Std future get

std::future::valid Returns whether the future object is currently associated with a shared state. For default-constructed future objects, this function returns false (unless move-assigned a valid future ).

To wait for a thread use the std::thread::join() function . This function makes the current thread wait until the thread identified by *this has finished executing.

– The promise object is the asynchronous provider and is expected to set a value for the shared state at some point. – The future object is an asynchronous return object that can retrieve the value of the shared state, waiting for it to be ready, if necessary.

On reaching the end of main , the std::future<int> object held in result is destroyed , which will wait for the task to finish, and then discard the result, cleaning up any resources used.

The returned std::future<> blocks on destruction until the value is available . However the normal destructor of std::future<> does not block: ~future();

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.

get() is not blocking .