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libstdc++: Move std::thread to a new header

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This makes it possible to use std::thread without including the whole of
<thread>. It also makes this_thread::get_id() and this_thread::yield()
available even when there is no gthreads support (e.g. when GCC is built
with --disable-threads or --enable-threads=single).

In order for the std:🧵:id return type of this_thread::get_id() to
be defined, std:thread itself is defined unconditionally. However the
constructor that creates new threads is not defined for single-threaded
builds. The thread::join() and thread::detach() member functions are
defined inline for single-threaded builds and just throw an exception
(because we know the thread cannot be joinable if the constructor that
creates joinable threads doesn't exit).

The thread::hardware_concurrency() member function is also defined
inline and returns 0 (as suggested by the standard when the value "is
not computable or well-defined").

The main benefit for most targets is that other headers such as <future>
do not need to include the whole of <thread> just to be able to create a
std::thread. That avoids including <stop_token> and std::jthread where
not required. This is another partial fix for PR 92546.

This also means we can use this_thread::get_id() and this_thread::yield()
in <stop_token> instead of using the gthread functions directly. This
removes some preprocessor conditionals, simplifying the code.

libstdc++-v3/ChangeLog:

	PR libstdc++/92546
	* include/Makefile.am: Add new <bits/std_thread.h> header.
	* include/Makefile.in: Regenerate.
	* include/std/future: Include new header instead of <thread>.
	* include/std/stop_token: Include new header instead of
	<bits/gthr.h>.
	(stop_token::_S_yield()): Use this_thread::yield().
	(_Stop_state_t::_M_requester): Change type to std:🧵:id.
	(_Stop_state_t::_M_request_stop()): Use this_thread::get_id().
	(_Stop_state_t::_M_remove_callback(_Stop_cb*)): Likewise.
	Use __is_single_threaded() to decide whether to synchronize.
	* include/std/thread (thread, operator==, this_thread::get_id)
	(this_thread::yield): Move to new header.
	(operator<=>, operator!=, operator<, operator<=, operator>)
	(operator>=, hash<thread::id>, operator<<): Define even when
	gthreads not available.
	* src/c++11/thread.cc: Include <memory>.
	* include/bits/std_thread.h: New file.
	(thread, operator==, this_thread::get_id, this_thread::yield):
	Define even when gthreads not available.
	[!_GLIBCXX_HAS_GTHREADS] (thread::join, thread::detach)
	(thread::hardware_concurrency): Define inline.
This commit is contained in:
Jonathan Wakely 2020-11-19 13:36:15 +00:00
parent b108faa940
commit b204d7722d
7 changed files with 362 additions and 283 deletions
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1
libstdc++-v3/include/Makefile.am
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@ -187,6 +187,7 @@ bits_headers = \
${bits_srcdir}/std_abs.h \
${bits_srcdir}/std_function.h \
${bits_srcdir}/std_mutex.h \
${bits_srcdir}/std_thread.h \
${bits_srcdir}/stl_algo.h \
${bits_srcdir}/stl_algobase.h \
${bits_srcdir}/stl_bvector.h \

1
libstdc++-v3/include/Makefile.in
View File

@ -533,6 +533,7 @@ bits_headers = \
${bits_srcdir}/std_abs.h \
${bits_srcdir}/std_function.h \
${bits_srcdir}/std_mutex.h \
${bits_srcdir}/std_thread.h \
${bits_srcdir}/stl_algo.h \
${bits_srcdir}/stl_algobase.h \
${bits_srcdir}/stl_bvector.h \

