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Editing: continuation_ucontext.hpp

//          Copyright Oliver Kowalke 2017.
// Distributed under the Boost Software License, Version 1.0.
//    (See accompanying file LICENSE_1_0.txt or copy at
//          http://www.boost.org/LICENSE_1_0.txt)

#ifndef BOOST_CONTEXT_CONTINUATION_H
#define BOOST_CONTEXT_CONTINUATION_H

#include <boost/predef.h>
#if BOOST_OS_MACOS
#define _XOPEN_SOURCE 600
#endif

extern "C" {
#include <ucontext.h>
}

#include <boost/context/detail/config.hpp>

#include <algorithm>
#include <cstddef>
#include <cstdint>
#include <cstdlib>
#include <cstring>
#include <functional>
#include <memory>
#include <ostream>
#include <system_error>
#include <tuple>
#include <utility>

#include <boost/assert.hpp>
#include <boost/config.hpp>

#include <boost/context/detail/disable_overload.hpp>
#if defined(BOOST_NO_CXX14_STD_EXCHANGE)
#include <boost/context/detail/exchange.hpp>
#endif
#include <boost/context/detail/externc.hpp>
#if defined(BOOST_NO_CXX17_STD_INVOKE)
#include <boost/context/detail/invoke.hpp>
#endif
#include <boost/context/fixedsize_stack.hpp>
#include <boost/context/flags.hpp>
#include <boost/context/preallocated.hpp>
#if defined(BOOST_USE_SEGMENTED_STACKS)
#include <boost/context/segmented_stack.hpp>
#endif
#include <boost/context/stack_context.hpp>

#ifdef BOOST_HAS_ABI_HEADERS
# include BOOST_ABI_PREFIX
#endif

namespace boost {
namespace context {
namespace detail {

// tampoline function
// entered if the execution context
// is resumed for the first time
template< typename Record >
static void entry_func( void * data) noexcept {
    Record * record = static_cast< Record * >( data);
    BOOST_ASSERT( nullptr != record);
    // start execution of toplevel context-function
    record->run();
}

struct BOOST_CONTEXT_DECL activation_record {
    ucontext_t                                                  uctx{};
    stack_context                                               sctx{};
    bool                                                        main_ctx{ true };
	activation_record                                       *	from{ nullptr };
    std::function< activation_record*(activation_record*&) >    ontop{};
    bool                                                        terminated{ false };
    bool                                                        force_unwind{ false };
#if defined(BOOST_USE_ASAN)
    void                                                    *   fake_stack{ nullptr };
    void                                                    *   stack_bottom{ nullptr };
    std::size_t                                                 stack_size{ 0 };
#endif

static activation_record *& current() noexcept;

// used for toplevel-context
    // (e.g. main context, thread-entry context)
    activation_record() {
        if ( BOOST_UNLIKELY( 0 != ::getcontext( & uctx) ) ) {
            throw std::system_error(
                    std::error_code( errno, std::system_category() ),
                    "getcontext() failed");
        }
    }

activation_record( stack_context sctx_) noexcept :
        sctx( sctx_ ),
        main_ctx( false ) {
    }

virtual ~activation_record() {
	}

activation_record( activation_record const&) = delete;
    activation_record & operator=( activation_record const&) = delete;

bool is_main_context() const noexcept {
        return main_ctx;
    }

activation_record * resume() {
		from = current();
        // store `this` in static, thread local pointer
        // `this` will become the active (running) context
        current() = this;
#if defined(BOOST_USE_SEGMENTED_STACKS)
        // adjust segmented stack properties
        __splitstack_getcontext( from->sctx.segments_ctx);
        __splitstack_setcontext( sctx.segments_ctx);
#endif
#if defined(BOOST_USE_ASAN)
        if ( terminated) {
            __sanitizer_start_switch_fiber( nullptr, stack_bottom, stack_size);
        } else {
            __sanitizer_start_switch_fiber( & from->fake_stack, stack_bottom, stack_size);
        }
#endif
        // context switch from parent context to `this`-context
        ::swapcontext( & from->uctx, & uctx);
#if defined(BOOST_USE_ASAN)
        __sanitizer_finish_switch_fiber( current()->fake_stack,
                                         (const void **) & current()->from->stack_bottom,
                                         & current()->from->stack_size);
#endif
#if defined(BOOST_NO_CXX14_STD_EXCHANGE)
        return exchange( current()->from, nullptr);
#else
        return std::exchange( current()->from, nullptr);
#endif
    }

