OS Chapter 5: Process Synchronization
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Questions and Answers

What is the purpose of the rw_mutex in the reader process?

  • To count the number of readers
  • To allow multiple readers to access the shared object simultaneously
  • To prevent writers from accessing the shared object (correct)
  • To signal the completion of the read operation

    • What is the problem with the dining-philosophers problem algorithm?

  • It allows multiple philosophers to eat at the same time
  • It leads to starvation and deadlock (correct)
  • It prevents philosophers from thinking
  • It does not allow philosophers to pick up chopsticks

    • What is the purpose of the read_count variable in the reader process?

  • To count the number of readers (correct)
  • To count the number of writers
  • To signal the completion of the read operation
  • To prevent writers from accessing the shared object

    • What is the main difference between the first and second variations of the readers-writers problem?

    <p>The first variation prioritizes writers, while the second variation prioritizes readers</p> Signup and view all the answers

    What is the shared data in the dining-philosophers problem?

    <p>A bowl of rice and a set of chopsticks</p> Signup and view all the answers

    What is the purpose of the wait(mutex) statement in the reader process?

    <p>To synchronize access to the read_count variable</p> Signup and view all the answers

    What is the consequence of starvation in the readers-writers problem?

    <p>Some processes may never access the shared object</p> Signup and view all the answers

    What is the function of the chopstick[i] semaphore in the dining-philosophers problem?

    <p>To prevent philosophers from eating at the same time</p> Signup and view all the answers

    What is the main purpose of the readers-writers problem?

    <p>To synchronize access to a shared object</p> Signup and view all the answers

    What is the significance of the signal(rw_mutex) statement in the reader process?

    <p>It allows writers to access the shared object</p> Signup and view all the answers

    Study Notes

    Process Synchronization

    • Process synchronization is necessary to maintain data consistency when multiple processes access shared data concurrently
    • Concurrent access to shared data can result in data inconsistency

    Critical-Section Problem

    • The critical-section problem arises when multiple processes access shared data and must execute a critical section of code
    • Three requirements to solve the critical-section problem:
      • Mutual Exclusion: only one process can execute in its critical section at a time
      • Progress: a process must eventually enter its critical section
      • Bounded Waiting: a bound on the number of times other processes can enter their critical sections before a requesting process is granted access

    Synchronization Hardware

    • Many systems provide hardware support for implementing critical section code
    • Solutions use locking mechanisms to protect critical regions
    • Uniprocessors can disable interrupts to implement critical sections, but this is inefficient on multiprocessor systems
    • Modern machines provide atomic hardware instructions for synchronization

    Mutex Locks

    • A mutex (mutual exclusion) lock is a binary lock that can be in one of two states: locked or unlocked
    • A process must acquire the lock before entering its critical section and release it afterwards
    • The test_and_set instruction is an atomic operation that returns the original value of the lock and sets it to TRUE

    Semaphores

    • A semaphore is a variable that controls access to a common resource by multiple processes
    • Semaphores can be used to solve the critical-section problem
    • There are two types of semaphores: binary semaphores (mutex locks) and counting semaphores
    • Deadlock and starvation can occur if semaphores are not used properly

    Classic Problems of Synchronization

    • The bounded-buffer problem, readers-writers problem, and dining-philosophers problem are classic synchronization problems used to test newly-proposed synchronization schemes
    • These problems illustrate common synchronization challenges, such as mutual exclusion, deadlocks, and starvation

    Bounded-Buffer Problem

    • A bounded-buffer is a buffer with a limited capacity
    • The problem is to synchronize access to the buffer by producer and consumer processes
    • Semaphores can be used to solve this problem

    Readers-Writers Problem

    • The readers-writers problem is a synchronization problem where multiple readers and writers access a shared resource
    • The problem is to synchronize access to the resource to avoid conflicts between readers and writers
    • Semaphores can be used to solve this problem

    Dining-Philosophers Problem

    • The dining-philosophers problem is a synchronization problem where multiple philosophers (processes) need to access a shared resource (chopsticks) to eat
    • The problem is to synchronize access to the chopsticks to avoid deadlocks and starvation
    • Semaphores can be used to solve this problem

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    Description

    This quiz covers the concepts of process synchronization in operating systems, including critical sections, Peterson's solution, and synchronization hardware.

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