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<>
76  struct is_error_code_enum<future_errc> : public true_type { };
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
89  make_error_condition(future_errc __errc) noexcept
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
114  future_error(error_code __ec)
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>
128  class shared_future;
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.
198  struct __future_base
199  {
200  /// Base class for results.
201  struct _Result_base
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>
223  using _Ptr = unique_ptr<_Res, _Result_base::_Deleter>;
224 
225  /// A result object that has storage for an object of type _Res.
226  template<typename _Res>
227  struct _Result : _Result_base
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>
287  static _Ptr<_Result_alloc<_Res, _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>
342  future_status
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>
376  future_status
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  __attribute__((__always_inline__))
537  static _Setter<_Res, _Arg&&>
538  __setter(promise<_Res>* __prom, _Arg&& __arg) noexcept
539  {
540  return _Setter<_Res, _Arg&&>{ __prom, std::__addressof(__arg) };
541  }
542 
543  template<typename _Res>
544  __attribute__((__always_inline__))
545  static _Setter<_Res, __exception_ptr_tag>
546  __setter(exception_ptr& __ex, promise<_Res>* __prom) noexcept
547  {
548  return _Setter<_Res, __exception_ptr_tag>{ __prom, &__ex };
549  }
550 
551  template<typename _Res>
552  __attribute__((__always_inline__))
553  static _Setter<_Res, void>
554  __setter(promise<_Res>* __prom) noexcept
555  {
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>
617  static std::shared_ptr<_State_base>
618  _S_make_deferred_state(_BoundFn&& __fn);
619 
620  template<typename _BoundFn>
621  static std::shared_ptr<_State_base>
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>
638  struct __future_base::_Result<_Res&> : __future_base::_Result_base
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<>
658  struct __future_base::_Result<void> : __future_base::_Result_base
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>
670  struct __is_location_invariant
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>
676  struct __is_location_invariant
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>
682  class __basic_future : public __future_base
683  {
684  protected:
685  typedef shared_ptr<_State_base> __state_type;
686  typedef __future_base::_Result<_Res>& __result_type;
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>
707  future_status
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>
715  future_status
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
724  __result_type
725  _M_get_result() const
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 
823  typedef __basic_future<_Res&> _Base_type;
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_state()._M_set_result(_State::__setter(this, __r)); }
1122 
1123  void
1124  set_value(_Res&& __r)
1125  { _M_state()._M_set_result(_State::__setter(this, std::move(__r))); }
1126 
1127  void
1128  set_exception(exception_ptr __p)
1129  { _M_state()._M_set_result(_State::__setter(__p, this)); }
1130 
1131  void
1132  set_value_at_thread_exit(const _Res& __r)
1133  {
1134  _M_state()._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_state()._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_state()._M_set_delayed_result(_State::__setter(__p, this),
1149  _M_future);
1150  }
1151 
1152  private:
1153  _State&
1154  _M_state()
1155  {
1156  __future_base::_State_base::_S_check(_M_future);
1157  return *_M_future;
1158  }
1159  };
1160 
1161  template<typename _Res>
1162  inline void
1163  swap(promise<_Res>& __x, promise<_Res>& __y) noexcept
1164  { __x.swap(__y); }
1165 
1166  template<typename _Res, typename _Alloc>
1167  struct uses_allocator<promise<_Res>, _Alloc>
1168  : public true_type { };
1169 
1170 
1171  /// Partial specialization for promise<R&>
1172  template<typename _Res>
1173  class promise<_Res&>
1174  {
1175  typedef __future_base::_State_base _State;
1176  typedef __future_base::_Result<_Res&> _Res_type;
1177  typedef __future_base::_Ptr<_Res_type> _Ptr_type;
1178  template<typename, typename> friend class _State::_Setter;
1179  friend _State;
1180 
1181  shared_ptr<_State> _M_future;
1182  _Ptr_type _M_storage;
1183 
1184  public:
1185  promise()
1186  : _M_future(std::make_shared<_State>()),
1187  _M_storage(new _Res_type())
1188  { }
1189 
1190  promise(promise&& __rhs) noexcept
1191  : _M_future(std::move(__rhs._M_future)),
1192  _M_storage(std::move(__rhs._M_storage))
