context.h

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#ifndef ZTH_CONTEXT_H
#define ZTH_CONTEXT_H
/*
 * Zth (libzth), a cooperative userspace multitasking library.
 * Copyright (C) 2019-2022  Jochem Rutgers
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at https://mozilla.org/MPL/2.0/.
 */
 
#include <libzth/config.h>
 
#ifdef ZTH_STACK_SWITCH
EXTERN_C ZTH_EXPORT void*
zth_stack_switch(void* stack, size_t size, void* (*f)(void*) noexcept, void* arg) noexcept;
#else // !ZTH_STACK_SWITCH
#       define zth_stack_switch(stack, size, f, arg) \
                ({                                    \
                        (void)(stack);                \
                        (void)(size);                 \
                        ((f)(arg));                   \
                })
#endif // !ZTH_STACK_SWITCH
 
#ifdef __cplusplus
#       include <libzth/util.h>
 
#       if __cplusplus >= 201103L
#               include <tuple>
#       endif
 
#       if __cplusplus < 201103L
#               undef ZTH_STACK_SWITCH98
// Always use C++98-compatible stack_switch() implementation.
#               define ZTH_STACK_SWITCH98 1
#       elif !defined(ZTH_STACK_SWITCH98)
// By default only use C++11 stack_switch() implementation, but this can be
// overridden for testing purposes.
#               define ZTH_STACK_SWITCH98 0
#       endif
 
namespace zth {
 
class Context;
 
struct ContextAttr {
        typedef void* EntryArg;
        typedef void (*Entry)(EntryArg);
 
        constexpr explicit ContextAttr(Entry entry = nullptr, EntryArg arg = EntryArg()) noexcept
                : stackSize(Config::DefaultFiberStackSize)
                , entry(entry)
                , arg(arg)
        {}
 
        size_t stackSize;
        Entry entry;
        EntryArg arg;
};
 
int context_init() noexcept;
void context_deinit() noexcept;
int context_create(Context*& context, ContextAttr const& attr) noexcept;
void context_switch(Context* from, Context* to) noexcept;
void context_destroy(Context* context) noexcept;
size_t context_stack_usage(Context* context) noexcept;
 
void stack_watermark_init(void* stack, size_t size) noexcept;
size_t stack_watermark_size(void* stack) noexcept;
size_t stack_watermark_maxused(void* stack) noexcept;
size_t stack_watermark_remaining(void* stack) noexcept;
 
 
 
namespace impl {
 
#       if ZTH_STACK_SWITCH98
template <typename R>
struct FunctionIO0 {
        union {
                struct {
                        R (*f)();
                };
                R r;
        };
 
        void* operator()()
        {
                r = f();
                return &r;
        }
};
 
template <>
struct FunctionIO0<void> {
        union {
                struct {
                        void (*f)();
                };
        };
 
        void* operator()()
        {
                f();
                return nullptr;
        }
};
 
template <typename R, typename A1>
struct FunctionIO1 {
        union {
                struct {
                        R (*f)(A1);
                        A1 a1;
                };
                R r;
        };
 
        void* operator()()
        {
                r = f(a1);
                return &r;
        }
};
 
template <typename A1>
struct FunctionIO1<void, A1> {
        union {
                struct {
                        void (*f)(A1);
                        A1 a1;
                };
        };
 
        void* operator()()
        {
                f(a1);
                return nullptr;
        }
};
 
template <typename R, typename A1, typename A2>
struct FunctionIO2 {
        union {
                struct {
                        R (*f)(A1, A2);
                        A1 a1;
                        A2 a2;
                };
                R r;
        };
 
        void* operator()()
        {
                r = f(a1, a2);
                return &r;
        }
};
 
template <typename A1, typename A2>
struct FunctionIO2<void, A1, A2> {
        union {
                struct {
                        void (*f)(A1, A2);
                        A1 a1;
                        A2 a2;
                };
        };
 
        void* operator()()
        {
                f(a1, a2);
                return nullptr;
        }
};
 
template <typename R, typename A1, typename A2, typename A3>
struct FunctionIO3 {
        union {
                struct {
                        R (*f)(A1, A2, A3);
                        A1 a1;
                        A2 a2;
                        A3 a3;
                };
                R r;
        };
        void* operator()()
        {
                r = f(a1, a2, a3);
                return &r;
        }
};
 
template <typename A1, typename A2, typename A3>
struct FunctionIO3<void, A1, A2, A3> {
        union {
                struct {
                        void (*f)(A1, A2, A3);
                        A1 a1;
                        A2 a2;
                        A3 a3;
                };
        };
 
        void* operator()()
        {
                f(a1, a2, a3);
                return nullptr;
        }
};
 
