📝 Priority Inversion in Semaphore (55 MCQs)

📖 From Operating System • 5. Process Synchronization • 55 questions available

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What is Priority Inversion in Semaphore?

Definition:
Priority inversion is a scheduling anomaly where a high-priority process waits for a low-priority process holding a semaphore, effectively inverting their intended execution order $pri_H < pri_L$ .

Example:
High-priority $H$ blocks on mutex held by low-priority $L$ , while medium-priority $M$ preempts $L$ , causing $H$ to wait for $M$ indirectly.

Reason:
This violates real-time predictability and requires protocols like priority inheritance or ceiling protocols to temporarily boost $L$ 's priority to $pri_H$ during lock ownership.

Easy

Medium

Hard

📝 All Priority Inversion in Semaphore MCQs

Q1. What is priority inversion?

A.A situation where a higher-priority process is delayed by a lower-priority process. ✅

B.A situation where a lower-priority process is delayed by a higher-priority process.

C.A situation where all processes have equal priority.

D.A situation where a process is terminated due to low priority.

💡 Difficulty: easy | ✅ Correct: A

📖 Explanation: Priority inversion occurs when a higher-priority process is forced to wait for a lower-priority process that holds a needed resource. This is a scheduling anomaly that can cause significant delays in real-time systems.

Q2. What causes priority inversion?

A.A higher-priority process needs a resource held by a lower-priority process. ✅

B.A lower-priority process needs a resource held by a higher-priority process.

C.All processes need the same resource.

D.The operating system schedules processes in FIFO order.

💡 Difficulty: easy | ✅ Correct: A

📖 Explanation: Priority inversion is caused when a higher-priority process requires a resource that is currently held by a lower-priority process. The higher-priority process is blocked until the lower-priority process releases the resource, violating priority scheduling principles.

Q3. What makes priority inversion more complicated?

A.When the lower-priority process is preempted by a medium-priority process. ✅

B.When the higher-priority process is terminated.

C.When the resource is released immediately.

D.When there are only two processes.

💡 Difficulty: medium | ✅ Correct: A

📖 Explanation: Priority inversion becomes more complicated when the lower-priority process holding the resource is preempted by a medium-priority process. This further delays the lower-priority process, which in turn delays the high-priority process waiting for the resource.

Q4. In the priority inversion example with processes L, M, and H, what are their priority relationships?

A.L has the highest priority, M has medium priority, H has lowest priority.

B.L has the lowest priority, M has medium priority, H has highest priority. ✅

C.L and H have the same priority, M has different priority.

D.All processes have equal priority.

💡 Difficulty: easy | ✅ Correct: B

📖 Explanation: In the classic priority inversion example, the priority order is L < M < H, meaning L has the lowest priority, M has medium priority, and H has the highest priority. This ordering is essential for the priority inversion scenario to occur.

Q5. What resource does process H need in the priority inversion example?

A.Resource R, which is held by process L. ✅

B.Resource R, which is held by process M.

C.Resource S, which is held by process L.

D.Resource S, which is held by process M.

💡 Difficulty: medium | ✅ Correct: A

📖 Explanation: In the example, high-priority process H needs resource R. However, resource R is currently being accessed by low-priority process L. This is the initial condition that leads to priority inversion when H is blocked waiting for L to release the resource.

Q6. What happens when process M becomes runnable in the priority inversion example?

A.Process M preempts process L, further delaying process H. ✅

B.Process M preempts process H, allowing L to continue.

C.Process M terminates.

D.Process M waits for process L.

💡 Difficulty: hard | ✅ Correct: A

📖 Explanation: When process M (medium priority) becomes runnable, it preempts process L (low priority) because M has higher priority. This means L cannot continue to release resource R, which H needs. M's preemption of L indirectly delays H, worsening the priority inversion.

Q7. What is the indirect effect of process M preempting process L in the priority inversion example?

A.Process H is able to continue.

B.Process H is delayed even longer because L cannot release the resource. ✅

C.Process M is blocked.

D.Process L terminates.

💡 Difficulty: medium | ✅ Correct: B

📖 Explanation: The indirect effect is that H is delayed even longer. Since L was preempted by M, L cannot finish using resource R and release it. H, which needs R, remains blocked. This is the essence of priority inversion: a medium-priority process indirectly delays a high-priority process.

