priority inheritance

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.

   (2005-02-11)