1193  { }
1194 
1195  template<typename _Allocator>
1196  promise(allocator_arg_t, const _Allocator& __a)
1197  : _M_future(std::allocate_shared<_State>(__a)),
1198  _M_storage(__future_base::_S_allocate_result<_Res&>(__a))
1199  { }
1200 
1201  template<typename _Allocator>
1202  promise(allocator_arg_t, const _Allocator&, promise&& __rhs)
1203  : _M_future(std::move(__rhs._M_future)),
1204  _M_storage(std::move(__rhs._M_storage))
1205  { }
1206 
1207  promise(const promise&) = delete;
1208 
1209  ~promise()
1210  {
1211  if (static_cast<bool>(_M_future) && !_M_future.unique())
1212  _M_future->_M_break_promise(std::move(_M_storage));
1213  }
1214 
1215  // Assignment
1216  promise&
1217  operator=(promise&& __rhs) noexcept
1218  {
1219  promise(std::move(__rhs)).swap(*this);
1220  return *this;
1221  }
1222 
1223  promise& operator=(const promise&) = delete;
1224 
1225  void
1226  swap(promise& __rhs) noexcept
1227  {
1228  _M_future.swap(__rhs._M_future);
1229  _M_storage.swap(__rhs._M_storage);
1230  }
1231 
1232  // Retrieving the result
1233  future<_Res&>
1234  get_future()
1235  { return future<_Res&>(_M_future); }
1236 
1237  // Setting the result
1238  void
1239  set_value(_Res& __r)
1240  { _M_state()._M_set_result(_State::__setter(this, __r)); }
1241 
1242  void
1243  set_exception(exception_ptr __p)
1244  { _M_state()._M_set_result(_State::__setter(__p, this)); }
1245 
1246  void
1247  set_value_at_thread_exit(_Res& __r)
1248  {
1249  _M_state()._M_set_delayed_result(_State::__setter(this, __r),
1250  _M_future);
1251  }
1252 
1253  void
1254  set_exception_at_thread_exit(exception_ptr __p)
1255  {
1256  _M_state()._M_set_delayed_result(_State::__setter(__p, this),
1257  _M_future);
1258  }
1259 
1260  private:
1261  _State&
1262  _M_state()
1263  {
1264  __future_base::_State_base::_S_check(_M_future);
1265  return *_M_future;
1266  }
1267  };
1268 
1269  /// Explicit specialization for promise<void>
1270  template<>
1271  class promise<void>
1272  {
1273  typedef __future_base::_State_base _State;
1274  typedef __future_base::_Result<void> _Res_type;
1275  typedef __future_base::_Ptr<_Res_type> _Ptr_type;
1276  template<typename, typename> friend class _State::_Setter;
1277  friend _State;
1278 
1279  shared_ptr<_State> _M_future;
1280  _Ptr_type _M_storage;
1281 
1282  public:
1283  promise()
1284  : _M_future(std::make_shared<_State>()),
1285  _M_storage(new _Res_type())
1286  { }
1287 
1288  promise(promise&& __rhs) noexcept
1289  : _M_future(std::move(__rhs._M_future)),
1290  _M_storage(std::move(__rhs._M_storage))
1291  { }
1292 
1293  template<typename _Allocator>
1294  promise(allocator_arg_t, const _Allocator& __a)
1295  : _M_future(std::allocate_shared<_State>(__a)),
1296  _M_storage(__future_base::_S_allocate_result<void>(__a))
1297  { }
1298 
1299  // _GLIBCXX_RESOLVE_LIB_DEFECTS
1300  // 2095. missing constructors needed for uses-allocator construction
1301  template<typename _Allocator>
1302  promise(allocator_arg_t, const _Allocator&, promise&& __rhs)
1303  : _M_future(std::move(__rhs._M_future)),
1304  _M_storage(std::move(__rhs._M_storage))
1305  { }
1306 
1307  promise(const promise&) = delete;
1308 
1309  ~promise()
1310  {
1311  if (static_cast<bool>(_M_future) && !_M_future.unique())
1312  _M_future->_M_break_promise(std::move(_M_storage));
1313  }
1314 
1315  // Assignment
1316  promise&
1317  operator=(promise&& __rhs) noexcept
1318  {
1319  promise(std::move(__rhs)).swap(*this);
1320  return *this;
1321  }
1322 
1323  promise& operator=(const promise&) = delete;
1324 
1325  void
1326  swap(promise& __rhs) noexcept
1327  {
1328  _M_future.swap(__rhs._M_future);
1329  _M_storage.swap(__rhs._M_storage);
1330  }
1331 
1332  // Retrieving the result
1333  future<void>
1334  get_future()
1335  { return future<void>(_M_future); }
1336 
1337  // Setting the result
1338  void
1339  set_value()
1340  { _M_state()._M_set_result(_State::__setter(this)); }
1341 
1342  void
1343  set_exception(exception_ptr __p)
1344  { _M_state()._M_set_result(_State::__setter(__p, this)); }
1345 
1346  void
1347  set_value_at_thread_exit()
1348  { _M_state()._M_set_delayed_result(_State::__setter(this), _M_future); }
1349 
1350  void
1351  set_exception_at_thread_exit(exception_ptr __p)
1352  {
1353  _M_state()._M_set_delayed_result(_State::__setter(__p, this),
1354  _M_future);
1355  }
1356 
1357  private:
1358  _State&
1359  _M_state()
1360  {
1361  __future_base::_State_base::_S_check(_M_future);
1362  return *_M_future;
1363  }
1364  };
1365 
1366  template<typename _Ptr_type, typename _Fn, typename _Res>
1367  struct __future_base::_Task_setter
1368  {
1369  // Invoke the function and provide the result to the caller.
