future game systems - Generation Z Gadgets
The class template std::future provides a mechanism to access the result of asynchronous operations: An asynchronous operation (created via std::async, std::packaged_task, or std::promise) can provide a std::future object to the creator of that asynchronous operation. The creator of the asynchronous operation can then use a variety of methods to query, wait for, or extract a value from the std ... Checks if the future refers to a shared state.
Understanding the Context
This is the case only for futures that were not default-constructed or moved from (i.e. returned by std::promise::get_future (), std::packaged_task::get_future () or std::async ()) until the first time get () or share () is called. The behavior is undefined if any member function other than the destructor, the move-assignment operator, or valid is ... Unlike std::future, which is only moveable (so only one instance can refer to any particular asynchronous result), std::shared_future is copyable and multiple shared future objects may refer to the same shared state.
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Key Insights
Access to the same shared state from multiple threads is safe if each thread does it through its own copy of a shared_future object. Future<String> someLongComputation() async { ... } above, someLongComputation will immediately return a future, and after some time, said future will resolve with a string. What the await keyword does is wait until the future has returned a value and then returns said value, basically turning an asynchronous computation into a synchronous one, of course this would negate the whole point of ... future (const future &) = delete; ~future (); future & operator =(const future &) = delete; future & operator =(future &&) noexcept; shared_future <R> share () noexcept; // retrieving the value /* see description */ get (); // functions to check state bool valid () const noexcept; void wait () const; template<class Rep, class Period> 2) Move constructor.
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Constructs a std::future with the shared state of other using move semantics. After construction, other.valid() == false. wait_until waits for a result to become available. It blocks until specified timeout_time has been reached or the result becomes available, whichever comes first. The return value indicates why wait_until returned. If the future is the result of a call to async that used lazy evaluation, this function returns immediately without waiting.
The behavior is undefined if valid () is false before ... Specifies state of a future as returned by wait_for and wait_until functions of std::future and std::shared_future. Constants