path: root/libstdc++-v3/include/std/future

// <future> -*- C++ -*-

// Copyright (C) 2009 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 3, or (at your option)
// any later version.

// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.

// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
// <http://www.gnu.org/licenses/>.

/** @file future
 *  This is a Standard C++ Library header.
 */

#ifndef _GLIBCXX_FUTURE
#define _GLIBCXX_FUTURE 1

#pragma GCC system_header

#ifndef __GXX_EXPERIMENTAL_CXX0X__
# include <c++0x_warning.h>
#else

#include <functional>
#include <memory>
#include <mutex>
#include <condition_variable>
#include <system_error>
#include <exception>
#include <cstdatomic>

namespace std
{
  /**
   * @defgroup futures Futures
   * @ingroup concurrency
   *
   * Classes for futures support.
   * @{
   */

  /// Error code for futures
  enum class future_errc
  { broken_promise, future_already_retrieved, promise_already_satisfied };

  // TODO: requires concepts
  // concept_map ErrorCodeEnum<future_errc> { }
  template<>
    struct is_error_code_enum<future_errc> : public true_type { };

  /// Points to a statically-allocated object derived from error_category.
  extern const error_category* const future_category;

  // TODO: requires constexpr
  inline error_code make_error_code(future_errc __errc)
  { return error_code(static_cast<int>(__errc), *future_category); }

  // TODO: requires constexpr
  inline error_condition make_error_condition(future_errc __errc)
  { return error_condition(static_cast<int>(__errc), *future_category); }

  /**
   *  @brief Exception type thrown by futures.
   *  @ingroup exceptions
   */
  class future_error : public logic_error
  {
    error_code 			_M_code;

  public:
    explicit future_error(future_errc __ec)
    : logic_error("std::future_error"), _M_code(make_error_code(__ec))
    { }

    virtual ~future_error() throw();

    virtual const char* 
    what() const throw();

    const error_code& 
    code() const throw() { return _M_code; }
  };

  // Forward declarations.
  template<typename _Res>
    class unique_future;

  template<typename _Res>
    class shared_future;

  template<typename> 
    class packaged_task;

  template<typename _Res>
    class promise;

#if defined(_GLIBCXX_HAS_GTHREADS) && defined(_GLIBCXX_USE_C99_STDINT_TR1) \
  && defined(_GLIBCXX_ATOMIC_BUILTINS_4)

  /// Base class and enclosing scope.
  struct __future_base
  {
    /// Base class for results.
    struct _Result_base
    {
      exception_ptr		_M_error;

      _Result_base() = default;
      _Result_base(const _Result_base&) = delete;
      _Result_base& operator=(const _Result_base&) = delete;

      // _M_destroy() allows derived classes to control deallocation,
      // which will be needed when allocator support is added to promise.
      // See http://gcc.gnu.org/ml/libstdc++/2009-06/msg00032.html
      virtual void _M_destroy() = 0;

      struct _Deleter
      {
	void operator()(_Result_base* __fr) const { __fr->_M_destroy(); }
      };

    protected:
      ~_Result_base();
    };

    /// Result.
    template<typename _Res>
      struct _Result : _Result_base
      {
      private:
	typedef alignment_of<_Res>				__a_of;
	typedef aligned_storage<sizeof(_Res), __a_of::value>	__align_storage;
	typedef typename __align_storage::type			__align_type;

	__align_type		_M_storage;
	bool 			_M_initialized;

      public:
	_Result() : _M_initialized() { }
	
	~_Result()
	{
	  if (_M_initialized)
	    _M_value().~_Res();
	}

	// Return lvalue, future will add const or rvalue-reference
	_Res& 
	_M_value() { return *static_cast<_Res*>(_M_addr()); }

	void
	_M_set(const _Res& __res)
	{
	  ::new (_M_addr()) _Res(__res);
	  _M_initialized = true;
	}

	void
	_M_set(_Res&& __res)
	{
	  ::new (_M_addr()) _Res(_Move_result<_Res>::_S_move(__res));
	  _M_initialized = true;
	}

      private:
	void _M_destroy() { delete this; }

	void* _M_addr() { return static_cast<void*>(&_M_storage); }
    };


