Operating System MCQs

Circular wait forms a closed chain of resource dependencies among processes.
Breaking the possibility of such a cycle prevents deadlock.

Resource-allocation graphs conventionally represent processes as circles.
Resource types are shown separately, commonly as rectangles containing instances.

Resource ordering prevents a cycle because all philosophers request forks according to one consistent order.
Without a cycle in resource requests, circular wait cannot occur.

The sleeping-barber problem represents customers arriving, waiting when seats exist, or leaving when full.
The barber sleeps when no customer is present and must be awakened safely.

A barrier synchronizes phases by holding early arrivals until the complete group reaches the same point.
A reusable barrier resets so the group can synchronize again in later phases.

The empty semaphore prevents a producer from inserting when no free slot remains.
It is decremented before insertion and incremented after a consumer removes an item.

The full semaphore prevents a consumer from removing an item when the buffer is empty.
A producer increments it after placing a new item in the buffer.

The first readers-writers formulation favors readers when no writer is currently active.
Multiple readers may enter together, which can delay waiting writers.

A continuous arrival of readers can repeatedly postpone a waiting writer.
Fair or writer-priority policies are used when bounded waiting for writers is required.

The simultaneous left-fork acquisition creates hold-and-wait and circular-wait conditions.
No philosopher can obtain the second fork, so none releases the first.

A binary semaphore uses two logical states and can provide mutual exclusion or event signaling.
A counting semaphore represents multiple available units of a resource.

A counting semaphore maintains a nonnegative count corresponding to available resource instances.
Each acquisition decrements the count, and each release increments it.