libstdc++
future
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1 // <future> -*- C++ -*-
2 
3 // Copyright (C) 2009-2024 Free Software Foundation, Inc.
4 //
5 // This file is part of the GNU ISO C++ Library. This library is free
6 // software; you can redistribute it and/or modify it under the
7 // terms of the GNU General Public License as published by the
8 // Free Software Foundation; either version 3, or (at your option)
9 // any later version.
10 
11 // This library is distributed in the hope that it will be useful,
12 // but WITHOUT ANY WARRANTY; without even the implied warranty of
13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 // GNU General Public License for more details.
15 
16 // Under Section 7 of GPL version 3, you are granted additional
17 // permissions described in the GCC Runtime Library Exception, version
18 // 3.1, as published by the Free Software Foundation.
19 
20 // You should have received a copy of the GNU General Public License and
21 // a copy of the GCC Runtime Library Exception along with this program;
22 // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
23 // <http://www.gnu.org/licenses/>.
24 
25 /** @file include/future
26  * This is a Standard C++ Library header.
27  */
28 
29 #ifndef _GLIBCXX_FUTURE
30 #define _GLIBCXX_FUTURE 1
31 
32 #pragma GCC system_header
33 
34 #include <bits/requires_hosted.h> // concurrency
35 
36 #if __cplusplus < 201103L
37 # include <bits/c++0x_warning.h>
38 #else
39 
40 #include <mutex> // call_once
41 #include <condition_variable> // __at_thread_exit_elt
42 #include <system_error>
43 #include <bits/atomic_base.h> // atomic_flag
44 #include <bits/allocated_ptr.h>
45 #include <bits/atomic_futex.h>
46 #include <bits/exception_defines.h>
47 #include <bits/invoke.h>
48 #include <bits/unique_ptr.h>
49 #include <bits/shared_ptr.h>
50 #include <bits/std_function.h>
51 #include <bits/std_thread.h>
52 #include <bits/uses_allocator.h>
53 #include <ext/aligned_buffer.h>
54 
55 namespace std _GLIBCXX_VISIBILITY(default)
56 {
57 _GLIBCXX_BEGIN_NAMESPACE_VERSION
58 
59  /**
60  * @defgroup futures Futures
61  * @ingroup concurrency
62  *
63  * Futures and promises provide support for retrieving the result from
64  * an asynchronous function, e.g. one that is running in another thread.
65  * A `std::future` represents an asynchronous result that will become
66  * ready at some later time. A consumer can wait on a future until the
67  * result is ready to be accessed.
68  *
69  * @since C++11
70  * @{
71  */
72 
73  /// Error code for futures
74  enum class future_errc
75  {
76  future_already_retrieved = 1,
77  promise_already_satisfied,
78  no_state,
79  broken_promise
80  };
81 
82  /// Specialization that allows `future_errc` to convert to `error_code`.
83  template<>
84  struct is_error_code_enum<future_errc> : public true_type { };
85 
86  /// Points to a statically-allocated object derived from error_category.
87  [[__nodiscard__, __gnu__::__const__]]
88  const error_category&
89  future_category() noexcept;
90 
91  /// Overload of make_error_code for `future_errc`.
92  [[__nodiscard__]]
93  inline error_code
94  make_error_code(future_errc __errc) noexcept
95  { return error_code(static_cast<int>(__errc), future_category()); }
96 
97  /// Overload of make_error_condition for `future_errc`.
98  [[__nodiscard__]]
99  inline error_condition
100  make_error_condition(future_errc __errc) noexcept
101  { return error_condition(static_cast<int>(__errc), future_category()); }
102 
103  /**
104  * @brief Exception type thrown by futures.
105  * @ingroup exceptions
106  * @since C++11
107  */
108  class future_error : public logic_error
109  {
110  public:
111  explicit
112  future_error(future_errc __errc)
113  : future_error(std::make_error_code(__errc))
114  { }
115 
116  virtual ~future_error() noexcept;
117 
118  virtual const char*
119  what() const noexcept;
120 
121  const error_code&
122  code() const noexcept { return _M_code; }
123 
124  private:
125  explicit
126  future_error(error_code __ec)
127  : logic_error("std::future_error: " + __ec.message()), _M_code(__ec)
128  { }
129 
130  friend void __throw_future_error(int);
131 
132  error_code _M_code;
133  };
134 
135  // Forward declarations.
136  template<typename _Res>
137  class future;
138 
139  template<typename _Res>
140  class shared_future;
141 
142  template<typename _Signature>
143  class packaged_task;
144 
145  template<typename _Res>
146  class promise;
147 
148  /// Launch code for futures
149  enum class launch
150  {
151  async = 1,
152  deferred = 2
153  };
154 
155  [[__nodiscard__]]
156  constexpr launch operator&(launch __x, launch __y) noexcept
157  {
158  return static_cast<launch>(
159  static_cast<int>(__x) & static_cast<int>(__y));
160  }
161 
162  [[__nodiscard__]]
163  constexpr launch operator|(launch __x, launch __y) noexcept
164  {
165  return static_cast<launch>(
166  static_cast<int>(__x) | static_cast<int>(__y));
167  }
168 
169  [[__nodiscard__]]
170  constexpr launch operator^(launch __x, launch __y) noexcept
171  {
172  return static_cast<launch>(
173  static_cast<int>(__x) ^ static_cast<int>(__y));
174  }
175 
176  [[__nodiscard__]]
177  constexpr launch operator~(launch __x) noexcept
178  { return static_cast<launch>(~static_cast<int>(__x)); }
179 
180  _GLIBCXX14_CONSTEXPR
181  inline launch& operator&=(launch& __x, launch __y) noexcept
182  { return __x = __x & __y; }
183 
184  _GLIBCXX14_CONSTEXPR
185  inline launch& operator|=(launch& __x, launch __y) noexcept
186  { return __x = __x | __y; }
187 
188  _GLIBCXX14_CONSTEXPR
189  inline launch& operator^=(launch& __x, launch __y) noexcept
190  { return __x = __x ^ __y; }
191 
192  /// Status code for futures
193  enum class future_status
194  {
195  ready,
196  timeout,
197  deferred
198  };
199 
200  /// @cond undocumented
201  // _GLIBCXX_RESOLVE_LIB_DEFECTS
202  // 2021. Further incorrect usages of result_of
203  template<typename _Fn, typename... _Args>
204  using __async_result_of = typename __invoke_result<
205  typename decay<_Fn>::type, typename decay<_Args>::type...>::type;
206  /// @endcond
207 
208  template<typename _Fn, typename... _Args>
209  future<__async_result_of<_Fn, _Args...>>
210  async(launch __policy, _Fn&& __fn, _Args&&... __args);
211 
212  template<typename _Fn, typename... _Args>
213  future<__async_result_of<_Fn, _Args...>>
214  async(_Fn&& __fn, _Args&&... __args);
215 
216 #if defined(_GLIBCXX_HAS_GTHREADS)
217 
218  /// @cond undocumented
219 
220  /// Base class and enclosing scope.
221  struct __future_base
222  {
223  /// Base class for results.
224  struct _Result_base
225  {
226  exception_ptr _M_error;
227 
228  _Result_base(const _Result_base&) = delete;
229  _Result_base& operator=(const _Result_base&) = delete;
230 
231  // _M_destroy() allows derived classes to control deallocation
232  virtual void _M_destroy() = 0;
233 
234  struct _Deleter
235  {
236  void operator()(_Result_base* __fr) const { __fr->_M_destroy(); }
237  };
238 
239  protected:
240  _Result_base();
241  virtual ~_Result_base();
242  };
243 
244  /// A unique_ptr for result objects.
245  template<typename _Res>
246  using _Ptr = unique_ptr<_Res, _Result_base::_Deleter>;
247 
248  /// A result object that has storage for an object of type _Res.
