Operating Systems Chapter 5
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What is the primary purpose of multiprogramming in an operating system?

  • To allow multiple programs to reside in the main memory simultaneously (correct)
  • To enhance the performance of distributed processing
  • To increase the physical memory capacity of the system
  • To reduce the amount of CPU time for individual processes

Which of the following best describes multiprocessing?

  • Using multiple processors to enhance processing power and reliability (correct)
  • Distributing tasks between separate operating systems
  • Using a single processor for all tasks in a system
  • Using an operating system to manage software applications only

What distinguishes distributed processing from other types of processing?

  • It does not require any networking capabilities.
  • It involves one computer handling all processing tasks.
  • It relies solely on a single computer with multiple applications.
  • It requires multiple computers working over a network on a single task. (correct)

How does structured programming relate to operating system design?

<p>It can help reduce the complexity of the operating system’s modular design. (B)</p> Signup and view all the answers

Which of the following is a key advantage of multiprocessing?

<p>Increased system reliability through task distribution (B)</p> Signup and view all the answers

What is a primary disadvantage of using busy-waiting in synchronization mechanisms?

<p>It wastes processor time while waiting. (A)</p> Signup and view all the answers

What is a characteristic of a binary semaphore?

<p>It can only be 0 or 1. (A)</p> Signup and view all the answers

Which operation on a semaphore may result in blocking a process?

<p>Decrement (B)</p> Signup and view all the answers

What guarantees that only one process can access a monitor at any given time?

<p>Access procedures (B)</p> Signup and view all the answers

Which of the following statements about mutexes is true?

<p>The process that locks the mutex must also unlock it. (D)</p> Signup and view all the answers

What could potentially happen when a process leaves a critical section?

<p>Possible starvation for waiting processes. (A)</p> Signup and view all the answers

What type of semaphore is primarily used for signaling among processes?

<p>Counting semaphore (C)</p> Signup and view all the answers

Which of the following is NOT a feature of monitors?

<p>Direct access to internal variables by processes. (A)</p> Signup and view all the answers

What is a primary challenge in managing concurrent processes in an operating system?

<p>Optimally allocating resources (C)</p> Signup and view all the answers

In concurrent processing, what typically determines the final value of a variable when multiple processes access it?

<p>The order of execution of the processes (D)</p> Signup and view all the answers

Which issue arises from two processes competing for the same resource?

<p>Race conditions (B)</p> Signup and view all the answers

What is a mutual exclusion problem in the context of concurrent processes?

<p>Only one process can access a critical section at a time (C)</p> Signup and view all the answers

What happens during a deadlock involving renewable resources?

<p>No process can proceed or be allocated new resources (A)</p> Signup and view all the answers

What effect does 'interrupt disabling' have in a uniprocessor system?

<p>Guarantees mutual exclusion (D)</p> Signup and view all the answers

What is the role of the operating system regarding process management in concurrency?

<p>To track and allocate resources for processes (C)</p> Signup and view all the answers

What is a significant issue that arises when multiple processes are directly aware of each other?

<p>Lack of mutual exclusion (C)</p> Signup and view all the answers

Which of the following describes 'starvation' in concurrent processing?

<p>Processes are unable to access critical sections indefinitely (D)</p> Signup and view all the answers

What does the 'compare and swap' instruction achieve in concurrent processing?

<p>Guarantees that only one process can update a memory value atomically (B)</p> Signup and view all the answers

Which scenario illustrates 'resource competition' in concurrent processing?

<p>Multiple processes try to write to the same file at the same time (D)</p> Signup and view all the answers

What is one disadvantage of interrupt disabling in a multiprocessor architecture?

<p>Can significantly degrade efficiency (A)</p> Signup and view all the answers

How does competition among processes typically affect resource management?

<p>Makes optimal allocation more challenging (B)</p> Signup and view all the answers

Which of the following best describes interleaving in concurrent processing?

<p>Processes alternate execution in overlapping time frames (A)</p> Signup and view all the answers

What is the primary function of a semaphore?

<p>To facilitate mutual exclusion among competing processes (C)</p> Signup and view all the answers

What happens when a process executes a semWait operation on a semaphore that is already at zero?

<p>The process will be blocked until the semaphore is signaled. (B)</p> Signup and view all the answers

Which of the following accurately describes a strong semaphore?

<p>Processes are released from the queue based on their arrival time (FIFO). (D)</p> Signup and view all the answers

How does a mailbox mechanism primarily facilitate inter-process communication?

