libstdc++
future
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1 // <future> -*- C++ -*-
2 
3 // Copyright (C) 2009-2020 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 #if __cplusplus < 201103L
35 # include <bits/c++0x_warning.h>
36 #else
37 
38 #include <mutex>
39 #include <thread>
40 #include <condition_variable>
41 #include <system_error>
42 #include <atomic>
43 #include <bits/atomic_futex.h>
44 #include <bits/functexcept.h>
45 #include <bits/invoke.h>
46 #include <bits/unique_ptr.h>
47 #include <bits/shared_ptr.h>
48 #include <bits/std_function.h>
49 #include <bits/uses_allocator.h>
50 #include <bits/allocated_ptr.h>
51 #include <ext/aligned_buffer.h>
52 
53 namespace std _GLIBCXX_VISIBILITY(default)
54 {
55 _GLIBCXX_BEGIN_NAMESPACE_VERSION
56 
57  /**
58  * @defgroup futures Futures
59  * @ingroup concurrency
60  *
61  * Classes for futures support.
62  * @{
63  */
64 
65  /// Error code for futures
66  enum class future_errc
67  {
68  future_already_retrieved = 1,
69  promise_already_satisfied,
70  no_state,
71  broken_promise
72  };
73 
74  /// Specialization.
75  template<>
77 
78  /// Points to a statically-allocated object derived from error_category.
79  const error_category&
80  future_category() noexcept;
81 
82  /// Overload for make_error_code.
83  inline error_code
84  make_error_code(future_errc __errc) noexcept
85  { return error_code(static_cast<int>(__errc), future_category()); }
86 
87  /// Overload for make_error_condition.
88  inline error_condition
90  { return error_condition(static_cast<int>(__errc), future_category()); }
91 
92  /**
93  * @brief Exception type thrown by futures.
94  * @ingroup exceptions
95  */
96  class future_error : public logic_error
97  {
98  public:
99  explicit
100  future_error(future_errc __errc)
101  : future_error(std::make_error_code(__errc))
102  { }
103 
104  virtual ~future_error() noexcept;
105 
106  virtual const char*
107  what() const noexcept;
108 
109  const error_code&
110  code() const noexcept { return _M_code; }
111 
112  private:
113  explicit
115  : logic_error("std::future_error: " + __ec.message()), _M_code(__ec)
116  { }
117 
118  friend void __throw_future_error(int);
119 
120  error_code _M_code;
121  };
122 
123  // Forward declarations.
124  template<typename _Res>
125  class future;
126 
127  template<typename _Res>
129 
130  template<typename _Signature>
131  class packaged_task;
132 
133  template<typename _Res>
134  class promise;
135 
136  /// Launch code for futures
137  enum class launch
138  {
139  async = 1,
140  deferred = 2
141  };
142 
143  constexpr launch operator&(launch __x, launch __y)
144  {
145  return static_cast<launch>(
146  static_cast<int>(__x) & static_cast<int>(__y));
147  }
148 
149  constexpr launch operator|(launch __x, launch __y)
150  {
151  return static_cast<launch>(
152  static_cast<int>(__x) | static_cast<int>(__y));
153  }
154 
155  constexpr launch operator^(launch __x, launch __y)
156  {
157  return static_cast<launch>(
158  static_cast<int>(__x) ^ static_cast<int>(__y));
159  }
160 
161  constexpr launch operator~(launch __x)
162  { return static_cast<launch>(~static_cast<int>(__x)); }
163 
164  inline launch& operator&=(launch& __x, launch __y)
165  { return __x = __x & __y; }
166 
167  inline launch& operator|=(launch& __x, launch __y)
168  { return __x = __x | __y; }
169 
170  inline launch& operator^=(launch& __x, launch __y)
171  { return __x = __x ^ __y; }
172 
173  /// Status code for futures
174  enum class future_status
175  {
176  ready,
177  timeout,
178  deferred
179  };
180 
181  // _GLIBCXX_RESOLVE_LIB_DEFECTS
182  // 2021. Further incorrect usages of result_of
183  template<typename _Fn, typename... _Args>
184  using __async_result_of = typename __invoke_result<
185  typename decay<_Fn>::type, typename decay<_Args>::type...>::type;
186 
187  template<typename _Fn, typename... _Args>
188  future<__async_result_of<_Fn, _Args...>>
189  async(launch __policy, _Fn&& __fn, _Args&&... __args);
190 
191  template<typename _Fn, typename... _Args>
192  future<__async_result_of<_Fn, _Args...>>
193  async(_Fn&& __fn, _Args&&... __args);
194 
195 #if defined(_GLIBCXX_HAS_GTHREADS)
196 
197  /// Base class and enclosing scope.
199  {
200  /// Base class for results.
202  {
203  exception_ptr _M_error;
204 
205  _Result_base(const _Result_base&) = delete;
206  _Result_base& operator=(const _Result_base&) = delete;
207 
208  // _M_destroy() allows derived classes to control deallocation
209  virtual void _M_destroy() = 0;
210 
211  struct _Deleter
212  {
213  void operator()(_Result_base* __fr) const { __fr->_M_destroy(); }
214  };
215 
216  protected:
217  _Result_base();
218  virtual ~_Result_base();
219  };
220 
221  /// A unique_ptr for result objects.
222  template<typename _Res>
224 
225  /// A result object that has storage for an object of type _Res.
226  template<typename _Res>
228  {
229  private:
230  __gnu_cxx::__aligned_buffer<_Res> _M_storage;
231  bool _M_initialized;
232 
233  public:
234  typedef _Res result_type;
235 
236  _Result() noexcept : _M_initialized() { }
237 
238  ~_Result()
239  {
240  if (_M_initialized)
241  _M_value().~_Res();
242  }
243 
244  // Return lvalue, future will add const or rvalue-reference
245  _Res&
246  _M_value() noexcept { return *_M_storage._M_ptr(); }
247 
248  void
249  _M_set(const _Res& __res)
250  {
251  ::new (_M_storage._M_addr()) _Res(__res);
252  _M_initialized = true;
253  }
254 
255  void
256  _M_set(_Res&& __res)
257  {
258  ::new (_M_storage._M_addr()) _Res(std::move(__res));
259  _M_initialized = true;
260  }
261 
262  private:
263  void _M_destroy() { delete this; }
264  };
265 
266  /// A result object that uses an allocator.
267  template<typename _Res, typename _Alloc>
268  struct _Result_alloc final : _Result<_Res>, _Alloc
269  {
270  using __allocator_type = __alloc_rebind<_Alloc, _Result_alloc>;
271 
272  explicit
273  _Result_alloc(const _Alloc& __a) : _Result<_Res>(), _Alloc(__a)
274  { }
275 
276  private:
277  void _M_destroy()
278  {
279  __allocator_type __a(*this);
280  __allocated_ptr<__allocator_type> __guard_ptr{ __a, this };
281  this->~_Result_alloc();
282  }
283  };
284 
285  // Create a result object that uses an allocator.
286  template<typename _Res, typename _Allocator>
288  _S_allocate_result(const _Allocator& __a)
289  {
290  using __result_type = _Result_alloc<_Res, _Allocator>;
291  typename __result_type::__allocator_type __a2(__a);
292  auto __guard = std::__allocate_guarded(__a2);
293  __result_type* __p = ::new((void*)__guard.get()) __result_type{__a};
294  __guard = nullptr;
295  return _Ptr<__result_type>(__p);
296  }
297 
298  // Keep it simple for std::allocator.
299  template<typename _Res, typename _Tp>
300  static _Ptr<_Result<_Res>>
301  _S_allocate_result(const std::allocator<_Tp>& __a)
302  {
303  return _Ptr<_Result<_Res>>(new _Result<_Res>);
304  }
305 
306  // Base class for various types of shared state created by an
307  // asynchronous provider (such as a std::promise) and shared with one
308  // or more associated futures.
