Parallel Programming Concepts Quiz
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What is the primary difference between data parallelism and task parallelism?

  • Data parallelism performs the same operation on each subset of data. (correct)
  • Task parallelism distributes the same data across multiple cores.
  • Task parallelism requires a single core to execute multiple threads.
  • Data parallelism involves unique operations on each core.

    • According to Amdahl’s Law, what effect does the serial portion of an application have on performance gains?

  • It has no effect on performance gains.
  • It has a minimal effect as more cores are added.
  • It improves the performance gains as more cores are added.
  • It disproportionately affects performance gains. (correct)

    • When moving from 1 to 2 cores in a 75% parallel and 25% serial application, what is the expected speedup according to Amdahl's Law?

  • 1.6 times (correct)
  • 2 times
  • 0.8 times
  • 1.28 times

    • What happens to the speedup as the number of processing cores approaches infinity?

    <p>Speedup approaches 1/S where S is the serial portion.</p> Signup and view all the answers

    Which of the following statements best describes task parallelism?

    <p>It distributes threads to cores where each thread performs a unique operation.</p> Signup and view all the answers

    What is the primary purpose of the ForkJoinTask class in Java?

    <p>To provide an abstract base for parallel tasks</p> Signup and view all the answers

    Which class extends ForkJoinTask and is used when a result needs to be returned?

    <p>RecursiveTask</p> Signup and view all the answers

    What is a key feature of Grand Central Dispatch in macOS and iOS?

    <p>It automatically manages thread details</p> Signup and view all the answers

    In OpenMP, what directive is used to create a parallel region?

    <p>#pragma omp parallel</p> Signup and view all the answers

    What type of queue in Grand Central Dispatch removes blocks in FIFO order, allowing only one block to be processed at a time?

    <p>Serial queue</p> Signup and view all the answers

    What does the term 'thread-local storage' refer to in threading contexts?

    <p>Dedicated storage allocated for each thread</p> Signup and view all the answers

    Which of the following describes the RecursiveAction class in Java's fork-join framework?

    <p>It does not return a result</p> Signup and view all the answers

    Which type of queues in Grand Central Dispatch allows multiple blocks to run simultaneously?

    <p>Concurrent queues</p> Signup and view all the answers

    What is a main concern regarding the semantics of fork() in thread implementations?

    <p>Whether fork() duplicates only the calling thread</p> Signup and view all the answers

    In Intel Threading Building Blocks, what is the advantage of using the parallel_for statement?

    <p>It enhances parallel loop execution.</p> Signup and view all the answers

    What is the purpose of a signal in UNIX systems?

    <p>To notify a process of a particular event</p> Signup and view all the answers

    In a multi-threaded environment, how can a signal be delivered?

    <p>To the thread to which the signal applies</p> Signup and view all the answers

    Which of the following approaches for thread cancellation allows a target thread to periodically check for termination?

    <p>Deferred cancellation</p> Signup and view all the answers

    What happens if a thread has cancellation disabled?

    <p>Cancellation remains pending until enabled</p> Signup and view all the answers

    In Linux systems, how are thread cancellations handled?

    <p>Through signals</p> Signup and view all the answers

    Which method is used for deferred cancellation in Java threads?

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

    What is the default behavior for signal handling in UNIX systems?

    <p>Kernel runs a default handler for every signal</p> Signup and view all the answers

    What are the two general approaches to thread cancellation?

    <p>Asynchronous and deferred cancellation</p> Signup and view all the answers

    Which statement about signal handlers is true?

    <p>A signal can be handled by either a default or a user-defined handler</p> Signup and view all the answers

    What is the result of invoking a thread cancellation request?

    <p>The cancellation effect depends on the thread state</p> Signup and view all the answers

    What does thread-local storage (TLS) allow for each thread?

    <p>An independent copy of data unique to that thread</p> Signup and view all the answers

    What is a characteristic of local variables compared to thread-local storage?