    /// Workaround for CWG issue 664 and c++/34022
    template<typename _Res, bool = is_scalar<_Res>::value>
      struct _Move_result;

     /// Specialization for scalar types returns rvalue not rvalue-reference.
    template<typename _Res>
      struct _Move_result<_Res, true>
      {
	typedef _Res __rval_type;
	static _Res _S_move(_Res __res) { return __res; }
      };
    
    /// Specialization for non-scalar types returns rvalue-reference.
    template<typename _Res>
      struct _Move_result<_Res, false>
      {
	typedef _Res&& __rval_type;
	static _Res&& _S_move(_Res& __res) { return std::move(__res); }
      };


    // TODO: use template alias when available
    /*
      template<typename _Res>
      using _Ptr = unique_ptr<_Res, _Result_base::_Deleter>;
    */
    /// A unique_ptr based on the instantiating type.
    template<typename _Res>
      struct _Ptr
      {
	typedef unique_ptr<_Res, _Result_base::_Deleter> type;
      };


    /// Shared state between a promise and one or more associated futures.
    class _State
    {
      typedef _Ptr<_Result_base>::type _Ptr_type;

      _Ptr_type			_M_result;
      mutex               	_M_mutex;
      condition_variable  	_M_cond;
      atomic_flag         	_M_retrieved;

    public:
      _State() : _M_result(), _M_retrieved(ATOMIC_FLAG_INIT) { }

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

      bool
      is_ready()
      { return _M_get() != 0; }

      bool
      has_exception()
      {
	_Result_base* const __res = _M_get();
	return __res && !(__res->_M_error == 0);
      }

      bool
      has_value()
      {
	_Result_base* const __res = _M_get();
	return __res && (__res->_M_error == 0);
      }

      _Result_base&
      wait()
      {
	unique_lock<mutex> __lock(_M_mutex);
	if (!_M_ready())
	  _M_cond.wait(__lock, std::bind(&_State::_M_ready, this));
	return *_M_result;
      }

      template<typename _Rep, typename _Period>
        bool
        wait_for(const chrono::duration<_Rep, _Period>& __rel)
        {
	  unique_lock<mutex> __lock(_M_mutex);
	  auto __bound = std::bind(&_State::_M_ready, this);
	  return _M_ready() || _M_cond.wait_for(__lock, __rel, __bound);
	}

      template<typename _Clock, typename _Duration>
        bool
        wait_until(const chrono::time_point<_Clock, _Duration>& __abs)
        {
	  unique_lock<mutex> __lock(_M_mutex);
	  auto __bound = std::bind(&_State::_M_ready, this);
	  return _M_ready() || _M_cond.wait_until(__lock, __abs, __bound);
	}

      void
      _M_set_result(_Ptr_type __res)
      {
	{
	  lock_guard<mutex> __lock(_M_mutex);
	  if (_M_ready())
	    __throw_future_error(int(future_errc::promise_already_satisfied));
	  _M_result.swap(__res);
	}
	_M_cond.notify_all();
      }

      void
      _M_break_promise(_Ptr_type __res)
      {
	if (static_cast<bool>(__res))
	  {
	    future_errc __ec(future_errc::broken_promise); // XXX
	    __res->_M_error = copy_exception(future_error(__ec));
	    {
	      lock_guard<mutex> __lock(_M_mutex);
	      _M_result.swap(__res);
	    }
	    _M_cond.notify_all();
	  }
      }

      // Called when this object is passed to a unique_future.
      void
      _M_set_retrieved_flag()
      {
	if (_M_retrieved.test_and_set())
	  __throw_future_error(int(future_errc::future_already_retrieved));
      }

    private:
      _Result_base*
      _M_get()
      {
	lock_guard<mutex> __lock(_M_mutex);
	return _M_result.get();
      }

      bool _M_ready() const { return static_cast<bool>(_M_result); }
    };
  };

  inline __future_base::_Result_base::~_Result_base() = default;

  /// Partial specialization for reference types.
  template<typename _Res>
    struct __future_base::_Result<_Res&> : __future_base::_Result_base
    {
      _Result() : _M_value_ptr() { }

      _Res* 			_M_value_ptr;
      
    private:
      void _M_destroy() { delete this; }
    };

