thread

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// <thread> -*- C++ -*-

// Copyright (C) 2008-2026 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 include/thread
 *  This is a Standard C++ Library header.
 */

#ifndef _GLIBCXX_THREAD
#define _GLIBCXX_THREAD 1

#ifdef _GLIBCXX_SYSHDR
#pragma GCC system_header
#endif

#include <bits/requires_hosted.h> // concurrency

#if __cplusplus < 201103L
# include <bits/c++0x_warning.h>
#else

#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/this_thread_sleep.h> // std::this_thread::sleep_for, sleep_until

#define __glibcxx_want_jthread
#define __glibcxx_want_formatters
#include <bits/version.h>

#if __cpp_lib_formatters
# include <format>
#endif

namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION

  /**
   * @defgroup threads Threads
   * @ingroup concurrency
   * @since C++11
   *
   * Classes for thread support.
   * @{
   */

  // std::thread is defined in <bits/std_thread.h>

  /// @relates std::thread::id @{

#if __cpp_lib_three_way_comparison
  inline strong_ordering
  operator<=>(thread::id __x, thread::id __y) noexcept
  { return __x._M_thread <=> __y._M_thread; }
#else
  inline bool
  operator!=(thread::id __x, thread::id __y) noexcept
  { return !(__x == __y); }

  inline bool
  operator<(thread::id __x, thread::id __y) noexcept
  {
    // Pthreads doesn't define any way to do this, so we just have to
    // assume native_handle_type is LessThanComparable.
    return __x._M_thread < __y._M_thread;
  }

  inline bool
  operator<=(thread::id __x, thread::id __y) noexcept
  { return !(__y < __x); }

  inline bool
  operator>(thread::id __x, thread::id __y) noexcept
  { return __y < __x; }

  inline bool
  operator>=(thread::id __x, thread::id __y) noexcept
  { return !(__x < __y); }
#endif // __cpp_lib_three_way_comparison

  template<class _CharT, class _Traits>
    inline basic_ostream<_CharT, _Traits>&
    operator<<(basic_ostream<_CharT, _Traits>& __out, thread::id __id)
    {
      // Convert non-void pointers to const void* for formatted output.
      using __output_type
        = __conditional_t<is_pointer<thread::native_handle_type>::value,
                          const void*,
                          thread::native_handle_type>;

      if (__id == thread::id())
        return __out << "thread::id of a non-executing thread";
      else
        return __out << static_cast<__output_type>(__id._M_thread);
    }
  /// @}

#ifdef __cpp_lib_jthread // C++ >= 20

  /// @cond undocumented
#ifndef __STRICT_ANSI__
    // As an extension we support invoking a pointer-to-member-function that
    // expects a stop_token as the first argument. See PR libstdc++/100612.
    template<typename _Callable, typename... _Args>
      constexpr bool __pmf_expects_stop_token = false;

    template<typename _Callable, typename _Obj, typename... _Args>
      requires is_member_function_pointer_v<remove_reference_t<_Callable>>
      constexpr bool __pmf_expects_stop_token<_Callable, _Obj, _Args...>
        = is_invocable_v<_Callable, _Obj, stop_token, _Args...>;
#endif
    /// @endcond

  /** A thread with cancellation and automatic joining.
   *
   * Unlike `std::thread`, destroying a joinable `std::jthread` will not
   * terminate the process. Instead, it will try to request its thread to
   * stop, then will join it.
   *
   * A `std::jthread` has a `std::stop_source` member which will be passed
   * as the first argument to the callable that runs in the new thread
   * (as long as the callable will accept that argument). That can then
   * be used to send a stop request that the new thread can test for.
   *
   * @headerfile thread
   * @since C++20
   */
  class jthread
  {
  public:
    using id = thread::id;
    using native_handle_type = thread::native_handle_type;

    jthread() noexcept
    : _M_stop_source{nostopstate}
    { }

    template<typename _Callable, typename... _Args,
             typename = enable_if_t<!is_same_v<remove_cvref_t<_Callable>,
                                               jthread>>>
      explicit
      jthread(_Callable&& __f, _Args&&... __args)
      : _M_thread{_S_create(_M_stop_source, std::forward<_Callable>(__f),
                            std::forward<_Args>(__args)...)}
      { }

    jthread(const jthread&) = delete;
    jthread(jthread&&) noexcept = default;

    ~jthread()
    {
      if (joinable())
        {
          request_stop();
          join();
        }
    }

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

    jthread&
    operator=(jthread&& __other) noexcept
    {
      std::jthread(std::move(__other)).swap(*this);
      return *this;
    }

    void
    swap(jthread& __other) noexcept
    {
      std::swap(_M_stop_source, __other._M_stop_source);
      std::swap(_M_thread, __other._M_thread);
    }

    [[nodiscard]] bool
    joinable() const noexcept
    {
      return _M_thread.joinable();
    }

    void
    join()
    {
      _M_thread.join();
    }

    void
    detach()
    {
      _M_thread.detach();
    }

    [[nodiscard]] id
    get_id() const noexcept
    {
      return _M_thread.get_id();
    }

