting and reference semantics of arguments +// that are bound by the Bind() function in base/bind.h. +// +// It also defines a set of simple functions and utilities that people want +// when using Callback<> and Bind(). +// +// +// ARGUMENT BINDING WRAPPERS +// +// The wrapper functions are base::Unretained(), base::Owned(), base::Passed(), +// base::ConstRef(), and base::IgnoreResult(). +// +// Unretained() allows Bind() to bind a non-refcounted class, and to disable +// refcounting on arguments that are refcounted objects. +// +// Owned() transfers ownership of an object to the Callback resulting from +// bind; the object will be deleted when the Callback is deleted. +// +// Passed() is for transferring movable-but-not-copyable types (eg. scoped_ptr) +// through a Callback. Logically, this signifies a destructive transfer of +// the state of the argument into the target function. Invoking +// Callback::Run() twice on a Callback that was created with a Passed() +// argument will CHECK() because the first invocation would have already +// transferred ownership to the target function. +// +// ConstRef() allows binding a constant reference to an argument rather +// than a copy. +// +// IgnoreResult() is used to adapt a function or Callback with a return type to +// one with a void return. This is most useful if you have a function with, +// say, a pesky ignorable bool return that you want to use with PostTask or +// something else that expect a Callback with a void return. +// +// EXAMPLE OF Unretained(): +// +// class Foo { +// public: +// void func() { cout << "Foo:f" << endl; } +// }; +// +// // In some function somewhere. +// Foo foo; +// Closure foo_callback = +// Bind(&Foo::func, Unretained(&foo)); +// foo_callback.Run(); // Prints "Foo:f". +// +// Without the Unretained() wrapper on |&foo|, the above call would fail +// to compile because Foo does not support the AddRef() and Release() methods. +// +// +// EXAMPLE OF Owned(): +// +// void foo(int* arg) { cout << *arg << endl } +// +// int* pn = new int(1); +// Closure foo_callback = Bind(&foo, Owned(pn)); +// +// foo_callback.Run(); // Prints "1" +// foo_callback.Run(); // Prints "1" +// *n = 2; +// foo_callback.Run(); // Prints "2" +// +// foo_callback.Reset(); // |pn| is deleted. Also will happen when +// // |foo_callback| goes out of scope. +// +// Without Owned(), someone would have to know to delete |pn| when the last +// reference to the Callback is deleted. +// +// +// EXAMPLE OF ConstRef(): +// +// void foo(int arg) { cout << arg << endl } +// +// int n = 1; +// Closure no_ref = Bind(&foo, n); +// Closure has_ref = Bind(&foo, ConstRef(n)); +// +// no_ref.Run(); // Prints "1" +// has_ref.Run(); // Prints "1" +// +// n = 2; +// no_ref.Run(); // Prints "1" +// has_ref.Run(); // Prints "2" +// +// Note that because ConstRef() takes a reference on |n|, |n| must outlive all +// its bound callbacks. +// +// +// EXAMPLE OF IgnoreResult(): +// +// int DoSomething(int arg) { cout << arg << endl; } +// +// // Assign to a Callback with a void return type. +// Callback<void(int)> cb = Bind(IgnoreResult(&DoSomething)); +// cb->Run(1); // Prints "1". +// +// // Prints "1" on |ml|. +// ml->PostTask(FROM_HERE, Bind(IgnoreResult(&DoSomething), 1); +// +// +// EXAMPLE OF Passed(): +// +// void TakesOwnership(scoped_ptr<Foo> arg) { } +// scoped_ptr<Foo> CreateFoo() { return scoped_ptr<Foo>(new Foo()); } +// +// scoped_ptr<Foo> f(new Foo()); +// +// // |cb| is given ownership of Foo(). |f| is now NULL. +// // You can use std::move(f) in place of &f, but it's more verbose. +// Closure cb = Bind(&TakesOwnership, Passed(&f)); +// +// // Run was never called so |cb| still owns Foo() and deletes +// // it on Reset(). +// cb.Reset(); +// +// // |cb| is given a new Foo created by CreateFoo(). +// cb = Bind(&TakesOwnership, Passed(CreateFoo())); +// +// // |arg| in TakesOwnership() is given ownership of Foo(). |cb| +// // no longer owns Foo() and, if reset, would not delete Foo(). +// cb.Run(); // Foo() is now transferred to |arg| and deleted. +// cb.Run(); // This CHECK()s since Foo() already been used once. +// +// Passed() is particularly useful with PostTask() when