Question

We discussed the use of spin-locks and semaphores for achieving mutual exclusion. Semaphores are designed to avoid busy waiting and provide fairness.

(a) Is it always desirable to use semaphores rather than spin-locks? To answer, address the overhead incurred in each approach.

(b) Discuss the situations in which each one is preferred.

Answer 1

(a) Spinlocks are abstract data types, or classes, that support a Busy-Wait solution for the Mutual Exclusion Problem. The operations on spinlocks are InitLock, Lock, and unlock.

A semaphore is a variable or abstract data type used to control access to a common resource by multiple processes in a concurrent system such as a multitasking operating system. Spinlocks are only valid within one process whereas semaphores can be used to synchronize between different precesses.

(b).The SpinLock is held for a very short period of time. SpinLocks are usually preferred in symmetric multiprocessor systems to constantly poll for availability of a resource in lieu of context switches.

   A semaphore is simply a variable. This variable is used to solve critical section problems and to achieve process synchronization in the multi processing environment.Semaphores are used when you need wait()- signal()type of semantics.