  /// Explicit specialization for void.
  template<>
    struct __future_base::_Result<void> : __future_base::_Result_base
    {
    private:
      void _M_destroy() { delete this; }
    };


  /// Common implementation for unique_future and shared_future.
  template<typename _Res>
    class __basic_future : public __future_base
    {
    protected:
      typedef shared_ptr<_State>		__state_type;
      typedef __future_base::_Result<_Res>&	__result_type;

    private:
      __state_type 		_M_state;

    public:
      // Disable copying.
      __basic_future(const __basic_future&) = delete;
      __basic_future& operator=(const __basic_future&) = delete;

      // Functions to check state and wait for ready.
      bool 
      is_ready() const { return this->_M_state->is_ready(); }

      bool 
      has_exception() const { return this->_M_state->has_exception(); }

      bool 
      has_value() const { return this->_M_state->has_value(); }

      void 
      wait() const { this->_M_state->wait(); }

      template<typename _Rep, typename _Period>
        bool
        wait_for(const chrono::duration<_Rep, _Period>& __rel) const
        { return this->_M_state->wait_for(__rel); }

      template<typename _Clock, typename _Duration>
        bool
        wait_until(const chrono::time_point<_Clock, _Duration>& __abs) const
        { return this->_M_state->wait_until(__abs); }

    protected:
      /// Wait for the state to be ready and rethrow any stored exception
      __result_type
      _M_get_result()
      {
        _Result_base& __res = this->_M_state->wait();
        if (!(__res._M_error == 0))
          rethrow_exception(__res._M_error);
        return static_cast<__result_type>(__res);
      }

      // Construction of a unique_future by promise::get_future()
      explicit
      __basic_future(const __state_type& __state) : _M_state(__state)
      {
        if (static_cast<bool>(this->_M_state))
          this->_M_state->_M_set_retrieved_flag();
        else
          __throw_future_error(int(future_errc::future_already_retrieved));
      }

      // Copy construction from a shared_future
      explicit
      __basic_future(const shared_future<_Res>&);

      // Move construction from a unique_future
      explicit
      __basic_future(unique_future<_Res>&&);
    };


  /// Primary template for unique_future.
  template<typename _Res>
    class unique_future : public __basic_future<_Res>
    {
      friend class promise<_Res>;

      typedef __basic_future<_Res> _Base_type;
      typedef typename _Base_type::__state_type __state_type;
      typedef __future_base::_Move_result<_Res> _Mover;

      explicit
      unique_future(const __state_type& __state) : _Base_type(__state) { }

    public:
      /// Move constructor
      unique_future(unique_future&& __uf) : _Base_type(std::move(__uf)) { }

      // Disable copying
      unique_future(const unique_future&) = delete;
      unique_future& operator=(const unique_future&) = delete;

      /// Retrieving the value
      typename _Mover::__rval_type
      get()
      { return _Mover::_S_move(this->_M_get_result()._M_value()); }
    };
 
  /// Partial specialization for unique_future<R&>
  template<typename _Res>
    class unique_future<_Res&> : public __basic_future<_Res&>
    {
      friend class promise<_Res&>;

      typedef __basic_future<_Res&> _Base_type;
      typedef typename _Base_type::__state_type __state_type;

      explicit
      unique_future(const __state_type& __state) : _Base_type(__state) { }

    public:
      /// Move constructor
      unique_future(unique_future&& __uf) : _Base_type(std::move(__uf)) { }

      // Disable copying
      unique_future(const unique_future&) = delete;
      unique_future& operator=(const unique_future&) = delete;

      /// Retrieving the value
      _Res& 
      get() { return *this->_M_get_result()._M_value_ptr; }
    };

  /// Explicit specialization for unique_future<void>
  template<>
    class unique_future<void> : public __basic_future<void>
    {
      friend class promise<void>;

      typedef __basic_future<void> _Base_type;
      typedef typename _Base_type::__state_type __state_type;

      explicit
      unique_future(const __state_type& __state) : _Base_type(__state) { }

    public:
      /// Move constructor
      unique_future(unique_future&& __uf) : _Base_type(std::move(__uf)) { }

