Future Grace Revised Edition The Purifying Power

The class template std::future provides a mechanism to access the result of asynchronous operations: An asynchronous operation (performed 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 ...

If the future is the result of a call to std::async that used lazy evaluation, this function returns immediately without waiting. This function may block for longer than timeout_duration due to scheduling or resource contention delays. The standard recommends that a steady clock is used to measure the duration.

Checks if the future refers to a shared state. 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 ...

A std::future is a handle to a result of work which is [potentially] not, yet, computed. You can imagine it as the receipt you get when you ask for work and the receipt is used to get the result back. For example, you may bring a bike to bike store for repair. You get a receipt to get back your bike. While the work is in progress (the bike being repaired) you can go about other business ...

Transfers the shared state of *this, if any, to a std::shared_future object. Multiple std::shared_future objects may reference the same shared state, which is not possible with std::future. After calling share on a std::future, valid() == false.