continuation_ucontext.hpp
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// 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 };
forced_unwind( activation_record * from_) noexcept :
from{ from_ } {
}
};
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 };
}
// 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