249  template<typename _Res>
250  struct _Result : _Result_base
251  {
252  private:
253  __gnu_cxx::__aligned_buffer<_Res> _M_storage;
254  bool _M_initialized;
255 
256  public:
257  typedef _Res result_type;
258 
259  _Result() noexcept : _M_initialized() { }
260 
261  ~_Result()
262  {
263  if (_M_initialized)
264  _M_value().~_Res();
265  }
266 
267  // Return lvalue, future will add const or rvalue-reference
268  _Res&
269  _M_value() noexcept { return *_M_storage._M_ptr(); }
270 
271  void
272  _M_set(const _Res& __res)
273  {
274  ::new (_M_storage._M_addr()) _Res(__res);
275  _M_initialized = true;
276  }
277 
278  void
279  _M_set(_Res&& __res)
280  {
281  ::new (_M_storage._M_addr()) _Res(std::move(__res));
282  _M_initialized = true;
283  }
284 
285  private:
286  void _M_destroy() { delete this; }
287  };
288 
289  /// A result object that uses an allocator.
290  template<typename _Res, typename _Alloc>
291  struct _Result_alloc final : _Result<_Res>, _Alloc
292  {
293  using __allocator_type = __alloc_rebind<_Alloc, _Result_alloc>;
294 
295  explicit
296  _Result_alloc(const _Alloc& __a) : _Result<_Res>(), _Alloc(__a)
297  { }
298 
299  private:
300  void _M_destroy()
301  {
302  __allocator_type __a(*this);
303  __allocated_ptr<__allocator_type> __guard_ptr{ __a, this };
304  this->~_Result_alloc();
305  }
306  };
307 
308  // Create a result object that uses an allocator.
309  template<typename _Res, typename _Allocator>
310  static _Ptr<_Result_alloc<_Res, _Allocator>>
311  _S_allocate_result(const _Allocator& __a)
312  {
313  using __result_type = _Result_alloc<_Res, _Allocator>;
314  typename __result_type::__allocator_type __a2(__a);
315  auto __guard = std::__allocate_guarded(__a2);
316  __result_type* __p = ::new((void*)__guard.get()) __result_type{__a};
317  __guard = nullptr;
318  return _Ptr<__result_type>(__p);
319  }
320 
321  // Keep it simple for std::allocator.
322  template<typename _Res, typename _Tp>
323  static _Ptr<_Result<_Res>>
324  _S_allocate_result(const std::allocator<_Tp>&)
325  {
326  return _Ptr<_Result<_Res>>(new _Result<_Res>);
327  }
328 
329  // Base class for various types of shared state created by an
330  // asynchronous provider (such as a std::promise) and shared with one
331  // or more associated futures.
332  class _State_baseV2
333  {
334  typedef _Ptr<_Result_base> _Ptr_type;
335 
336  enum _Status : unsigned {
337  __not_ready,
338  __ready
339  };
340 
341  _Ptr_type _M_result;
342  __atomic_futex_unsigned<> _M_status;
343  atomic_flag _M_retrieved = ATOMIC_FLAG_INIT;
344  once_flag _M_once;
345 
346  public:
347  _State_baseV2() noexcept : _M_result(), _M_status(_Status::__not_ready)
348  { }
349  _State_baseV2(const _State_baseV2&) = delete;
350  _State_baseV2& operator=(const _State_baseV2&) = delete;
351  virtual ~_State_baseV2() = default;
352 
353  _Result_base&
354  wait()
355  {
356  // Run any deferred function or join any asynchronous thread:
357  _M_complete_async();
358  // Acquire MO makes sure this synchronizes with the thread that made
359  // the future ready.
360  _M_status._M_load_when_equal(_Status::__ready, memory_order_acquire);
361  return *_M_result;
362  }
363 
364  template<typename _Rep, typename _Period>
365  future_status
366  wait_for(const chrono::duration<_Rep, _Period>& __rel)
367  {
368  // First, check if the future has been made ready. Use acquire MO
369  // to synchronize with the thread that made it ready.
370  if (_M_status._M_load(memory_order_acquire) == _Status::__ready)
371  return future_status::ready;
372 
373  if (_M_is_deferred_future())
374  return future_status::deferred;
375 
376  // Don't wait unless the relative time is greater than zero.
377  if (__rel > __rel.zero()
378  && _M_status._M_load_when_equal_for(_Status::__ready,
379  memory_order_acquire,
380  __rel))
381  {
382  // _GLIBCXX_RESOLVE_LIB_DEFECTS
383  // 2100. timed waiting functions must also join
384  // This call is a no-op by default except on an async future,
385  // in which case the async thread is joined. It's also not a
386  // no-op for a deferred future, but such a future will never
387  // reach this point because it returns future_status::deferred
388  // instead of waiting for the future to become ready (see
389  // above). Async futures synchronize in this call, so we need
390  // no further synchronization here.
391  _M_complete_async();
392 
393  return future_status::ready;
394  }
395  return future_status::timeout;
396  }
397 
398  template<typename _Clock, typename _Duration>
399  future_status
400  wait_until(const chrono::time_point<_Clock, _Duration>& __abs)
401  {
402 #if __cplusplus > 201703L
403  static_assert(chrono::is_clock_v<_Clock>);
404 #endif
405  // First, check if the future has been made ready. Use acquire MO
406  // to synchronize with the thread that made it ready.
407  if (_M_status._M_load(memory_order_acquire) == _Status::__ready)
408  return future_status::ready;
409 
410  if (_M_is_deferred_future())
411  return future_status::deferred;
412 
413  if (_M_status._M_load_when_equal_until(_Status::__ready,
414  memory_order_acquire,
415  __abs))
416  {
417  // _GLIBCXX_RESOLVE_LIB_DEFECTS
418  // 2100. timed waiting functions must also join
419  // See wait_for(...) above.
420  _M_complete_async();
421 
422  return future_status::ready;
423  }
424  return future_status::timeout;
425  }
426 
427  // Provide a result to the shared state and make it ready.
428  // Calls at most once: _M_result = __res();
429  void
430  _M_set_result(function<_Ptr_type()> __res, bool __ignore_failure = false)
431  {
432  bool __did_set = false;
433  // all calls to this function are serialized,
434  // side-effects of invoking __res only happen once
435  call_once(_M_once, &_State_baseV2::_M_do_set, this,
436  std::__addressof(__res), std::__addressof(__did_set));
437  if (__did_set)
438  // Use release MO to synchronize with observers of the ready state.
439  _M_status._M_store_notify_all(_Status::__ready,
440  memory_order_release);
441  else if (!__ignore_failure)
442  __throw_future_error(int(future_errc::promise_already_satisfied));
443  }
444 
445  // Provide a result to the shared state but delay making it ready
446  // until the calling thread exits.
447  // Calls at most once: _M_result = __res();
448  void
449  _M_set_delayed_result(function<_Ptr_type()> __res,
450  weak_ptr<_State_baseV2> __self)
451  {
452  bool __did_set = false;
453  unique_ptr<_Make_ready> __mr{new _Make_ready};
454  // all calls to this function are serialized,
455  // side-effects of invoking __res only happen once
456  call_once(_M_once, &_State_baseV2::_M_do_set, this,
457  std::__addressof(__res), std::__addressof(__did_set));
458  if (!__did_set)
459  __throw_future_error(int(future_errc::promise_already_satisfied));
460  __mr->_M_shared_state = std::move(__self);
461  __mr->_M_set();
462  __mr.release();
463  }
464 
465  // Abandon this shared state.
466  void
467  _M_break_promise(_Ptr_type __res)
468  {
469  if (static_cast<bool>(__res))
470  {
471  __res->_M_error =
472  make_exception_ptr(future_error(future_errc::broken_promise));
473  // This function is only called when the last asynchronous result
474  // provider is abandoning this shared state, so noone can be
475  // trying to make the shared state ready at the same time, and
476  // we can access _M_result directly instead of through call_once.