337
libstdc++-v3/include/bits/std_thread.h Normal file
View File

@ -0,0 +1,337 @@
// std::thread declarations -*- C++ -*-
// Copyright (C) 2008-2020 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library. This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 3, or (at your option)
// any later version.
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.
// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
// <http://www.gnu.org/licenses/>.
/** @file bits/std_thread.h
* This is an internal header file, included by other library headers.
* Do not attempt to use it directly. @headername{thread}
*/
#ifndef _GLIBCXX_THREAD_H
#define _GLIBCXX_THREAD_H 1
#pragma GCC system_header
#if __cplusplus >= 201103L
#include <bits/c++config.h>
#include <exception> // std::terminate
#include <iosfwd> // std::basic_ostream
#include <tuple> // std::tuple
#include <bits/invoke.h> // std::__invoke
#include <bits/refwrap.h> // not required, but helpful to users
#include <bits/unique_ptr.h> // std::unique_ptr
#ifdef _GLIBCXX_HAS_GTHREADS
# include <bits/gthr.h>
#else
# include <errno.h>
# include <bits/functexcept.h>
#endif
namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
/** @addtogroup threads
* @{
*/
/// thread
class thread
{
public:
#ifdef _GLIBCXX_HAS_GTHREADS
// Abstract base class for types that wrap arbitrary functors to be
// invoked in the new thread of execution.
struct _State
{
virtual ~_State();
virtual void _M_run() = 0;
};
using _State_ptr = unique_ptr<_State>;
using native_handle_type = __gthread_t;
#else
using native_handle_type = int;
#endif
/// thread::id
class id
{
native_handle_type _M_thread;
public:
id() noexcept : _M_thread() { }
explicit
id(native_handle_type __id) : _M_thread(__id) { }
private:
friend class thread;
friend struct hash<id>;
friend bool
operator==(id __x, id __y) noexcept;
#if __cpp_lib_three_way_comparison
friend strong_ordering
operator<=>(id __x, id __y) noexcept;
#else
friend bool
operator<(id __x, id __y) noexcept;
#endif
template<class _CharT, class _Traits>
friend basic_ostream<_CharT, _Traits>&
operator<<(basic_ostream<_CharT, _Traits>& __out, id __id);
};
private:
id _M_id;
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 2097. packaged_task constructors should be constrained
// 3039. Unnecessary decay in thread and packaged_task
template<typename _Tp>
using __not_same = __not_<is_same<__remove_cvref_t<_Tp>, thread>>;
public:
thread() noexcept = default;
#ifdef _GLIBCXX_HAS_GTHREADS
template<typename _Callable, typename... _Args,
typename = _Require<__not_same<_Callable>>>
explicit
thread(_Callable&& __f, _Args&&... __args)
{
static_assert( __is_invocable<typename decay<_Callable>::type,
typename decay<_Args>::type...>::value,
"std::thread arguments must be invocable after conversion to rvalues"
);
#ifdef GTHR_ACTIVE_PROXY
// Create a reference to pthread_create, not just the gthr weak symbol.
auto __depend = reinterpret_cast<void(*)()>(&pthread_create);
#else
auto __depend = nullptr;
#endif
using _Wrapper = _Call_wrapper<_Callable, _Args...>;
// Create a call wrapper with DECAY_COPY(__f) as its target object
// and DECAY_COPY(__args)... as its bound argument entities.
_M_start_thread(_State_ptr(new _State_impl<_Wrapper>(
std::forward<_Callable>(__f), std::forward<_Args>(__args)...)),
__depend);
}
#endif // _GLIBCXX_HAS_GTHREADS
~thread()
{
if (joinable())
std::terminate();
}
thread(const thread&) = delete;
thread(thread&& __t) noexcept
{ swap(__t); }
thread& operator=(const thread&) = delete;
thread& operator=(thread&& __t) noexcept
{
if (joinable())
std::terminate();
swap(__t);
return *this;
}
void
swap(thread& __t) noexcept
{ std::swap(_M_id, __t._M_id); }
bool
joinable() const noexcept
{ return !(_M_id == id()); }
void
join();
void
detach();
id
get_id() const noexcept
{ return _M_id; }
/** @pre thread is joinable
*/
native_handle_type
native_handle()
{ return _M_id._M_thread; }
// Returns a value that hints at the number of hardware thread contexts.
static unsigned int
hardware_concurrency() noexcept;
#ifdef _GLIBCXX_HAS_GTHREADS
private:
template<typename _Callable>
struct _State_impl : public _State
{
_Callable _M_func;
template<typename... _Args>
_State_impl(_Args&&... __args)
: _M_func{{std::forward<_Args>(__args)...}}
{ }
void
_M_run() { _M_func(); }
};
void
_M_start_thread(_State_ptr, void (*)());
#if _GLIBCXX_THREAD_ABI_COMPAT
public:
struct _Impl_base;
typedef shared_ptr<_Impl_base> __shared_base_type;
struct _Impl_base
{
__shared_base_type _M_this_ptr;
virtual ~_Impl_base() = default;
virtual void _M_run() = 0;
};
private:
void
_M_start_thread(__shared_base_type, void (*)());
void
_M_start_thread(__shared_base_type);
#endif
private:
// A call wrapper that does INVOKE(forwarded tuple elements...)
template<typename _Tuple>
struct _Invoker
{
_Tuple _M_t;
template<typename>
struct __result;
template<typename _Fn, typename... _Args>
struct __result<tuple<_Fn, _Args...>>
: __invoke_result<_Fn, _Args...>
{ };
template<size_t... _Ind>
typename __result<_Tuple>::type
_M_invoke(_Index_tuple<_Ind...>)
{ return std::__invoke(std::get<_Ind>(std::move(_M_t))...); }
typename __result<_Tuple>::type
operator()()
{
using _Indices
= typename _Build_index_tuple<tuple_size<_Tuple>::value>::__type;
return _M_invoke(_Indices());
}
};
public:
template<typename... _Tp>
using _Call_wrapper = _Invoker<tuple<typename decay<_Tp>::type...>>;
#endif // _GLIBCXX_HAS_GTHREADS
};
#ifndef _GLIBCXX_HAS_GTHREADS
inline void thread::join() { std::__throw_system_error(EINVAL); }
inline void thread::detach() { std::__throw_system_error(EINVAL); }
inline unsigned int thread::hardware_concurrency() { return 0; }
#endif
inline void
swap(thread& __x, thread& __y) noexcept
{ __x.swap(__y); }
inline bool
operator==(thread::id __x, thread::id __y) noexcept
{
// pthread_equal is undefined if either thread ID is not valid, so we
// can't safely use __gthread_equal on default-constructed values (nor
// the non-zero value returned by this_thread::get_id() for
// single-threaded programs using GNU libc). Assume EqualityComparable.
return __x._M_thread == __y._M_thread;
}
// N.B. other comparison operators are defined in <thread>
namespace this_thread
{
/// this_thread::get_id
inline thread::id
get_id() noexcept
{
#ifdef _GLIBCXX_HAS_GTHREADS
#ifdef __GLIBC__
// For the GNU C library pthread_self() is usable without linking to
// libpthread, but prior to version 2.27 the version in libc returns 0,
// which breaks the invariant this_thread::get_id() != thread::id{}.
//
// We know that pthread_t is a scalar type in the GNU C library,
// so just use (__gthread_t)1 as the ID of the main (and only) thread.
//
// This uses __gthread_active_p not __gnu_cxx::__is_single_threaded
// because we don't want the thread::id of the main thread to change
// if additional threads are created later.
if (!__gthread_active_p())
return thread::id((__gthread_t)1);
#endif
return thread::id(__gthread_self());
#else
return thread::id(1);
#endif
}
/// this_thread::yield
inline void
yield() noexcept
{
#if defined _GLIBCXX_HAS_GTHREADS && defined _GLIBCXX_USE_SCHED_YIELD
__gthread_yield();
#endif
}
} // namespace this_thread
/// @}
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace
#endif // C++11
#endif // _GLIBCXX_THREAD_H