    <p>Local variables are restricted to a single function invocation</p> Signup and view all the answers

    In the context of scheduler activations, what is the role of a lightweight process (LWP)?

    <p>It represents a virtual processor for scheduling user threads</p> Signup and view all the answers

    What is a primary requirement for both M:M and Two-level threading models?

    <p>Communication to manage kernel thread allocation</p> Signup and view all the answers

    How does thread-local storage (TLS) compare to static data?

    <p>TLS is unique to each thread, while static data is shared</p> Signup and view all the answers

    What is the role of scheduler activations in a thread library?

    <p>To facilitate communication between the kernel and the application.</p> Signup and view all the answers

    Which of the following statements about Windows threads is accurate?

    <p>Each thread has a unique thread id.</p> Signup and view all the answers

    What is the function of the ETHREAD in the Windows threading model?

    <p>It serves as a reference to the process to which the thread belongs.</p> Signup and view all the answers

    How does Linux refer to its threads?

    <p>Tasks</p> Signup and view all the answers

    Which system call is used to create a thread in Linux?

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

    What do the KTHREAD and TEB structures have in common?

    <p>Both are data structures utilized by Windows threads.</p> Signup and view all the answers

    What is the purpose of the clone() function's flags in Linux?

    <p>To configure which resources to share between parent and child tasks.</p> Signup and view all the answers

    What defines the context of a thread in the Windows threading model?

    <p>The thread id, user and kernel stacks, and private storage area.</p> Signup and view all the answers

    What is the primary management difference between user threads and kernel threads?

    <p>User threads are managed by user-level threads library.</p> Signup and view all the answers

    Which multithreading model allows only one user-level thread to be active at a time?

    <p>Many-to-One</p> Signup and view all the answers

    What is a characteristic of the One-to-One threading model?

    <p>Each user-level thread directly maps to a kernel thread.</p> Signup and view all the answers

    Which thread library is a POSIX standard for thread creation and synchronization?

    <p>Pthreads</p> Signup and view all the answers

    What is the main function of the Java Executor framework?

    <p>To handle thread creation around the Executor interface.</p> Signup and view all the answers

    What is a benefit of using thread pools?

    <p>They improve performance by reusing existing threads.</p> Signup and view all the answers

    What does the Many-to-Many model allow for threading?

    <p>Mapping of multiple user threads to multiple kernel threads.</p> Signup and view all the answers

    Which of the following is true about Java threads?

    <p>Java threads are managed by the Java Virtual Machine (JVM).</p> Signup and view all the answers

    What does Amdahl’s Law primarily address?

    <p>The effectiveness of parallel processing.</p> Signup and view all the answers

    What is a fundamental disadvantage of the Many-to-One threading model?

    <p>Blocking one thread causes all threads to block.</p> Signup and view all the answers

    Which threading library is commonly used in UNIX operating systems?

    <p>Pthreads</p> Signup and view all the answers

    What is a key feature of the implicit threading model?

    <p>Thread creation and management is automated.</p> Signup and view all the answers

    What does the Fork-Join parallelism model emphasize?

    <p>Dividing tasks into sub-tasks that are subsequently joined.</p> Signup and view all the answers

    Study Notes

    Chapter 4: Threads & Concurrency

    • Modern applications are multithreaded
    • Threads run within applications
    • Multiple tasks within an application can be implemented by separate threads (e.g., updating a display, fetching data, spell checking, network requests)
    • Process creation is heavy-weight, while thread creation is light-weight
    • Multithreading simplifies code and increases efficiency
    • Kernels are generally multithreaded

    Single and Multithreaded Processes

    • A single-threaded process has one path of execution
    • A multithreaded process has multiple paths of execution sharing the same code, data, and files
    • Multithreaded processes have multiple program counters, stacks, and registers

    Multithreaded Server Architecture

    • A client sends a request to a server
    • The server creates a new thread to service the request
    • The server resumes listening for additional client requests