477  _M_result.swap(__res);
478  // Use release MO to synchronize with observers of the ready state.
479  _M_status._M_store_notify_all(_Status::__ready,
480  memory_order_release);
481  }
482  }
483 
484  // Called when this object is first passed to a future.
485  void
486  _M_set_retrieved_flag()
487  {
488  if (_M_retrieved.test_and_set())
489  __throw_future_error(int(future_errc::future_already_retrieved));
490  }
491 
492  template<typename _Res, typename _Arg>
493  struct _Setter;
494 
495  // set lvalues
496  template<typename _Res, typename _Arg>
497  struct _Setter<_Res, _Arg&>
498  {
499  // check this is only used by promise<R>::set_value(const R&)
500  // or promise<R&>::set_value(R&)
501  static_assert(is_same<_Res, _Arg&>::value // promise<R&>
502  || is_same<const _Res, _Arg>::value, // promise<R>
503  "Invalid specialisation");
504 
505  // Used by std::promise to copy construct the result.
506  typename promise<_Res>::_Ptr_type operator()() const
507  {
508  _M_promise->_M_storage->_M_set(*_M_arg);
509  return std::move(_M_promise->_M_storage);
510  }
511  promise<_Res>* _M_promise;
512  _Arg* _M_arg;
513  };
514 
515  // set rvalues
516  template<typename _Res>
517  struct _Setter<_Res, _Res&&>
518  {
519  // Used by std::promise to move construct the result.
520  typename promise<_Res>::_Ptr_type operator()() const
521  {
522  _M_promise->_M_storage->_M_set(std::move(*_M_arg));
523  return std::move(_M_promise->_M_storage);
524  }
525  promise<_Res>* _M_promise;
526  _Res* _M_arg;
527  };
528 
529  // set void
530  template<typename _Res>
531  struct _Setter<_Res, void>
532  {
533  static_assert(is_void<_Res>::value, "Only used for promise<void>");
534 
535  typename promise<_Res>::_Ptr_type operator()() const
536  { return std::move(_M_promise->_M_storage); }
537 
538  promise<_Res>* _M_promise;
539  };
540 
541  struct __exception_ptr_tag { };
542 
543  // set exceptions
544  template<typename _Res>
545  struct _Setter<_Res, __exception_ptr_tag>
546  {
547  // Used by std::promise to store an exception as the result.
548  typename promise<_Res>::_Ptr_type operator()() const
549  {
550  _M_promise->_M_storage->_M_error = *_M_ex;
551  return std::move(_M_promise->_M_storage);
552  }
553 
554  promise<_Res>* _M_promise;
555  exception_ptr* _M_ex;
556  };
557 
558  template<typename _Res, typename _Arg>
559  __attribute__((__always_inline__))
560  static _Setter<_Res, _Arg&&>
561  __setter(promise<_Res>* __prom, _Arg&& __arg) noexcept
562  {
563  return _Setter<_Res, _Arg&&>{ __prom, std::__addressof(__arg) };
564  }
565 
566  template<typename _Res>
567  __attribute__((__always_inline__))
568  static _Setter<_Res, __exception_ptr_tag>
569  __setter(exception_ptr& __ex, promise<_Res>* __prom) noexcept
570  {
571  __glibcxx_assert(__ex != nullptr); // LWG 2276
572  return _Setter<_Res, __exception_ptr_tag>{ __prom, &__ex };
573  }
574 
575  template<typename _Res>
576  __attribute__((__always_inline__))
577  static _Setter<_Res, void>
578  __setter(promise<_Res>* __prom) noexcept
579  {
580  return _Setter<_Res, void>{ __prom };
581  }
582 
583  template<typename _Tp>
584  static void
585  _S_check(const shared_ptr<_Tp>& __p)
586  {
587  if (!static_cast<bool>(__p))
588  __throw_future_error((int)future_errc::no_state);
589  }
590 
591  private:
592  // The function invoked with std::call_once(_M_once, ...).
593  void
594  _M_do_set(function<_Ptr_type()>* __f, bool* __did_set)
595  {
596  _Ptr_type __res = (*__f)();
597  // Notify the caller that we did try to set; if we do not throw an
598  // exception, the caller will be aware that it did set (e.g., see
599  // _M_set_result).
600  *__did_set = true;
601  _M_result.swap(__res); // nothrow
602  }
603 
604  // Wait for completion of async function.
605  virtual void _M_complete_async() { }
606 
607  // Return true if state corresponds to a deferred function.
608  virtual bool _M_is_deferred_future() const { return false; }
609 
610  struct _Make_ready final : __at_thread_exit_elt
611  {
612  weak_ptr<_State_baseV2> _M_shared_state;
613  static void _S_run(void*);
614  void _M_set();
615  };
616  };
617 
618 #ifdef _GLIBCXX_ASYNC_ABI_COMPAT
619  class _State_base;
620  class _Async_state_common;
621 #else
622  using _State_base = _State_baseV2;
623  class _Async_state_commonV2;
624 #endif
625 
626  template<typename _BoundFn,
627  typename _Res = decltype(std::declval<_BoundFn&>()())>
628  class _Deferred_state;
629 
630  template<typename _BoundFn,
631  typename _Res = decltype(std::declval<_BoundFn&>()())>
632  class _Async_state_impl;
633 
634  template<typename _Signature>
635  struct _Task_state_base;
636 
637  template<typename _Fn, typename _Alloc, typename _Signature>
638  struct _Task_state;
639 
640  template<typename _Res_ptr, typename _Fn,
641  typename _Res = typename _Res_ptr::element_type::result_type>
642  struct _Task_setter;
643 
644  template<typename _Res_ptr, typename _BoundFn>
645  static _Task_setter<_Res_ptr, _BoundFn>
646  _S_task_setter(_Res_ptr& __ptr, _BoundFn& __call)
647  {
648  return { std::__addressof(__ptr), std::__addressof(__call) };
649  }
650  };
651 
652  /// Partial specialization for reference types.
653  template<typename _Res>
654  struct __future_base::_Result<_Res&> : __future_base::_Result_base
655  {
656  typedef _Res& result_type;
657 
658  _Result() noexcept : _M_value_ptr() { }
659 
660  void
661  _M_set(_Res& __res) noexcept
662  { _M_value_ptr = std::addressof(__res); }
663 
664  _Res& _M_get() noexcept { return *_M_value_ptr; }
665 
666  private:
667  _Res* _M_value_ptr;
668 
669  void _M_destroy() { delete this; }
670  };
671 
672  /// Explicit specialization for void.
673  template<>
674  struct __future_base::_Result<void> : __future_base::_Result_base
675  {
676  typedef void result_type;
677 
678  private:
679  void _M_destroy() { delete this; }
680  };
681 
682  /// @endcond
683 
684 #ifndef _GLIBCXX_ASYNC_ABI_COMPAT
685 
686  /// @cond undocumented
687  // Allow _Setter objects to be stored locally in std::function
688  template<typename _Res, typename _Arg>
689  struct __is_location_invariant
690  <__future_base::_State_base::_Setter<_Res, _Arg>>
691  : true_type { };
692 
693  // Allow _Task_setter objects to be stored locally in std::function
694  template<typename _Res_ptr, typename _Fn, typename _Res>
695  struct __is_location_invariant
696  <__future_base::_Task_setter<_Res_ptr, _Fn, _Res>>
697  : true_type { };
698  /// @endcond
699 
700  /// Common implementation for future and shared_future.
701  template<typename _Res>
702  class __basic_future : public __future_base
703  {
704  protected:
705  typedef shared_ptr<_State_base> __state_type;
706  typedef __future_base::_Result<_Res>& __result_type;
707 
708  private:
709  __state_type _M_state;
710 
711  public:
712  // Disable copying.
