stdpromiseT

stdpromiseT is a C++ template class defined in the <future> header, part of the C++ Standard Library. It represents a future result of an asynchronous operation. A stdpromiseT object is associated with a stdfutureT object. The stdpromiseT is used by the producer of the asynchronous operation to set the value or exception that the associated stdfutureT will eventually hold. The stdfutureT, conversely, is used by the consumer to retrieve this value or exception when it becomes available.

The primary purpose of stdpromiseT is to provide a mechanism for transferring a value or an exception from one thread to another. When a task is executed asynchronously, the thread performing the task can obtain a stdpromiseT object. It then uses methods like set_value() or set_exception() to signal the completion of the task and provide the result. The thread waiting for the result can use the corresponding stdfutureT object, which was obtained from the stdpromiseT using std::async or std::packaged_task, to retrieve this result.

This separation of concerns between the producer (stdpromiseT) and the consumer (stdfutureT) allows for flexible asynchronous programming. It enables scenarios such as deferred computation, where a result is computed in the background and retrieved later, or the implementation of complex concurrency patterns. The template parameter of stdpromiseT specifies the type of the value that will be eventually stored.