template< typename Ctx, typename Fn >
    activation_record * resume_with( Fn && fn) {
		from = current();
        // store `this` in static, thread local pointer
        // `this` will become the active (running) context
        // returned by continuation::current()
        current() = this;
#if defined(BOOST_NO_CXX14_GENERIC_LAMBDAS)
        current()->ontop = std::bind(
                [](typename std::decay< Fn >::type & fn, activation_record *& ptr){
                    Ctx c{ ptr };
                    c = fn( std::move( c) );
                    if ( ! c) {
                        ptr = nullptr;
                    }
#if defined(BOOST_NO_CXX14_STD_EXCHANGE)
                    return exchange( c.ptr_, nullptr);
#else
                    return std::exchange( c.ptr_, nullptr);
#endif
                },
                std::forward< Fn >( fn),
                std::placeholders::_1);
#else
        current()->ontop = [fn=std::forward<Fn>(fn)](activation_record *& ptr){
            Ctx c{ ptr };
            c = fn( std::move( c) );
            if ( ! c) {
                ptr = nullptr;
            }
#if defined(BOOST_NO_CXX14_STD_EXCHANGE)
            return exchange( c.ptr_, nullptr);
#else
            return std::exchange( c.ptr_, nullptr);
#endif
        };
#endif
#if defined(BOOST_USE_SEGMENTED_STACKS)
        // adjust segmented stack properties
        __splitstack_getcontext( from->sctx.segments_ctx);
        __splitstack_setcontext( sctx.segments_ctx);
#endif
#if defined(BOOST_USE_ASAN)
        __sanitizer_start_switch_fiber( & from->fake_stack, stack_bottom, stack_size);
#endif
        // context switch from parent context to `this`-context
        ::swapcontext( & from->uctx, & uctx);
#if defined(BOOST_USE_ASAN)
        __sanitizer_finish_switch_fiber( current()->fake_stack,
                                         (const void **) & current()->from->stack_bottom,
                                         & current()->from->stack_size);
#endif
#if defined(BOOST_NO_CXX14_STD_EXCHANGE)
        return exchange( current()->from, nullptr);
#else
        return std::exchange( current()->from, nullptr);
#endif
    }

virtual void deallocate() noexcept {
    }
};

struct BOOST_CONTEXT_DECL activation_record_initializer {
    activation_record_initializer() noexcept;
    ~activation_record_initializer();
};

struct forced_unwind {
    activation_record   *   from{ nullptr };
#ifndef BOOST_ASSERT_IS_VOID
    bool                    caught{ false };
#endif

forced_unwind( activation_record * from_) noexcept :
        from{ from_ } {
    }

#ifndef BOOST_ASSERT_IS_VOID
    ~forced_unwind() {
        BOOST_ASSERT( caught);
    }
#endif
};

template< typename Ctx, typename StackAlloc, typename Fn >
class capture_record : public activation_record {
private:
    typename std::decay< StackAlloc >::type             salloc_;
    typename std::decay< Fn >::type                     fn_;

static void destroy( capture_record * p) noexcept {
        typename std::decay< StackAlloc >::type salloc = std::move( p->salloc_);
        stack_context sctx = p->sctx;
        // deallocate activation record
        p->~capture_record();
        // destroy stack with stack allocator
        salloc.deallocate( sctx);
    }

public:
    capture_record( stack_context sctx, StackAlloc && salloc, Fn && fn) noexcept :
        activation_record{ sctx },
        salloc_{ std::forward< StackAlloc >( salloc) },
        fn_( std::forward< Fn >( fn) ) {
    }

void deallocate() noexcept override final {
        BOOST_ASSERT( main_ctx || ( ! main_ctx && terminated) );
        destroy( this);
    }

void run() {
#if defined(BOOST_USE_ASAN)
        __sanitizer_finish_switch_fiber( fake_stack,
                                         (const void **) & from->stack_bottom,
                                         & from->stack_size);
#endif
        Ctx c{ from };
        try {
            // invoke context-function
#if defined(BOOST_NO_CXX17_STD_INVOKE)
            c = boost::context::detail::invoke( fn_, std::move( c) );
#else
            c = std::invoke( fn_, std::move( c) );
#endif  
        } catch ( forced_unwind const& ex) {
            c = Ctx{ ex.from };
#ifndef BOOST_ASSERT_IS_VOID
            const_cast< forced_unwind & >( ex).caught = true;
#endif
        }
        // this context has finished its task
		from = nullptr;
        ontop = nullptr;
        terminated = true;
        force_unwind = false;
        c.resume();
        BOOST_ASSERT_MSG( false, "continuation already terminated");
    }
};

template< typename Ctx, typename StackAlloc, typename Fn >
static activation_record * create_context1( StackAlloc && salloc, Fn && fn) {
    typedef capture_record< Ctx, StackAlloc, Fn >  capture_t;