    Benefits of Multithreading

    • Responsiveness: Allows continued execution even if part of the process is blocked, crucial for user interfaces
    • Resource sharing: Threads share resources of a process, easier than shared memory or message passing
    • Economy: Cheaper than process creation, lower overhead than context switching
    • Scalability: Processes can take advantage of multicore architectures

    Multicore Programming

    • Multicore/multiprocessor systems challenge programmers in dividing activities, balancing workload, managing data dependencies, and testing/debugging parallel code
    • Parallelism allows more than one task to happen simultaneously
    • Concurrency allows tasks to happen progressively even on a single processor

    Concurrency vs. Parallelism

    • Concurrency occurs on a single core; tasks are executed one after another in time slots
    • Parallelism occurs on multiple cores; tasks can run simultaneously (at the same time)

    Types of Parallelism

    • Data parallelism: Subsets of data are distributed across multiple cores with the same operations on each
    • Task parallelism: Threads are distributed across cores, each performing a unique operation

    Amdahl's Law

    • Identifies the performance gains from adding additional cores to applications with both serial and parallel components
    • S is the serial portion of the application
    • N is the number of processing cores

    User Threads and Kernel Threads

    • User threads are managed by user-level thread libraries
      • POSIX Pthreads
      • Windows threads
      • Java threads
    • Kernel threads are supported by the kernel (e.g., Windows, Linux).

    Multithreading Models

    • Many-to-One: Many user-level threads are mapped to a single kernel thread, but multiple threads may not run in parallel
    • One-to-One: Each user-level thread maps to a kernel thread allowing for more concurrency
    • Many-to-Many: Many user-level threads are mapped to many kernel threads

    Thread Libraries

    • A thread library provides an API to programmers for creating and managing threads, typically in user space or supported by the OS

    Pthreads

    • POSIX standard (IEEE 1003.1c) thread library
    • APIs for thread creation and synchronization

    Windows Threads

    • Windows API providing kernel-level thread support, using one-to-one mapping
    • Each thread has a unique ID, register set, and storage area (context)

    Linux Threads

    • Uses tasks instead of threads
    • Thread creation through the "clone" system call, with flags to control process behavior (e.g., sharing address space, file descriptors)

    Implicit Threading

    • Thread creation and management are handled by compilers and run-time libraries, rather than programmers
      • Thread pools
      • Fork-Join
      • OpenMP
      • Grand Central Dispatch
      • Intel Threading Building Blocks

    Thread Pools

    • Advantages: increased speed, reusable threads, and bounds on the number of existing threads
    • Create a number of threads in a pool. They then await work

    Fork-Join Parallelism

    • Multiple threads (tasks) are created & joined.
    • Small tasks are solved directly, while larger tasks are broken down for concurrent work

    OpenMP

    • Provides compiler support for parallel programming in shared-memory environments.
    • Identifies parallel regions (blocks of code to run concurrently).

    Grand Central Dispatch (GCD)

    • Apple technology for macOS and iOS that manages parallel threading details.
    • Serial and concurrent queues to organize tasks.

    Intel Threading Building Blocks (TBB)

    • A template library for writing parallel C++ programs by specifying parallel code blocks.

    Threading Issues

    • Semantics of system calls (fork/exec)
    • Signal handling (delivering signals appropriately in multithreaded environments)
    • Thread cancellation (asynchronous and deferred cancellation)
    • Thread-local storage (provides each thread with its own data copy)
    • Scheduler activations (communication between user and kernel threads)

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    Chapter 4: Threads & Concurrency PDF

    Description

    Test your knowledge on the essential concepts of parallel programming, including data parallelism, task parallelism, and Amdahl's Law. This quiz covers key classes in Java, features of Grand Central Dispatch, and OpenMP directives. Assess your understanding of threading and the performance implications of parallel execution.

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