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What is priority inversion?


Priority inversion is a situation where in lower priority
tasks will run blocking higher priority tasks waiting for
resource (mutex). For ex: consider 3 tasks. A, B and C, A
being highest priority task and C is lowest. Look at
sequence of context swaps

A goes for I/O . unlocks mutex.
C was ready to run. So C starts running. locks mutex
B is ready to run. Swaps out C and takes mutex.
A is ready to run. but A is blocked as mutex is locked by B.
but B will never relinqishes the mutex as its higher
priority than C.

The solution to priority inversion is Priority inheritance.

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