auto sctx = salloc.allocate();
    // reserve space for control structure
    void * storage = reinterpret_cast< void * >(
            ( reinterpret_cast< uintptr_t >( sctx.sp) - static_cast< uintptr_t >( sizeof( capture_t) ) )
            & ~ static_cast< uintptr_t >( 0xff) );
    // placment new for control structure on context stack
    capture_t * record = new ( storage) capture_t{
            sctx, std::forward< StackAlloc >( salloc), std::forward< Fn >( fn) };
    // stack bottom
    void * stack_bottom = reinterpret_cast< void * >(
            reinterpret_cast< uintptr_t >( sctx.sp) - static_cast< uintptr_t >( sctx.size) );
    // create user-context
    if ( BOOST_UNLIKELY( 0 != ::getcontext( & record->uctx) ) ) {
        record->~capture_t();
        salloc.deallocate( sctx);
        throw std::system_error(
                std::error_code( errno, std::system_category() ),
                "getcontext() failed");
    }
    record->uctx.uc_stack.ss_sp = stack_bottom;
    // 64byte gap between control structure and stack top
    record->uctx.uc_stack.ss_size = reinterpret_cast< uintptr_t >( storage) -
            reinterpret_cast< uintptr_t >( stack_bottom) - static_cast< uintptr_t >( 64);
    record->uctx.uc_link = nullptr;
    ::makecontext( & record->uctx, ( void (*)() ) & entry_func< capture_t >, 1, record);
#if defined(BOOST_USE_ASAN)
    record->stack_bottom = record->uctx.uc_stack.ss_sp;
    record->stack_size = record->uctx.uc_stack.ss_size;
#endif
    return record;
}

template< typename Ctx, typename StackAlloc, typename Fn >
static activation_record * create_context2( preallocated palloc, StackAlloc && salloc, Fn && fn) {
    typedef capture_record< Ctx, StackAlloc, Fn >  capture_t;

// reserve space for control structure
    void * storage = reinterpret_cast< void * >(
            ( reinterpret_cast< uintptr_t >( palloc.sp) - static_cast< uintptr_t >( sizeof( capture_t) ) )
            & ~ static_cast< uintptr_t >( 0xff) );
    // placment new for control structure on context stack
    capture_t * record = new ( storage) capture_t{
            palloc.sctx, std::forward< StackAlloc >( salloc), std::forward< Fn >( fn) };
    // stack bottom
    void * stack_bottom = reinterpret_cast< void * >(
            reinterpret_cast< uintptr_t >( palloc.sctx.sp) - static_cast< uintptr_t >( palloc.sctx.size) );
    // create user-context
    if ( BOOST_UNLIKELY( 0 != ::getcontext( & record->uctx) ) ) {
        record->~capture_t();
        salloc.deallocate( palloc.sctx);
        throw std::system_error(
                std::error_code( errno, std::system_category() ),
                "getcontext() failed");
    }
    record->uctx.uc_stack.ss_sp = stack_bottom;
    // 64byte gap between control structure and stack top
    record->uctx.uc_stack.ss_size = reinterpret_cast< uintptr_t >( storage) -
            reinterpret_cast< uintptr_t >( stack_bottom) - static_cast< uintptr_t >( 64);
    record->uctx.uc_link = nullptr;
    ::makecontext( & record->uctx,  ( void (*)() ) & entry_func< capture_t >, 1, record);
#if defined(BOOST_USE_ASAN)
    record->stack_bottom = record->uctx.uc_stack.ss_sp;
    record->stack_size = record->uctx.uc_stack.ss_size;
#endif
    return record;
}

}

class BOOST_CONTEXT_DECL continuation {
private:
    friend struct detail::activation_record;

template< typename Ctx, typename StackAlloc, typename Fn >
    friend class detail::capture_record;

template< typename Ctx, typename StackAlloc, typename Fn >
	friend detail::activation_record * detail::create_context1( StackAlloc &&, Fn &&);

template< typename Ctx, typename StackAlloc, typename Fn >
	friend detail::activation_record * detail::create_context2( preallocated, StackAlloc &&, Fn &&);

template< typename StackAlloc, typename Fn >
    friend continuation
    callcc( std::allocator_arg_t, StackAlloc &&, Fn &&);

template< typename StackAlloc, typename Fn >
    friend continuation
    callcc( std::allocator_arg_t, preallocated, StackAlloc &&, Fn &&);

detail::activation_record   *   ptr_{ nullptr };

continuation( detail::activation_record * ptr) noexcept :
        ptr_{ ptr } {
    }

public:
    continuation() = default;