713  __basic_future(const __basic_future&) = delete;
714  __basic_future& operator=(const __basic_future&) = delete;
715 
716  bool
717  valid() const noexcept { return static_cast<bool>(_M_state); }
718 
719  void
720  wait() const
721  {
722  _State_base::_S_check(_M_state);
723  _M_state->wait();
724  }
725 
726  template<typename _Rep, typename _Period>
727  future_status
728  wait_for(const chrono::duration<_Rep, _Period>& __rel) const
729  {
730  _State_base::_S_check(_M_state);
731  return _M_state->wait_for(__rel);
732  }
733 
734  template<typename _Clock, typename _Duration>
735  future_status
736  wait_until(const chrono::time_point<_Clock, _Duration>& __abs) const
737  {
738  _State_base::_S_check(_M_state);
739  return _M_state->wait_until(__abs);
740  }
741 
742  protected:
743  /// Wait for the state to be ready and rethrow any stored exception
744  __result_type
745  _M_get_result() const
746  {
747  _State_base::_S_check(_M_state);
748  _Result_base& __res = _M_state->wait();
749  if (!(__res._M_error == nullptr))
750  rethrow_exception(__res._M_error);
751  return static_cast<__result_type>(__res);
752  }
753 
754  void _M_swap(__basic_future& __that) noexcept
755  {
756  _M_state.swap(__that._M_state);
757  }
758 
759  // Construction of a future by promise::get_future()
760  explicit
761  __basic_future(const __state_type& __state) : _M_state(__state)
762  {
763  _State_base::_S_check(_M_state);
764  _M_state->_M_set_retrieved_flag();
765  }
766 
767  // Copy construction from a shared_future
768  explicit
769  __basic_future(const shared_future<_Res>&) noexcept;
770 
771  // Move construction from a shared_future
772  explicit
773  __basic_future(shared_future<_Res>&&) noexcept;
774 
775  // Move construction from a future
776  explicit
777  __basic_future(future<_Res>&&) noexcept;
778 
779  constexpr __basic_future() noexcept : _M_state() { }
780 
781  struct _Reset
782  {
783  explicit _Reset(__basic_future& __fut) noexcept : _M_fut(__fut) { }
784  ~_Reset() { _M_fut._M_state.reset(); }
785  __basic_future& _M_fut;
786  };
787  };
788 
789 
790  /// Primary template for future.
791  template<typename _Res>
792  class future : public __basic_future<_Res>
793  {
794  // _GLIBCXX_RESOLVE_LIB_DEFECTS
795  // 3458. Is shared_future intended to work with arrays or function types?
796  static_assert(!is_array<_Res>{}, "result type must not be an array");
797  static_assert(!is_function<_Res>{}, "result type must not be a function");
798  static_assert(is_destructible<_Res>{},
799  "result type must be destructible");
800 
801  friend class promise<_Res>;
802  template<typename> friend class packaged_task;
803  template<typename _Fn, typename... _Args>
804  friend future<__async_result_of<_Fn, _Args...>>
805  async(launch, _Fn&&, _Args&&...);
806 
807  typedef __basic_future<_Res> _Base_type;
808  typedef typename _Base_type::__state_type __state_type;
809 
810  explicit
811  future(const __state_type& __state) : _Base_type(__state) { }
812 
813  public:
814  constexpr future() noexcept : _Base_type() { }
815 
816  /// Move constructor
817  future(future&& __uf) noexcept : _Base_type(std::move(__uf)) { }
818 
819  // Disable copying
820  future(const future&) = delete;
821  future& operator=(const future&) = delete;
822 
823  future& operator=(future&& __fut) noexcept
824  {
825  future(std::move(__fut))._M_swap(*this);
826  return *this;
827  }
828 
829  /// Retrieving the value
830  _Res
831  get()
832  {
833  typename _Base_type::_Reset __reset(*this);
834  return std::move(this->_M_get_result()._M_value());
835  }
836 
837  shared_future<_Res> share() noexcept;
838  };
839 
840  /// Partial specialization for future<R&>
841  template<typename _Res>
842  class future<_Res&> : public __basic_future<_Res&>
843  {
844  friend class promise<_Res&>;
845  template<typename> friend class packaged_task;
846  template<typename _Fn, typename... _Args>
847  friend future<__async_result_of<_Fn, _Args...>>
848  async(launch, _Fn&&, _Args&&...);
849 
850  typedef __basic_future<_Res&> _Base_type;
851  typedef typename _Base_type::__state_type __state_type;
852 
853  explicit
854  future(const __state_type& __state) : _Base_type(__state) { }
855 
856  public:
857  constexpr future() noexcept : _Base_type() { }
858 
859  /// Move constructor
860  future(future&& __uf) noexcept : _Base_type(std::move(__uf)) { }
861 
862  // Disable copying
863  future(const future&) = delete;
864  future& operator=(const future&) = delete;
865 
866  future& operator=(future&& __fut) noexcept
867  {
868  future(std::move(__fut))._M_swap(*this);
869  return *this;
870  }
871 
872  /// Retrieving the value
873  _Res&
874  get()
875  {
876  typename _Base_type::_Reset __reset(*this);
877  return this->_M_get_result()._M_get();
878  }
879 
880  shared_future<_Res&> share() noexcept;
881  };
882 
883  /// Explicit specialization for future<void>
884  template<>
885  class future<void> : public __basic_future<void>
886  {
887  friend class promise<void>;
888  template<typename> friend class packaged_task;
889  template<typename _Fn, typename... _Args>
890  friend future<__async_result_of<_Fn, _Args...>>
891  async(launch, _Fn&&, _Args&&...);
892 
893  typedef __basic_future<void> _Base_type;
894  typedef typename _Base_type::__state_type __state_type;
895 
896  explicit
897  future(const __state_type& __state) : _Base_type(__state) { }
898 
899  public:
900  constexpr future() noexcept : _Base_type() { }
901 
902  /// Move constructor
903  future(future&& __uf) noexcept : _Base_type(std::move(__uf)) { }
904 
905  // Disable copying
906  future(const future&) = delete;
907  future& operator=(const future&) = delete;
908 
909  future& operator=(future&& __fut) noexcept
910  {
911  future(std::move(__fut))._M_swap(*this);
912  return *this;
913  }
914 
915  /// Retrieving the value
916  void
917  get()
918  {
919  typename _Base_type::_Reset __reset(*this);
920  this->_M_get_result();
921  }
922 
923  shared_future<void> share() noexcept;
924  };
925 
926 
927  /// Primary template for shared_future.
928  template<typename _Res>
929  class shared_future : public __basic_future<_Res>
930  {
931  // _GLIBCXX_RESOLVE_LIB_DEFECTS
932  // 3458. Is shared_future intended to work with arrays or function types?