2
libstdc++-v3/include/std/future
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@ -36,7 +36,6 @@
#else
#include <mutex> // call_once
#include <thread>
#include <condition_variable> // __at_thread_exit_elt
#include <system_error>
#include <atomic>
@ -46,6 +45,7 @@
#include <bits/unique_ptr.h>
#include <bits/shared_ptr.h>
#include <bits/std_function.h>
#include <bits/std_thread.h>
#include <bits/uses_allocator.h>
#include <ext/aligned_buffer.h>

37
libstdc++-v3/include/std/stop_token
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@ -32,15 +32,14 @@
#if __cplusplus > 201703L
#include <atomic>
#include <bits/std_thread.h>
#ifdef _GLIBCXX_HAS_GTHREADS
# define __cpp_lib_jthread 201911L
# include <bits/gthr.h>
# if __has_include(<semaphore>)
# include <semaphore>
# endif
#if __has_include(<semaphore>)
# include <semaphore>
#endif
#define __cpp_lib_jthread 201911L
namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
@ -105,9 +104,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
{
#if defined __i386__ || defined __x86_64__
__builtin_ia32_pause();
#elif defined _GLIBCXX_HAS_GTHREADS && defined _GLIBCXX_USE_SCHED_YIELD
__gthread_yield();
#endif
this_thread::yield();
}
#ifndef __cpp_lib_semaphore
@ -162,18 +160,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
std::atomic<value_type> _M_owners{1};
std::atomic<value_type> _M_value{_S_ssrc_counter_inc};
_Stop_cb* _M_head = nullptr;
struct
{
#ifdef _GLIBCXX_HAS_GTHREADS
__gthread_t _M_id;
void _M_set() { _M_id = __gthread_self(); }
bool _M_is_current_thread() const
{ return __gthread_equal(_M_id, __gthread_self()); }
#else
void _M_set() { }
constexpr bool _M_is_current_thread() const { return true; }
#endif
} _M_requester;
std::thread::id _M_requester;
_Stop_state_t() = default;
@ -246,7 +233,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
}
while (!_M_try_lock_and_stop(__old));
_M_requester._M_set();
_M_requester = this_thread::get_id();
while (_M_head)
{
@ -273,10 +260,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
if (!__destroyed)
{
__cb->_M_destroyed = nullptr;
#ifdef _GLIBCXX_HAS_GTHREADS
// synchronize with destructor of stop_callback that owns *__cb
__cb->_M_done.release();
#endif
if (!__gnu_cxx::__is_single_threaded())
__cb->_M_done.release();
}
// Avoid relocking if we already know there are no more callbacks.
@ -353,7 +340,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
// Despite appearances there is no data race on _M_requester. The only
// write to it happens before the callback is removed from the list,
// and removing it from the list happens before this read.
if (!_M_requester._M_is_current_thread())
if (!(_M_requester == this_thread::get_id()))
{
// Synchronize with completion of callback.
__cb->_M_done.acquire();

