Basic program structures for avoiding priority inversions

Structuring real-time concurrent programs in the form of groups of fixed-priority processes is an old art which is appropriate for only a small fraction of modem real-time distributed computing application systems. However, it is still practiced on the basis of an insufficient technical foundation. One of the basic issues in using the fixed-priority process structuring approach is to avoid the priority inversion phenomenon. It is argued that priority inversions are essentially due to the inappropriate approach used for structuring programs including the specification of the policy for allocating resources. Several basic program structuring techniques which are effective means of avoiding priority inversions are presented.