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| #ifndef BASE_FUNCTION_REF_H_ |
| #define BASE_FUNCTION_REF_H_ |
| #include "config.h" |
| |
| #include <type_traits> |
| #include <utility> |
| |
| namespace tcmalloc { |
| |
| template <typename T> |
| struct FunctionRef; |
| |
| // FunctionRef is to std::function what std::string_view is to |
| // std::string. That is non-owning, trivially copyable reference-like |
| // type to anything that can be invoked. It is mostly equivalent to |
| // absl::FunctionRef. Just like std::string_view we encourage people |
| // to pass it by value and in most most modern ABIs it will be |
| // efficiently passed in two registers. |
| // |
| // It avoids any memory allocation (unlike std::function). So good to |
| // use everywhere even inside tightest guts of malloc or |
| // super-early. Of course, since it doesn't own it's invokable, it |
| // must not outlive it. |
| // |
| // Our version also explicitly exposes pure C-style function and data |
| // arguments to be used by legacy C-style API's that pass callback |
| // function and callback argument in order to implement closure-like |
| // features. |
| template <typename R, typename... Args> |
| struct FunctionRef<R(Args...)> { |
| template <typename F, |
| typename FR = std::invoke_result_t<F, Args&&...>> |
| using EnableIfCompatible = |
| typename std::enable_if<std::is_void<R>::value || |
| std::is_convertible<FR, R>::value>::type; |
| |
| template <typename Body, typename = EnableIfCompatible<const Body&>> |
| FunctionRef(const Body& body) |
| : fn([] (Args... args, void* data) { |
| const Body& b = *(reinterpret_cast<const Body*>(data)); |
| return b(std::forward<Args>(args)...); |
| }), data(const_cast<void*>(reinterpret_cast<const void*>(&body))) {} |
| |
| R operator()(Args... args) const { |
| return fn(std::forward<Args>(args)..., data); |
| } |
| |
| R (*const fn)(Args... args, void* data); |
| void* const data; |
| }; |
| |
| template <typename T> |
| struct FunctionRefFirstDataArg; |
| |
| // FunctionRefFirstDataArg is same as FunctionRef except it's fn's |
| // function type accepts data argument in first position. |
| template <typename R, typename... Args> |
| struct FunctionRefFirstDataArg<R(Args...)> { |
| template <typename F, |
| typename FR = std::invoke_result_t<F, Args&&...>> |
| using EnableIfCompatible = |
| typename std::enable_if<std::is_void<R>::value || |
| std::is_convertible<FR, R>::value>::type; |
| |
| template <typename Body> |
| FunctionRefFirstDataArg(const Body& body) |
| : fn([] (void* data, Args... args) { |
| const Body& b = *(reinterpret_cast<const Body*>(data)); |
| return b(std::forward<Args>(args)...); |
| }), data(const_cast<void*>(reinterpret_cast<const void*>(&body))) {} |
| |
| R operator()(Args... args) const { |
| return fn(std::forward<Args>(args)..., data); |
| } |
| |
| R (*const fn)(void* data, Args... args); |
| void* const data; |
| }; |
| |
| } // namespace tcmalloc |
| |
| #endif // BASE_FUNCTION_REF_H_ |