309  class _State_baseV2
310  {
311  typedef _Ptr<_Result_base> _Ptr_type;
312 
313  enum _Status : unsigned {
314  __not_ready,
315  __ready
316  };
317 
318  _Ptr_type _M_result;
319  __atomic_futex_unsigned<> _M_status;
320  atomic_flag _M_retrieved = ATOMIC_FLAG_INIT;
321  once_flag _M_once;
322 
323  public:
324  _State_baseV2() noexcept : _M_result(), _M_status(_Status::__not_ready)
325  { }
326  _State_baseV2(const _State_baseV2&) = delete;
327  _State_baseV2& operator=(const _State_baseV2&) = delete;
328  virtual ~_State_baseV2() = default;
329 
330  _Result_base&
331  wait()
332  {
333  // Run any deferred function or join any asynchronous thread:
334  _M_complete_async();
335  // Acquire MO makes sure this synchronizes with the thread that made
336  // the future ready.
337  _M_status._M_load_when_equal(_Status::__ready, memory_order_acquire);
338  return *_M_result;
339  }
340 
341  template<typename _Rep, typename _Period>
343  wait_for(const chrono::duration<_Rep, _Period>& __rel)
344  {
345  // First, check if the future has been made ready. Use acquire MO
346  // to synchronize with the thread that made it ready.
347  if (_M_status._M_load(memory_order_acquire) == _Status::__ready)
348  return future_status::ready;
349 
350  if (_M_is_deferred_future())
351  return future_status::deferred;
352 
353  // Don't wait unless the relative time is greater than zero.
354  if (__rel > __rel.zero()
355  && _M_status._M_load_when_equal_for(_Status::__ready,
356  memory_order_acquire,
357  __rel))
358  {
359  // _GLIBCXX_RESOLVE_LIB_DEFECTS
360  // 2100. timed waiting functions must also join
361  // This call is a no-op by default except on an async future,
362  // in which case the async thread is joined. It's also not a
363  // no-op for a deferred future, but such a future will never
364  // reach this point because it returns future_status::deferred
365  // instead of waiting for the future to become ready (see
366  // above). Async futures synchronize in this call, so we need
367  // no further synchronization here.
368  _M_complete_async();
369 
370  return future_status::ready;
371  }
372  return future_status::timeout;
373  }
374 
375  template<typename _Clock, typename _Duration>
377  wait_until(const chrono::time_point<_Clock, _Duration>& __abs)
378  {
379 #if __cplusplus > 201703L
380  static_assert(chrono::is_clock_v<_Clock>);
381 #endif
382  // First, check if the future has been made ready. Use acquire MO
383  // to synchronize with the thread that made it ready.
384  if (_M_status._M_load(memory_order_acquire) == _Status::__ready)
385  return future_status::ready;
386 
387  if (_M_is_deferred_future())
388  return future_status::deferred;
389 
390  if (_M_status._M_load_when_equal_until(_Status::__ready,
391  memory_order_acquire,
392  __abs))
393  {
394  // _GLIBCXX_RESOLVE_LIB_DEFECTS
395  // 2100. timed waiting functions must also join
396  // See wait_for(...) above.
397  _M_complete_async();
398 
399  return future_status::ready;
400  }
401  return future_status::timeout;
402  }
403 
404  // Provide a result to the shared state and make it ready.
405  // Calls at most once: _M_result = __res();
406  void
407  _M_set_result(function<_Ptr_type()> __res, bool __ignore_failure = false)
408  {
409  bool __did_set = false;
410  // all calls to this function are serialized,
411  // side-effects of invoking __res only happen once
412  call_once(_M_once, &_State_baseV2::_M_do_set, this,
413  std::__addressof(__res), std::__addressof(__did_set));
414  if (__did_set)
415  // Use release MO to synchronize with observers of the ready state.
416  _M_status._M_store_notify_all(_Status::__ready,
417  memory_order_release);
418  else if (!__ignore_failure)
419  __throw_future_error(int(future_errc::promise_already_satisfied));
420  }
421 
422  // Provide a result to the shared state but delay making it ready
423  // until the calling thread exits.
424  // Calls at most once: _M_result = __res();
425  void
426  _M_set_delayed_result(function<_Ptr_type()> __res,
427  weak_ptr<_State_baseV2> __self)
428  {
429  bool __did_set = false;
430  unique_ptr<_Make_ready> __mr{new _Make_ready};
431  // all calls to this function are serialized,
432  // side-effects of invoking __res only happen once
433  call_once(_M_once, &_State_baseV2::_M_do_set, this,
434  std::__addressof(__res), std::__addressof(__did_set));
435  if (!__did_set)
436  __throw_future_error(int(future_errc::promise_already_satisfied));
437  __mr->_M_shared_state = std::move(__self);
438  __mr->_M_set();
439  __mr.release();
440  }
441 
442  // Abandon this shared state.
443  void
444  _M_break_promise(_Ptr_type __res)
445  {
446  if (static_cast<bool>(__res))
447  {
448  __res->_M_error =
449  make_exception_ptr(future_error(future_errc::broken_promise));
450  // This function is only called when the last asynchronous result
451  // provider is abandoning this shared state, so noone can be
452  // trying to make the shared state ready at the same time, and
453  // we can access _M_result directly instead of through call_once.
454  _M_result.swap(__res);
455  // Use release MO to synchronize with observers of the ready state.
456  _M_status._M_store_notify_all(_Status::__ready,
457  memory_order_release);
458  }
459  }
460 
461  // Called when this object is first passed to a future.
462  void
463  _M_set_retrieved_flag()
464  {
465  if (_M_retrieved.test_and_set())
466  __throw_future_error(int(future_errc::future_already_retrieved));
467  }
468 
469  template<typename _Res, typename _Arg>
470  struct _Setter;
471 
472  // set lvalues
473  template<typename _Res, typename _Arg>
474  struct _Setter<_Res, _Arg&>
475  {
476  // check this is only used by promise<R>::set_value(const R&)
477  // or promise<R&>::set_value(R&)
478  static_assert(is_same<_Res, _Arg&>::value // promise<R&>
479  || is_same<const _Res, _Arg>::value, // promise<R>
480  "Invalid specialisation");
481 
482  // Used by std::promise to copy construct the result.
483  typename promise<_Res>::_Ptr_type operator()() const
484  {
485  _M_promise->_M_storage->_M_set(*_M_arg);
486  return std::move(_M_promise->_M_storage);
487  }
488  promise<_Res>* _M_promise;
489  _Arg* _M_arg;
490  };
491 
492  // set rvalues
493  template<typename _Res>
494  struct _Setter<_Res, _Res&&>
495  {
496  // Used by std::promise to move construct the result.
497  typename promise<_Res>::_Ptr_type operator()() const
498  {
499  _M_promise->_M_storage->_M_set(std::move(*_M_arg));
500  return std::move(_M_promise->_M_storage);
501  }
502  promise<_Res>* _M_promise;
503  _Res* _M_arg;
504  };
505 
506  // set void
507  template<typename _Res>
508  struct _Setter<_Res, void>
509  {
510  static_assert(is_void<_Res>::value, "Only used for promise<void>");
511 
512  typename promise<_Res>::_Ptr_type operator()() const
513  { return std::move(_M_promise->_M_storage); }
514 
515  promise<_Res>* _M_promise;
516  };
517 
518  struct __exception_ptr_tag { };
519 
520  // set exceptions
521  template<typename _Res>
522  struct _Setter<_Res, __exception_ptr_tag>
523  {
524  // Used by std::promise to store an exception as the result.