#       elif __cplusplus >= 201103L
 
template <typename T>
struct Packed {
        using type = typename std::decay<T>::type;
};
 
template <typename T>
struct Packed<T&> {
        using type = std::reference_wrapper<typename std::decay<T>::type>;
};
 
template <typename... A>
struct Arguments {
        template <typename R>
        using function_type = R(A...);
        using tuple_type = std::tuple<typename Packed<A>::type...>;
        constexpr static size_t size = sizeof...(A);
};
 
template <typename R, typename A, typename A_>
struct FunctionION {
        union {
                struct {
                        typename A::template function_type<R>* f;
                        typename A_::tuple_type a;
                };
                typename Packed<R>::type r;
        };
 
        void* operator()() noexcept
        {
                call(typename SequenceGenerator<A::size>::type(), A());
                return &r;
        }
 
private:
        template <size_t... S, typename... _A>
        void call(Sequence<S...>, Arguments<_A...>) noexcept
        {
                r = f(std::forward<_A>(std::get<S>(a))...);
        }
};
 
template <typename A, typename A_>
struct FunctionION<void, A, A_> {
        union {
                struct {
                        typename A::template function_type<void>* f;
                        typename A_::tuple_type a;
                };
        };
 
        void* operator()() noexcept
        {
                call(typename SequenceGenerator<A::size>::type(), A());
                return nullptr;
        }
 
private:
        template <size_t... S, typename... _A>
        void call(Sequence<S...>, Arguments<_A...>) noexcept
        {
                f(std::forward<_A>(std::get<S>(a))...);
        }
};
#       endif // C++11
 
template <typename F>
void* stack_switch_fwd(void* f) noexcept
{
        return (*static_cast<F*>(f))();
}
 
} // namespace impl
 
#       if ZTH_STACK_SWITCH98
template <typename R>
inline R stack_switch(void* stack, size_t size, R (*f)())
{
        impl::FunctionIO0<R> f_ = {{f}};
        return *static_cast<R*>(
                zth_stack_switch(stack, size, &impl::stack_switch_fwd<decltype(f_)>, &f_));
}
 
inline void stack_switch(void* stack, size_t size, void (*f)())
{
        impl::FunctionIO0<void> f_ = {{f}};
        zth_stack_switch(stack, size, &impl::stack_switch_fwd<decltype(f_)>, &f_);
}
 
template <typename R, typename A1>
inline R stack_switch(void* stack, size_t size, R (*f)(A1), A1 a1)
{
        impl::FunctionIO1<R, A1> f_ = {{f, a1}};
        return *static_cast<R*>(
                zth_stack_switch(stack, size, &impl::stack_switch_fwd<decltype(f_)>, &f_));
}
 
template <typename A1>
inline void stack_switch(void* stack, size_t size, void (*f)(A1), A1 a1)
{
        impl::FunctionIO1<void, A1> f_ = {{f, a1}};
        zth_stack_switch(stack, size, &impl::stack_switch_fwd<decltype(f_)>, &f_);
}
 
template <typename R, typename A1, typename A2>
inline R stack_switch(void* stack, size_t size, R (*f)(A1, A2), A1 a1, A2 a2)
{
        impl::FunctionIO2<R, A1, A2> f_ = {{f, a1, a2}};
        return *static_cast<R*>(
                zth_stack_switch(stack, size, &impl::stack_switch_fwd<decltype(f_)>, &f_));
}
 
template <typename A1, typename A2>
inline void stack_switch(void* stack, size_t size, void (*f)(A1, A2), A1 a1, A2 a2)
{
        impl::FunctionIO2<void, A1, A2> f_ = {{f, a1, a2}};
        zth_stack_switch(stack, size, &impl::stack_switch_fwd<decltype(f_)>, &f_);
}
 
template <typename R, typename A1, typename A2, typename A3>
inline R stack_switch(void* stack, size_t size, R (*f)(A1, A2, A3), A1 a1, A2 a2, A3 a3)
{
        impl::FunctionIO3<R, A1, A2, A3> f_ = {{f, a1, a2, a3}};
        return *static_cast<R*>(
                zth_stack_switch(stack, size, &impl::stack_switch_fwd<decltype(f_)>, &f_));
}
 
template <typename A1, typename A2, typename A3>
inline void stack_switch(void* stack, size_t size, void (*f)(A1, A2, A3), A1 a1, A2 a2, A3 a3)
{
        impl::FunctionIO3<void, A1, A2, A3> f_ = {{f, a1, a2, a3}};
        zth_stack_switch(stack, size, &impl::stack_switch_fwd<decltype(f_)>, &f_);
}
 
#       elif __cplusplus >= 201103L // !ZTH_STACK_SWITCH98
 
template <typename R, typename... A, typename... A_>
inline typename std::enable_if<!std::is_void<R>::value, R>::type
stack_switch(void* stack, size_t size, R (*f)(A...) noexcept, A_&&... a) noexcept
{
        impl::FunctionION<R, impl::Arguments<A...>, impl::Arguments<A_&&...>> f_{
                {f, {std::forward<A_>(a)...}}};
        return std::move(*static_cast<typename impl::Packed<R>::type*>(
                zth_stack_switch(stack, size, &impl::stack_switch_fwd<decltype(f_)>, &f_)));
}
 
template <typename... A, typename... A_>
inline void stack_switch(void* stack, size_t size, void (*f)(A...) noexcept, A_&&... a) noexcept
{
        impl::FunctionION<void, impl::Arguments<A...>, impl::Arguments<A_&&...>> f_{
                {f, {std::forward<A_>(a)...}}};
        zth_stack_switch(stack, size, &impl::stack_switch_fwd<decltype(f_)>, &f_);
}
#       endif                        // !ZTH_STACK_SWITCH98
 
} // namespace zth
#endif // __cplusplus
#endif // ZTH_CONTEXT_H