<p>By allowing two processes to send messages to each other directly (C)</p> Signup and view all the answers

What operation is used to increment the value of a semaphore?

<p>semSignal (A)</p> Signup and view all the answers

In the context of spinlocks, what is the main characteristic?

<p>Processes execute in a loop checking the lock status. (B)</p> Signup and view all the answers

What is an event flag primarily used for?

<p>As a synchronization mechanism among threads (B)</p> Signup and view all the answers

Which statement is true regarding weak semaphores?

<p>They may not maintain any specific order when releasing processes from their queue. (C)</p> Signup and view all the answers

What is a primary consequence of using semaphores?

<p>There is no mechanism to prioritize which process gets unblocked first. (B)</p> Signup and view all the answers

How is a binary semaphore defined in terms of its value?

<p>It can only hold a value of zero or one. (B)</p> Signup and view all the answers

What occurs if two processes attempt to execute semWait on the same semaphore simultaneously?

<p>One may block until the semaphore is released by the other. (A)</p> Signup and view all the answers

When can a process continue execution after issuing a semSignal operation?

<p>When there are no other processes waiting on the semaphore. (D)</p> Signup and view all the answers

Which best describes the role of a queue in semaphore mechanisms?

<p>It is used to hold processes waiting on a semaphore. (A)</p> Signup and view all the answers

What scenario illustrates a semaphore being decremented to a negative value?

<p>A process executes semSignal while others are waiting. (A)</p> Signup and view all the answers

Flashcards

Multiprogramming

Allows many programs to exist in memory at once, improving processor use.

Multiprocessing

Using two or more processors in one computer to increase speed and reliability.

Distributed Processing

Using multiple computers working together over a network to complete a job.

Structured Applications

Applications designed to divide processing time among many tasks, making operating systems more manageable.

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Operating Systems Design

Managing processes and tasks in multiple programs, processors or networks.

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Concurrency

The ability of multiple processes or threads to execute seemingly at the same time.

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Interleaving

The intermingling of the execution of different processes or threads in a processor.

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Overlapping

Processes or threads start at different times, they can finish at the same time.

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Uniprocessor

A computer with only one central processing unit (CPU).

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Global resources

Resources like memory or I/O devices that are shared among multiple processes.

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Mutual Exclusion

Ensuring that only one process accesses a shared resource at a time.

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Deadlock

A situation where two or more processes are blocked indefinitely, waiting for each other to release resources.

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Starvation

A process repeatedly denied access to a resource, so it never gets a chance to proceed.

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Critical section

A section of code where a process accesses and modifies shared resources.

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Interrupt Disabling

A method of achieving mutual exclusion by temporarily disabling interrupts.

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Compare-and-Swap

An atomic instruction that compares a memory value to a test value and swaps them if they are equal.

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Data Coherence

Maintaining consistency in shared data across multiple processes.

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Resource Competition

Processes conflicting over the use of the same resources like memory, I/O devices, or the processor.

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Scheduling policies

Rules implemented by the OS to decide which process gets processor time next.

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Operating System Concerns

Management and design issues arising from concurrent processes, including process tracking, resource allocation, and protection.

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Compare and Swap Instruction

An atomic instruction used to compare a memory location with a value and swap the memory location with another value if they match. Used for synchronization.

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Semaphore

An integer variable used to manage access to shared resources by multiple processes. Provides a signaling mechanism.

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Binary Semaphore

A semaphore that can only take on the values 0 or 1. Acts like a lock.

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Mutex

A type of binary semaphore where the thread that acquires the lock must also release it. Ensures exclusive access.

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Condition Variable

A data type used to wait for a specific condition to become true. A signaling mechanism between processes waiting on a condition.

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Monitor

A programming language construct that groups shared variables and procedures for enforcing mutual exclusion while accessing shared data.

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Critical Section

A section of code in which multiple processes cannot concurrently access shared resources.

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Busy-Waiting

A process continuously checks for a condition without performing any useful work. Inefficient.

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Concurrency

Processes or threads appearing to run simultaneously, though on a single processor.

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Event Flags

Memory used to synchronize threads. Bits in the flag signal events.

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Mailboxes/Messages

Mechanisms for processes to send and receive data, potentially as a synchronization tool.

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Spinlocks

Mutual exclusion where a process loops constantly checking a lock's state.

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Semaphore

Integer value with operations (init, decrement, increment) used for synchronization.

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semWait

Decrements a semaphore's value.

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semSignal

Increments a semaphore's value.

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Binary Semaphore

A semaphore with values 0 or 1, controlling exclusive access.