Q8. When does priority inversion occur?

A.Only in systems with two priorities.

B.Only in systems with more than two priorities. ✅

C.In systems with any number of priorities.

D.In systems with no priorities.

💡 Difficulty: medium | ✅ Correct: B

📖 Explanation: Priority inversion occurs only in systems with more than two priorities. With only two priorities, a high-priority process would always run before a low-priority one, and there would be no medium-priority process to preempt the low-priority process, preventing the inversion scenario.

Q9. What is the primary solution to priority inversion?

A.Priority inheritance protocol. ✅

B.Terminating the low-priority process.

C.Increasing the priority of all processes.

D.Using only two priority levels.

💡 Difficulty: easy | ✅ Correct: A

📖 Explanation: The primary solution to priority inversion is the priority inheritance protocol. This protocol temporarily raises the priority of a low-priority process holding a resource needed by a high-priority process, preventing medium-priority processes from preempting it.

Q10. How does priority inheritance work?

A.A low-priority process inherits the priority of the high-priority process waiting for its resource. ✅

B.A high-priority process inherits the priority of a low-priority process.

C.All processes inherit the highest priority.

D.Priorities are ignored.

💡 Difficulty: medium | ✅ Correct: A

📖 Explanation: Priority inheritance works by allowing a low-priority process to temporarily inherit the priority of the high-priority process that is waiting for a resource it holds. This prevents medium-priority processes from preempting the low-priority process, allowing it to finish and release the resource quickly.

Q11. What happens to the inherited priority after the low-priority process releases the resource?

A.It remains high permanently.

B.It reverts to the process's original priority. ✅

C.It is transferred to another process.

D.It is set to zero.

💡 Difficulty: easy | ✅ Correct: B

📖 Explanation: After the low-priority process finishes using the resource and releases it, the inherited priority is relinquished. The process reverts to its original priority. This ensures that the priority inheritance is temporary and only active when necessary.

Q12. What real-world example is cited for priority inversion?

A.The Mars Pathfinder mission. ✅

B.The Apollo 11 mission.

C.The International Space Station.

D.The Space Shuttle program.

💡 Difficulty: easy | ✅ Correct: A

📖 Explanation: The Mars Pathfinder mission is a famous real-world example of priority inversion. The mission experienced frequent computer resets due to priority inversion, which was eventually solved by enabling priority inheritance in the VxWorks operating system.

Q13. What was the cause of the computer resets on the Mars Pathfinder?

A.Hardware failure.

B.Priority inversion causing a high-priority task to take too long. ✅

C.Software bugs in the navigation system.

D.Power supply issues.

💡 Difficulty: medium | ✅ Correct: B

📖 Explanation: The resets were caused by priority inversion. The high-priority 'bc dist' task was forced to wait for a resource held by a lower-priority task, which was preempted by medium-priority tasks. This caused the high-priority task to take longer than expected, triggering a system reset.

Q14. What operating system was running on the Mars Pathfinder?

A.Linux.

B.Windows CE.

C.VxWorks. ✅

D.QNX.

💡 Difficulty: easy | ✅ Correct: C

📖 Explanation: The Mars Pathfinder used the VxWorks real-time operating system. VxWorks had a global variable to enable priority inheritance on all semaphores, which was used to solve the priority inversion problem on the spacecraft.

Q15. How was the priority inversion problem solved on the Mars Pathfinder?

A.By terminating the low-priority task.

B.By enabling priority inheritance on semaphores. ✅

C.By increasing the priority of all tasks.

D.By rebooting the system.

💡 Difficulty: medium | ✅ Correct: B

📖 Explanation: The problem was solved by enabling priority inheritance on all semaphores in the VxWorks operating system. This allowed low-priority tasks holding resources needed by high-priority tasks to inherit the higher priority, preventing medium-priority tasks from preempting them.

Q16. What is the impact of priority inversion on real-time systems?

A.It can cause processes to miss deadlines and lead to system failure. ✅

B.It improves system performance.

C.It has no impact.

D.It only affects non-real-time systems.