933  static_assert(!is_array<_Res>{}, "result type must not be an array");
934  static_assert(!is_function<_Res>{}, "result type must not be a function");
935  static_assert(is_destructible<_Res>{},
936  "result type must be destructible");
937 
938  typedef __basic_future<_Res> _Base_type;
939 
940  public:
941  constexpr shared_future() noexcept : _Base_type() { }
942 
943  /// Copy constructor
944  shared_future(const shared_future& __sf) noexcept : _Base_type(__sf) { }
945 
946  /// Construct from a future rvalue
947  shared_future(future<_Res>&& __uf) noexcept
948  : _Base_type(std::move(__uf))
949  { }
950 
951  /// Construct from a shared_future rvalue
952  shared_future(shared_future&& __sf) noexcept
953  : _Base_type(std::move(__sf))
954  { }
955 
956  shared_future& operator=(const shared_future& __sf) noexcept
957  {
958  shared_future(__sf)._M_swap(*this);
959  return *this;
960  }
961 
962  shared_future& operator=(shared_future&& __sf) noexcept
963  {
964  shared_future(std::move(__sf))._M_swap(*this);
965  return *this;
966  }
967 
968  /// Retrieving the value
969  const _Res&
970  get() const { return this->_M_get_result()._M_value(); }
971  };
972 
973  /// Partial specialization for shared_future<R&>
974  template<typename _Res>
975  class shared_future<_Res&> : public __basic_future<_Res&>
976  {
977  typedef __basic_future<_Res&> _Base_type;
978 
979  public:
980  constexpr shared_future() noexcept : _Base_type() { }
981 
982  /// Copy constructor
983  shared_future(const shared_future& __sf) : _Base_type(__sf) { }
984 
985  /// Construct from a future rvalue
986  shared_future(future<_Res&>&& __uf) noexcept
987  : _Base_type(std::move(__uf))
988  { }
989 
990  /// Construct from a shared_future rvalue
991  shared_future(shared_future&& __sf) noexcept
992  : _Base_type(std::move(__sf))
993  { }
994 
995  shared_future& operator=(const shared_future& __sf)
996  {
997  shared_future(__sf)._M_swap(*this);
998  return *this;
999  }
1000 
1001  shared_future& operator=(shared_future&& __sf) noexcept
1002  {
1003  shared_future(std::move(__sf))._M_swap(*this);
1004  return *this;
1005  }
1006 
1007  /// Retrieving the value
1008  _Res&
1009  get() const { return this->_M_get_result()._M_get(); }
1010  };
1011 
1012  /// Explicit specialization for shared_future<void>
1013  template<>
1014  class shared_future<void> : public __basic_future<void>
1015  {
1016  typedef __basic_future<void> _Base_type;
1017 
1018  public:
1019  constexpr shared_future() noexcept : _Base_type() { }
1020 
1021  /// Copy constructor
1022  shared_future(const shared_future& __sf) : _Base_type(__sf) { }
1023 
1024  /// Construct from a future rvalue
1025  shared_future(future<void>&& __uf) noexcept
1026  : _Base_type(std::move(__uf))
1027  { }
1028 
1029  /// Construct from a shared_future rvalue
1030  shared_future(shared_future&& __sf) noexcept
1031  : _Base_type(std::move(__sf))
1032  { }
1033 
1034  shared_future& operator=(const shared_future& __sf)
1035  {
1036  shared_future(__sf)._M_swap(*this);
1037  return *this;
1038  }
1039 
1040  shared_future& operator=(shared_future&& __sf) noexcept
1041  {
1042  shared_future(std::move(__sf))._M_swap(*this);
1043  return *this;
1044  }
1045 
1046  // Retrieving the value
1047  void
1048  get() const { this->_M_get_result(); }
1049  };
1050 
1051  // Now we can define the protected __basic_future constructors.
1052  template<typename _Res>
1053  inline __basic_future<_Res>::
1054  __basic_future(const shared_future<_Res>& __sf) noexcept
1055  : _M_state(__sf._M_state)
1056  { }
1057 
1058  template<typename _Res>
1059  inline __basic_future<_Res>::
1060  __basic_future(shared_future<_Res>&& __sf) noexcept
1061  : _M_state(std::move(__sf._M_state))
1062  { }
1063 
1064  template<typename _Res>
1065  inline __basic_future<_Res>::
1066  __basic_future(future<_Res>&& __uf) noexcept
1067  : _M_state(std::move(__uf._M_state))
1068  { }
1069 
1070  // _GLIBCXX_RESOLVE_LIB_DEFECTS
1071  // 2556. Wide contract for future::share()
1072  template<typename _Res>
1073  inline shared_future<_Res>
1074  future<_Res>::share() noexcept
1075  { return shared_future<_Res>(std::move(*this)); }
1076 
1077  template<typename _Res>
1078  inline shared_future<_Res&>
1079  future<_Res&>::share() noexcept
1080  { return shared_future<_Res&>(std::move(*this)); }
1081 
1082  inline shared_future<void>
1083  future<void>::share() noexcept
1084  { return shared_future<void>(std::move(*this)); }
1085 
1086  /// Primary template for promise
1087  template<typename _Res>
1088  class promise
1089  {
1090  // _GLIBCXX_RESOLVE_LIB_DEFECTS
1091  // 3466: Specify the requirements for promise/future/[...] consistently
1092  static_assert(!is_array<_Res>{}, "result type must not be an array");
1093  static_assert(!is_function<_Res>{}, "result type must not be a function");
1094  static_assert(is_destructible<_Res>{},
1095  "result type must be destructible");
1096 
1097  typedef __future_base::_State_base _State;
1098  typedef __future_base::_Result<_Res> _Res_type;
1099  typedef __future_base::_Ptr<_Res_type> _Ptr_type;
1100  template<typename, typename> friend struct _State::_Setter;
1101  friend _State;
1102 
1103  shared_ptr<_State> _M_future;
1104  _Ptr_type _M_storage;
1105 
1106  public:
1107  promise()
1108  : _M_future(std::make_shared<_State>()),
1109  _M_storage(new _Res_type())
1110  { }
1111 
1112  promise(promise&& __rhs) noexcept
1113  : _M_future(std::move(__rhs._M_future)),
1114  _M_storage(std::move(__rhs._M_storage))
1115  { }
1116 
1117  template<typename _Allocator>
1118  promise(allocator_arg_t, const _Allocator& __a)
1119  : _M_future(std::allocate_shared<_State>(__a)),
1120  _M_storage(__future_base::_S_allocate_result<_Res>(__a))
1121  { }
1122 
1123  template<typename _Allocator>
1124  promise(allocator_arg_t, const _Allocator&, promise&& __rhs)
1125  : _M_future(std::move(__rhs._M_future)),
1126  _M_storage(std::move(__rhs._M_storage))
1127  { }
1128 
1129  promise(const promise&) = delete;
1130 
1131  ~promise()
1132  {
1133  if (static_cast<bool>(_M_future) && !_M_future.unique())
1134  _M_future->_M_break_promise(std::move(_M_storage));
1135  }
1136 
1137  // Assignment
1138  promise&
1139  operator=(promise&& __rhs) noexcept
1140  {
1141  promise(std::move(__rhs)).swap(*this);
1142  return *this;
1143  }
1144 
1145  promise& operator=(const promise&) = delete;
1146 
1147  void
1148  swap(promise& __rhs) noexcept
1149  {
1150  _M_future.swap(__rhs._M_future);
1151  _M_storage.swap(__rhs._M_storage);
1152  }
1153 
1154  // Retrieving the result
1155  future<_Res>
1156  get_future()
1157  { return future<_Res>(_M_future); }
1158 
1159  // Setting the result
1160  void
1161  set_value(const _Res& __r)
1162  { _M_state()._M_set_result(_State::__setter(this, __r)); }
1163 
1164  void
1165  set_value(_Res&& __r)
1166  { _M_state()._M_set_result(_State::__setter(this, std::move(__r))); }
1167 
1168  void
1169  set_exception(exception_ptr __p)
1170  { _M_state()._M_set_result(_State::__setter(__p, this)); }
1171 
1172  void
1173  set_value_at_thread_exit(const _Res& __r)
1174  {
1175  _M_state()._M_set_delayed_result(_State::__setter(this, __r),
1176  _M_future);
1177  }
1178 