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Strong Semaphore

Semaphore with FIFO (First In, First Out) queue to release waiting processes

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Weak Semaphore

Semaphore where the order of releasing waiting processes is not specified.

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Mutual Exclusion

Ensuring only one process accesses a shared resource at a time.

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Critical Section

Code section needing mutual exclusion to prevent data corruption.

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Resource Competition

Processes contending for shared resources like memory and I/O.

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Deadlock

A situation where two or more processes are permanently blocked waiting for each other.

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Starvation

A process repeatedly denied access to a resource.

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Study Notes

Operating Systems: Internals and Design Principles

  • Chapter 5 focuses on concurrency, mutual exclusion, and synchronization.
  • Operating system design manages processes and threads.
  • Multiprogramming allows multiple programs to reside in memory simultaneously to maximize CPU utilization.
  • Multiprocessing uses two or more processors within one computer system, increasing processing power and reliability.
  • Distributed processing utilizes multiple computers working together over a network to complete tasks.
  • Concurrency arises in multiple application contexts, structured applications, and operating system structure.
  • Large applications are decomposed into smaller segments.
  • Structured applications employ modular and structured design to manage complexity.
  • Operating systems implement functionalities as processes or threads.

Concurrency Concepts

  • Atomic operation: A sequence of instructions treated as indivisible; the entire sequence executes or none at all. Prevents intermediate states being seen by other processes.
  • Critical section: A section of code requiring access to shared resources, not to be executed concurrently by another process.
  • Deadlock: A condition where two or more processes are unable to proceed due to each waiting for the other.
  • Livelock: A situation where multiple processes continuously alter their states without accomplishing useful work as a result of their interaction.
  • Mutual exclusion: Ensures only one process accesses shared resources at any given time during the critical section.
  • Race condition: The final result of multiple processes reading and writing shared data depends on their timing.
  • Starvation: A runnable process is indefinitely overlooked by the scheduler, despite being able to proceed.

Principles of Concurrency

  • Interleaving and overlapping are examples of concurrent processing and present similar problems.
  • Uniprocessor execution speed is not predictable due to other processes' activities, interrupt handling, and OS scheduling policies.
  • Concurrency complicates resource management and introduces difficulty in locating errors.

Difficulties of Concurrency

  • Sharing global resources.
  • Management of resource allocation.
  • Identifying programming errors (non-deterministic and non-repeatable results).

Race Condition

  • Multiple processes or threads read and write data items simultaneously, causing final result to depend on execution order.
  • The process "winning" the race (last updating the variable) dictates the final value of the shared variable.

Operating System Concerns

  • The OS must manage concurrent processes in terms of tracking them, allocating and de-allocating resources, protecting data, and maintaining process/output independence of processor speed.

Process Interaction

  • Processes can be unaware, indirectly aware or directly aware of each other.
  • Awareness levels affect competition, cooperation and control problems.

Resource Competition

  • Processes compete for shared resources like I/O devices, memory, processor time, and clocks.
  • Problems include mutual exclusion, deadlock and starvation.

Mutual Exclusion: Hardware Support

  • Interrupt Disabling: Guarantees mutual exclusion on uniprocessor systems, but inefficient on multiprocessor machines.
  • Compare-and-Swap Instruction: Atomically compares and swaps values, but might suffer from busy-waiting and potential starvation/deadlock.

Semaphores

  • Variables used for process synchronization.

  • Only three operations (initialized, decremented, incremented).

  • No manipulation methods beside those three.

  • Can be initialized to a non-negative integer value

  • semWait operation decrements value.

  • semSignal operation increments value.

  • Strong Semaphores:FIFO queue ensures the process blocked the longest is released first.

  • Weak Semaphores: No queue order guarantee,

  • Mutual exclusion implementation examples using semaphores are presented.

Consequences of Semaphore Use

  • Inability to determine whether a process will be blocked or not before decrement.
  • Inability to predict which process will proceed in uniprocessor systems with concurrent processes.
  • Uncertainty about the number of unblocked processes.

Definition of Semaphore Primitives

  • Primitives ( semWait and semSignal) manipulate semaphore values.
  • They handle process scheduling and queueing to manage concurrent processes.

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Operating Systems Lecture 1 PDF

Description

Explore the concepts of concurrency, mutual exclusion, and synchronization as presented in Chapter 5 of 'Operating Systems: Internals and Design Principles'. Learn about process management, multiprogramming, and the importance of atomic operations in ensuring reliability in system performance.

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