1370  _Ptr_type operator()() const
1371  {
1372  __try
1373  {
1374  (*_M_result)->_M_set((*_M_fn)());
1375  }
1376  __catch(const __cxxabiv1::__forced_unwind&)
1377  {
1378  __throw_exception_again; // will cause broken_promise
1379  }
1380  __catch(...)
1381  {
1382  (*_M_result)->_M_error = current_exception();
1383  }
1384  return std::move(*_M_result);
1385  }
1386  _Ptr_type* _M_result;
1387  _Fn* _M_fn;
1388  };
1389 
1390  template<typename _Ptr_type, typename _Fn>
1391  struct __future_base::_Task_setter<_Ptr_type, _Fn, void>
1392  {
1393  _Ptr_type operator()() const
1394  {
1395  __try
1396  {
1397  (*_M_fn)();
1398  }
1399  __catch(const __cxxabiv1::__forced_unwind&)
1400  {
1401  __throw_exception_again; // will cause broken_promise
1402  }
1403  __catch(...)
1404  {
1405  (*_M_result)->_M_error = current_exception();
1406  }
1407  return std::move(*_M_result);
1408  }
1409  _Ptr_type* _M_result;
1410  _Fn* _M_fn;
1411  };
1412 
1413  // Holds storage for a packaged_task's result.
1414  template<typename _Res, typename... _Args>
1415  struct __future_base::_Task_state_base<_Res(_Args...)>
1416  : __future_base::_State_base
1417  {
1418  typedef _Res _Res_type;
1419 
1420  template<typename _Alloc>
1421  _Task_state_base(const _Alloc& __a)
1422  : _M_result(_S_allocate_result<_Res>(__a))
1423  { }
1424 
1425  // Invoke the stored task and make the state ready.
1426  virtual void
1427  _M_run(_Args&&... __args) = 0;
1428 
1429  // Invoke the stored task and make the state ready at thread exit.
1430  virtual void
1431  _M_run_delayed(_Args&&... __args, weak_ptr<_State_base>) = 0;
1432 
1433  virtual shared_ptr<_Task_state_base>
1434  _M_reset() = 0;
1435 
1436  typedef __future_base::_Ptr<_Result<_Res>> _Ptr_type;
1437  _Ptr_type _M_result;
1438  };
1439 
1440  // Holds a packaged_task's stored task.
