priority inheritance


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priority inheritance

(parallel)
A technique for avoiding priority inversion by temporarily raising the prioriry of all processes that want to access a shared resource to the highest priority level of any of them. Priority inversion occurs where a low priority process, L is holding a resource required by a high priority process, H, but L is not running because a medium priority process, M is running. Under priority inheritance, L temporarily inherits H's priority, allowing L to run and release the resource H is waiting for.

For example, an ambulance (H) is stuck behind a lorry (L) waiting at a junction (the shared resource) for a gap in a line of cars (M) using the junction. Applying priority inheritance, the cars give way to the lorry as they would to the ambulance, thus allowing the lorry and then the ambulance to use the junction.
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References in periodicals archive ?
The Priority Inheritance Protocol requires a check of the more strong condition (relative to SP and PIP) when task [[tau].sub.i] requests a resource g: if a resource g with pc(g) [greater than or equal to] prio([[tau].sub.i]) is occupied by [[tau].sub.j] (j is not equal to i) then task [[tau].sub.i] is converted into the waiting state until all resources g with such high priority ceiling will be released.
--SEM_PRTYINHERIT: If it is set, the RT-kernel applies the Basic Priority Inheritance Protocol to RT-Semaphore operations.
Star/OS supports priority inheritance in situations such as Ada rendezvous.
ThreadX also brings round-robin scheduling, Preemption-Threshold Scheduling[TM], priority inheritance, event-chaining, event-trace, run-time stack analysis, and completely deterministic processing.
There is significant innovation around real-time functionality in the open source community in which Novell is participating, including, among other things, work on kernel locking optimizations (to reduce busy wait), priority inheritance, execution of interrupts in kernel threads with definable priority and high resolution timers that improve synchronization and process accounting.

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