Asynchronous methods and progress reporting is achieved using threads and events. The pattern is to return a token from a synchronous method invocation which spawns a thread to do work asynchronously. This worker thread is then responsible for providing notifications to interested parties events.
Example:
An interface has a method which returns a Task object. The method is called installpkg and takes one argument, the name of the package to install.
Task installpkg(string pkgname);
The Task instance returned by the method, contains enough information to identify a task. Prior to invoking installpkg, the client subscribes to a task-update event. The worker thread is responsible for issuing events about the progress of the work. These events contain information about the progress of the task.
In a minimal implementation, the worker thread would issue one event to notify the client that the task was complete and what the outcome of the task was. A more complex implementation would provide multiple events documenting progress and possibly also provide an additional method that a client could invoke to interrogate the server for a progress report.