1179  void
1180  set_value_at_thread_exit(_Res&& __r)
1181  {
1182  _M_state()._M_set_delayed_result(
1183  _State::__setter(this, std::move(__r)), _M_future);
1184  }
1185 
1186  void
1187  set_exception_at_thread_exit(exception_ptr __p)
1188  {
1189  _M_state()._M_set_delayed_result(_State::__setter(__p, this),
1190  _M_future);
1191  }
1192 
1193  private:
1194  _State&
1195  _M_state()
1196  {
1197  __future_base::_State_base::_S_check(_M_future);
1198  return *_M_future;
1199  }
1200  };
1201 
1202  template<typename _Res>
1203  inline void
1204  swap(promise<_Res>& __x, promise<_Res>& __y) noexcept
1205  { __x.swap(__y); }
1206 
1207  template<typename _Res, typename _Alloc>
1208  struct uses_allocator<promise<_Res>, _Alloc>
1209  : public true_type { };
1210 
1211 
1212  /// Partial specialization for promise<R&>
1213  template<typename _Res>
1214  class promise<_Res&>
1215  {
1216  typedef __future_base::_State_base _State;
1217  typedef __future_base::_Result<_Res&> _Res_type;
1218  typedef __future_base::_Ptr<_Res_type> _Ptr_type;
1219  template<typename, typename> friend struct _State::_Setter;
1220  friend _State;
1221 
1222  shared_ptr<_State> _M_future;
1223  _Ptr_type _M_storage;
1224 
1225  public:
1226  promise()
1227  : _M_future(std::make_shared<_State>()),
1228  _M_storage(new _Res_type())
1229  { }
1230 
1231  promise(promise&& __rhs) noexcept
1232  : _M_future(std::move(__rhs._M_future)),
1233  _M_storage(std::move(__rhs._M_storage))
1234  { }
1235 
1236  template<typename _Allocator>
1237  promise(allocator_arg_t, const _Allocator& __a)
1238  : _M_future(std::allocate_shared<_State>(__a)),
1239  _M_storage(__future_base::_S_allocate_result<_Res&>(__a))
1240  { }
1241 
1242  template<typename _Allocator>
1243  promise(allocator_arg_t, const _Allocator&, promise&& __rhs)
1244  : _M_future(std::move(__rhs._M_future)),
1245  _M_storage(std::move(__rhs._M_storage))
1246  { }
1247 
1248  promise(const promise&) = delete;
1249 
1250  ~promise()
1251  {
1252  if (static_cast<bool>(_M_future) && !_M_future.unique())
1253  _M_future->_M_break_promise(std::move(_M_storage));
1254  }
1255 
1256  // Assignment
1257  promise&
1258  operator=(promise&& __rhs) noexcept
1259  {
1260  promise(std::move(__rhs)).swap(*this);
1261  return *this;
1262  }
1263 
1264  promise& operator=(const promise&) = delete;
1265 
1266  void
1267  swap(promise& __rhs) noexcept
1268  {
1269  _M_future.swap(__rhs._M_future);
1270  _M_storage.swap(__rhs._M_storage);
1271  }
1272 
1273  // Retrieving the result
1274  future<_Res&>
1275  get_future()
1276  { return future<_Res&>(_M_future); }
1277 
1278  // Setting the result
1279  void
1280  set_value(_Res& __r)
1281  { _M_state()._M_set_result(_State::__setter(this, __r)); }
1282 
1283  void
1284  set_exception(exception_ptr __p)
1285  { _M_state()._M_set_result(_State::__setter(__p, this)); }
1286 
1287  void
1288  set_value_at_thread_exit(_Res& __r)
1289  {
1290  _M_state()._M_set_delayed_result(_State::__setter(this, __r),
1291  _M_future);
1292  }
1293 
1294  void
1295  set_exception_at_thread_exit(exception_ptr __p)
1296  {
1297  _M_state()._M_set_delayed_result(_State::__setter(__p, this),
1298  _M_future);
1299  }
1300 
1301  private:
1302  _State&
1303  _M_state()
1304  {
1305  __future_base::_State_base::_S_check(_M_future);
1306  return *_M_future;
1307  }
1308  };
1309 
1310  /// Explicit specialization for promise<void>
1311  template<>
1312  class promise<void>
1313  {
1314  typedef __future_base::_State_base _State;
1315  typedef __future_base::_Result<void> _Res_type;
1316  typedef __future_base::_Ptr<_Res_type> _Ptr_type;
1317  template<typename, typename> friend struct _State::_Setter;
1318  friend _State;
1319 
1320  shared_ptr<_State> _M_future;
1321  _Ptr_type _M_storage;
1322 
1323  public:
1324  promise()
1325  : _M_future(std::make_shared<_State>()),
1326  _M_storage(new _Res_type())
1327  { }
1328 
1329  promise(promise&& __rhs) noexcept
1330  : _M_future(std::move(__rhs._M_future)),
1331  _M_storage(std::move(__rhs._M_storage))
1332  { }
1333 
1334  template<typename _Allocator>
1335  promise(allocator_arg_t, const _Allocator& __a)
1336  : _M_future(std::allocate_shared<_State>(__a)),
1337  _M_storage(__future_base::_S_allocate_result<void>(__a))
1338  { }
1339 
1340  // _GLIBCXX_RESOLVE_LIB_DEFECTS
1341  // 2095. missing constructors needed for uses-allocator construction
1342  template<typename _Allocator>
1343  promise(allocator_arg_t, const _Allocator&, promise&& __rhs)
1344  : _M_future(std::move(__rhs._M_future)),
1345  _M_storage(std::move(__rhs._M_storage))
1346  { }
1347 
1348  promise(const promise&) = delete;
1349 
1350  ~promise()
1351  {
1352  if (static_cast<bool>(_M_future) && !_M_future.unique())
1353  _M_future->_M_break_promise(std::move(_M_storage));
1354  }
1355 
1356  // Assignment
1357  promise&
1358  operator=(promise&& __rhs) noexcept
1359  {
1360  promise(std::move(__rhs)).swap(*this);
1361  return *this;
1362  }
1363 
1364  promise& operator=(const promise&) = delete;
1365 
1366  void
1367  swap(promise& __rhs) noexcept
1368  {
1369  _M_future.swap(__rhs._M_future);
1370  _M_storage.swap(__rhs._M_storage);
1371  }
1372 
1373  // Retrieving the result
1374  future<void>
1375  get_future()
1376  { return future<void>(_M_future); }
1377 
1378  // Setting the result
1379  void
1380  set_value()
1381  { _M_state()._M_set_result(_State::__setter(this)); }
1382 
1383  void
1384  set_exception(exception_ptr __p)
1385  { _M_state()._M_set_result(_State::__setter(__p, this)); }
1386 
1387  void
1388  set_value_at_thread_exit()
1389  { _M_state()._M_set_delayed_result(_State::__setter(this), _M_future); }
1390 
1391  void
1392  set_exception_at_thread_exit(exception_ptr __p)
1393  {
1394  _M_state()._M_set_delayed_result(_State::__setter(__p, this),
1395  _M_future);
1396  }
1397 
1398  private:
1399  _State&
1400  _M_state()
1401  {
1402  __future_base::_State_base::_S_check(_M_future);
1403  return *_M_future;
1404  }
1405  };
1406 
1407  /// @cond undocumented
1408  template<typename _Ptr_type, typename _Fn, typename _Res>
1409  struct __future_base::_Task_setter
1410  {
1411  // Invoke the function and provide the result to the caller.
1412  _Ptr_type operator()() const
1413  {
1414  __try
1415  {
1416  (*_M_result)->_M_set((*_M_fn)());
1417  }
1418  __catch(const __cxxabiv1::__forced_unwind&)
1419  {
1420  __throw_exception_again; // will cause broken_promise
1421  }
1422  __catch(...)
1423  {
1424  (*_M_result)->_M_error = current_exception();
1425  }
1426  return std::move(*_M_result);
1427  }
1428  _Ptr_type* _M_result;
1429  _Fn* _M_fn;
1430  };
1431 
1432  template<typename _Ptr_type, typename _Fn>
1433  struct __future_base::_Task_setter<_Ptr_type, _Fn, void>
1434  {
1435  _Ptr_type operator()() const
1436  {
1437  __try
1438  {
1439  (*_M_fn)();
1440  }
1441  __catch(const __cxxabiv1::__forced_unwind&)
1442  {
1443  __throw_exception_again; // will cause broken_promise
1444  }
1445  __catch(...)
1446  {
1447  (*_M_result)->_M_error = current_exception();
1448  }
1449  return std::move(*_M_result);
1450  }
1451  _Ptr_type* _M_result;
1452  _Fn* _M_fn;
1453  };
1454 
1455  // Holds storage for a packaged_task's result.