💡 Difficulty: easy | ✅ Correct: A

📖 Explanation: In real-time systems, priority inversion can cause high-priority processes to miss their deadlines. This can lead to system failures, as processes may not complete critical tasks on time, causing cascading failures in time-sensitive applications.

Q17. What is the role of priority inheritance in preventing priority inversion?

A.It ensures low-priority processes are not preempted by medium-priority processes when they hold resources needed by high-priority processes. ✅

B.It increases the priority of all processes.

C.It decreases the priority of high-priority processes.

D.It ignores priorities.

💡 Difficulty: medium | ✅ Correct: A

📖 Explanation: Priority inheritance prevents priority inversion by temporarily boosting the priority of a low-priority process holding a resource needed by a high-priority process. This ensures the low-priority process runs to completion, releasing the resource without being preempted by medium-priority processes.

Q18. What task on the Mars Pathfinder was affected by priority inversion?

A.The navigation task.

B.The 'bc dist' task. ✅

C.The communication task.

D.The landing task.

💡 Difficulty: medium | ✅ Correct: B

📖 Explanation: The 'bc dist' task was the high-priority task affected by priority inversion. It was taking longer than expected to complete its work because it was forced to wait for a shared resource held by a lower-priority task that was preempted by medium-priority tasks.

Q19. What task discovered the problem and performed the reset on the Mars Pathfinder?

A.The 'bc dist' task.

B.The 'ASI/MET' task.

C.The 'bc sched' task. ✅

D.The navigation task.

💡 Difficulty: hard | ✅ Correct: C

📖 Explanation: The 'bc sched' task discovered the problem with the 'bc dist' task and performed the reset. The 'bc dist' task had stalled waiting for the shared resource due to priority inversion, and 'bc sched' detected this stall and initiated the reset to recover the system.

Q20. What task held the shared resource on the Mars Pathfinder?

A.The 'bc dist' task.

B.The 'ASI/MET' task. ✅

C.The 'bc sched' task.

D.The communication task.

💡 Difficulty: medium | ✅ Correct: B

📖 Explanation: The 'ASI/MET' task was the lower-priority task that held the shared resource needed by the high-priority 'bc dist' task. The 'ASI/MET' task was preempted by multiple medium-priority tasks, causing the priority inversion that led to the system resets.

Q21. What is the relationship between priority inversion and Mars Pathfinder?

A.Priority inversion caused the Mars Pathfinder to experience frequent computer resets. ✅

B.Priority inversion improved the Mars Pathfinder's performance.

C.Priority inversion was unrelated to the Mars Pathfinder.

D.Priority inversion caused the Mars Pathfinder to land incorrectly.

💡 Difficulty: easy | ✅ Correct: A

📖 Explanation: Priority inversion caused the Mars Pathfinder to experience frequent computer resets. The high-priority 'bc dist' task was delayed by lower-priority tasks, causing the 'bc sched' task to reset the system. This is a famous example of priority inversion in a real-time system.

Q22. What is a key characteristic of priority inversion?

A.It only occurs in single-processor systems.

B.It involves a high-priority process waiting for a low-priority process. ✅

C.It involves a low-priority process waiting for a high-priority process.

D.It occurs when all processes have equal priority.

💡 Difficulty: easy | ✅ Correct: B

📖 Explanation: A key characteristic of priority inversion is that a high-priority process is forced to wait for a low-priority process. This violates the expected behavior of priority scheduling and can lead to significant performance issues.

Q23. Why does priority inversion require more than two priority levels?

A.Because with only two priorities, the high-priority process would always preempt the low-priority process. ✅

B.Because priority inversion is impossible with two priorities.

C.Because priorities are irrelevant.

D.Because all systems have multiple priorities.

💡 Difficulty: medium | ✅ Correct: A

📖 Explanation: Priority inversion requires more than two priority levels because with only two priorities, a high-priority process would always be scheduled before a low-priority process. The presence of a medium-priority process is necessary for the inversion scenario, as it can preempt the low-priority process holding the resource.

Q24. What is the purpose of priority inheritance?

A.To allow a low-priority process to inherit the priority of a higher-priority process waiting for a resource it holds. ✅

B.To increase the priority of all processes equally.

C.To decrease the priority of high-priority processes.