525  typename promise<_Res>::_Ptr_type operator()() const
526  {
527  _M_promise->_M_storage->_M_error = *_M_ex;
528  return std::move(_M_promise->_M_storage);
529  }
530 
531  promise<_Res>* _M_promise;
532  exception_ptr* _M_ex;
533  };
534 
535  template<typename _Res, typename _Arg>
536  static _Setter<_Res, _Arg&&>
537  __setter(promise<_Res>* __prom, _Arg&& __arg)
538  {
539  _S_check(__prom->_M_future);
540  return _Setter<_Res, _Arg&&>{ __prom, std::__addressof(__arg) };
541  }
542 
543  template<typename _Res>
544  static _Setter<_Res, __exception_ptr_tag>
545  __setter(exception_ptr& __ex, promise<_Res>* __prom)
546  {
547  _S_check(__prom->_M_future);
548  return _Setter<_Res, __exception_ptr_tag>{ __prom, &__ex };
549  }
550 
551  template<typename _Res>
552  static _Setter<_Res, void>
553  __setter(promise<_Res>* __prom)
554  {
555  _S_check(__prom->_M_future);
556  return _Setter<_Res, void>{ __prom };
557  }
558 
559  template<typename _Tp>
560  static void
561  _S_check(const shared_ptr<_Tp>& __p)
562  {
563  if (!static_cast<bool>(__p))
564  __throw_future_error((int)future_errc::no_state);
565  }
566 
567  private:
568  // The function invoked with std::call_once(_M_once, ...).
569  void
570  _M_do_set(function<_Ptr_type()>* __f, bool* __did_set)
571  {
572  _Ptr_type __res = (*__f)();
573  // Notify the caller that we did try to set; if we do not throw an
574  // exception, the caller will be aware that it did set (e.g., see
575  // _M_set_result).
576  *__did_set = true;
577  _M_result.swap(__res); // nothrow
578  }
579 
580  // Wait for completion of async function.
581  virtual void _M_complete_async() { }
582 
583  // Return true if state corresponds to a deferred function.
584  virtual bool _M_is_deferred_future() const { return false; }
585 
586  struct _Make_ready final : __at_thread_exit_elt
587  {
588  weak_ptr<_State_baseV2> _M_shared_state;
589  static void _S_run(void*);
590  void _M_set();
591  };
592  };
593 
594 #ifdef _GLIBCXX_ASYNC_ABI_COMPAT
595  class _State_base;
596  class _Async_state_common;
597 #else
598  using _State_base = _State_baseV2;
599  class _Async_state_commonV2;
600 #endif
601 
602  template<typename _BoundFn,
603  typename _Res = decltype(std::declval<_BoundFn&>()())>
604  class _Deferred_state;
605 
606  template<typename _BoundFn,
607  typename _Res = decltype(std::declval<_BoundFn&>()())>
608  class _Async_state_impl;
609 
610  template<typename _Signature>
611  class _Task_state_base;
612 
613  template<typename _Fn, typename _Alloc, typename _Signature>
614  class _Task_state;
615 
616  template<typename _BoundFn>
618  _S_make_deferred_state(_BoundFn&& __fn);
619 
620  template<typename _BoundFn>
622  _S_make_async_state(_BoundFn&& __fn);
623 
624  template<typename _Res_ptr, typename _Fn,
625  typename _Res = typename _Res_ptr::element_type::result_type>
626  struct _Task_setter;
627 
628  template<typename _Res_ptr, typename _BoundFn>
629  static _Task_setter<_Res_ptr, _BoundFn>
630  _S_task_setter(_Res_ptr& __ptr, _BoundFn& __call)
631  {
632  return { std::__addressof(__ptr), std::__addressof(__call) };
633  }
634  };
635 
636  /// Partial specialization for reference types.
637  template<typename _Res>
639  {
640  typedef _Res& result_type;
641 
642  _Result() noexcept : _M_value_ptr() { }
643 
644  void
645  _M_set(_Res& __res) noexcept
646  { _M_value_ptr = std::addressof(__res); }
647 
648  _Res& _M_get() noexcept { return *_M_value_ptr; }
649 
650  private:
651  _Res* _M_value_ptr;
652 
653  void _M_destroy() { delete this; }
654  };
655 
656  /// Explicit specialization for void.
657  template<>
659  {
660  typedef void result_type;
661 
662  private:
663  void _M_destroy() { delete this; }
664  };
665 
666 #ifndef _GLIBCXX_ASYNC_ABI_COMPAT
667 
668  // Allow _Setter objects to be stored locally in std::function
669  template<typename _Res, typename _Arg>
671  <__future_base::_State_base::_Setter<_Res, _Arg>>
672  : true_type { };
673 
674  // Allow _Task_setter objects to be stored locally in std::function
675  template<typename _Res_ptr, typename _Fn, typename _Res>
677  <__future_base::_Task_setter<_Res_ptr, _Fn, _Res>>
678  : true_type { };
679 
680  /// Common implementation for future and shared_future.
681  template<typename _Res>
683  {
684  protected:
687 
688  private:
689  __state_type _M_state;
690 
691  public:
692  // Disable copying.
693  __basic_future(const __basic_future&) = delete;
694  __basic_future& operator=(const __basic_future&) = delete;
695 
696  bool
697  valid() const noexcept { return static_cast<bool>(_M_state); }
698 
699  void
700  wait() const
701  {
702  _State_base::_S_check(_M_state);
703  _M_state->wait();
704  }
705 
706  template<typename _Rep, typename _Period>
708  wait_for(const chrono::duration<_Rep, _Period>& __rel) const
709  {
710  _State_base::_S_check(_M_state);
711  return _M_state->wait_for(__rel);
712  }
713 
714  template<typename _Clock, typename _Duration>
716  wait_until(const chrono::time_point<_Clock, _Duration>& __abs) const
717  {
718  _State_base::_S_check(_M_state);
719  return _M_state->wait_until(__abs);
720  }
721 
722  protected:
723  /// Wait for the state to be ready and rethrow any stored exception
726  {
727  _State_base::_S_check(_M_state);
728  _Result_base& __res = _M_state->wait();
729  if (!(__res._M_error == 0))
730  rethrow_exception(__res._M_error);
731  return static_cast<__result_type>(__res);
732  }
733 
734  void _M_swap(__basic_future& __that) noexcept
735  {
736  _M_state.swap(__that._M_state);
737  }
738 
739  // Construction of a future by promise::get_future()
740  explicit
741  __basic_future(const __state_type& __state) : _M_state(__state)
742  {
743  _State_base::_S_check(_M_state);
744  _M_state->_M_set_retrieved_flag();
745  }
746 
747  // Copy construction from a shared_future
748  explicit
749  __basic_future(const shared_future<_Res>&) noexcept;
750 
751  // Move construction from a shared_future
752  explicit
753  __basic_future(shared_future<_Res>&&) noexcept;
754 
755  // Move construction from a future
756  explicit
757  __basic_future(future<_Res>&&) noexcept;
758 
759  constexpr __basic_future() noexcept : _M_state() { }
760 
761  struct _Reset
762  {
763  explicit _Reset(__basic_future& __fut) noexcept : _M_fut(__fut) { }
764  ~_Reset() { _M_fut._M_state.reset(); }
765  __basic_future& _M_fut;
766  };
767  };
768 
769 
770  /// Primary template for future.