1456  template<typename _Res, typename... _Args>
1457  struct __future_base::_Task_state_base<_Res(_Args...)>
1458  : __future_base::_State_base
1459  {
1460  typedef _Res _Res_type;
1461 
1462  template<typename _Alloc>
1463  _Task_state_base(const _Alloc& __a)
1464  : _M_result(_S_allocate_result<_Res>(__a))
1465  { }
1466 
1467  // Invoke the stored task and make the state ready.
1468  virtual void
1469  _M_run(_Args&&... __args) = 0;
1470 
1471  // Invoke the stored task and make the state ready at thread exit.
1472  virtual void
1473  _M_run_delayed(_Args&&... __args, weak_ptr<_State_base>) = 0;
1474 
1475  virtual shared_ptr<_Task_state_base>
1476  _M_reset() = 0;
1477 
1478  typedef __future_base::_Ptr<_Result<_Res>> _Ptr_type;
1479  _Ptr_type _M_result;
1480  };
1481 
1482  // Holds a packaged_task's stored task.
1483  template<typename _Fn, typename _Alloc, typename _Res, typename... _Args>
1484  struct __future_base::_Task_state<_Fn, _Alloc, _Res(_Args...)> final
1485  : __future_base::_Task_state_base<_Res(_Args...)>
1486  {
1487  template<typename _Fn2>
1488  _Task_state(_Fn2&& __fn, const _Alloc& __a)
1489  : _Task_state_base<_Res(_Args...)>(__a),
1490  _M_impl(std::forward<_Fn2>(__fn), __a)
1491  { }
1492 
1493  private:
1494  virtual void
1495  _M_run(_Args&&... __args)
1496  {
1497  auto __boundfn = [&] () -> _Res {
1498  return std::__invoke_r<_Res>(_M_impl._M_fn,
1499  std::forward<_Args>(__args)...);
1500  };
1501  this->_M_set_result(_S_task_setter(this->_M_result, __boundfn));
1502  }
1503 
1504  virtual void
1505  _M_run_delayed(_Args&&... __args, weak_ptr<_State_base> __self)
1506  {
1507  auto __boundfn = [&] () -> _Res {
1508  return std::__invoke_r<_Res>(_M_impl._M_fn,
1509  std::forward<_Args>(__args)...);
1510  };
1511  this->_M_set_delayed_result(_S_task_setter(this->_M_result, __boundfn),
1512  std::move(__self));
1513  }
1514 
1515  virtual shared_ptr<_Task_state_base<_Res(_Args...)>>
1516  _M_reset();
1517 
1518  struct _Impl : _Alloc
1519  {
1520  template<typename _Fn2>
1521  _Impl(_Fn2&& __fn, const _Alloc& __a)
1522  : _Alloc(__a), _M_fn(std::forward<_Fn2>(__fn)) { }
1523  _Fn _M_fn;
1524  } _M_impl;
1525  };
1526 
1527  template<typename _Signature, typename _Fn,
1528  typename _Alloc = std::allocator<int>>
1529  static shared_ptr<__future_base::_Task_state_base<_Signature>>
1530  __create_task_state(_Fn&& __fn, const _Alloc& __a = _Alloc())
1531  {
1532  typedef typename decay<_Fn>::type _Fn2;
1533  typedef __future_base::_Task_state<_Fn2, _Alloc, _Signature> _State;
1534  return std::allocate_shared<_State>(__a, std::forward<_Fn>(__fn), __a);
1535  }
1536 
1537  template<typename _Fn, typename _Alloc, typename _Res, typename... _Args>
1538  shared_ptr<__future_base::_Task_state_base<_Res(_Args...)>>
1539  __future_base::_Task_state<_Fn, _Alloc, _Res(_Args...)>::_M_reset()
1540  {
1541  return __create_task_state<_Res(_Args...)>(std::move(_M_impl._M_fn),
1542  static_cast<_Alloc&>(_M_impl));
1543  }
1544  /// @endcond
1545 
1546  /// packaged_task
1547  template<typename _Res, typename... _ArgTypes>
1548  class packaged_task<_Res(_ArgTypes...)>
1549  {
1550  typedef __future_base::_Task_state_base<_Res(_ArgTypes...)> _State_type;
1551  shared_ptr<_State_type> _M_state;
1552 
1553  // _GLIBCXX_RESOLVE_LIB_DEFECTS
1554  // 3039. Unnecessary decay in thread and packaged_task
1555  template<typename _Fn, typename _Fn2 = __remove_cvref_t<_Fn>>
1556  using __not_same
1557  = typename enable_if<!is_same<packaged_task, _Fn2>::value>::type;
1558 
1559  public:
1560  // Construction and destruction
1561  packaged_task() noexcept { }
1562 
1563  template<typename _Fn, typename = __not_same<_Fn>>
1564  explicit
1565  packaged_task(_Fn&& __fn)
1566  : _M_state(
1567  __create_task_state<_Res(_ArgTypes...)>(std::forward<_Fn>(__fn)))
1568  { }
1569 
1570 #if __cplusplus < 201703L
1571  // _GLIBCXX_RESOLVE_LIB_DEFECTS
1572  // 2097. packaged_task constructors should be constrained
1573  // 2407. [this constructor should not be] explicit
1574  // 2921. packaged_task and type-erased allocators
1575  template<typename _Fn, typename _Alloc, typename = __not_same<_Fn>>
1576  packaged_task(allocator_arg_t, const _Alloc& __a, _Fn&& __fn)
1577  : _M_state(__create_task_state<_Res(_ArgTypes...)>(
1578  std::forward<_Fn>(__fn), __a))
1579  { }
1580 
1581  // _GLIBCXX_RESOLVE_LIB_DEFECTS
1582  // 2095. missing constructors needed for uses-allocator construction
1583  template<typename _Allocator>
1584  packaged_task(allocator_arg_t, const _Allocator&) noexcept
1585  { }
1586 
1587  template<typename _Allocator>
1588  packaged_task(allocator_arg_t, const _Allocator&,
1589  const packaged_task&) = delete;
1590 
1591  template<typename _Allocator>
1592  packaged_task(allocator_arg_t, const _Allocator&,
1593  packaged_task&& __other) noexcept
1594  { this->swap(__other); }
1595 #endif
1596 
1597  ~packaged_task()
1598  {
1599  if (static_cast<bool>(_M_state) && !_M_state.unique())
1600  _M_state->_M_break_promise(std::move(_M_state->_M_result));
1601  }
1602 
1603  // No copy
1604  packaged_task(const packaged_task&) = delete;
1605  packaged_task& operator=(const packaged_task&) = delete;
1606 
1607  // Move support
1608  packaged_task(packaged_task&& __other) noexcept
1609  { this->swap(__other); }
1610 
1611  packaged_task& operator=(packaged_task&& __other) noexcept
1612  {
1613  packaged_task(std::move(__other)).swap(*this);
1614  return *this;
1615  }
1616 
1617  void
1618  swap(packaged_task& __other) noexcept
1619  { _M_state.swap(__other._M_state); }
1620 
1621  bool
1622  valid() const noexcept
1623  { return static_cast<bool>(_M_state); }
1624 
1625  // Result retrieval
1626  future<_Res>
1627  get_future()
1628  { return future<_Res>(_M_state); }
1629 
1630  // Execution
1631  void
1632  operator()(_ArgTypes... __args)
1633  {
1634  __future_base::_State_base::_S_check(_M_state);
1635  _M_state->_M_run(std::forward<_ArgTypes>(__args)...);
1636  }
1637 
1638  void
1639  make_ready_at_thread_exit(_ArgTypes... __args)
1640  {
1641  __future_base::_State_base::_S_check(_M_state);
1642  _M_state->_M_run_delayed(std::forward<_ArgTypes>(__args)..., _M_state);
1643  }
1644 
1645  void
1646  reset()
1647  {
1648  __future_base::_State_base::_S_check(_M_state);
1649  packaged_task __tmp;
1650  __tmp._M_state = _M_state;
1651  _M_state = _M_state->_M_reset();
1652  }
1653  };
1654 
1655  // _GLIBCXX_RESOLVE_LIB_DEFECTS
1656  // 3117. Missing packaged_task deduction guides
1657 #if __cpp_deduction_guides >= 201606
1658  template<typename _Res, typename... _ArgTypes>
1659  packaged_task(_Res(*)(_ArgTypes...)) -> packaged_task<_Res(_ArgTypes...)>;
1660 
1661  template<typename _Fun, typename _Signature
1662  = __function_guide_t<_Fun, decltype(&_Fun::operator())>>
1663  packaged_task(_Fun) -> packaged_task<_Signature>;
1664 #endif
1665 
1666  /// swap
1667  template<typename _Res, typename... _ArgTypes>
1668  inline void
1669  swap(packaged_task<_Res(_ArgTypes...)>& __x,
1670  packaged_task<_Res(_ArgTypes...)>& __y) noexcept
1671  { __x.swap(__y); }
1672 
1673 #if __cplusplus < 201703L
1674  // _GLIBCXX_RESOLVE_LIB_DEFECTS
1675  // 2976. Dangling uses_allocator specialization for packaged_task
1676  template<typename _Res, typename _Alloc>
1677  struct uses_allocator<packaged_task<_Res>, _Alloc>
1678  : public true_type { };
1679 #endif
1680 
1681  /// @cond undocumented
1682 
1683  // Shared state created by std::async().