D.To eliminate priorities altogether.

💡 Difficulty: easy | ✅ Correct: A

📖 Explanation: The purpose of priority inheritance is to allow a low-priority process to temporarily inherit the priority of a higher-priority process that is waiting for a resource held by the low-priority process. This prevents medium-priority processes from preempting the low-priority process, solving the priority inversion problem.

Q25. What happens to a low-priority process that inherits a higher priority?

A.It continues to run at the higher priority until it releases the resource. ✅

B.It is terminated.

C.It is blocked.

D.Its priority is permanently changed.

💡 Difficulty: medium | ✅ Correct: A

📖 Explanation: A low-priority process that inherits a higher priority continues to run at that higher priority until it releases the resource that the high-priority process needs. Once the resource is released, the low-priority process reverts to its original priority.

Q26. What is the result of priority inheritance on a medium-priority process?

A.It is preempted by the low-priority process that inherited the higher priority. ✅

B.It is terminated.

C.It continues to run normally.

D.Its priority is increased.

💡 Difficulty: hard | ✅ Correct: A

📖 Explanation: When a low-priority process inherits a higher priority, it will preempt any medium-priority processes. This prevents the medium-priority process from delaying the low-priority process, allowing the low-priority process to release the resource quickly and unblock the high-priority process.

Q27. What is the significance of the VxWorks operating system in the priority inversion discussion?

A.It was used on the Mars Pathfinder and had a priority inheritance feature. ✅

B.It was the first operating system to support priority inversion.

C.It does not support priority inheritance.

D.It was developed specifically for Mars missions.

💡 Difficulty: medium | ✅ Correct: A

📖 Explanation: VxWorks is significant because it was the operating system used on the Mars Pathfinder. It had a global variable to enable priority inheritance on all semaphores, which was used to solve the priority inversion problem that was causing computer resets on the spacecraft.

Q28. What happens when a low-priority process holding a resource is preempted by a medium-priority process?

A.The high-priority process waiting for the resource is delayed. ✅

B.The high-priority process is able to continue.

C.The medium-priority process is terminated.

D.The resource is released automatically.

💡 Difficulty: easy | ✅ Correct: A

📖 Explanation: When a low-priority process holding a resource is preempted by a medium-priority process, the high-priority process waiting for the resource is further delayed. This is because the low-priority process cannot release the resource until it resumes execution, but it is blocked by the medium-priority process.

Q29. What is the main goal of priority inheritance?

A.To ensure the high-priority process is not delayed by lower-priority processes indefinitely. ✅

B.To give all processes equal priority.

C.To terminate low-priority processes.

D.To reduce system complexity.

💡 Difficulty: medium | ✅ Correct: A

📖 Explanation: The main goal of priority inheritance is to ensure that a high-priority process is not indefinitely delayed by lower-priority processes. By temporarily raising the priority of the lower-priority process holding the resource, the high-priority process can be unblocked more quickly.

Q30. What is the effect of priority inversion on system performance?

A.It can degrade system performance and cause missed deadlines. ✅

B.It improves system performance.

C.It has no effect on performance.

D.It only affects memory usage.

💡 Difficulty: easy | ✅ Correct: A

📖 Explanation: Priority inversion can degrade system performance by causing high-priority processes to wait longer than expected. In real-time systems, this can lead to missed deadlines and system failures. It is a serious scheduling problem that must be addressed.

Q31. How can priority inversion be detected?

A.By monitoring the execution times of high-priority processes. ✅

B.By monitoring CPU usage.

C.By checking memory usage.

D.By checking disk I/O.

💡 Difficulty: medium | ✅ Correct: A

📖 Explanation: Priority inversion can be detected by monitoring the execution times of high-priority processes. If a high-priority process takes longer than expected to complete, it may be a sign of priority inversion. In the Mars Pathfinder, the 'bc sched' task detected the issue by monitoring the 'bc dist' task.

Q32. What is the role of semaphores in priority inversion?

A.Priority inversion occurs when semaphores are used to protect resources. ✅

B.Priority inversion occurs when semaphores are not used.

C.Semaphores prevent priority inversion.

D.Semaphores have no role in priority inversion.

