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 ...
The get member function waits (by calling wait ()) until the shared state is ready, then retrieves the value stored in the shared state (if any). Right after calling this function, valid () is false. If valid () is false before the call to this function, the behavior is undefined.
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 future represents the result of an asynchronous operation, and can have two states: uncompleted or completed. Most likely, as you aren't doing this just for fun, you actually need the results of that Future<T> to progress in your application. You need to display the number from the database or the list of movies found.
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.
To opt-in to the future behavior, set `pd.set_option('future.no_silent_downcasting', True)` 0 1 1 0 2 2 3 1 dtype: int64 If I understand the warning correctly, the object dtype is "downcast" to int64. Perhaps pandas wants me to do this explicitly, but I don't see how I could downcast a string to a numerical type before the replacement happens.
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 ...
In summary: std::future is an object used in multithreaded programming to receive data or an exception from a different thread; it is one end of a single-use, one-way communication channel between two threads, std::promise object being the other end.
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. 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.
impl<F> Future for Box<F> where F: Unpin + Future + ?Sized, Boxed futures only implement the Future trait when the future inside the Box implements Unpin. Since your function doesn't guarantee that the returned future implements Unpin, your return value will be considered to not implement Future. You'll not able to await it because your type is basically not a Future. The solution from ...