      // Disable copying
      unique_future(const unique_future&) = delete;
      unique_future& operator=(const unique_future&) = delete;

      /// Retrieving the value
      void 
      get() { this->_M_get_result(); }
    };


  /// Primary template for shared_future.
  template<typename _Res>
    class shared_future : public __basic_future<_Res>
    {
      typedef __basic_future<_Res> _Base_type;

    public:
      /// Copy constructor
      shared_future(const shared_future& __sf) : _Base_type(__sf) { }

      /// Construct from a unique_future rvalue
      shared_future(unique_future<_Res>&& __uf)
      : _Base_type(std::move(__uf))
      { }

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

      /// Retrieving the value
      const _Res&
      get()
      { 
	typename _Base_type::__result_type __r = this->_M_get_result();
	_Res& __rs(__r._M_value());
	return __rs;
      }
    };
 
  /// Partial specialization for shared_future<R&>
  template<typename _Res>
    class shared_future<_Res&> : public __basic_future<_Res&>
    {
      typedef __basic_future<_Res&>           _Base_type;

    public:
      /// Copy constructor
      shared_future(const shared_future& __sf) : _Base_type(__sf) { }

      /// Construct from a unique_future rvalue
      shared_future(unique_future<_Res&>&& __uf)
      : _Base_type(std::move(__uf))
      { }

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

      /// Retrieving the value
      _Res& 
      get() { return *this->_M_get_result()._M_value_ptr; }
    };

  /// Explicit specialization for shared_future<void>
  template<>
    class shared_future<void> : public __basic_future<void>
    {
      typedef __basic_future<void> _Base_type;

    public:
      /// Copy constructor
      shared_future(const shared_future& __sf) : _Base_type(__sf) { }

      /// Construct from a unique_future rvalue
      shared_future(unique_future<void>&& __uf)
      : _Base_type(std::move(__uf))
      { }

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

      // Retrieving the value
      void 
      get() { this->_M_get_result(); }
    };

  // Now we can define the protected __basic_future constructors.
  template<typename _Res>
    __basic_future<_Res>::__basic_future(const shared_future<_Res>& __sf)
    : _M_state(__sf._M_state)
    { }

  template<typename _Res>
    __basic_future<_Res>::__basic_future(unique_future<_Res>&& __uf)
    : _M_state(std::move(__uf._M_state))
    { }


  /// Primary template for promise
  template<typename _Res>
    class promise
    {
      template<typename> friend class packaged_task;

      typedef __future_base::_State 		_State;
      typedef __future_base::_Move_result<_Res>	_Mover;
      typedef __future_base::_Result<_Res>	result_type;
      
      shared_ptr<_State>                        _M_future;
      typename __future_base::_Ptr<result_type>::type	_M_storage;

    public:
      promise()
      : _M_future(std::make_shared<_State>()), _M_storage(new result_type())
      { }

      promise(promise&& __rhs)
      : _M_future(std::move(__rhs._M_future)),
      _M_storage(std::move(__rhs._M_storage))
      { }

      // TODO: requires allocator concepts
      /*
      template<typename _Allocator>
        promise(allocator_arg_t, const _Allocator& __a);

      template<typename _Allocator>
        promise(allocator_arg_t, const _Allocator&, promise&& __rhs);
       */

      promise(const promise&) = delete;

      ~promise()
      {
        if (static_cast<bool>(_M_future) && !_M_future.unique())
          _M_future->_M_break_promise(std::move(_M_storage));
      }

      // Assignment
      promise&
      operator=(promise&& __rhs)
      {
        promise(std::move(__rhs)).swap(*this);
        return *this;
      }

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

      void
      swap(promise& __rhs)
      {
        _M_future.swap(__rhs._M_future);
        _M_storage.swap(__rhs._M_storage);
      }

      // Retrieving the result
      unique_future<_Res>
      get_future()
      { return unique_future<_Res>(_M_future); }