1441  template<typename _Fn, typename _Alloc, typename _Res, typename... _Args>
1442  struct __future_base::_Task_state<_Fn, _Alloc, _Res(_Args...)> final
1443  : __future_base::_Task_state_base<_Res(_Args...)>
1444  {
1445  template<typename _Fn2>
1446  _Task_state(_Fn2&& __fn, const _Alloc& __a)
1447  : _Task_state_base<_Res(_Args...)>(__a),
1448  _M_impl(std::forward<_Fn2>(__fn), __a)
1449  { }
1450 
1451  private:
1452  virtual void
1453  _M_run(_Args&&... __args)
1454  {
1455  auto __boundfn = [&] () -> _Res {
1456  return std::__invoke_r<_Res>(_M_impl._M_fn,
1457  std::forward<_Args>(__args)...);
1458  };
1459  this->_M_set_result(_S_task_setter(this->_M_result, __boundfn));
1460  }
1461 
1462  virtual void
1463  _M_run_delayed(_Args&&... __args, weak_ptr<_State_base> __self)
1464  {
1465  auto __boundfn = [&] () -> _Res {
1466  return std::__invoke_r<_Res>(_M_impl._M_fn,
1467  std::forward<_Args>(__args)...);
1468  };
1469  this->_M_set_delayed_result(_S_task_setter(this->_M_result, __boundfn),
1470  std::move(__self));
1471  }
1472 
1473  virtual shared_ptr<_Task_state_base<_Res(_Args...)>>
1474  _M_reset();
1475 
1476  struct _Impl : _Alloc
1477  {
1478  template<typename _Fn2>
1479  _Impl(_Fn2&& __fn, const _Alloc& __a)
1480  : _Alloc(__a), _M_fn(std::forward<_Fn2>(__fn)) { }
1481  _Fn _M_fn;
1482  } _M_impl;
1483  };
1484 
1485  template<typename _Signature, typename _Fn,
1486  typename _Alloc = std::allocator<int>>
1487  static shared_ptr<__future_base::_Task_state_base<_Signature>>
1488  __create_task_state(_Fn&& __fn, const _Alloc& __a = _Alloc())
1489  {
1490  typedef typename decay<_Fn>::type _Fn2;
1491  typedef __future_base::_Task_state<_Fn2, _Alloc, _Signature> _State;
1492  return std::allocate_shared<_State>(__a, std::forward<_Fn>(__fn), __a);
1493  }
1494 
1495  template<typename _Fn, typename _Alloc, typename _Res, typename... _Args>
1496  shared_ptr<__future_base::_Task_state_base<_Res(_Args...)>>
1497  __future_base::_Task_state<_Fn, _Alloc, _Res(_Args...)>::_M_reset()
1498  {
1499  return __create_task_state<_Res(_Args...)>(std::move(_M_impl._M_fn),
1500  static_cast<_Alloc&>(_M_impl));
1501  }
1502 
1503  /// packaged_task
1504  template<typename _Res, typename... _ArgTypes>
1505  class packaged_task<_Res(_ArgTypes...)>
1506  {
1507  typedef __future_base::_Task_state_base<_Res(_ArgTypes...)> _State_type;
1508  shared_ptr<_State_type> _M_state;
1509 
1510  // _GLIBCXX_RESOLVE_LIB_DEFECTS
1511  // 3039. Unnecessary decay in thread and packaged_task
1512  template<typename _Fn, typename _Fn2 = __remove_cvref_t<_Fn>>
1513  using __not_same
1514  = typename enable_if<!is_same<packaged_task, _Fn2>::value>::type;
1515 
1516  public:
1517  // Construction and destruction
1518  packaged_task() noexcept { }
1519 
1520  template<typename _Fn, typename = __not_same<_Fn>>
1521  explicit
1522  packaged_task(_Fn&& __fn)
1523  : _M_state(
1524  __create_task_state<_Res(_ArgTypes...)>(std::forward<_Fn>(__fn)))
1525  { }
1526 
1527 #if __cplusplus < 201703L
1528  // _GLIBCXX_RESOLVE_LIB_DEFECTS
1529  // 2097. packaged_task constructors should be constrained
1530  // 2407. [this constructor should not be] explicit
1531  // 2921. packaged_task and type-erased allocators
1532  template<typename _Fn, typename _Alloc, typename = __not_same<_Fn>>
1533  packaged_task(allocator_arg_t, const _Alloc& __a, _Fn&& __fn)
1534  : _M_state(__create_task_state<_Res(_ArgTypes...)>(
1535  std::forward<_Fn>(__fn), __a))
1536  { }
1537 
1538  // _GLIBCXX_RESOLVE_LIB_DEFECTS
1539  // 2095. missing constructors needed for uses-allocator construction
1540  template<typename _Allocator>
1541  packaged_task(allocator_arg_t, const _Allocator& __a) noexcept
1542  { }
1543 
1544  template<typename _Allocator>
1545  packaged_task(allocator_arg_t, const _Allocator&,
1546  const packaged_task&) = delete;
1547 
1548  template<typename _Allocator>
1549  packaged_task(allocator_arg_t, const _Allocator&,
1550  packaged_task&& __other) noexcept
1551  { this->swap(__other); }
1552 #endif
1553 
1554  ~packaged_task()
1555  {
1556  if (static_cast<bool>(_M_state) && !_M_state.unique())
1557  _M_state->_M_break_promise(std::move(_M_state->_M_result));
1558  }
1559 
1560  // No copy
