Waits Until

Abstract

In the models we have examined so far, we have been able to express the action histories of entities as sequences of activities, usually of the form

• acquire R1; acquire R2; ... acquire Rn;

• HOLD(activity duration);... release R’m;

• release R’1; release R’2 ... release R’m;

where the extra resources required (R1, R2, ..., Rn), be they modelled as RES, BIN or ENTITY objects, have been requested and acquired one at a time. In this chapter, we consider some models in which this is not possible. For example, an entity may not be able to start its next activity unless ALL the resources required for its commencement are available; or it may need to wait and see which resources turn up next before deciding what it should do. Such complications arise all the time in real life simulations. We now give several short, but illustrative, examples.