266
libstdc++-v3/include/std/thread
View File

@ -37,26 +37,18 @@
#include <chrono> // std::chrono::*
#ifdef _GLIBCXX_USE_NANOSLEEP
# include <cerrno> // errno, EINTR
# include <time.h> // nanosleep
#endif
#if defined(_GLIBCXX_HAS_GTHREADS)
#include <bits/gthr.h>
#include <memory> // std::unique_ptr
#include <tuple> // std::tuple
#if __cplusplus > 201703L
# include <compare> // std::strong_ordering
# include <stop_token> // std::stop_source, std::stop_token, std::nostopstate
#endif
#include <bits/std_thread.h> // std::thread, get_id, yield
#include <bits/functional_hash.h> // std::hash
#include <bits/invoke.h> // std::__invoke
#endif // _GLIBCXX_HAS_GTHREADS
#ifdef _GLIBCXX_USE_NANOSLEEP
# include <cerrno> // errno, EINTR
# include <time.h> // nanosleep
#endif
namespace std _GLIBCXX_VISIBILITY(default)
{
@ -70,221 +62,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
* @{
*/
#if defined(_GLIBCXX_HAS_GTHREADS)
/// thread
class thread
{
public:
// Abstract base class for types that wrap arbitrary functors to be
// invoked in the new thread of execution.
struct _State
{
virtual ~_State();
virtual void _M_run() = 0;
};
using _State_ptr = unique_ptr<_State>;
typedef __gthread_t native_handle_type;
/// thread::id
class id
{
native_handle_type _M_thread;
public:
id() noexcept : _M_thread() { }
explicit
id(native_handle_type __id) : _M_thread(__id) { }
private:
friend class thread;
friend struct hash<id>;
friend bool
operator==(id __x, id __y) noexcept;
#if __cpp_lib_three_way_comparison
friend strong_ordering
operator<=>(id __x, id __y) noexcept;
#else
friend bool
operator<(id __x, id __y) noexcept;
#endif
template<class _CharT, class _Traits>
friend basic_ostream<_CharT, _Traits>&
operator<<(basic_ostream<_CharT, _Traits>& __out, id __id);
};
private:
id _M_id;
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 2097. packaged_task constructors should be constrained
// 3039. Unnecessary decay in thread and packaged_task
template<typename _Tp>
using __not_same = __not_<is_same<__remove_cvref_t<_Tp>, thread>>;
public:
thread() noexcept = default;
template<typename _Callable, typename... _Args,
typename = _Require<__not_same<_Callable>>>
explicit
thread(_Callable&& __f, _Args&&... __args)
{
static_assert( __is_invocable<typename decay<_Callable>::type,
typename decay<_Args>::type...>::value,
"std::thread arguments must be invocable after conversion to rvalues"
);
#ifdef GTHR_ACTIVE_PROXY
// Create a reference to pthread_create, not just the gthr weak symbol.
auto __depend = reinterpret_cast<void(*)()>(&pthread_create);
#else
auto __depend = nullptr;
#endif
using _Wrapper = _Call_wrapper<_Callable, _Args...>;
// Create a call wrapper with DECAY_COPY(__f) as its target object
// and DECAY_COPY(__args)... as its bound argument entities.
_M_start_thread(_State_ptr(new _State_impl<_Wrapper>(
std::forward<_Callable>(__f), std::forward<_Args>(__args)...)),
__depend);
}
~thread()
{
if (joinable())
std::terminate();
}
thread(const thread&) = delete;
thread(thread&& __t) noexcept
{ swap(__t); }
thread& operator=(const thread&) = delete;
thread& operator=(thread&& __t) noexcept
{
if (joinable())
std::terminate();
swap(__t);
return *this;
}
void
swap(thread& __t) noexcept
{ std::swap(_M_id, __t._M_id); }
bool
joinable() const noexcept
{ return !(_M_id == id()); }
void
join();
void
detach();
id
get_id() const noexcept
{ return _M_id; }
/** @pre thread is joinable
*/
native_handle_type
native_handle()
{ return _M_id._M_thread; }
// Returns a value that hints at the number of hardware thread contexts.
static unsigned int
hardware_concurrency() noexcept;
private:
template<typename _Callable>
struct _State_impl : public _State
