meaning of priority interrupt

1. priority interrupt [hardware] Describes any stimulus compelling enough to yank one right out of hack mode. Classically used to describe being dragged away by an SO for immediate sex, but may also refer to more mundane interruptions such as a fire alarm going off in the near vicinity. Also called an NMI non-maskable interrupt, especially in PC-land. [Jargon File] priority inversion The state of a concurrent system where a high priority task is waiting for a low priority task which is waiting for a medium priority task. The system may become unstable and crash under these circumstances. In an operating system that uses multiple tasks, each task or context may be given a priority. These priorities help the scheduler decide which task to run next. Consider tasks, L, M, and H, with priorities Low, Medium, and High. M is running and H is blocked waiting for some resource that is held by L. So long as any task with a priority higher than L is runable, it will prevent task L, and thus task H, from running. Priority inversion is generally considered either as a high-level design failure or an implementation issue to be taken into account depending on who is talking. Most operating systems have methods in place to prevent or take inversion into account. Priority inheritance is one method. The most public instance of priority inversion is the repeated fail-safe rebooting of the Mars Pathfinder http://research. microsoft. com/~mbj/Mars_Pathfinder/Mars_Pathf base station Sagan Memorial Station.

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