The Waking Mechanism

Suspended goals are woken by submitting at least one of the suspension lists in which they occur to the waking scheduler. The waking scheduler which maintains a global priority queue inserts them into this queue according to their priority (see figure 17.1).

A suspension list can be passed to the scheduler by either of the predicates schedule_suspensions/1 or schedule_suspensions/2. A suspension which has been scheduled in this way and awaits its execution is called a scheduled suspension.

Note, however, that scheduling a suspension by means of schedule_suspensions/1 or schedule_suspensions/2 alone does not implicitly start the waking scheduler. Instead, execution continues normally with the next goal in sequence after schedule_suspensions/1,2. The scheduler must be explicitly invoked by calling wake/0. Only then it starts to execute the woken suspensions.

The reason for having wake/0 is to be able to schedule several suspension lists before the priority-driven execution begins ^17.1.