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The following Preemption Matrix shows the possibilities of entities and downtimes preempting each other in the use of a resource. "Current" refers to the entity or downtime in possession of the resource when the requesting entity or downtime attempts to capture it. Downtimes below refer to clock and usage-based downtimes only.
Priority values are divided into ten levels (0 to 99, 100 to 199,..., 900-999), with values beyond 99 used for preempting entities or downtimes of a lower priority level.
|
|
To Preempt The Current Owner |
To Preempt The Current Downtime |
|
Requesting Entity or Another Resource or Location’s Downtime |
1 priority level higher |
2 priority levels higher |
|
Requesting Downtime
|
1 priority level higher |
1 priority level higher |
• The upper-left quadrant shows that if an entity tries to seize a resource currently owned by another entity (or another resource’s or a location’s downtime), the entity must have a priority at least one level higher than the current entity to preempt the resource.
• The lower-left quadrant shows that a downtime must have a priority at least one level higher than the entity currently owning a resource if the resource is to be preempted.
• The upper-right quadrant shows that an entity must have a priority at least 2 levels higher than the current downtime priority to preempt a downed resource.
• The lower-right quadrant shows that a preempting downtime must have a priority at least one level higher than the current downtime to preempt it.
The following graphics demonstrate basic preemption concepts.