1684  // Holds a deferred function and storage for its result.
1685  template<typename _BoundFn, typename _Res>
1686  class __future_base::_Deferred_state final
1687  : public __future_base::_State_base
1688  {
1689  public:
1690  template<typename... _Args>
1691  explicit
1692  _Deferred_state(_Args&&... __args)
1693  : _M_result(new _Result<_Res>()),
1694  _M_fn(std::forward<_Args>(__args)...)
1695  { }
1696 
1697  private:
1698  typedef __future_base::_Ptr<_Result<_Res>> _Ptr_type;
1699  _Ptr_type _M_result;
1700  _BoundFn _M_fn;
1701 
1702  // Run the deferred function.
1703  virtual void
1704  _M_complete_async()
1705  {
1706  // Multiple threads can call a waiting function on the future and
1707  // reach this point at the same time. The call_once in _M_set_result
1708  // ensures only the first one run the deferred function, stores the
1709  // result in _M_result, swaps that with the base _M_result and makes
1710  // the state ready. Tell _M_set_result to ignore failure so all later
1711  // calls do nothing.
1712  _M_set_result(_S_task_setter(_M_result, _M_fn), true);
1713  }
1714 
1715  // Caller should check whether the state is ready first, because this
1716  // function will return true even after the deferred function has run.
1717  virtual bool _M_is_deferred_future() const { return true; }
1718  };
1719 
1720  // Common functionality hoisted out of the _Async_state_impl template.
1721  class __future_base::_Async_state_commonV2
1722  : public __future_base::_State_base
1723  {
1724  protected:
1725  ~_Async_state_commonV2() = default;
1726 
1727  // Make waiting functions block until the thread completes, as if joined.
1728  //
1729  // This function is used by wait() to satisfy the first requirement below
1730  // and by wait_for() / wait_until() to satisfy the second.
1731  //
1732  // [futures.async]:
1733  //
1734  // - a call to a waiting function on an asynchronous return object that
1735  // shares the shared state created by this async call shall block until
1736  // the associated thread has completed, as if joined, or else time out.
1737  //
1738  // - the associated thread completion synchronizes with the return from
1739  // the first function that successfully detects the ready status of the
1740  // shared state or with the return from the last function that releases
1741  // the shared state, whichever happens first.
1742  virtual void _M_complete_async() { _M_join(); }
1743 
1744  void _M_join() { std::call_once(_M_once, &thread::join, &_M_thread); }
1745 
1746  thread _M_thread;
1747  once_flag _M_once;
1748  };
1749 
1750  // Shared state created by std::async().
1751  // Starts a new thread that runs a function and makes the shared state ready.
1752  template<typename _BoundFn, typename _Res>
1753  class __future_base::_Async_state_impl final
1754  : public __future_base::_Async_state_commonV2
1755  {
1756  public:
1757  template<typename... _Args>
1758  explicit
1759  _Async_state_impl(_Args&&... __args)
1760  : _M_result(new _Result<_Res>()),
1761  _M_fn(std::forward<_Args>(__args)...)
1762  {
1763  _M_thread = std::thread{&_Async_state_impl::_M_run, this};
1764  }
1765 
1766  // Must not destroy _M_result and _M_fn until the thread finishes.
1767  // Call join() directly rather than through _M_join() because no other
1768  // thread can be referring to this state if it is being destroyed.
1769  ~_Async_state_impl()
1770  {
1771  if (_M_thread.joinable())
1772  _M_thread.join();
1773  }
1774 
1775  private:
1776  void
1777  _M_run()
1778  {
1779  __try
1780  {
1781  _M_set_result(_S_task_setter(_M_result, _M_fn));
1782  }
1783  __catch (const __cxxabiv1::__forced_unwind&)
1784  {
1785  // make the shared state ready on thread cancellation
1786  if (static_cast<bool>(_M_result))
1787  this->_M_break_promise(std::move(_M_result));
1788  __throw_exception_again;
1789  }
1790  }
1791 
1792  typedef __future_base::_Ptr<_Result<_Res>> _Ptr_type;
1793  _Ptr_type _M_result;
1794  _BoundFn _M_fn;
1795  };
1796  /// @endcond
1797 
1798  /// async
1799  template<typename _Fn, typename... _Args>
1800  _GLIBCXX_NODISCARD future<__async_result_of<_Fn, _Args...>>
1801  async(launch __policy, _Fn&& __fn, _Args&&... __args)
1802  {
1803  using _Wr = std::thread::_Call_wrapper<_Fn, _Args...>;
1804  using _As = __future_base::_Async_state_impl<_Wr>;
1805  using _Ds = __future_base::_Deferred_state<_Wr>;
1806 
1807  std::shared_ptr<__future_base::_State_base> __state;
1808  if ((__policy & launch::async) == launch::async)
1809  {
1810  __try
1811  {
1812  __state = std::make_shared<_As>(std::forward<_Fn>(__fn),
1813  std::forward<_Args>(__args)...);
1814  }
1815 #if __cpp_exceptions
1816  catch(const system_error& __e)
1817  {
1818  if (__e.code() != errc::resource_unavailable_try_again
1819  || (__policy & launch::deferred) != launch::deferred)
1820  throw;
1821  }
1822 #endif
1823  }
1824  if (!__state)
1825  {
1826  __state = std::make_shared<_Ds>(std::forward<_Fn>(__fn),
1827  std::forward<_Args>(__args)...);
1828  }
1829  return future<__async_result_of<_Fn, _Args...>>(std::move(__state));
1830  }
1831 
1832  /// async, potential overload
1833  template<typename _Fn, typename... _Args>
1834  _GLIBCXX_NODISCARD inline future<__async_result_of<_Fn, _Args...>>
1835  async(_Fn&& __fn, _Args&&... __args)
1836  {
1837  return std::async(launch::async|launch::deferred,
1838  std::forward<_Fn>(__fn),
1839  std::forward<_Args>(__args)...);
1840  }
1841 
1842 #endif // _GLIBCXX_ASYNC_ABI_COMPAT
1843 #endif // _GLIBCXX_HAS_GTHREADS
1844 
1845  /// @} group futures
1846 _GLIBCXX_END_NAMESPACE_VERSION
1847 } // namespace
1848 
1849 #endif // C++11
1850 
1851 #endif // _GLIBCXX_FUTURE