1. A method performed by a scheduler of a process executing on a computer system, the method comprising: providing a first processing resource of the scheduler for use by a first execution context such that the first processing resource is not under control of the scheduler, the first execution context is external to the scheduler and is created and controlled by the process; registering for a notification of an exit event associated with the first external context; and regaining control of the first processing resource in response to receiving the notification of the exit event.