💡 Difficulty: medium | ✅ Correct: A

📖 Explanation: Priority inversion occurs when semaphores are used to protect shared resources. A high-priority process may be blocked on a semaphore held by a low-priority process, leading to priority inversion. Priority inheritance protocols are often implemented on semaphores to address this issue.

Q33. What is the result of priority inversion on the 'bc dist' task on Mars Pathfinder?

A.It took longer than expected to complete its work. ✅

B.It completed its work faster.

C.It was terminated.

D.It had no effect.

💡 Difficulty: easy | ✅ Correct: A

📖 Explanation: Priority inversion caused the 'bc dist' task to take longer than expected to complete its work. This was because the task was forced to wait for a resource held by a lower-priority task that was preempted by medium-priority tasks, leading to the system resets.

Q34. What is the key insight from the Mars Pathfinder priority inversion example?

A.Priority inversion can cause system failures in real-time systems. ✅

B.Priority inversion is a theoretical problem with no practical impact.

C.Priority inversion only affects non-critical systems.

D.Priority inversion is easily avoidable.

💡 Difficulty: medium | ✅ Correct: A

📖 Explanation: The Mars Pathfinder example demonstrates that priority inversion is a practical problem that can cause system failures in real-time systems. It highlights the importance of addressing priority inversion, especially in mission-critical applications where timing constraints are crucial.

Q35. What is the priority of process L in the priority inversion example?

A.Highest priority.

B.Medium priority.

C.Lowest priority. ✅

D.No priority.

💡 Difficulty: easy | ✅ Correct: C

📖 Explanation: In the priority inversion example, process L has the lowest priority. It holds resource R, which process H (highest priority) needs. This creates the condition where H is blocked by L, leading to priority inversion.

Q36. What is the priority of process H in the priority inversion example?

A.Highest priority. ✅

B.Medium priority.

C.Lowest priority.

D.No priority.

💡 Difficulty: easy | ✅ Correct: A

📖 Explanation: In the priority inversion example, process H has the highest priority. However, it is blocked waiting for resource R held by process L (lowest priority). This is the central conflict in priority inversion, where the highest-priority process is delayed by a lower-priority one.

Q37. What is the priority of process M in the priority inversion example?

A.Highest priority.

B.Medium priority. ✅

C.Lowest priority.

D.No priority.

💡 Difficulty: easy | ✅ Correct: B

📖 Explanation: In the priority inversion example, process M has medium priority. It preempts process L (low priority) when it becomes runnable, further delaying L from releasing resource R. This worsens the priority inversion for process H (highest priority).

Q38. What is the purpose of a priority inheritance protocol?

A.To temporarily increase the priority of a lower-priority process holding a resource needed by a higher-priority process. ✅

B.To permanently increase the priority of lower-priority processes.

C.To decrease the priority of higher-priority processes.

D.To eliminate priorities.

💡 Difficulty: easy | ✅ Correct: A

📖 Explanation: The purpose of a priority inheritance protocol is to temporarily increase the priority of a lower-priority process that holds a resource needed by a higher-priority process. This prevents medium-priority processes from preempting the lower-priority process, allowing it to finish and release the resource quickly.

Q39. What happens after a low-priority process releases the resource in priority inheritance?

A.It reverts to its original priority. ✅

B.It retains the inherited priority.

C.It is terminated.

D.Its priority is decreased further.

💡 Difficulty: easy | ✅ Correct: A

📖 Explanation: After the low-priority process releases the resource that the high-priority process needed, it reverts to its original priority. The inherited priority is temporary and only lasts as long as the process holds the resource needed by the higher-priority process.

Q40. Why is priority inversion a significant problem in real-time systems?

A.Because real-time systems have tight deadlines that can be missed due to priority inversion. ✅

B.Because real-time systems do not use priorities.

C.Because real-time systems are not affected by scheduling.

D.Because real-time systems have unlimited resources.

💡 Difficulty: medium | ✅ Correct: A

📖 Explanation: Priority inversion is significant in real-time systems because these systems have tight deadlines. If a high-priority process is delayed by priority inversion, it may miss its deadline, leading to system failure. This is why priority inheritance is crucial in real-time systems.

Q41. What is the relationship between priority inversion and resource locks?

