stdsharedfutureT

stdsharedfutureT is a C++ template class defined in the `<future>` header that represents a shared asynchronous state. It is a type of `future` that can be retrieved by multiple threads concurrently. Unlike a regular `std::future`, which can only be retrieved once, a `std::shared_future` can be accessed multiple times, allowing several threads to wait for the same asynchronous operation to complete and retrieve its result.

The shared state is set by a `std::promise` or `std::packaged_task`. When the promise is fulfilled or the task is executed, the shared state is updated with the result or an exception. All `std::shared_future` objects associated with that shared state will then become ready.

To obtain a `std::shared_future`, one typically calls the `.share()` method on a `std::future` object. This creates a new `std::shared_future` that references the same underlying shared state. The original `std::future` remains valid, but subsequent calls to `.get()` on it would invalidate it.

Key operations on `std::shared_futureT` include `.get()`, which retrieves the result or exception from the shared state. If the shared state is not yet ready, `.get()` will block until it becomes ready. It is important to note that calling `.get()` on a `std::shared_future` does not invalidate it, allowing for repeated retrieval of the result. Another useful member function is `.wait()`, which blocks until the shared state becomes ready.