Concurrency Concepts Quiz: Race Conditions, Locks, and Deadlocks Quiz

Test your understanding of concurrency basics, including race conditions, critical sections, locks, and deadlock avoidance. This quiz helps reinforce key concepts for beginners in multithreaded programming and concurrent system design.

1. Identifying a Race Condition

   What is a race condition in concurrent programming?

   1. A process where each thread must wait its turn to execute.
   2. A scheduling method used to evenly distribute tasks.
   3. A situation where two threads update shared data at the same time, leading to unpredictable results.
   4. A mechanism for preventing memory leaks in threads.

   Explanation: A race condition occurs when threads access shared resources concurrently and the final result depends on the timing of their execution, which can lead to unpredictable behavior. Waiting one's turn to execute is more characteristic of locking or synchronization. Scheduling methods are about organizing task execution, not preventing data inconsistency. Memory leak prevention is unrelated to the term 'race condition.'

2. Understanding a Critical Section

   Which best describes a critical section in a concurrent program?

   1. A section in a program reserved for performance monitoring.
   2. A place in the code where threads are destroyed.
   3. A block of code used for error handling.
   4. A segment of code that only one thread should execute at a time to avoid conflicts.

   Explanation: A critical section is a code segment where shared resources are accessed and must be protected to prevent data corruption. The other options describe unrelated concepts: error handling, thread destruction, and performance monitoring are not specific to concurrency control or critical sections.

3. Purpose of Locks

   What is the main purpose of using a lock in a multithreaded application?

   1. To permanently stop a thread from executing.
   2. To ensure only one thread can access a shared resource at a time.
   3. To speed up the execution of threads.
   4. To force all threads to execute simultaneously.

   Explanation: Locks are used to provide exclusive access to shared resources, preventing multiple threads from causing conflicts. Speeding up execution and forcing simultaneous execution are not the goals of locks. Locks do not stop threads permanently; they synchronize resource access.

4. Deadlock Scenario

   Which of the following best illustrates a deadlock situation?

   1. A thread running faster than another.
   2. A thread holding multiple locks without contention.
   3. All threads completing their tasks at the same time.
   4. Two threads each wait forever for a lock held by the other.

   Explanation: Deadlock occurs when two or more threads are each waiting for resources held by the other, so none of them progress. Thread speed differences do not create deadlock. Threads completing at the same time is desirable, not a problem. Holding multiple locks is only problematic when combined with improper acquisition order.

5. Best Practice for Deadlock Avoidance

   What is a common method to avoid deadlock in concurrent programs?

   1. Start all threads at the same time.
   2. Terminate threads immediately after acquiring a lock.
   3. Always acquire multiple locks in a consistent global order.
   4. Use as many locks as possible on each resource.

   Explanation: By ensuring all threads acquire locks in the same order, circular wait conditions leading to deadlocks are avoided. Simultaneous thread start or using many locks does not prevent deadlocks and could make problems worse. Terminating threads after acquiring a lock is not practical or effective.

6. When Race Conditions Occur

   Which scenario is most likely to result in a race condition?

   1. Threads reading only from separate files.
   2. Threads sleeping for different durations.
   3. A single thread accessing its private variables.
   4. Multiple threads updating a shared counter without synchronization.

   Explanation: Race conditions commonly happen when shared data is updated by several threads without proper synchronization like locks. Reading from separate files and private variables involve no shared state, so no race. Sleeping threads may affect timing but not resource conflicts alone.

7. Busy Waiting Definition

   What does busy waiting mean in the context of concurrency?

   1. A process that is dormant but ready to execute.
   2. A thread terminated due to an error.
   3. Continuously checking a condition in a loop rather than yielding control.
   4. A thread waiting on a network response.

   Explanation: Busy waiting occurs when a thread repeatedly checks a condition in a loop, consuming CPU cycles needlessly. Waiting on a network response is not actively consuming CPU. Dormant threads are not busy, and terminated threads are no longer executing. Only the first describes busy waiting.

8. Choosing Synchronization Primitives

   Which synchronization primitive would you typically use to protect a single shared variable from concurrent modification?

   1. A recursive function
   2. A cache invalidation policy
   3. A mutex lock
   4. A stack trace

   Explanation: A mutex lock is designed to provide mutually exclusive access to shared resources. Recursive functions do not control thread access. Cache invalidation relates to memory management, and stack traces help with debugging, not synchronization.

9. Atomic Operations

   Which property best describes an atomic operation?

   1. It completes in a single step without interruption.
   2. It always requires a lock.
   3. It is a type of function call.
   4. It can be partially completed by multiple threads.

   Explanation: An atomic operation is indivisible, meaning no other thread can see it in a partially completed state. Not all atomic operations require locks, so option two is incorrect. Being a function call is unrelated, and atomicity rules out partial completion.

10. Thread-Safe Code

    What does it mean for code to be thread-safe?

    1. It cannot access any shared data.
    2. It is only run on single-processor systems.
    3. It does not use any loops.
    4. It functions correctly when accessed simultaneously by multiple threads.

    Explanation: Thread-safe code properly manages shared data, ensuring correct behavior regardless of thread interleaving. The absence of loops or running on a single processor has nothing to do with being thread-safe. Thread-safe code may access shared data as long as it's protected.