    [[nodiscard]] native_handle_type
    native_handle()
    {
      return _M_thread.native_handle();
    }

    [[nodiscard]] static unsigned
    hardware_concurrency() noexcept
    {
      return thread::hardware_concurrency();
    }

    [[nodiscard]] stop_source
    get_stop_source() noexcept
    {
      return _M_stop_source;
    }

    [[nodiscard]] stop_token
    get_stop_token() const noexcept
    {
      return _M_stop_source.get_token();
    }

    bool request_stop() noexcept
    {
      return _M_stop_source.request_stop();
    }

    friend void swap(jthread& __lhs, jthread& __rhs) noexcept
    {
      __lhs.swap(__rhs);
    }

  private:
    template<typename _Callable, typename... _Args>
      static thread
      _S_create(stop_source& __ssrc, _Callable&& __f, _Args&&... __args)
      {
#ifndef __STRICT_ANSI__
        if constexpr (__pmf_expects_stop_token<_Callable, _Args...>)
          return _S_create_pmf(__ssrc, __f, std::forward<_Args>(__args)...);
        else
#endif
        if constexpr(is_invocable_v<decay_t<_Callable>, stop_token,
                                    decay_t<_Args>...>)
          return thread{std::forward<_Callable>(__f), __ssrc.get_token(),
                        std::forward<_Args>(__args)...};
        else
          {
            static_assert(is_invocable_v<decay_t<_Callable>,
                                         decay_t<_Args>...>,
                          "std::jthread arguments must be invocable after"
                          " conversion to rvalues");
            return thread{std::forward<_Callable>(__f),
                          std::forward<_Args>(__args)...};
          }
      }

#ifndef __STRICT_ANSI__
    template<typename _Callable, typename _Obj, typename... _Args>
      static thread
      _S_create_pmf(stop_source& __ssrc, _Callable __f, _Obj&& __obj,
                    _Args&&... __args)
      {
        return thread{__f, std::forward<_Obj>(__obj), __ssrc.get_token(),
                      std::forward<_Args>(__args)...};
      }
#endif

    stop_source _M_stop_source;
    thread _M_thread;
  };

  /// @cond undocumented
  namespace __detail::__variant
  {
    template<typename> struct _Never_valueless_alt; // see <variant>

    // Provide the strong exception-safety guarantee when emplacing a
    // jthread into a variant.
    template<>
      struct _Never_valueless_alt<std::jthread>
      : true_type
      { };
  }  // namespace __detail::__variant
  /// @endcond
#endif // __cpp_lib_jthread

#ifdef __cpp_lib_formatters // C++ >= 23
  // We deviate from the standard, that does not put requirements
  // on _CharT here.
  template<__format::__char _CharT>
    requires is_pointer_v<thread::native_handle_type>
      || is_integral_v<thread::native_handle_type>
    class formatter<thread::id, _CharT>
    {
    public:
      constexpr typename basic_format_parse_context<_CharT>::iterator
      parse(basic_format_parse_context<_CharT>& __pc)
      {
        __format::_Spec<_CharT> __spec{};
        __spec._M_align = __format::_Align_right;
        const auto __last = __pc.end();
        auto __first = __pc.begin();

        auto __finalize = [this, &__spec] {
          _M_spec = __spec;
        };

        auto __finished = [&] {
          if (__first == __last || *__first == '}')
            {
              __finalize();
              return true;
            }
          return false;
        };

        if (__finished())
          return __first;

        __first = __spec._M_parse_fill_and_align(__first, __last);
        if (__finished())
          return __first;

        __first = __spec._M_parse_width(__first, __last, __pc);
        if (__finished())
          return __first;

        std::__throw_format_error("format error: invalid format-spec for "
                                  "std::thread::id");
      }

      template<typename _Out>
        typename basic_format_context<_Out, _CharT>::iterator
        format(thread::id __id, basic_format_context<_Out, _CharT>& __fc) const
        {

          if (__id == thread::id())
            {
              const _CharT* __msg;
              if constexpr (is_same_v<_CharT, char>)
                __msg = "thread::id of a non-executing thread";
              else
                __msg = L"thread::id of a non-executing thread";

              __format::__formatter_str<_CharT> __formatter(_M_spec);
              return __formatter.format(__msg, __fc);
            }

          using _HandleFormatter
            = __conditional_t<is_pointer_v<thread::native_handle_type>,
                              __format::__formatter_ptr<_CharT>,
                              __format::__formatter_int<_CharT>>;

          _HandleFormatter __formatter(_M_spec);
          return __formatter.format(__id._M_thread, __fc);
        }

    private:
      __format::_Spec<_CharT> _M_spec;
    };

#if __glibcxx_print >= 202406L
  template<>
    inline constexpr bool
    enable_nonlocking_formatter_optimization<thread::id> = true;
#endif

#endif // __cpp_lib_formatters

  /// @} group threads

_GLIBCXX_END_NAMESPACE_VERSION
} // namespace
#endif // C++11
#endif // _GLIBCXX_THREAD