Which one of the following is not a condition for a process to transition from…
2021
Which one of the following is not a condition for a process to transition from the running state to the wait (blocked) state?
- A.
If a process requests an Input/Output operation
- B.
If a higher priority process arrived
- C.
If a lower priority process arrived
- D.
If a process waits for some action performed by another process
Attempted by 414 students.
Show answer & explanation
Correct answer: C
Concept
A process leaves the running state only for one of two reasons. It moves to blocked / wait when it voluntarily gives up the CPU because it cannot proceed until some external event finishes — it is waiting for something. It instead moves to ready when it is forced off the CPU by the scheduler even though it could still run, for example through preemption. A running-to-wait transition therefore requires that the process itself becomes unable to continue and must await an event.
Applying the rule to each event
Requesting an I/O operation: the process cannot continue until the I/O completes, so it gives up the CPU and waits. This is a genuine running-to-wait cause.
Waiting for an action performed by another process (a signal, a semaphore, a released resource, an IPC reply): the process is blocked on that event, so it moves to wait. This is also a genuine running-to-wait cause.
A higher-priority process arriving: under preemptive scheduling this forces the running process off the CPU, but the process is still able to run — it is sent to ready, not to wait. So it is a running-to-ready event, not running-to-wait.
A lower-priority process arriving: a lower-priority process cannot preempt the one already running, and the running process is waiting for nothing, so it simply keeps executing. No state change happens at all.
Choosing the single intended answer
Strictly, neither “higher-priority arrival” nor “lower-priority arrival” produces a running-to-wait transition, so both are “not a condition” for it. The two differ, though, in what they do: a higher-priority arrival is still a real state change of the running process (running-to-ready), whereas a lower-priority arrival changes nothing — the process keeps running. The event that is in no way associated with leaving the running state, and is therefore the cleanest “not a condition,” is the arrival of a lower-priority process. That is the intended answer.
Answer: If a lower priority process arrived.