A.Priority inversion occurs when a high-priority process is blocked on a lock held by a lower-priority process. ✅

B.Priority inversion prevents resource locks.

C.Resource locks eliminate priority inversion.

D.Priority inversion is unrelated to resource locks.

💡 Difficulty: medium | ✅ Correct: A

📖 Explanation: Priority inversion occurs when a high-priority process is blocked on a lock (such as a semaphore) held by a lower-priority process. The lock is used to protect a shared resource, and the high-priority process cannot access the resource until the lower-priority process releases the lock.

Q42. What is the role of priority inheritance in real-time operating systems?

A.It ensures that high-priority processes are not indefinitely delayed by lower-priority processes. ✅

B.It decreases system performance.

C.It eliminates all scheduling issues.

D.It is not used in real-time systems.

💡 Difficulty: medium | ✅ Correct: A

📖 Explanation: Priority inheritance in real-time operating systems ensures that high-priority processes are not indefinitely delayed by lower-priority processes. It helps maintain predictability and meeting deadlines, which is critical in real-time applications.

Q43. What is the result of priority inversion on a real-time system?

A.It can cause the system to miss deadlines and experience failures. ✅

B.It improves the system's ability to meet deadlines.

C.It has no effect on deadlines.

D.It causes the system to terminate all processes.

💡 Difficulty: easy | ✅ Correct: A

📖 Explanation: Priority inversion can cause a real-time system to miss deadlines, as high-priority processes may be delayed by lower-priority ones. This can lead to system failures, as seen in the Mars Pathfinder mission, where priority inversion caused frequent computer resets.

Q44. What is the significance of the global variable in VxWorks for priority inheritance?

A.It allowed priority inheritance to be enabled on all semaphores. ✅

B.It disabled priority inheritance.

C.It had no effect on priority inheritance.

D.It was used to terminate processes.

💡 Difficulty: medium | ✅ Correct: A

📖 Explanation: The global variable in VxWorks allowed priority inheritance to be enabled on all semaphores. This was significant because it provided a simple way to address priority inversion in the system. By enabling this variable, the Mars Pathfinder team was able to solve the priority inversion problem.

Q45. What is the effect of priority inheritance on process L in the example?

A.Process L inherits the priority of process H and runs at that priority until it releases resource R. ✅

B.Process L is terminated.

C.Process L's priority is decreased.

D.Process L is blocked.

💡 Difficulty: hard | ✅ Correct: A

📖 Explanation: With priority inheritance, process L inherits the priority of process H. This means L runs at the same high priority as H, preventing process M (medium priority) from preempting L. L can then finish using resource R and release it, unblocking H.

Q46. What is the key takeaway from the priority inversion problem?

A.Priority inversion can be solved by priority inheritance. ✅

B.Priority inversion is impossible to solve.

C.Priority inversion only affects non-critical systems.

D.Priority inversion is not a real problem.

💡 Difficulty: easy | ✅ Correct: A

📖 Explanation: The key takeaway is that priority inversion is a real problem that can be solved by priority inheritance. By temporarily raising the priority of processes holding resources needed by higher-priority processes, the system can prevent priority inversion and ensure timely execution of critical tasks.

Q47. What is the benefit of priority inheritance for high-priority processes?

A.It allows them to be unblocked more quickly when waiting for resources. ✅

B.It decreases their priority.

C.It blocks them permanently.

D.It has no benefit.

💡 Difficulty: easy | ✅ Correct: A

📖 Explanation: Priority inheritance benefits high-priority processes by allowing them to be unblocked more quickly. When a low-priority process inherits the high priority, it can finish its work and release the resource faster, reducing the waiting time for the high-priority process.

Q48. What is the relationship between priority inversion and the scheduling algorithm?

A.Priority inversion is a scheduling anomaly that violates priority-based scheduling. ✅

B.Priority inversion is a feature of priority-based scheduling.

C.Priority inversion improves scheduling.

D.Priority inversion is unrelated to scheduling.

💡 Difficulty: medium | ✅ Correct: A

📖 Explanation: Priority inversion is a scheduling anomaly that occurs in priority-based scheduling systems. It violates the expected behavior where a higher-priority process should always run before a lower-priority one. This anomaly leads to delays and performance degradation.