      // Setting the result
      void
      set_value(const _Res& __r)
      {
        if (!_M_satisfied())
          _M_storage->_M_set(__r);
        _M_future->_M_set_result(std::move(_M_storage));
      }

      void
      set_value(_Res&& __r)
      {
        if (!_M_satisfied())
          _M_storage->_M_set(_Mover::_S_move(__r));
        _M_future->_M_set_result(std::move(_M_storage));
      }

      void
      set_exception(exception_ptr __p)
      {
        if (!_M_satisfied())
          _M_storage->_M_error = __p;
        _M_future->_M_set_result(std::move(_M_storage));
      }

    private:
      bool _M_satisfied() { return !static_cast<bool>(_M_storage); }
    };

  /// Partial specialization for promise<R&>
  template<typename _Res>
    class promise<_Res&>
    {
      template<typename> friend class packaged_task;
      typedef __future_base::_State 		_State;
 
      typedef __future_base::_Result<_Res&> result_type;

      shared_ptr<_State>                        _M_future;
      typename __future_base::_Ptr<result_type>::type  _M_storage;

    public:
      promise()
      : _M_future(std::make_shared<_State>()), _M_storage(new result_type())
      { }

      promise(promise&& __rhs)
      : _M_future(std::move(__rhs._M_future)), 
	_M_storage(std::move(__rhs._M_storage))
      { }

      // TODO: requires allocator concepts
      /*
      template<typename _Allocator>
        promise(allocator_arg_t, const _Allocator& __a);

      template<typename _Allocator>
        promise(allocator_arg_t, const _Allocator&, promise&& __rhs);
       */

      promise(const promise&) = delete;

      ~promise()
      {
        if (static_cast<bool>(_M_future) && !_M_future.unique())
          _M_future->_M_break_promise(std::move(_M_storage));
      }

      // Assignment
      promise&
      operator=(promise&& __rhs)
      {
        promise(std::move(__rhs)).swap(*this);
        return *this;
      }

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

      void
      swap(promise& __rhs)
      {
        _M_future.swap(__rhs._M_future);
        _M_storage.swap(__rhs._M_storage);
      }

      // Retrieving the result
      unique_future<_Res&>
      get_future()
      { return unique_future<_Res&>(_M_future); }

      // Setting the result
      void
      set_value(_Res& __r)
      {
        if (!_M_satisfied())
          _M_storage->_M_value_ptr = &__r;
        _M_future->_M_set_result(std::move(_M_storage));
      }

      void
      set_exception(exception_ptr __p)
      {
        if (!_M_satisfied())
          _M_storage->_M_error = __p;
        _M_future->_M_set_result(std::move(_M_storage));
      }

    private:
      bool _M_satisfied() { return !static_cast<bool>(_M_storage); }
    };

  /// Explicit specialization for promise<void>
  template<>
    class promise<void>
    {
      template<typename> friend class packaged_task;
      typedef __future_base::_State 		_State;
      typedef __future_base::_Result<void>	result_type;

      shared_ptr<__future_base::_State>                 _M_future;
      typename __future_base::_Ptr<result_type>::type   _M_storage;

    public:
      promise()
      : _M_future(std::make_shared<_State>()),
	_M_storage(new result_type())
      { }

      promise(promise&& __rhs)
      : _M_future(std::move(__rhs._M_future)),
      _M_storage(std::move(__rhs._M_storage))
      { }

      // TODO: requires allocator concepts
      /*
      template<typename _Allocator>
        promise(allocator_arg_t, const _Allocator& __a);

      template<typename _Allocator>
        promise(allocator_arg_t, const _Allocator&, promise&& __rhs);
       */

      promise(const promise&) = delete;

      ~promise()
      {
        if (static_cast<bool>(_M_future) && !_M_future.unique())
          _M_future->_M_break_promise(std::move(_M_storage));
      }

      // Assignment
      promise&
      operator=(promise&& __rhs)
      {
        promise(std::move(__rhs)).swap(*this);
        return *this;
      }

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

      void
      swap(promise& __rhs)
      {
        _M_future.swap(__rhs._M_future);
        _M_storage.swap(__rhs._M_storage);
      }

      // Retrieving the result
      unique_future<void>
      get_future()
      { return unique_future<void>(_M_future); }

      // Setting the result
      void
      set_value()
      {
        _M_future->_M_set_result(std::move(_M_storage));
      }

      void
      set_exception(exception_ptr __p)
      {
        if (!_M_satisfied())
          _M_storage->_M_error = __p;
        _M_future->_M_set_result(std::move(_M_storage));
      }

    private:
      bool _M_satisfied() { return !static_cast<bool>(_M_storage); }
    };

