The code above might look ugly, but all you have to understand is that the FutureBuilder widget takes two arguments: future and builder, future is just the future you want to use, while builder is a function that takes two parameters and returns a widget. FutureBuilder will run this function before and after the future completes.
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::future.
These actions will not block for the shared state to become ready, except that they may block if all following conditions are satisfied: The shared state was created by a call to std::async. The shared state is not yet ready. The current object was the last reference to the shared state. (since C++14)
C++ includes built-in support for threads, atomic operations, mutual exclusion, condition variables, and futures.
The class template std::packaged_task wraps any Callable target (function, lambda expression, bind expression, or another function object) so that it can be invoked asynchronously. Its return value or exception thrown is stored in a shared state which can be accessed through std::future objects.
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.
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 ...
The scoped enumeration std::future_errc defines the error codes reported by std::future and related classes in std::future_error exception objects. Only four error codes are required, although the implementation may define additional error codes.
The U.S. Postal Service (USPS) is opening a bidding process for retailers, brands and logistics companies to gain access to its last-mile delivery network, offering them same-day or next-day delivery.
Yet, as with any new mode of transport, the value of UAVs depends on how well they integrate into the broader logistics ecosystem. In New York City, the potential is already on display. Consider the ...