Thread Priorities and Starvation Handling Quiz Quiz

Explore key concepts of thread priorities and strategies to handle thread starvation in concurrent programming environments. Assess your understanding of scheduling, priority control, and effective techniques to ensure fair resource allocation among threads.

1. Understanding Thread Priority Basics

   What is the primary purpose of assigning priorities to threads in a multithreaded environment?

   1. To allocate more memory to high-priority threads
   2. To reduce the CPU speed for low-priority threads
   3. To ensure all threads finish at the same time
   4. To influence the order in which threads are scheduled for execution

   Explanation: Thread priority mainly influences the order in which threads are selected by the scheduler. Assigning a higher priority increases a thread's chance to be executed sooner. Memory allocation and CPU speed are not directly affected by thread priority, so those options are incorrect. Priority does not guarantee all threads finish simultaneously.

2. Identifying Thread Starvation

   Which scenario best illustrates thread starvation in a scheduling system?

   1. A thread blocks itself with a sleep statement
   2. All threads execute in a fixed round-robin order
   3. A low-priority thread never gets CPU time because high-priority threads keep running
   4. Threads share CPU time equally, regardless of workload

   Explanation: Starvation occurs when a thread cannot access CPU resources due to others, often higher-priority threads, monopolizing the processor. Fixed round-robin and equal CPU sharing do not lead to starvation. Self-blocking through sleep is not starvation, as it is intentional suspension.

3. Priority Inversion Scenario

   If a low-priority thread holds a resource needed by a high-priority thread, causing the high-priority thread to wait, what is this situation called?

   1. Deadlock
   2. Resource waiting
   3. Priority inversion
   4. Livelock

   Explanation: Priority inversion happens when a high-priority thread is indirectly blocked by a lower-priority thread holding a resource it needs. Deadlock involves threads waiting on each other indefinitely, and livelock is when threads keep changing state, not making progress. 'Resource waiting' is not the standard term for this issue.

4. Effect of Dynamic Priority Changes

   What is a typical effect when the scheduler dynamically raises a starving thread's priority?

   1. The thread's memory usage will increase
   2. The thread will be terminated immediately
   3. Other threads automatically lower their priorities
   4. The thread is likely to get CPU time sooner and avoid starvation

   Explanation: Raising a starving thread's priority helps ensure it gets scheduled sooner, reducing the risk of starvation. Threads are not terminated nor do they see increased memory allocation as a direct result. Other threads do not automatically change their priorities because one thread’s priority was raised.

5. Aging as a Starvation Solution

   What does the aging technique do to prevent thread starvation?

   1. Puts all threads to sleep at intervals
   2. Gradually increases the priority of waiting threads over time
   3. Decreases the priority of running threads immediately
   4. Randomly assigns new priorities to all threads

   Explanation: Aging boosts the priority of threads waiting a long time, promoting fairness and avoiding starvation. Randomly assigning priorities can introduce chaos without ensuring fairness. Decreasing running threads' priority immediately isn't what aging entails. Putting threads to sleep doesn't target starvation directly.

6. Default Priority Assignment

   If no explicit priority is set, what happens to a thread’s priority in most systems?

   1. It is always given the highest possible priority
   2. It is not allowed to execute
   3. It shares its priority with another random thread
   4. It receives a default (medium) priority defined by the system

   Explanation: By default, threads usually get a system-defined medium priority, which allows fair scheduling. Automatically giving the highest priority could lead to resource contention, while denying execution or random assignment is impractical and unsupported by most systems.

7. Priority Setting Validity

   When attempting to set a thread’s priority, why must the chosen value fall within a system-defined range?

   1. To allow unlimited thread creation
   2. To ensure compatibility with the scheduler and prevent errors
   3. To allocate maximum CPU power to every thread
   4. To avoid using memory beyond system limits

   Explanation: Valid priority values are restricted to work seamlessly with the scheduler; setting out-of-range values can cause runtime errors or undefined behavior. CPU power allocation and memory usage are managed separately. Unlimited thread creation is unrelated to priority range.

8. Outcome of Equal Priority

   When several threads have the same priority, how does a typical thread scheduler decide which one to run next?

   1. It always picks the first thread created
   2. It only runs even-numbered threads
   3. It may use round-robin or another fair scheduling algorithm
   4. It sorts threads alphabetically by name

   Explanation: Schedulers typically use fair algorithms like round-robin to alternate between equal-priority threads. Picking the first created or sorting alphabetically is unreliable and not standard. Choosing only even-numbered threads is arbitrary and not practiced in real systems.

9. Impact of Constant High Priorities

   What is a potential system impact if multiple high-priority threads constantly run without yielding?

   1. The computer will automatically shut down
   2. All user input will be ignored
   3. It will improve overall system performance
   4. Lower-priority threads may experience starvation

   Explanation: When high-priority threads monopolize the CPU, low-priority threads may wait indefinitely, a classic starvation scenario. System shutdown is unlikely unless there's a critical failure. Performance typically degrades, not improves, and user input isn't universally ignored unless all threads handling it are starved.

10. Choosing a Starvation Solution

    Which method is commonly used to reduce thread starvation in systems with mixed priority threads?

    1. Limiting the number of threads to one
    2. Assigning the same priority to all threads
    3. Employing an aging mechanism to adjust priorities over time
    4. Disabling thread priorities altogether

    Explanation: Aging is widely applied to gradually increase low-priority threads’ priorities, reducing starvation. Disabling priorities removes important scheduling controls. Restricting to one thread or assigning equal priority oversimplifies scheduling and removes the benefits of priorities.