771  template<typename _Res>
772  class future : public __basic_future<_Res>
773  {
774  friend class promise<_Res>;
775  template<typename> friend class packaged_task;
776  template<typename _Fn, typename... _Args>
777  friend future<__async_result_of<_Fn, _Args...>>
778  async(launch, _Fn&&, _Args&&...);
779 
780  typedef __basic_future<_Res> _Base_type;
781  typedef typename _Base_type::__state_type __state_type;
782 
783  explicit
784  future(const __state_type& __state) : _Base_type(__state) { }
785 
786  public:
787  constexpr future() noexcept : _Base_type() { }
788 
789  /// Move constructor
790  future(future&& __uf) noexcept : _Base_type(std::move(__uf)) { }
791 
792  // Disable copying
793  future(const future&) = delete;
794  future& operator=(const future&) = delete;
795 
796  future& operator=(future&& __fut) noexcept
797  {
798  future(std::move(__fut))._M_swap(*this);
799  return *this;
800  }
801 
802  /// Retrieving the value
803  _Res
804  get()
805  {
806  typename _Base_type::_Reset __reset(*this);
807  return std::move(this->_M_get_result()._M_value());
808  }
809 
810  shared_future<_Res> share() noexcept;
811  };
812 
813  /// Partial specialization for future<R&>
814  template<typename _Res>
815  class future<_Res&> : public __basic_future<_Res&>
816  {
817  friend class promise<_Res&>;
818  template<typename> friend class packaged_task;
819  template<typename _Fn, typename... _Args>
820  friend future<__async_result_of<_Fn, _Args...>>
821  async(launch, _Fn&&, _Args&&...);
822 
824  typedef typename _Base_type::__state_type __state_type;
825 
826  explicit
827  future(const __state_type& __state) : _Base_type(__state) { }
828 
829  public:
830  constexpr future() noexcept : _Base_type() { }
831 
832  /// Move constructor
833  future(future&& __uf) noexcept : _Base_type(std::move(__uf)) { }
834 
835  // Disable copying
836  future(const future&) = delete;
837  future& operator=(const future&) = delete;
838 
839  future& operator=(future&& __fut) noexcept
840  {
841  future(std::move(__fut))._M_swap(*this);
842  return *this;
843  }
844 
845  /// Retrieving the value
846  _Res&
847  get()
848  {
849  typename _Base_type::_Reset __reset(*this);
850  return this->_M_get_result()._M_get();
851  }
852 
853  shared_future<_Res&> share() noexcept;
854  };
855 
856  /// Explicit specialization for future<void>
857  template<>
858  class future<void> : public __basic_future<void>
859  {
860  friend class promise<void>;
861  template<typename> friend class packaged_task;
862  template<typename _Fn, typename... _Args>
863  friend future<__async_result_of<_Fn, _Args...>>
864  async(launch, _Fn&&, _Args&&...);
865 
866  typedef __basic_future<void> _Base_type;
867  typedef typename _Base_type::__state_type __state_type;
868 
869  explicit
870  future(const __state_type& __state) : _Base_type(__state) { }
871 
872  public:
873  constexpr future() noexcept : _Base_type() { }
874 
875  /// Move constructor
876  future(future&& __uf) noexcept : _Base_type(std::move(__uf)) { }
877 
878  // Disable copying
879  future(const future&) = delete;
880  future& operator=(const future&) = delete;
881 
882  future& operator=(future&& __fut) noexcept
883  {
884  future(std::move(__fut))._M_swap(*this);
885  return *this;
886  }
887 
888  /// Retrieving the value
889  void
890  get()
891  {
892  typename _Base_type::_Reset __reset(*this);
893  this->_M_get_result();
894  }
895 
896  shared_future<void> share() noexcept;
897  };
898 
899 
900  /// Primary template for shared_future.
901  template<typename _Res>
902  class shared_future : public __basic_future<_Res>
903  {
904  typedef __basic_future<_Res> _Base_type;
905 
906  public:
907  constexpr shared_future() noexcept : _Base_type() { }
908 
909  /// Copy constructor
910  shared_future(const shared_future& __sf) noexcept : _Base_type(__sf) { }
911 
912  /// Construct from a future rvalue
913  shared_future(future<_Res>&& __uf) noexcept
914  : _Base_type(std::move(__uf))
915  { }
916 
917  /// Construct from a shared_future rvalue
918  shared_future(shared_future&& __sf) noexcept
919  : _Base_type(std::move(__sf))
920  { }
921 
922  shared_future& operator=(const shared_future& __sf) noexcept
923  {
924  shared_future(__sf)._M_swap(*this);
925  return *this;
926  }
927 
928  shared_future& operator=(shared_future&& __sf) noexcept
929  {
930  shared_future(std::move(__sf))._M_swap(*this);
931  return *this;
932  }
933 
934  /// Retrieving the value
935  const _Res&
936  get() const { return this->_M_get_result()._M_value(); }
937  };
938 
939  /// Partial specialization for shared_future<R&>
940  template<typename _Res>
941  class shared_future<_Res&> : public __basic_future<_Res&>
942  {
943  typedef __basic_future<_Res&> _Base_type;
944 
945  public:
946  constexpr shared_future() noexcept : _Base_type() { }
947 
948  /// Copy constructor
949  shared_future(const shared_future& __sf) : _Base_type(__sf) { }
950 
951  /// Construct from a future rvalue
952  shared_future(future<_Res&>&& __uf) noexcept
953  : _Base_type(std::move(__uf))
954  { }
955 
956  /// Construct from a shared_future rvalue
957  shared_future(shared_future&& __sf) noexcept
958  : _Base_type(std::move(__sf))
959  { }
960 
961  shared_future& operator=(const shared_future& __sf)
962  {
963  shared_future(__sf)._M_swap(*this);
964  return *this;
965  }
966 
967  shared_future& operator=(shared_future&& __sf) noexcept
968  {
969  shared_future(std::move(__sf))._M_swap(*this);
970  return *this;
971  }
972 
973  /// Retrieving the value
974  _Res&
975  get() const { return this->_M_get_result()._M_get(); }
976  };
977 
978  /// Explicit specialization for shared_future<void>
979  template<>
980  class shared_future<void> : public __basic_future<void>
981  {
982  typedef __basic_future<void> _Base_type;
983 
984  public:
985  constexpr shared_future() noexcept : _Base_type() { }
986 
987  /// Copy constructor
988  shared_future(const shared_future& __sf) : _Base_type(__sf) { }
989 
990  /// Construct from a future rvalue
991  shared_future(future<void>&& __uf) noexcept
992  : _Base_type(std::move(__uf))
993  { }
994 
995  /// Construct from a shared_future rvalue
996  shared_future(shared_future&& __sf) noexcept
997  : _Base_type(std::move(__sf))
998  { }
999 
1000  shared_future& operator=(const shared_future& __sf)
1001  {
1002  shared_future(__sf)._M_swap(*this);
1003  return *this;
1004  }
1005 
1006  shared_future& operator=(shared_future&& __sf) noexcept
1007  {
1008  shared_future(std::move(__sf))._M_swap(*this);
1009  return *this;
1010  }
1011 
1012  // Retrieving the value
1013  void
1014  get() const { this->_M_get_result(); }
1015  };
1016 
1017  // Now we can define the protected __basic_future constructors.