  // TODO: requires allocator concepts
  /*
  template<typename _Res, class Alloc>
    concept_map UsesAllocator<promise<_Res>, Alloc>
    {
      typedef Alloc allocator_type;
    }
   */
  /// Primary template.
  template<typename _Res, typename... _ArgTypes>
    struct _Run_task
    {
      static void
      _S_run(promise<_Res>& __p, function<_Res(_ArgTypes...)>& __f,
	     _ArgTypes... __args)
      {
        __p.set_value(__f(std::forward<_ArgTypes>(__args)...));
      }
    };

  /// Specialization used by packaged_task<void(...)>
  template<typename... _ArgTypes>
    struct _Run_task<void, _ArgTypes...>
    {
      static void
      _S_run(promise<void>& __p, function<void(_ArgTypes...)>& __f,
	     _ArgTypes... __args)
      {
        __f(std::forward<_ArgTypes>(__args)...);
        __p.set_value();
      }
    };


  /// packaged_task
  template<typename _Res, typename... _ArgTypes>
    class packaged_task<_Res(_ArgTypes...)>
    {
      function<_Res(_ArgTypes...)>   _M_task;
      promise<_Res>                  _M_promise;

    public:
      typedef _Res result_type;

      // Construction and destruction
      packaged_task() { }

      template<typename _Fn>
        explicit
        packaged_task(const _Fn& __fn) : _M_task(__fn) { }

      template<typename _Fn>
        explicit
        packaged_task(_Fn&& __fn) : _M_task(std::move(__fn)) { }

      explicit
      packaged_task(_Res(*__fn)(_ArgTypes...)) : _M_task(__fn) { }

      // TODO: requires allocator concepts
      /*
      template<typename _Fn, typename _Allocator>
        explicit
        packaged_task(allocator_arg_t __tag, const _Allocator& __a, _Fn __fn)
        : _M_task(__tag, __a, __fn), _M_promise(__tag, __a)
        { }

      template<typename _Fn, typename _Allocator>
        explicit
        packaged_task(allocator_arg_t __tag, const _Allocator& __a, _Fn&& __fn)
        : _M_task(__tag, __a, std::move(__fn)), _M_promise(__tag, __a)
        { }
       */

      ~packaged_task() = default;

      // No copy
      packaged_task(packaged_task&) = delete;
      packaged_task& operator=(packaged_task&) = delete;

      // Move support
      packaged_task(packaged_task&& __other)
      { this->swap(__other); }

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

      void
      swap(packaged_task& __other)
      {
        _M_task.swap(__other._M_task);
        _M_promise.swap(__other._M_promise);
      }

      explicit operator bool() const { return static_cast<bool>(_M_task); }

      // Result retrieval
      unique_future<_Res>
      get_future()
      {
        __try
        {
          return _M_promise.get_future();
        }
        __catch (const future_error& __e)
        {
#ifdef __EXCEPTIONS
          if (__e.code() == future_errc::future_already_retrieved)
	    throw std::bad_function_call();
	  throw;
#endif
        }
      }

      // Execution
      void
      operator()(_ArgTypes... __args)
      {
        if (!static_cast<bool>(_M_task) || _M_promise._M_satisfied())
	  {
#ifdef __EXCEPTIONS
	    throw std::bad_function_call();
#else
	    __builtin_abort();
#endif
	  }

        __try
        {
          _Run_task<_Res, _ArgTypes...>::_S_run(_M_promise, _M_task,
              std::forward<_ArgTypes>(__args)...);
        }
        __catch (...)
        {
          _M_promise.set_exception(current_exception());
        }
      }

      void reset() { promise<_Res>().swap(_M_promise); }
    };

#endif // _GLIBCXX_HAS_GTHREADS && _GLIBCXX_USE_C99_STDINT_TR1
       // && _GLIBCXX_ATOMIC_BUILTINS_4

  // @} group futures
}

#endif // __GXX_EXPERIMENTAL_CXX0X__

#endif // _GLIBCXX_FUTURE