Liveness deadlock and priority inheritance

Liveness

Processes may have to wait indefinitely while trying to acquire a shared resource.

Liveness refers to a set of properties that the system must satisfy to ensure processes make progress.

Deadlock

A deadlock occurs when two or more processes are indefinitely waiting for an event that can only be caused by one of the other waiting processes.

Let P0 be:

wait(S)
wait(Q)
signal(S)
signal(Q)

and P1:

wait(Q)
wait(S)
signal(Q)
signal(S)

If P0 executes wait(S) and P1 executes wait(Q), the signal calls are never reached because the processes are mutually waiting for a resource held by the other.

Priority inheritance

This is a scheduling problem that arises when a resource is shared between low and high-priority processes.

If a low-priority process locks the resource but is then not run, higher-priority processes get stuck waiting for that low-priority process to complete.

In this case, processes with high priority are restricted to inherit the priority of the process holding the resource.