1018  template<typename _Res>
1019  inline __basic_future<_Res>::
1020  __basic_future(const shared_future<_Res>& __sf) noexcept
1021  : _M_state(__sf._M_state)
1022  { }
1023 
1024  template<typename _Res>
1025  inline __basic_future<_Res>::
1026  __basic_future(shared_future<_Res>&& __sf) noexcept
1027  : _M_state(std::move(__sf._M_state))
1028  { }
1029 
1030  template<typename _Res>
1031  inline __basic_future<_Res>::
1032  __basic_future(future<_Res>&& __uf) noexcept
1033  : _M_state(std::move(__uf._M_state))
1034  { }
1035 
1036  // _GLIBCXX_RESOLVE_LIB_DEFECTS
1037  // 2556. Wide contract for future::share()
1038  template<typename _Res>
1039  inline shared_future<_Res>
1040  future<_Res>::share() noexcept
1041  { return shared_future<_Res>(std::move(*this)); }
1042 
1043  template<typename _Res>
1044  inline shared_future<_Res&>
1045  future<_Res&>::share() noexcept
1046  { return shared_future<_Res&>(std::move(*this)); }
1047 
1048  inline shared_future<void>
1049  future<void>::share() noexcept
1050  { return shared_future<void>(std::move(*this)); }
1051 
1052  /// Primary template for promise
1053  template<typename _Res>
1054  class promise
1055  {
1056  typedef __future_base::_State_base _State;
1057  typedef __future_base::_Result<_Res> _Res_type;
1058  typedef __future_base::_Ptr<_Res_type> _Ptr_type;
1059  template<typename, typename> friend class _State::_Setter;
1060  friend _State;
1061 
1062  shared_ptr<_State> _M_future;
1063  _Ptr_type _M_storage;
1064 
1065  public:
1066  promise()
1067  : _M_future(std::make_shared<_State>()),
1068  _M_storage(new _Res_type())
1069  { }
1070 
1071  promise(promise&& __rhs) noexcept
1072  : _M_future(std::move(__rhs._M_future)),
1073  _M_storage(std::move(__rhs._M_storage))
1074  { }
1075 
1076  template<typename _Allocator>
1077  promise(allocator_arg_t, const _Allocator& __a)
1078  : _M_future(std::allocate_shared<_State>(__a)),
1079  _M_storage(__future_base::_S_allocate_result<_Res>(__a))
1080  { }
1081 
1082  template<typename _Allocator>
1083  promise(allocator_arg_t, const _Allocator&, promise&& __rhs)
1084  : _M_future(std::move(__rhs._M_future)),
1085  _M_storage(std::move(__rhs._M_storage))
1086  { }
1087 
1088  promise(const promise&) = delete;
1089 
1090  ~promise()
1091  {
1092  if (static_cast<bool>(_M_future) && !_M_future.unique())
1093  _M_future->_M_break_promise(std::move(_M_storage));
1094  }
1095 
1096  // Assignment
1097  promise&
1098  operator=(promise&& __rhs) noexcept
1099  {
1100  promise(std::move(__rhs)).swap(*this);
1101  return *this;
1102  }
1103 
1104  promise& operator=(const promise&) = delete;
1105 
1106  void
1107  swap(promise& __rhs) noexcept
1108  {
1109  _M_future.swap(__rhs._M_future);
1110  _M_storage.swap(__rhs._M_storage);
1111  }
1112 
1113  // Retrieving the result
1114  future<_Res>
1115  get_future()
1116  { return future<_Res>(_M_future); }
1117 
1118  // Setting the result
1119  void
1120  set_value(const _Res& __r)
1121  { _M_future->_M_set_result(_State::__setter(this, __r)); }
1122 
1123  void
1124  set_value(_Res&& __r)
1125  { _M_future->_M_set_result(_State::__setter(this, std::move(__r))); }
1126 
1127  void
1128  set_exception(exception_ptr __p)
1129  { _M_future->_M_set_result(_State::__setter(__p, this)); }
1130 
1131  void
1132  set_value_at_thread_exit(const _Res& __r)
1133  {
1134  _M_future->_M_set_delayed_result(_State::__setter(this, __r),
1135  _M_future);
1136  }
1137 
1138  void
1139  set_value_at_thread_exit(_Res&& __r)
1140  {
1141  _M_future->_M_set_delayed_result(
1142  _State::__setter(this, std::move(__r)), _M_future);
1143  }
1144 
1145  void
1146  set_exception_at_thread_exit(exception_ptr __p)
1147  {
1148  _M_future->_M_set_delayed_result(_State::__setter(__p, this),
1149  _M_future);
1150  }
1151  };
1152 
1153  template<typename _Res>
1154  inline void
1155  swap(promise<_Res>& __x, promise<_Res>& __y) noexcept
1156  { __x.swap(__y); }
1157 
1158  template<typename _Res, typename _Alloc>
1159  struct uses_allocator<promise<_Res>, _Alloc>
1160  : public true_type { };
1161 
1162 
1163  /// Partial specialization for promise<R&>
1164  template<typename _Res>
1165  class promise<_Res&>
1166  {
1167  typedef __future_base::_State_base _State;
1170  template<typename, typename> friend class _State::_Setter;
1171  friend _State;
1172 
1173  shared_ptr<_State> _M_future;
1174  _Ptr_type _M_storage;
1175 
1176  public:
1177  promise()
1178  : _M_future(std::make_shared<_State>()),
1179  _M_storage(new _Res_type())
1180  { }
1181 
1182  promise(promise&& __rhs) noexcept
1183  : _M_future(std::move(__rhs._M_future)),
1184  _M_storage(std::move(__rhs._M_storage))
1185  { }
1186 
1187  template<typename _Allocator>
1188  promise(allocator_arg_t, const _Allocator& __a)
1189  : _M_future(std::allocate_shared<_State>(__a)),
1190  _M_storage(__future_base::_S_allocate_result<_Res&>(__a))
1191  { }
1192 
1193  template<typename _Allocator>
1194  promise(allocator_arg_t, const _Allocator&, promise&& __rhs)
1195  : _M_future(std::move(__rhs._M_future)),
1196  _M_storage(std::move(__rhs._M_storage))
1197  { }
1198 
1199  promise(const promise&) = delete;
1200 
1201  ~promise()
1202  {
1203  if (static_cast<bool>(_M_future) && !_M_future.unique())
1204  _M_future->_M_break_promise(std::move(_M_storage));
1205  }
1206 
1207  // Assignment
1208  promise&
1209  operator=(promise&& __rhs) noexcept
1210  {
1211  promise(std::move(__rhs)).swap(*this);
1212  return *this;
1213  }
1214 
1215  promise& operator=(const promise&) = delete;
1216 
1217  void
1218  swap(promise& __rhs) noexcept
1219  {
1220  _M_future.swap(__rhs._M_future);
1221  _M_storage.swap(__rhs._M_storage);
1222  }
1223 
1224  // Retrieving the result
1226  get_future()
1227  { return future<_Res&>(_M_future); }
1228 
1229  // Setting the result
1230  void
1231  set_value(_Res& __r)
1232  { _M_future->_M_set_result(_State::__setter(this, __r)); }
1233 
1234  void
1235  set_exception(exception_ptr __p)
1236  { _M_future->_M_set_result(_State::__setter(__p, this)); }
1237 
1238  void
1239  set_value_at_thread_exit(_Res& __r)
1240  {
1241  _M_future->_M_set_delayed_result(_State::__setter(this, __r),
1242  _M_future);
1243  }
1244 
1245  void
1246  set_exception_at_thread_exit(exception_ptr __p)
1247  {
1248  _M_future->_M_set_delayed_result(_State::__setter(__p, this),
1249  _M_future);
1250  }
1251  };
1252 
1253  /// Explicit specialization for promise<void>
1254  template<>
1255  class promise<void>
1256  {
1257  typedef __future_base::_State_base _State;
1260  template<typename, typename> friend class _State::_Setter;
1261  friend _State;
1262 
1263  shared_ptr<_State> _M_future;
1264  _Ptr_type _M_storage;
1265 
1266  public:
1267  promise()
1268  : _M_future(std::make_shared<_State>()),
1269  _M_storage(new _Res_type())
1270  { }
1271 
1272  promise(promise&& __rhs) noexcept
1273  : _M_future(std::move(__rhs._M_future)),
1274  _M_storage(std::move(__rhs._M_storage))
1275  { }
1276 
1277  template<typename _Allocator>
1278  promise(allocator_arg_t, const _Allocator& __a)
1279  : _M_future(std::allocate_shared<_State>(__a)),
1280  _M_storage(__future_base::_S_allocate_result<void>(__a))
1281  { }
1282 
1283  // _GLIBCXX_RESOLVE_LIB_DEFECTS
1284  // 2095. missing constructors needed for uses-allocator construction
1285  template<typename _Allocator>
1286  promise(allocator_arg_t, const _Allocator&, promise&& __rhs)
1287  : _M_future(std::move(__rhs._M_future)),
1288  _M_storage(std::move(__rhs._M_storage))
1289  { }
1290 
1291  promise(const promise&) = delete;
1292 
1293  ~promise()
1294  {
1295  if (static_cast<bool>(_M_future) && !_M_future.unique())
1296  _M_future->_M_break_promise(std::move(_M_storage));
1297  }
1298 
1299  // Assignment
1300  promise&
1301  operator=(promise&& __rhs) noexcept
1302  {
1303  promise(std::move(__rhs)).swap(*this);
1304  return *this;
1305  }
1306 
1307  promise& operator=(const promise&) = delete;
1308 
1309  void
1310  swap(promise& __rhs) noexcept
1311  {
1312  _M_future.swap(__rhs._M_future);
1313  _M_storage.swap(__rhs._M_storage);
1314  }
1315 
1316  // Retrieving the result
1317  future<void>
1318  get_future()
1319  { return future<void>(_M_future); }
1320 
1321  // Setting the result
1322  void
1323  set_value()
1324  { _M_future->_M_set_result(_State::__setter(this)); }
1325 
1326  void
1327  set_exception(exception_ptr __p)
1328  { _M_future->_M_set_result(_State::__setter(__p, this)); }
1329 
1330  void
1331  set_value_at_thread_exit()
1332  { _M_future->_M_set_delayed_result(_State::__setter(this), _M_future); }
1333 
1334  void
1335  set_exception_at_thread_exit(exception_ptr __p)
1336  {
1337  _M_future->_M_set_delayed_result(_State::__setter(__p, this),
1338  _M_future);
1339  }
1340  };
1341 
1342  template<typename _Ptr_type, typename _Fn, typename _Res>
1343  struct __future_base::_Task_setter
1344  {
1345  // Invoke the function and provide the result to the caller.