1561  packaged_task(const packaged_task&) = delete;
1562  packaged_task& operator=(const packaged_task&) = delete;
1563 
1564  // Move support
1565  packaged_task(packaged_task&& __other) noexcept
1566  { this->swap(__other); }
1567 
1568  packaged_task& operator=(packaged_task&& __other) noexcept
1569  {
1570  packaged_task(std::move(__other)).swap(*this);
1571  return *this;
1572  }
1573 
1574  void
1575  swap(packaged_task& __other) noexcept
1576  { _M_state.swap(__other._M_state); }
1577 
1578  bool
1579  valid() const noexcept
1580  { return static_cast<bool>(_M_state); }
1581 
1582  // Result retrieval
1583  future<_Res>
1584  get_future()
1585  { return future<_Res>(_M_state); }
1586 
1587  // Execution
1588  void
1589  operator()(_ArgTypes... __args)
1590  {
1591  __future_base::_State_base::_S_check(_M_state);
1592  _M_state->_M_run(std::forward<_ArgTypes>(__args)...);
1593  }
1594 
1595  void
1596  make_ready_at_thread_exit(_ArgTypes... __args)
1597  {
1598  __future_base::_State_base::_S_check(_M_state);
1599  _M_state->_M_run_delayed(std::forward<_ArgTypes>(__args)..., _M_state);
1600  }
1601 
1602  void
1603  reset()
1604  {
1605  __future_base::_State_base::_S_check(_M_state);
1606  packaged_task __tmp;
1607  __tmp._M_state = _M_state;
1608  _M_state = _M_state->_M_reset();
1609  }
1610  };
1611 
1612  /// swap
1613  template<typename _Res, typename... _ArgTypes>
1614  inline void
1615  swap(packaged_task<_Res(_ArgTypes...)>& __x,
1616  packaged_task<_Res(_ArgTypes...)>& __y) noexcept
1617  { __x.swap(__y); }
1618 
1619 #if __cplusplus < 201703L
1620  // _GLIBCXX_RESOLVE_LIB_DEFECTS
1621  // 2976. Dangling uses_allocator specialization for packaged_task
1622  template<typename _Res, typename _Alloc>
1623  struct uses_allocator<packaged_task<_Res>, _Alloc>
1624  : public true_type { };
1625 #endif
1626 
1627  // Shared state created by std::async().
1628  // Holds a deferred function and storage for its result.
1629  template<typename _BoundFn, typename _Res>
1630  class __future_base::_Deferred_state final
1631  : public __future_base::_State_base
1632  {
1633  public:
1634  explicit
1635  _Deferred_state(_BoundFn&& __fn)
1636  : _M_result(new _Result<_Res>()), _M_fn(std::move(__fn))
1637  { }
1638 
1639  private:
1640  typedef __future_base::_Ptr<_Result<_Res>> _Ptr_type;
1641  _Ptr_type _M_result;
1642  _BoundFn _M_fn;
1643 
1644  // Run the deferred function.
1645  virtual void
1646  _M_complete_async()
1647  {
1648  // Multiple threads can call a waiting function on the future and
1649  // reach this point at the same time. The call_once in _M_set_result
1650  // ensures only the first one run the deferred function, stores the
1651  // result in _M_result, swaps that with the base _M_result and makes
1652  // the state ready. Tell _M_set_result to ignore failure so all later
1653  // calls do nothing.
1654  _M_set_result(_S_task_setter(_M_result, _M_fn), true);
1655  }
1656 
1657  // Caller should check whether the state is ready first, because this
1658  // function will return true even after the deferred function has run.
1659  virtual bool _M_is_deferred_future() const { return true; }
1660  };
1661 
1662  // Common functionality hoisted out of the _Async_state_impl template.
1663  class __future_base::_Async_state_commonV2
1664  : public __future_base::_State_base
1665  {
1666  protected:
1667  ~_Async_state_commonV2() = default;
1668 
1669  // Make waiting functions block until the thread completes, as if joined.
1670  //
1671  // This function is used by wait() to satisfy the first requirement below
1672  // and by wait_for() / wait_until() to satisfy the second.
1673  //
1674  // [futures.async]:
1675  //
1676  // - a call to a waiting function on an asynchronous return object that
1677  // shares the shared state created by this async call shall block until
1678  // the associated thread has completed, as if joined, or else time out.
1679  //
1680  // - the associated thread completion synchronizes with the return from
1681  // the first function that successfully detects the ready status of the
1682  // shared state or with the return from the last function that releases
1683  // the shared state, whichever happens first.
