Can a process waiting for a spin lock be indefinitely postponed even if all processes guarantee to leave their critical sections after a finite amount of time?Aprocess waiting for a sleep/wakeup lock? If you answered yes, suggest a way to prevent indefinite postponement.

Question

What will be an ideal response?

Answer 1

Yes, a process waiting for a spin lock can be indefinitely postponed. If, each time the
lock becomes available, another process grabs the lock first, the process will never enter its
critical section.One way around this is to maintain a FIFO queue of processes waiting for the
spin lock; a releasing process hands the lock to the first process in the queue. Processes still
spin to minimize reaction time to the lock’s availability.Aprocess waiting for a sleep/wakeup
lock also can be indefinitely postponed. This occurs if higher-priority processes continue to
wait for the lock, preventing a lower-priority process from ever entering its critical section.
One way to combat this is to periodically boost a process’s priority if it has been waiting for a
long time. Eventually, it will attain the highest priority and be guaranteed to enter its critical
section (assuming priority ties are broken by length of wait).