C++ Multithreading and Concurrency Fundamentals Quiz Quiz

Explore core concepts, key terms, and best practices in C++ multithreading and concurrency with these essential interview-style questions. Learn about thread creation, synchronization, atomic operations, and strategies to write efficient, safe multi-threaded programs in C++.

1. Creating Threads in C++

   Which C++ construct introduced in C++11 is primarily used to create a new thread of execution?

   1. std::thread
   2. std::mutex
   3. std::atomic
   4. std::future

   Explanation: std::thread is the standard C++11 construct used to create and manage threads. std::mutex is used for locking data, std::atomic provides atomic operations, and std::future is for handling asynchronous results, not for thread creation.

2. Understanding Race Conditions

   In a program where two threads update the same variable without synchronization, what condition can occur?

   1. Race condition
   2. Deadlock
   3. Thread starvation
   4. Thread pooling

   Explanation: A race condition happens when multiple threads access shared data unsafely, causing unpredictable outcomes. Deadlock involves threads waiting indefinitely, thread starvation is when a thread never gets CPU time, and thread pooling is a method for reusing threads.

3. Preventing Race Conditions

   What is the standard way to prevent race conditions when multiple threads access shared variables?

   1. Using std::mutex
   2. Using std::cout
   3. Using std::vector
   4. Using std::algorithm

   Explanation: std::mutex provides a locking mechanism that ensures only one thread can access a critical section at a time. std::cout is for output, std::vector is a container, and std::algorithm provides generic algorithms but does not handle synchronization.

4. Deadlock Scenario

   What is a deadlock in the context of multithreaded C++ programs?

   1. When threads wait indefinitely for each other to release resources
   2. When all threads finish their tasks successfully
   3. When a thread exits early
   4. When no threads are created

   Explanation: A deadlock occurs when threads are stuck waiting on each other’s resources, resulting in no thread progressing. Finishing tasks, thread exits, or having no threads do not describe deadlock conditions.

5. Avoiding Deadlocks

   Which technique helps to avoid deadlocks in a multithreaded C++ application?

   1. Acquiring locks in the same order
   2. Ignoring shared resources
   3. Outputting debug information
   4. Declaring all variables as static

   Explanation: Acquiring locks in a consistent order prevents circular waiting, which is a key factor in deadlocks. Ignoring shared resources does not resolve potential issues. Outputting debug info and declaring variables static are unrelated to deadlock avoidance.

6. Thread Synchronization Tools

   Which C++ literal is used for declaring thread-local storage variables?

   1. thread_local
   2. local_thread
   3. static_thread
   4. thread_static

   Explanation: thread_local is the correct keyword for thread-specific storage in C++. The other options are either misspellings or non-existent in the C++ standard.

7. Understanding Concurrency

   In C++ multithreading, what does 'concurrency' mean?

   1. Managing several tasks at one time
   2. Multiplying two numbers
   3. Printing output to the console
   4. Sorting arrays in order

   Explanation: Concurrency refers to handling multiple tasks or threads in overlapping periods, not necessarily simultaneously. Multiplying numbers, printing, or sorting arrays are unrelated to the concept of concurrency.

8. Distinguishing Parallelism

   What is the main difference between concurrency and parallelism in C++?

   1. Concurrency manages tasks at one time, parallelism runs them simultaneously
   2. Concurrency and parallelism are the same
   3. Parallelism sorts data, concurrency does not
   4. Concurrency is only for input/output

   Explanation: Concurrency is about managing multiple tasks, possibly interleaved, while parallelism means executing tasks at the same time. They are not identical, and the other options confuse their definitions.

9. Using std::atomic

   Why would a C++ developer use std::atomic for shared variables?

   1. To enable lock-free, thread-safe operations
   2. To speed up math functions
   3. To increase memory allocation
   4. To print debug messages

   Explanation: std::atomic provides atomic access to variables, ensuring thread safety without locks. It does not affect math speed, memory allocation, or printing debug messages.

10. Thread Pools Explained

    What is the purpose of a thread pool in multi-threaded programming?

    1. To manage a collection of reusable threads for tasks
    2. To store data temporarily
    3. To sort large arrays
    4. To create graphical windows

    Explanation: A thread pool allows efficient task management by reusing threads, reducing creation overhead. Storing data, sorting arrays, or creating windows are unrelated to thread pools.

11. std::future Role

    What is std::future mainly used for in C++ multithreading?

    1. To retrieve results from asynchronous operations
    2. To create new threads directly
    3. To declare constant variables
    4. To sort threads by priority

    Explanation: std::future allows asynchronous retrieval of computation results. It does not create threads, declare constants, or manage thread priority.

12. Mutex Types

    Which C++ mutex allows multiple threads to read but only one thread to write?

    1. std::shared_mutex
    2. std::mutex
    3. std::atomic_mutex
    4. std::timed_mutex

    Explanation: std::shared_mutex enables multi-reader, single-writer scenarios. std::mutex allows only exclusive locking, std::atomic_mutex does not exist, and std::timed_mutex is for timed locking.

13. Lock-Free Programming

    What technique is commonly used to write lock-free programs in C++?

    1. Using std::atomic operations
    2. Sharing all variables freely
    3. Using static local variables
    4. Pausing threads repeatedly

    Explanation: std::atomic enables lock-free, thread-safe manipulation of variables, boosting performance. Sharing variables without control invites race conditions; static locals and thread pausing don’t offer lock-free guarantees.

14. Best Practices

    Which of these is a best practice for writing multi-threaded C++ programs?

    1. Minimize shared resources
    2. Share all resources between threads
    3. Avoid using synchronization
    4. Always use global variables

    Explanation: Reducing shared resources lowers contention risk and potential synchronization issues. Sharing everything or using global variables increases risk, and avoiding synchronization can result in bugs.

15. Testing Multithreaded Code

    Why is thorough testing important for C++ multithreaded programs?

    1. Bugs can be non-deterministic and hard to reproduce
    2. Threads are always tested automatically
    3. No errors occur in multithreaded code
    4. Testing deletes all bugs instantly

    Explanation: Multithreaded bugs often depend on timing, making them subtle and difficult to detect. Testing is not automatic, errors can still exist, and no testing method instantly removes all bugs.