~continuation() {
        if ( BOOST_UNLIKELY( nullptr != ptr_) && ! ptr_->main_ctx) {
            if ( BOOST_LIKELY( ! ptr_->terminated) ) {
                ptr_->force_unwind = true;
                ptr_->resume();
                BOOST_ASSERT( ptr_->terminated);
            }
            ptr_->deallocate();
        }
    }

continuation( continuation const&) = delete;
    continuation & operator=( continuation const&) = delete;

continuation( continuation && other) noexcept {
        swap( other);
    }

continuation & operator=( continuation && other) noexcept {
        if ( BOOST_LIKELY( this != & other) ) {
            continuation tmp = std::move( other);
            swap( tmp);
        }
        return * this;
    }

continuation resume() & {
        return std::move( * this).resume();
    }

continuation resume() && {
#if defined(BOOST_NO_CXX14_STD_EXCHANGE)
        detail::activation_record * ptr = detail::exchange( ptr_, nullptr)->resume();
#else
        detail::activation_record * ptr = std::exchange( ptr_, nullptr)->resume();
#endif
        if ( BOOST_UNLIKELY( detail::activation_record::current()->force_unwind) ) {
            throw detail::forced_unwind{ ptr};
        } else if ( BOOST_UNLIKELY( nullptr != detail::activation_record::current()->ontop) ) {
            ptr = detail::activation_record::current()->ontop( ptr);
            detail::activation_record::current()->ontop = nullptr;
        }
        return { ptr };
    }

template< typename Fn >
    continuation resume_with( Fn && fn) & {
        return std::move( * this).resume_with( std::forward< Fn >( fn) );
    }

template< typename Fn >
    continuation resume_with( Fn && fn) && {
#if defined(BOOST_NO_CXX14_STD_EXCHANGE)
        detail::activation_record * ptr =
            detail::exchange( ptr_, nullptr)->resume_with< continuation >( std::forward< Fn >( fn) );
#else
        detail::activation_record * ptr =
            std::exchange( ptr_, nullptr)->resume_with< continuation >( std::forward< Fn >( fn) );
#endif
        if ( BOOST_UNLIKELY( detail::activation_record::current()->force_unwind) ) {
            throw detail::forced_unwind{ ptr};
        } else if ( BOOST_UNLIKELY( nullptr != detail::activation_record::current()->ontop) ) {
            ptr = detail::activation_record::current()->ontop( ptr);
            detail::activation_record::current()->ontop = nullptr;
        }
        return { ptr };
    }

explicit operator bool() const noexcept {
        return nullptr != ptr_ && ! ptr_->terminated;
    }

bool operator!() const noexcept {
        return nullptr == ptr_ || ptr_->terminated;
    }

bool operator<( continuation const& other) const noexcept {
        return ptr_ < other.ptr_;
    }

#if !defined(BOOST_EMBTC)
    
    template< typename charT, class traitsT >
    friend std::basic_ostream< charT, traitsT > &
    operator<<( std::basic_ostream< charT, traitsT > & os, continuation const& other) {
        if ( nullptr != other.ptr_) {
            return os << other.ptr_;
        } else {
            return os << "{not-a-context}";
        }
    }

#else
    
    template< typename charT, class traitsT >
    friend std::basic_ostream< charT, traitsT > &
    operator<<( std::basic_ostream< charT, traitsT > & os, continuation const& other);

#endif

void swap( continuation & other) noexcept {
        std::swap( ptr_, other.ptr_);
    }
};

#if defined(BOOST_EMBTC)

template< typename charT, class traitsT >
    inline std::basic_ostream< charT, traitsT > &
    operator<<( std::basic_ostream< charT, traitsT > & os, continuation const& other) {
        if ( nullptr != other.ptr_) {
            return os << other.ptr_;
        } else {
            return os << "{not-a-context}";
        }
    }

#endif
    
template<
    typename Fn,
    typename = detail::disable_overload< continuation, Fn >
>
continuation
callcc( Fn && fn) {
	return callcc(
			std::allocator_arg,
#if defined(BOOST_USE_SEGMENTED_STACKS)
			segmented_stack(),
#else
			fixedsize_stack(),
#endif
			std::forward< Fn >( fn) );
}

template< typename StackAlloc, typename Fn >
continuation
callcc( std::allocator_arg_t, StackAlloc && salloc, Fn && fn) {
	return continuation{
		detail::create_context1< continuation >(
				std::forward< StackAlloc >( salloc), std::forward< Fn >( fn) ) }.resume();
}

template< typename StackAlloc, typename Fn >
continuation
callcc( std::allocator_arg_t, preallocated palloc, StackAlloc && salloc, Fn && fn) {
	return continuation{
		detail::create_context2< continuation >(
				palloc, std::forward< StackAlloc >( salloc), std::forward< Fn >( fn) ) }.resume();
}

inline
void swap( continuation & l, continuation & r) noexcept {
    l.swap( r);
}

}}

#ifdef BOOST_HAS_ABI_HEADERS
# include BOOST_ABI_SUFFIX
#endif

#endif // BOOST_CONTEXT_CONTINUATION_H

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