Thread pools in Operating Systems - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

What is the main advantage of using a thread pool?

Thread pools are used in many systems to manage multiple tasks efficiently. What is the primary benefit of using a thread pool instead of creating a new thread for each task?

A It reduces the overhead of creating and destroying threads repeatedly.

B It guarantees that tasks will run in the order they are received.

C It allows threads to run without any synchronization mechanisms.

D It ensures that only one task runs at a time.

💡 Hint

Think about what happens when threads are created and destroyed frequently.

Creating and destroying threads takes time and system resources. A thread pool keeps a set of threads ready to run tasks, so it avoids this overhead and improves performance.

📋 Factual

intermediate

How does a thread pool manage tasks when all threads are busy?

In a thread pool, what happens to new tasks when all threads are currently executing other tasks?

A New tasks are rejected and lost.

B New tasks are placed in a queue to wait until a thread becomes free.

C New threads are created immediately to handle the tasks.

D The system pauses all running threads to make room for new tasks.

💡 Hint

Consider how a thread pool controls the number of active threads.

Thread pools usually have a fixed number of threads. When all are busy, new tasks wait in a queue until a thread finishes its current task and becomes available.

🔍 Analysis

advanced

Identify the problem caused by an unbounded task queue in a thread pool

What issue can arise if a thread pool uses an unbounded queue to hold waiting tasks?

A The system may run out of memory due to too many queued tasks.

B Tasks will be executed out of order.

C Threads will be created beyond the pool size limit.

D Tasks will be rejected immediately when the queue is full.

💡 Hint

Think about what happens if tasks keep arriving faster than they can be processed.

An unbounded queue can grow indefinitely if tasks arrive faster than threads can process them, potentially exhausting system memory and causing crashes.

❓ Comparison

advanced

Difference between fixed-size and cached thread pools

Which statement correctly describes the difference between a fixed-size thread pool and a cached thread pool?

A Cached pools reject tasks when all threads are busy; fixed-size pools queue tasks indefinitely.

B Fixed-size pools create threads on demand; cached pools have a fixed number of threads.

C Fixed-size pools have a set number of threads; cached pools create new threads as needed and reuse idle ones.

D Both pools create unlimited threads but differ in task queue size.

💡 Hint

Consider how each pool manages thread creation and reuse.

Fixed-size pools maintain a constant number of threads. Cached pools create new threads when needed and reuse idle threads, allowing flexible scaling.

❓ Reasoning

expert

Why might a thread pool cause deadlocks in certain applications?

Consider an application using a thread pool where tasks submit other tasks to the same pool and wait for their completion. Why can this design cause deadlocks?

A Because the thread pool automatically cancels tasks that wait for others.

B Because thread pools do not support nested task submission.

C Because tasks submitted later always have lower priority and never run.

D Because all threads may be blocked waiting for subtasks, no thread is free to run those subtasks.

💡 Hint

Think about what happens if threads are waiting for other threads that cannot start.

If all threads in the pool are busy running tasks that wait for other tasks to finish, and those subtasks cannot run because no threads are free, the system deadlocks.