Q49. What is the result of priority inversion on the high-priority task in the Mars Pathfinder?

A.The task took longer than expected to complete, causing system resets. ✅

B.The task completed faster than expected.

C.The task was terminated.

D.The task had no effect.

💡 Difficulty: easy | ✅ Correct: A

📖 Explanation: Priority inversion caused the high-priority 'bc dist' task to take longer than expected to complete. This delay triggered the 'bc sched' task to perform a system reset, which reinitialized the hardware and software, causing frequent resets on the Mars Pathfinder.

Q50. What is the significance of enabling priority inheritance on semaphores?

A.It prevents priority inversion by allowing low-priority processes to inherit higher priorities. ✅

B.It prevents deadlock.

C.It increases system complexity.

D.It has no effect on priority inversion.

💡 Difficulty: medium | ✅ Correct: A

📖 Explanation: Enabling priority inheritance on semaphores prevents priority inversion by allowing low-priority processes holding resources to inherit the priority of higher-priority processes waiting for those resources. This ensures that low-priority processes are not preempted by medium-priority processes, solving the priority inversion problem.

Q51. What is the purpose of the priority inheritance protocol in semaphores?

A.To avoid priority inversion by temporarily boosting the priority of low-priority tasks holding resources needed by high-priority tasks. ✅

B.To decrease the priority of all tasks.

C.To eliminate semaphores.

D.To increase the priority of all tasks.

💡 Difficulty: medium | ✅ Correct: A

📖 Explanation: The priority inheritance protocol in semaphores is designed to avoid priority inversion by temporarily boosting the priority of a low-priority task that holds a resource needed by a high-priority task. This ensures the low-priority task runs to completion without being preempted by medium-priority tasks, solving the priority inversion problem.

Q52. What is the result of priority inversion on system reliability?

A.It can cause system failures and reduced reliability. ✅

B.It improves system reliability.

C.It has no effect on reliability.

D.It only affects performance, not reliability.

💡 Difficulty: easy | ✅ Correct: A

📖 Explanation: Priority inversion can cause system failures, as seen in the Mars Pathfinder mission. When high-priority tasks miss deadlines due to priority inversion, it can lead to system resets and failures, reducing the overall reliability of the system.

Q53. What is the role of medium-priority processes in priority inversion?

A.They can preempt low-priority processes, worsening the inversion and delaying high-priority processes. ✅

B.They are not involved in priority inversion.

C.They prevent priority inversion.

D.They are always preempted by low-priority processes.

💡 Difficulty: medium | ✅ Correct: A

📖 Explanation: Medium-priority processes play a key role in priority inversion. They can preempt the low-priority process that holds the resource needed by the high-priority process. This delays the low-priority process from releasing the resource, causing the high-priority process to wait longer and worsening the priority inversion.

Q54. What is the key requirement for priority inheritance to be effective?

A.The system must be able to temporarily elevate the priority of processes holding resources needed by higher-priority processes. ✅

B.The system must have only two priorities.

C.The system must have no priorities.

D.The system must terminate low-priority processes.

💡 Difficulty: medium | ✅ Correct: A

📖 Explanation: For priority inheritance to be effective, the system must be able to temporarily elevate the priority of processes holding resources needed by higher-priority processes. This ability to boost priority is essential for preventing priority inversion and ensuring that high-priority processes are not unduly delayed.

Q55. What is the result of priority inheritance on the medium-priority process in the example?

A.It is preempted by the low-priority process that inherited the higher priority. ✅

B.It is terminated.

C.It continues to run normally.

D.Its priority is increased.

💡 Difficulty: hard | ✅ Correct: A

📖 Explanation: When the low-priority process L inherits the high priority of process H, it will preempt any medium-priority processes, including M. This ensures L can run to completion without being blocked by M, releasing the resource R so H can proceed.

🔗 Related Topics (MCQs)

📝 Process Synchronization in operating system MCQs 📝 The Critical Section Problem in Process Synchronization MCQs 📝 Peterson's Solution MCQs 📝 Synchronization hardware in operating system MCQs 📝 Mutex Locks in Process Synchronization MCQs

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