you are transferring +// ownership of an argument into a task, but don't necessarily know if the +// task will always be executed. This can happen if the task is cancellable +// or if it is posted to a TaskRunner. +// +// +// SIMPLE FUNCTIONS AND UTILITIES. +// +// DoNothing() - Useful for creating a Closure that does nothing when called. +// DeletePointer<T>() - Useful for creating a Closure that will delete a +// pointer when invoked. Only use this when necessary. +// In most cases MessageLoop::DeleteSoon() is a better +// fit. + +#ifndef BASE_BIND_HELPERS_H_ +#define BASE_BIND_HELPERS_H_ + +#include <stddef.h> + +#include <type_traits> +#include <utility> + +#include "base/callback.h" +#include "base/memory/weak_ptr.h" +#include "base/template_util.h" +#include "build/build_config.h" + +namespace base { +namespace internal { + +// Use the Substitution Failure Is Not An Error (SFINAE) trick to inspect T +// for the existence of AddRef() and Release() functions of the correct +// signature. +// +// http://en.wikipedia.org/wiki/Substitution_failure_is_not_an_error +// http://stackoverflow.com/questions/257288/is-it-possible-to-write-a-c-template-to-check-for-a-functions-existence +// http://stackoverflow.com/questions/4358584/sfinae-approach-comparison +// http://stackoverflow.com/questions/1966362/sfinae-to-check-for-inherited-member-functions +// +// The last link in particular show the method used below. +// +// For SFINAE to work with inherited methods, we need to pull some extra tricks +// with multiple inheritance. In the more standard formulation, the overloads +// of Check would be: +// +// template <typename C> +// Yes NotTheCheckWeWant(Helper<&C::TargetFunc>*); +// +// template <typename C> +// No NotTheCheckWeWant(...); +// +// static const bool value = sizeof(NotTheCheckWeWant<T>(0)) == sizeof(Yes); +// +// The problem here is that template resolution will not match +// C::TargetFunc if TargetFunc does not exist directly in C. That is, if +// TargetFunc in inherited from an ancestor, &C::TargetFunc will not match, +// |value| will be false. This formulation only checks for whether or +// not TargetFunc exist directly in the class being introspected. +// +// To get around this, we play a dirty trick with multiple inheritance. +// First, We create a class BaseMixin that declares each function that we +// want to probe for. Then we create a class Base that inherits from both T +// (the class we wish to probe) and BaseMixin. Note that the function +// signature in BaseMixin does not need to match the signature of the function +// we are probing for; thus it's easiest to just use void(). +// +// Now, if TargetFunc exists somewhere in T, then &Base::TargetFunc has an +// ambiguous resolution between BaseMixin and T. This lets us write the +// following: +// +// template <typename C> +// No GoodCheck(Helper<&C::TargetFunc>*); +// +// template <typename C> +// Yes GoodCheck(...); +// +// static const bool value = sizeof(GoodCheck<Base>(0)) == sizeof(Yes); +// +// Notice here that the variadic version of GoodCheck() returns Yes here +// instead of No like the previous one. Also notice that we calculate |value| +// by specializing GoodCheck() on Base instead of T. +// +// We've reversed the roles of the variadic, and Helper overloads. +// GoodCheck(Helper<&C::TargetFunc>*), when C = Base, fails to be a valid +// substitution if T::TargetFunc exists. Thus GoodCheck<Base>(0) will resolve +// to the variadic version if T has TargetFunc. If T::TargetFunc does not +// exist, then &C::TargetFunc is not ambiguous, and the overload resolution +// will prefer GoodCheck(Helper<&C::TargetFunc>*). +// +// This method of SFINAE will correctly probe for inherited names, but it cannot +// typecheck those names. It's still a good enough sanity check though. +// +// Works on gcc-4.2, gcc-4.4, and Visual Studio 2008. +// +// TODO(ajwong): Move to ref_counted.h or template_util.h when we've vetted +// this works well. +// +// TODO(ajwong): Make this check for Release() as well. +// See http://crbug.com/82038. +template <typename T> +class SupportsAddRefAndRelease { + using Yes = char[1]; + using No = char[2]; + + struct BaseMixin { + void AddRef(); + }; + +// MSVC warns when you try to use Base if T has a private destructor, the +// common pattern for refcounted types. It does this even though no attempt to +// instantiate Base is made. We disable the warning for this definition. +#if defined(OS_WIN) +#pragma warning(push) +#pragma warning(disable:4624) +#endif + struct Base : public T, public BaseMixin { + }; +#if defined(OS_WIN) +#pragma warning(pop) +#endif + + template <void(BaseMixin::*)()> struct Helper {}; + + template <typename C> + static No& Check(Helper<&C::AddRef>*); + + template <typename > + static Yes& Check(...); + + public: + enum { value = sizeof(Check<Base>(0)) == sizeof(Yes) }; +}; + +// Helpers to assert that arguments of a recounted type are bound with a +// scoped_refptr. +template <bool IsClasstype, typename T> +struct UnsafeBindtoRefCountedArgHelper : false_type { +}; + +template <typename T> +struct UnsafeBindtoRefCountedArgHelper<true, T> + : integral_constant<bool, SupportsAddRefAndRelease<T>::value> { +}; + +template <typename T> +struct UnsafeBindtoRefCountedArg : false_type { +}; + +template <typename T> +struct UnsafeBindtoRefCountedArg<T*> + : UnsafeBindtoRefCountedArgHelper<is_class<T>::value, T> { +}; + +template <typename T> +class HasIsMethodTag { + using Yes = char[1]; + using No = char[2]; + + template <typename U> + static Yes& Check(typename U::IsMethod*); + + template <typename U> + static No& Check(...); + + public: + enum { value = sizeof(Check<T>(0)) == sizeof(Yes) }; +}; + +template <typename T> +class UnretainedWrapper { + public: + explicit UnretainedWrapper(T* o) : ptr_(o) {} + T* get() const { return ptr_; } + private: + T* ptr_; +}; + +template <typename T> +class ConstRefWrapper { + public: + explicit ConstRefWrapper(const T& o) : ptr_(&o) {} + const T& get() const { return *ptr_; } + private: + const T* ptr_; +}; + +template <typename T> +struct IgnoreResultHelper { + explicit IgnoreResultHelper(T functor) : functor_(functor) {} + + T functor_; +}; + +template <typename T> +struct IgnoreResultHelper<Callback<T> > { + explicit IgnoreResultHelper(const Callback<T>& functor) : functor_(functor) {} + + const Callback<T>& functor_; +}; + +// An alternate implementation is to avoid the destructive copy, and instead +// specialize ParamTraits<> for OwnedWrapper<> to change the StorageType to +// a class that is essentially a scoped_ptr<>. +// +// The current implementation has the benefit though of leaving ParamTraits<> +// fully in callback_internal.h as well as avoiding type conversions during +// storage. +template <typename T> +class OwnedWrapper { + public: + explicit OwnedWrapper(T* o) : ptr_(o) {} + ~OwnedWrapper() { delete ptr_; } + T* get() const { return ptr_; } + OwnedWrapper(const OwnedWrapper& other) { + ptr_ = other.ptr_; + other.ptr_ = NULL; + } + + private: + mutable T* 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(const PassedWrapper& other) + : is_valid_(other.is_valid_), scoper_(std::move(other.scoper_)) {} + T Pass() const { + CHECK(is_valid_); + is_valid_ = false; + return std::move(scoper_); + } + + private: + mutable bool is_valid_; + mutable T scoper_; +}; + +// Unwrap the stored parameters for the wrappers above. +template <typename T> +struct UnwrapTraits { + using ForwardType = const T&; + static ForwardType Unwrap(const T& o) { return o; } +}; + +template <typename T> +struct UnwrapTraits<UnretainedWrapper<T> > { + using ForwardType = T*; + static ForwardType Unwrap(UnretainedWrapper<T> unretained) { + return unretained.get(); + } +}; + +template <typename T> +struct UnwrapTraits<ConstRefWrapper<T> > { + using ForwardType = const T&; + static ForwardType Unwrap(ConstRefWrapper<T> const_ref) { + return const_ref.get(); + } +}; + +template <typename T> +struct UnwrapTraits<scoped_refptr<T> > { + using ForwardType = T*; + static ForwardType Unwrap(const scoped_refptr<T>& o) { return o.get(); } +}; + +template <typename T> +struct UnwrapTraits<WeakPtr<T> > { + using ForwardType = const WeakPtr<T>&; + static ForwardType Unwrap(const WeakPtr<T>& o) { return o; } +}; + +template <typename T> +struct UnwrapTraits<OwnedWrapper<T> > { + using ForwardType = T*; + static ForwardType Unwrap(const OwnedWrapper<T>& o) { + return o.get(); + } +}; + +template <typename T> +struct UnwrapTraits<PassedWrapper<T> > { + using ForwardType = T; + static T Unwrap(PassedWrapper<T>& o) { + return o.Pass(); + } +}; + +// Utility for handling different refcounting semantics in the Bind() +// function. +template <bool is_method, typename... T> +struct MaybeScopedRefPtr; + +template <bool is_method> +struct MaybeScopedRefPtr<is_method> { + MaybeScopedRefPtr() {} +}; + +template <typename T, typename... Rest> +struct MaybeScopedRefPtr<false, T, Rest...