1346  _Ptr_type operator()() const
1347  {
1348  __try
1349  {
1350  (*_M_result)->_M_set((*_M_fn)());
1351  }
1352  __catch(const __cxxabiv1::__forced_unwind&)
1353  {
1354  __throw_exception_again; // will cause broken_promise
1355  }
1356  __catch(...)
1357  {
1358  (*_M_result)->_M_error = current_exception();
1359  }
1360  return std::move(*_M_result);
1361  }
1362  _Ptr_type* _M_result;
1363  _Fn* _M_fn;
1364  };
1365 
1366  template<typename _Ptr_type, typename _Fn>
1367  struct __future_base::_Task_setter<_Ptr_type, _Fn, void>
1368  {
1369  _Ptr_type operator()() const
1370  {
1371  __try
1372  {
1373  (*_M_fn)();
1374  }
1375  __catch(const __cxxabiv1::__forced_unwind&)
1376  {
1377  __throw_exception_again; // will cause broken_promise
1378  }
1379  __catch(...)
1380  {
1381  (*_M_result)->_M_error = current_exception();
1382  }
1383  return std::move(*_M_result);
1384  }
1385  _Ptr_type* _M_result;
1386  _Fn* _M_fn;
1387  };
1388 
1389  // Holds storage for a packaged_task's result.
1390  template<typename _Res, typename... _Args>
1391  struct __future_base::_Task_state_base<_Res(_Args...)>
1392  : __future_base::_State_base
1393  {
1394  typedef _Res _Res_type;
1395 
1396  template<typename _Alloc>
1397  _Task_state_base(const _Alloc& __a)
1398  : _M_result(_S_allocate_result<_Res>(__a))
1399  { }
1400 
1401  // Invoke the stored task and make the state ready.
1402  virtual void
1403  _M_run(_Args&&... __args) = 0;
1404 
1405  // Invoke the stored task and make the state ready at thread exit.
1406  virtual void
1407  _M_run_delayed(_Args&&... __args, weak_ptr<_State_base>) = 0;
1408 
1409  virtual shared_ptr<_Task_state_base>
1410  _M_reset() = 0;
1411 
1412  typedef __future_base::_Ptr<_Result<_Res>> _Ptr_type;
1413  _Ptr_type _M_result;
1414  };
1415 
1416  // Holds a packaged_task's stored task.
1417  template<typename _Fn, typename _Alloc, typename _Res, typename... _Args>
1418  struct __future_base::_Task_state<_Fn, _Alloc, _Res(_Args...)> final
1419  : __future_base::_Task_state_base<_Res(_Args...)>
1420  {
1421  template<typename _Fn2>
1422  _Task_state(_Fn2&& __fn, const _Alloc& __a)
1423  : _Task_state_base<_Res(_Args...)>(__a),
1424  _M_impl(std::forward<_Fn2>(__fn), __a)
1425  { }
1426 
1427  private:
1428  virtual void
1429  _M_run(_Args&&... __args)
1430  {
1431  auto __boundfn = [&] () -> _Res {
1432  return std::__invoke_r<_Res>(_M_impl._M_fn,
1433  std::forward<_Args>(__args)...);
1434  };
1435  this->_M_set_result(_S_task_setter(this->_M_result, __boundfn));
1436  }
1437 
1438  virtual void
1439  _M_run_delayed(_Args&&... __args, weak_ptr<_State_base> __self)
1440  {
1441  auto __boundfn = [&] () -> _Res {
1442  return std::__invoke_r<_Res>(_M_impl._M_fn,
1443  std::forward<_Args>(__args)...);
1444  };
1445  this->_M_set_delayed_result(_S_task_setter(this->_M_result, __boundfn),
1446  std::move(__self));
1447  }
1448 
1449  virtual shared_ptr<_Task_state_base<_Res(_Args...)>>
1450  _M_reset();
1451 
1452  struct _Impl : _Alloc
1453  {
1454  template<typename _Fn2>
1455  _Impl(_Fn2&& __fn, const _Alloc& __a)
1456  : _Alloc(__a), _M_fn(std::forward<_Fn2>(__fn)) { }
1457  _Fn _M_fn;
1458  } _M_impl;
1459  };
1460 
1461  template<typename _Signature, typename _Fn,
1462  typename _Alloc = std::allocator<int>>
1463  static shared_ptr<__future_base::_Task_state_base<_Signature>>
1464  __create_task_state(_Fn&& __fn, const _Alloc& __a = _Alloc())
1465  {
1466  typedef typename decay<_Fn>::type _Fn2;
1467  typedef __future_base::_Task_state<_Fn2, _Alloc, _Signature> _State;
1468  return std::allocate_shared<_State>(__a, std::forward<_Fn>(__fn), __a);
1469  }
1470 
1471  template<typename _Fn, typename _Alloc, typename _Res, typename... _Args>
1472  shared_ptr<__future_base::_Task_state_base<_Res(_Args...)>>
1473  __future_base::_Task_state<_Fn, _Alloc, _Res(_Args...)>::_M_reset()
1474  {
1475  return __create_task_state<_Res(_Args...)>(std::move(_M_impl._M_fn),
1476  static_cast<_Alloc&>(_M_impl));
1477  }
1478 
1479  /// packaged_task
1480  template<typename _Res, typename... _ArgTypes>
1481  class packaged_task<_Res(_ArgTypes...)>
1482  {
1483  typedef __future_base::_Task_state_base<_Res(_ArgTypes...)> _State_type;
1484  shared_ptr<_State_type> _M_state;
1485 
1486  // _GLIBCXX_RESOLVE_LIB_DEFECTS
1487  // 3039. Unnecessary decay in thread and packaged_task
1488  template<typename _Fn, typename _Fn2 = __remove_cvref_t<_Fn>>
1489  using __not_same
1491 
1492  public:
1493  // Construction and destruction
1494  packaged_task() noexcept { }
1495 
1496  template<typename _Fn, typename = __not_same<_Fn>>
1497  explicit
1498  packaged_task(_Fn&& __fn)
1499  : _M_state(
1500  __create_task_state<_Res(_ArgTypes...)>(std::forward<_Fn>(__fn)))
1501  { }
1502 
1503 #if __cplusplus < 201703L
1504  // _GLIBCXX_RESOLVE_LIB_DEFECTS
1505  // 2097. packaged_task constructors should be constrained
1506  // 2407. [this constructor should not be] explicit
1507  // 2921. packaged_task and type-erased allocators
1508  template<typename _Fn, typename _Alloc, typename = __not_same<_Fn>>
1509  packaged_task(allocator_arg_t, const _Alloc& __a, _Fn&& __fn)
1510  : _M_state(__create_task_state<_Res(_ArgTypes...)>(
1511  std::forward<_Fn>(__fn), __a))
1512  { }
1513 
1514  // _GLIBCXX_RESOLVE_LIB_DEFECTS
1515  // 2095. missing constructors needed for uses-allocator construction
1516  template<typename _Allocator>
1517  packaged_task(allocator_arg_t, const _Allocator& __a) noexcept
1518  { }
1519 
1520  template<typename _Allocator>
1521  packaged_task(allocator_arg_t, const _Allocator&,
1522  const packaged_task&) = delete;
1523 
1524  template<typename _Allocator>
1525  packaged_task(allocator_arg_t, const _Allocator&,
1526  packaged_task&& __other) noexcept
