Synchronization Primitives: Mutexes, Semaphores, and Monitors Quiz Quiz

Explore fundamental concepts of mutexes, semaphores, and monitors with these easy quiz questions, designed to reinforce your understanding of process synchronization, critical sections, and concurrency control in operating systems or concurrent programming environments.

1. Basic Mutex Concept

   Which synchronization primitive allows only one thread to enter a critical section at a time, using locking and unlocking mechanisms?

   1. Pipe
   2. Semaphore
   3. Mutex
   4. Cache

   Explanation: A mutex is designed to enforce mutual exclusion, ensuring that only one thread holds the lock and can access the critical section at a time. Semaphores can allow more than one context if initialized with a count greater than one. Caches store data and are unrelated to synchronization. Pipes are used for inter-process communication, not for guarding critical sections.

2. Semaphore Types

   When initialized to a value greater than one, which type of semaphore allows multiple threads to access the critical section simultaneously?

   1. Counting semaphore
   2. Binary semaphore
   3. Terminal
   4. Mutex

   Explanation: A counting semaphore can be initialized with an integer value, permitting that many threads to access the shared resource at once. A binary semaphore only allows one or zero, behaving like a mutex. 'Mutex' refers to mutual exclusion and only allows single-thread entry. 'Terminal' is unrelated to synchronization.

3. Monitor Feature

   What characteristic distinguishes a monitor from other synchronization primitives, making it easier to manage thread coordination within a shared resource?

   1. Non-blocking data transfer
   2. Integrated condition variables and mutual exclusion
   3. Direct hardware support only
   4. Unlimited access for threads

   Explanation: Monitors provide built-in condition variables and mutual exclusion, which help coordinate access and waiting in a structured way. Non-blocking data transfer is not directly related to monitors. Unlimited access would defeat the purpose of synchronization. Monitors can be implemented in software, not just hardware.

4. Critical Section Problem

   If two processes enter a critical section without synchronization, what kind of issue is most likely to occur?

   1. Paging
   2. Pipelining
   3. Race condition
   4. Deadlock

   Explanation: A race condition occurs when multiple processes change shared data concurrently, leading to unpredictable results if not synchronized. Deadlock involves processes waiting on each other indefinitely, which is a different issue. Paging relates to memory management, and pipelining is a concept in instruction execution, not synchronization.

5. Binary Semaphore Usage

   When would you use a binary semaphore instead of a counting semaphore?

   1. When access must be limited to only one thread
   2. When supporting priority scheduling
   3. When tracking memory allocation
   4. When allowing multiple threads to access a resource

   Explanation: A binary semaphore only has two states: locked and unlocked, making it ideal for mutual exclusion situations. Priority scheduling is unrelated to binary or counting semaphores specifically. Allowing multiple threads requires a counting semaphore. Memory allocation tracking does not use semaphores directly.

6. Deadlock Avoidance

   Which primitive requires careful design to avoid deadlock when multiple locks are acquired by different threads simultaneously?

   1. Buffer
   2. Channel
   3. Mutex
   4. Array

   Explanation: Improper use of multiple mutexes can lead to deadlocks if threads wait for each other's locks in a circular manner. Buffers, channels, and arrays refer to storage and communication mechanisms, but they do not inherently cause deadlocks without synchronization context.

7. Semaphore Operation Names

   What are the standard names for the two fundamental semaphore operations?

   1. Wait and Signal
   2. Increment and Decrement
   3. Start and Stop
   4. Lock and Unlock

   Explanation: Semaphore operations are typically called 'Wait' (or 'P') and 'Signal' (or 'V'). Increment and Decrement refer to the internal counter but are not standard operation names. Lock and Unlock are used for mutexes. Start and Stop do not apply to semaphores.

8. Monitor Synchronization

   Within a monitor, how is access to procedures designed to avoid simultaneous entry by multiple threads?

   1. Procedures are run in parallel with no restriction
   2. Procedures are automatically executed with mutual exclusion
   3. Threads are prioritized by CPU time
   4. Procedures are only available in batch processing

   Explanation: Monitors ensure that only one thread executes a procedure at a time, providing built-in mutual exclusion. CPU time prioritization is unrelated to monitor internals. Batch processing terms and parallel, unrestricted execution do not address synchronization.

9. Resource Starvation

   Which scenario best describes resource starvation in synchronization?

   1. A mutex is released and reacquired immediately
   2. A thread continually waits because other threads always gain access first
   3. A thread is interrupted by an exception
   4. All threads enter the critical section at once

   Explanation: Starvation happens when a thread is perpetually denied access due to other threads repeatedly acquiring the resource. Allowing all threads into the critical section defeats the concept of synchronization. Interruptions are not starvation. Releasing and reacquiring a mutex doesn't inherently lead to starvation unless scheduling is unfair.

10. Purpose of Mutual Exclusion

    Why is mutual exclusion essential in concurrent programming with shared resources?

    1. To prevent conflicting updates to shared data
    2. To manage user input efficiently
    3. To accelerate thread execution
    4. To allocate more memory to threads

    Explanation: Mutual exclusion ensures that only one thread can modify shared data at a time, preventing conflicts and unpredictable behavior. Allocating memory, accelerating execution, and handling user input are not directly related to mutual exclusion's core purpose.