1684  virtual void _M_complete_async() { _M_join(); }
1685 
1686  void _M_join() { std::call_once(_M_once, &thread::join, &_M_thread); }
1687 
1688  thread _M_thread;
1689  once_flag _M_once;
1690  };
1691 
1692  // Shared state created by std::async().
1693  // Starts a new thread that runs a function and makes the shared state ready.
1694  template<typename _BoundFn, typename _Res>
1695  class __future_base::_Async_state_impl final
1696  : public __future_base::_Async_state_commonV2
1697  {
1698  public:
1699  explicit
1700  _Async_state_impl(_BoundFn&& __fn)
1701  : _M_result(new _Result<_Res>()), _M_fn(std::move(__fn))
1702  {
1703  _M_thread = std::thread{ [this] {
1704  __try
1705  {
1706  _M_set_result(_S_task_setter(_M_result, _M_fn));
1707  }
1708  __catch (const __cxxabiv1::__forced_unwind&)
1709  {
1710  // make the shared state ready on thread cancellation
1711  if (static_cast<bool>(_M_result))
1712  this->_M_break_promise(std::move(_M_result));
1713  __throw_exception_again;
1714  }
1715  } };
1716  }
1717 
1718  // Must not destroy _M_result and _M_fn until the thread finishes.
1719  // Call join() directly rather than through _M_join() because no other
1720  // thread can be referring to this state if it is being destroyed.
1721  ~_Async_state_impl() { if (_M_thread.joinable()) _M_thread.join(); }
1722 
1723  private:
1724  typedef __future_base::_Ptr<_Result<_Res>> _Ptr_type;
1725  _Ptr_type _M_result;
1726  _BoundFn _M_fn;
1727  };
1728 
1729  template<typename _BoundFn>
1730  inline std::shared_ptr<__future_base::_State_base>
1731  __future_base::_S_make_deferred_state(_BoundFn&& __fn)
1732  {
1733  typedef typename remove_reference<_BoundFn>::type __fn_type;
1734  typedef _Deferred_state<__fn_type> __state_type;
1735  return std::make_shared<__state_type>(std::move(__fn));
1736  }
1737 
1738  template<typename _BoundFn>
1739  inline std::shared_ptr<__future_base::_State_base>
1740  __future_base::_S_make_async_state(_BoundFn&& __fn)
1741  {
1742  typedef typename remove_reference<_BoundFn>::type __fn_type;
1743  typedef _Async_state_impl<__fn_type> __state_type;
1744  return std::make_shared<__state_type>(std::move(__fn));
1745  }
1746 
1747 
1748  /// async
1749  template<typename _Fn, typename... _Args>
1750  _GLIBCXX_NODISCARD future<__async_result_of<_Fn, _Args...>>
1751  async(launch __policy, _Fn&& __fn, _Args&&... __args)
1752  {
1753  std::shared_ptr<__future_base::_State_base> __state;
1754  if ((__policy & launch::async) == launch::async)
1755  {
1756  __try
1757  {
1758  __state = __future_base::_S_make_async_state(
1759  std::thread::__make_invoker(std::forward<_Fn>(__fn),
1760  std::forward<_Args>(__args)...)
1761  );
1762  }
1763 #if __cpp_exceptions
1764  catch(const system_error& __e)
1765  {
1766  if (__e.code() != errc::resource_unavailable_try_again
1767  || (__policy & launch::deferred) != launch::deferred)
1768  throw;
1769  }
1770 #endif
1771  }
1772  if (!__state)
1773  {
1774  __state = __future_base::_S_make_deferred_state(
1775  std::thread::__make_invoker(std::forward<_Fn>(__fn),
1776  std::forward<_Args>(__args)...));
1777  }
1778  return future<__async_result_of<_Fn, _Args...>>(__state);
1779  }
1780 
1781  /// async, potential overload
1782  template<typename _Fn, typename... _Args>
1783  _GLIBCXX_NODISCARD inline future<__async_result_of<_Fn, _Args...>>
1784  async(_Fn&& __fn, _Args&&... __args)
1785  {
1786  return std::async(launch::async|launch::deferred,
1787  std::forward<_Fn>(__fn),
1788  std::forward<_Args>(__args)...);
1789  }
1790 
1791 #endif // _GLIBCXX_ASYNC_ABI_COMPAT
1792 #endif // _GLIBCXX_HAS_GTHREADS
1793 
1794  /// @} group futures
1795 _GLIBCXX_END_NAMESPACE_VERSION
1796 } // namespace
1797 
1798 #endif // C++11
1799 
1800 #endif // _GLIBCXX_FUTURE