{
_Callable _M_func;
template<typename... _Args>
_State_impl(_Args&&... __args)
: _M_func{{std::forward<_Args>(__args)...}}
{ }
void
_M_run() { _M_func(); }
};
void
_M_start_thread(_State_ptr, void (*)());
#if _GLIBCXX_THREAD_ABI_COMPAT
public:
struct _Impl_base;
typedef shared_ptr<_Impl_base> __shared_base_type;
struct _Impl_base
{
__shared_base_type _M_this_ptr;
virtual ~_Impl_base() = default;
virtual void _M_run() = 0;
};
private:
void
_M_start_thread(__shared_base_type, void (*)());
void
_M_start_thread(__shared_base_type);
#endif
private:
// A call wrapper that does INVOKE(forwarded tuple elements...)
template<typename _Tuple>
struct _Invoker
{
_Tuple _M_t;
template<typename>
struct __result;
template<typename _Fn, typename... _Args>
struct __result<tuple<_Fn, _Args...>>
: __invoke_result<_Fn, _Args...>
{ };
template<size_t... _Ind>
typename __result<_Tuple>::type
_M_invoke(_Index_tuple<_Ind...>)
{ return std::__invoke(std::get<_Ind>(std::move(_M_t))...); }
typename __result<_Tuple>::type
operator()()
{
using _Indices
= typename _Build_index_tuple<tuple_size<_Tuple>::value>::__type;
return _M_invoke(_Indices());
}
};
public:
template<typename... _Tp>
using _Call_wrapper = _Invoker<tuple<typename decay<_Tp>::type...>>;
};
inline void
swap(thread& __x, thread& __y) noexcept
{ __x.swap(__y); }
inline bool
operator==(thread::id __x, thread::id __y) noexcept
{
// pthread_equal is undefined if either thread ID is not valid, so we
// can't safely use __gthread_equal on default-constructed values (nor
// the non-zero value returned by this_thread::get_id() for
// single-threaded programs using GNU libc). Assume EqualityComparable.
return __x._M_thread == __y._M_thread;
}
// std::thread is defined in <bits/std_thread.h>
#if __cpp_lib_three_way_comparison
inline strong_ordering
@ -336,7 +114,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
else
return __out << __id._M_thread;
}
#endif // _GLIBCXX_HAS_GTHREADS
/** @namespace std::this_thread
* @brief ISO C++ 2011 namespace for interacting with the current thread
@ -345,36 +122,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
*/
namespace this_thread
{
#if defined _GLIBCXX_HAS_GTHREADS
/// get_id
inline thread::id
get_id() noexcept
{
#ifdef __GLIBC__
// For the GNU C library pthread_self() is usable without linking to
// libpthread.so but returns 0, so we cannot use it in single-threaded
// programs, because this_thread::get_id() != thread::id{} must be true.
// We know that pthread_t is an integral type in the GNU C library.
if (!__gthread_active_p())
return thread::id(1);
#endif
return thread::id(__gthread_self());
}
#endif // _GLIBCXX_HAS_GTHREADS
/// yield
inline void
yield() noexcept
{
#if defined _GLIBCXX_HAS_GTHREADS && defined _GLIBCXX_USE_SCHED_YIELD
__gthread_yield();
#endif
}
void
__sleep_for(chrono::seconds, chrono::nanoseconds);
/// sleep_for
/// this_thread::sleep_for
template<typename _Rep, typename _Period>
inline void
sleep_for(const chrono::duration<_Rep, _Period>& __rtime)
@ -396,7 +147,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
#endif
}
/// sleep_until
/// this_thread::sleep_until
template<typename _Clock, typename _Duration>
inline void
sleep_until(const chrono::time_point<_Clock, _Duration>& __atime)
@ -421,6 +172,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
#ifdef __cpp_lib_jthread
/// A thread that can be requested to stop and automatically joined.
class jthread
{
public:

1
libstdc++-v3/src/c++11/thread.cc
View File

@ -24,6 +24,7 @@
#define _GLIBCXX_THREAD_ABI_COMPAT 1
#include <memory> // include this first so <thread> can use shared_ptr
#include <thread>
#include <system_error>
#include <cerrno>