> { + MaybeScopedRefPtr(const T&, const Rest&...) {} +}; + +template <typename T, size_t n, typename... Rest> +struct MaybeScopedRefPtr<false, T[n], Rest...> { + MaybeScopedRefPtr(const T*, const Rest&...) {} +}; + +template <typename T, typename... Rest> +struct MaybeScopedRefPtr<true, T, Rest...> { + MaybeScopedRefPtr(const T& o, const Rest&...) {} +}; + +template <typename T, typename... Rest> +struct MaybeScopedRefPtr<true, T*, Rest...> { + MaybeScopedRefPtr(T* o, const Rest&...) : ref_(o) {} + scoped_refptr<T> ref_; +}; + +// No need to additionally AddRef() and Release() since we are storing a +// scoped_refptr<> inside the storage object already. +template <typename T, typename... Rest> +struct MaybeScopedRefPtr<true, scoped_refptr<T>, Rest...> { + MaybeScopedRefPtr(const scoped_refptr<T>&, const Rest&...) {} +}; + +template <typename T, typename... Rest> +struct MaybeScopedRefPtr<true, const T*, Rest...> { + MaybeScopedRefPtr(const T* o, const Rest&...) : ref_(o) {} + scoped_refptr<const T> ref_; +}; + +// 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 IsMethod, typename... Args> +struct IsWeakMethod : public false_type {}; + +template <typename T, typename... Args> +struct IsWeakMethod<true, WeakPtr<T>, Args...> : public true_type {}; + +template <typename T, typename... Args> +struct IsWeakMethod<true, ConstRefWrapper<WeakPtr<T>>, Args...> + : public true_type {}; + + +// 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. +template <typename Signature> +struct ExtractArgsImpl; + +template <typename R, typename... Args> +struct ExtractArgsImpl<R(Args...)> { + using Type = 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>::Type; + +} // namespace internal + +template <typename T> +static inline internal::UnretainedWrapper<T> Unretained(T* o) { + return internal::UnretainedWrapper<T>(o); +} + +template <typename T> +static inline internal::ConstRefWrapper<T> ConstRef(const T& o) { + return internal::ConstRefWrapper<T>(o); +} + +template <typename T> +static inline internal::OwnedWrapper<T> Owned(T* o) { + return internal::OwnedWrapper<T>(o); +} + +// We offer 2 syntaxes for calling Passed(). The first takes an rvalue and +// is best suited for use with the return value of a function or other temporary +// rvalues. The second takes a pointer to the scoper and is just syntactic sugar +// to avoid having to write Passed(std::move(scoper)). +// +// Both versions of Passed() prevent T from being an lvalue reference. The first +// via use of enable_if, and the second takes a T* which will not bind to T&. +template <typename T, + typename std::enable_if<internal::IsMoveOnlyType<T>::value && + !std::is_lvalue_reference<T>::value>::type* = + nullptr> +static inline internal::PassedWrapper<T> Passed(T&& scoper) { + return internal::PassedWrapper<T>(std::move(scoper)); +} +template <typename T, + typename std::enable_if<internal::IsMoveOnlyType<T>::value>::type* = + nullptr> +static inline internal::PassedWrapper<T> Passed(T* scoper) { + return internal::PassedWrapper<T>(std::move(*scoper)); +} + +template <typename T> +static inline internal::IgnoreResultHelper<T> IgnoreResult(T data) { + return internal::IgnoreResultHelper<T>(data); +} + +template <typename T> +static inline internal::IgnoreResultHelper<Callback<T> > +IgnoreResult(const Callback<T>& data) { + return internal::IgnoreResultHelper<Callback<T> >(data); +} + +BASE_EXPORT void DoNothing(); + +template<typename T> +void DeletePointer(T* obj) { + delete obj; +} + +} // namespace base + +#endif // BASE_BIND_HELPERS_H_ |