1527  { this->swap(__other); }
1528 #endif
1529 
1530  ~packaged_task()
1531  {
1532  if (static_cast<bool>(_M_state) && !_M_state.unique())
1533  _M_state->_M_break_promise(std::move(_M_state->_M_result));
1534  }
1535 
1536  // No copy
1537  packaged_task(const packaged_task&) = delete;
1538  packaged_task& operator=(const packaged_task&) = delete;
1539 
1540  // Move support
1541  packaged_task(packaged_task&& __other) noexcept
1542  { this->swap(__other); }
1543 
1544  packaged_task& operator=(packaged_task&& __other) noexcept
1545  {
1546  packaged_task(std::move(__other)).swap(*this);
1547  return *this;
1548  }
1549 
1550  void
1551  swap(packaged_task& __other) noexcept
1552  { _M_state.swap(__other._M_state); }
1553 
1554  bool
1555  valid() const noexcept
1556  { return static_cast<bool>(_M_state); }
1557 
1558  // Result retrieval
1559  future<_Res>
1560  get_future()
1561  { return future<_Res>(_M_state); }
1562 
1563  // Execution
1564  void
1565  operator()(_ArgTypes... __args)
1566  {
1567  __future_base::_State_base::_S_check(_M_state);
1568  _M_state->_M_run(std::forward<_ArgTypes>(__args)...);
1569  }
1570 
1571  void
1572  make_ready_at_thread_exit(_ArgTypes... __args)
1573  {
1574  __future_base::_State_base::_S_check(_M_state);
1575  _M_state->_M_run_delayed(std::forward<_ArgTypes>(__args)..., _M_state);
1576  }
1577 
1578  void
1579  reset()
1580  {
1581  __future_base::_State_base::_S_check(_M_state);
1582  packaged_task __tmp;
1583  __tmp._M_state = _M_state;
1584  _M_state = _M_state->_M_reset();
1585  }
1586  };
1587 
1588  /// swap
1589  template<typename _Res, typename... _ArgTypes>
1590  inline void
1591  swap(packaged_task<_Res(_ArgTypes...)>& __x,
1592  packaged_task<_Res(_ArgTypes...)>& __y) noexcept
1593  { __x.swap(__y); }
1594 
1595 #if __cplusplus < 201703L
1596  // _GLIBCXX_RESOLVE_LIB_DEFECTS
1597  // 2976. Dangling uses_allocator specialization for packaged_task
1598  template<typename _Res, typename _Alloc>
1599  struct uses_allocator<packaged_task<_Res>, _Alloc>
1600  : public true_type { };
1601 #endif
1602 
1603  // Shared state created by std::async().
1604  // Holds a deferred function and storage for its result.
1605  template<typename _BoundFn, typename _Res>
1606  class __future_base::_Deferred_state final
1607  : public __future_base::_State_base
1608  {
1609  public:
1610  explicit
1611  _Deferred_state(_BoundFn&& __fn)
1612  : _M_result(new _Result<_Res>()), _M_fn(std::move(__fn))
1613  { }
1614 
1615  private:
1616  typedef __future_base::_Ptr<_Result<_Res>> _Ptr_type;
1617  _Ptr_type _M_result;
1618  _BoundFn _M_fn;
1619 
1620  // Run the deferred function.
1621  virtual void
1622  _M_complete_async()
1623  {
1624  // Multiple threads can call a waiting function on the future and
1625  // reach this point at the same time. The call_once in _M_set_result
1626  // ensures only the first one run the deferred function, stores the
1627  // result in _M_result, swaps that with the base _M_result and makes
1628  // the state ready. Tell _M_set_result to ignore failure so all later
1629  // calls do nothing.
1630  _M_set_result(_S_task_setter(_M_result, _M_fn), true);
1631  }
1632 
1633  // Caller should check whether the state is ready first, because this
1634  // function will return true even after the deferred function has run.
1635  virtual bool _M_is_deferred_future() const { return true; }
1636  };
1637 
1638  // Common functionality hoisted out of the _Async_state_impl template.
1639  class __future_base::_Async_state_commonV2
1640  : public __future_base::_State_base
1641  {
1642  protected:
1643  ~_Async_state_commonV2() = default;
1644 
1645  // Make waiting functions block until the thread completes, as if joined.
1646  //
1647  // This function is used by wait() to satisfy the first requirement below
1648  // and by wait_for() / wait_until() to satisfy the second.
1649  //
1650  // [futures.async]:
1651  //
1652  // - a call to a waiting function on an asynchronous return object that
1653  // shares the shared state created by this async call shall block until
1654  // the associated thread has completed, as if joined, or else time out.
1655  //
1656  // - the associated thread completion synchronizes with the return from
1657  // the first function that successfully detects the ready status of the
1658  // shared state or with the return from the last function that releases
1659  // the shared state, whichever happens first.
1660  virtual void _M_complete_async() { _M_join(); }
1661 
1662  void _M_join() { std::call_once(_M_once, &thread::join, &_M_thread); }
1663 
1664  thread _M_thread;
1665  once_flag _M_once;
1666  };
1667 
1668  // Shared state created by std::async().
1669  // Starts a new thread that runs a function and makes the shared state ready.
1670  template<typename _BoundFn, typename _Res>
1671  class __future_base::_Async_state_impl final
1672  : public __future_base::_Async_state_commonV2
1673  {
1674  public:
1675  explicit
1676  _Async_state_impl(_BoundFn&& __fn)
1677  : _M_result(new _Result<_Res>()), _M_fn(std::move(__fn))
1678  {
1679  _M_thread = std::thread{ [this] {
1680  __try
1681  {
1682  _M_set_result(_S_task_setter(_M_result, _M_fn));
1683  }
1684  __catch (const __cxxabiv1::__forced_unwind&)
1685  {
1686  // make the shared state ready on thread cancellation
1687  if (static_cast<bool>(_M_result))
1688  this->_M_break_promise(std::move(_M_result));
1689  __throw_exception_again;
1690  }
1691  } };
1692  }
1693 
1694  // Must not destroy _M_result and _M_fn until the thread finishes.
1695  // Call join() directly rather than through _M_join() because no other
1696  // thread can be referring to this state if it is being destroyed.
1697  ~_Async_state_impl() { if (_M_thread.joinable()) _M_thread.join(); }
1698 
1699  private:
1700  typedef __future_base::_Ptr<_Result<_Res>> _Ptr_type;
1701  _Ptr_type _M_result;
1702  _BoundFn _M_fn;
1703  };
1704 
1705  template<typename _BoundFn>
1707  __future_base::_S_make_deferred_state(_BoundFn&& __fn)
1708  {
1709  typedef typename remove_reference<_BoundFn>::type __fn_type;
1710  typedef _Deferred_state<__fn_type> __state_type;
1711  return std::make_shared<__state_type>(std::move(__fn));
1712  }
1713 
1714  template<typename _BoundFn>
1716  __future_base::_S_make_async_state(_BoundFn&& __fn)
1717  {
1718  typedef typename remove_reference<_BoundFn>::type __fn_type;
1719  typedef _Async_state_impl<__fn_type> __state_type;
1720  return std::make_shared<__state_type>(std::move(__fn));
1721  }
1722 
1723 
1724  /// async
1725  template<typename _Fn, typename... _Args>
1726  _GLIBCXX_NODISCARD future<__async_result_of<_Fn, _Args...>>
1727  async(launch __policy, _Fn&& __fn, _Args&&... __args)
1728  {
1730  if ((__policy & launch::async) == launch::async)
1731  {
1732  __try
1733  {
1734  __state = __future_base::_S_make_async_state(
1735  std::thread::__make_invoker(std::forward<_Fn>(__fn),
1736  std::forward<_Args>(__args)...)
1737  );
1738  }
1739 #if __cpp_exceptions
1740  catch(const system_error& __e)
1741  {
1742  if (__e.code() != errc::resource_unavailable_try_again
1743  || (__policy & launch::deferred) != launch::deferred)
1744  throw;
1745  }
1746 #endif
1747  }
1748  if (!__state)
1749  {
1750  __state = __future_base::_S_make_deferred_state(
1751  std::thread::__make_invoker(std::forward<_Fn>(__fn),
1752  std::forward<_Args>(__args)...));
1753  }
1754  return future<__async_result_of<_Fn, _Args...>>(__state);
1755  }
1756 
1757  /// async, potential overload
1758  template<typename _Fn, typename... _Args>
1759  _GLIBCXX_NODISCARD inline future<__async_result_of<_Fn, _Args...>>
1760  async(_Fn&& __fn, _Args&&... __args)
1761  {
1762  return std::async(launch::async|launch::deferred,
1763  std::forward<_Fn>(__fn),
1764  std::forward<_Args>(__args)...);
1765  }
1766 
1767 #endif // _GLIBCXX_ASYNC_ABI_COMPAT
1768 #endif // _GLIBCXX_HAS_GTHREADS
1769 
1770  // @} group futures
1771 _GLIBCXX_END_NAMESPACE_VERSION
1772 } // namespace
1773 
1774 #endif // C++11
1775 
1776 #endif // _GLIBCXX_FUTURE
Partial specialization for shared_future&lt;R&amp;&gt;
Definition: future:941
bitset< _Nb > operator&(const bitset< _Nb > &__x, const bitset< _Nb > &__y) noexcept
Global bitwise operations on bitsets.
Definition: bitset:1435
Primary template for future.
Definition: future:125
Base class and enclosing scope.
Definition: future:198
shared_future(shared_future &&__sf) noexcept
Construct from a shared_future rvalue.
Definition: future:918
constexpr _Tp * addressof(_Tp &__r) noexcept
Returns the actual address of the object or function referenced by r, even in the presence of an over...
Definition: move.h:140
shared_future(future< _Res & > &&__uf) noexcept
Construct from a future rvalue.
Definition: future:952
A result object that has storage for an object of type _Res.
Definition: future:227
__result_type _M_get_result() const
Wait for the state to be ready and rethrow any stored exception.
Definition: future:725
constexpr _Tp * __addressof(_Tp &__r) noexcept
Same as C++11 std::addressof.
Definition: move.h:49
integral_constant
Definition: type_traits:57
virtual const char * what() const noexcept
__allocated_ptr< _Alloc > __allocate_guarded(_Alloc &__a)
Allocate space for a single object using __a.
Definition: allocated_ptr.h:95
Primary template for shared_future.
Definition: future:128
shared_future(const shared_future &__sf)
Copy constructor.
Definition: future:988
Exception type thrown by futures.
Definition: future:96
future(future &&__uf) noexcept
Move constructor.
Definition: future:876
Define a member typedef type only if a boolean constant is true.
Definition: type_traits:2182
thread
Definition: thread:73
A result object that uses an allocator.
Definition: future:268
exception_ptr current_exception() noexcept
const error_category & future_category() noexcept
Points to a statically-allocated object derived from error_category.
exception_ptr make_exception_ptr(_Ex) noexcept
Obtain an exception_ptr pointing to a copy of the supplied object.
void swap(unique_ptr &__u) noexcept
Exchange the pointer and deleter with another object.
Definition: unique_ptr.h:461
Primary template for promise.
Definition: future:134
Thrown as part of forced unwinding.A magic placeholder class that can be caught by reference to recog...
Definition: cxxabi_forced.h:48
launch
Launch code for futures.
Definition: future:137
Explicit specialization for future&lt;void&gt;
Definition: future:858
logic_error(const string &__arg) _GLIBCXX_TXN_SAFE
One of two subclasses of exception.
Definition: stdexcept:113
bitset< _Nb > operator^(const bitset< _Nb > &__x, const bitset< _Nb > &__y) noexcept
Global bitwise operations on bitsets.
Definition: bitset:1453
The standard allocator, as per [20.4].
Definition: allocator.h:116
Explicit specialization for void.
Definition: future:658
shared_future(future< void > &&__uf) noexcept
Construct from a future rvalue.
Definition: future:991
shared_future(const shared_future &__sf)
Copy constructor.
Definition: future:949
future_status
Status code for futures.
Definition: future:174
error_condition make_error_condition(future_errc __errc) noexcept
Overload for make_error_condition.
Definition: future:89
future(future &&__uf) noexcept
Move constructor.
Definition: future:833
constexpr _Tp && forward(typename std::remove_reference< _Tp >::type &__t) noexcept
Forward an lvalue.
Definition: move.h:76
duration
Definition: chrono:71
Explicit specialization for shared_future&lt;void&gt;
Definition: future:980
shared_future(future< _Res > &&__uf) noexcept
Construct from a future rvalue.
Definition: future:913
Common implementation for future and shared_future.
Definition: future:682
future< __async_result_of< _Fn, _Args...> > async(_Fn &&__fn, _Args &&...__args)
async, potential overload
Definition: future:1760
shared_future(const shared_future &__sf) noexcept
Copy constructor.
Definition: future:910
future< __async_result_of< _Fn, _Args...> > async(launch __policy, _Fn &&__fn, _Args &&...__args)
async
Definition: future:1727
void rethrow_exception(exception_ptr)
Throw the object pointed to by the exception_ptr.
Partial specialization for future&lt;R&amp;&gt;
Definition: future:815
time_point
Definition: chrono:74
future_errc
Error code for futures.
Definition: future:66
constexpr std::remove_reference< _Tp >::type && move(_Tp &&__t) noexcept
Convert a value to an rvalue.
Definition: move.h:101
bitset< _Nb > operator|(const bitset< _Nb > &__x, const bitset< _Nb > &__y) noexcept
Global bitwise operations on bitsets.
Definition: bitset:1444
An exception type that includes an error_code value.
Definition: system_error:428
Partial specialization for reference types.
Definition: future:638
is_error_code_enum
Definition: system_error:60
future(future &&__uf) noexcept
Move constructor.
Definition: future:790
void call_once(once_flag &__once, _Callable &&__f, _Args &&...__args)
Invoke a callable and synchronize with other calls using the same flag.
Definition: mutex:712
[allocator.tag]
integral_constant< bool, true > true_type
The type used as a compile-time boolean with true value.
Definition: type_traits:75
shared_future(shared_future &&__sf) noexcept
Construct from a shared_future rvalue.
Definition: future:996
Non-standard RAII type for managing pointers obtained from allocators.
Definition: allocated_ptr.h:46
20.7.1.2 unique_ptr for single objects.
Definition: unique_ptr.h:242
Base class for results.
Definition: future:201
shared_future(shared_future &&__sf) noexcept
Construct from a shared_future rvalue.
Definition: future:957