Operating System Chapter 4: Threads
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Questions and Answers

What is a thread?

  • A type of storage device
  • A graphic user interface
  • A fundamental unit of CPU utilization in multithreaded computer systems (correct)
  • A component of a motherboard

    • What is a benefit of using threads in an application?

  • Responsiveness
  • Resource sharing
  • Economy
  • All of the above (correct)

    • Thread creation is heavier than process creation.

    False

    What does Amdahl's Law identify?

    <p>performance gains from adding additional cores to an application that has both serial and parallel components</p> Signup and view all the answers

    Which primary thread libraries are used for managing user threads?

    <p>Java threads</p> Signup and view all the answers

    What is the primary difference between User threads and Kernel threads?

    <p>User threads are managed by user-level thread libraries, while Kernel threads are supported by the Kernel.</p> Signup and view all the answers

    Match the multithreading model with its description:

    <p>Many-to-One = Many user-level threads mapped to single kernel thread One-to-One = Each user-level thread maps to kernel thread Many-to-Many = Multiple user threads mapped to multiple kernel threads</p> Signup and view all the answers

    Many-to-One threading model allows multiple threads to run in parallel on a multicore system.

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

    What does the Two-level Model allow that differs from Many-to-Many?

    <p>Allows user threads to be bound to kernel threads</p> Signup and view all the answers

    Java threads may be created by either extending the ______ class or implementing the Runnable interface.

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

    What does Implicit Threading involve?

    <p>Implicit Threading involves the creation and management of threads done by compilers and run-time libraries.</p> Signup and view all the answers

    What is the main advantage of using Thread Pools?

    <p>Allows binding the number of threads to the pool size</p> Signup and view all the answers

    Study Notes

    Chapter 4: Threads

    • Threads: a fundamental unit of CPU utilization that forms the basis of multithreaded computer systems

    Motivation

    • Most modern applications are multithreaded, where multiple tasks within an application can be implemented by separate threads
    • Examples of tasks: update display, fetch data, spell checking, answer a network request
    • Process creation is heavy-weight, while thread creation is light-weight
    • Kernels are generally multithreaded

    Multithreaded Server Architecture

    • Benefits:
      • Responsiveness: allows continued execution if part of process is blocked, especially important for user interfaces
      • Resource Sharing: threads share resources of process, easier than shared memory or message passing
      • Economy: cheaper than process creation, thread switching lower overhead than context switching
      • Scalability: process can take advantage of multiprocessor architectures

    Multicore Programming

    • Challenges:
      • Dividing activities
      • Balance
      • Data splitting
      • Data dependency
      • Testing and debugging
    • Parallelism: a system can perform more than one task simultaneously
    • Concurrency: supports more than one task making progress, single processor/core, scheduler providing concurrency

    Multicore Programming (Cont.)

    • Types of parallelism:
      • Data parallelism: distributes subsets of the same data across multiple cores, same operation on each
      • Task parallelism: distributing threads across cores, each thread performing unique operation
    • Architectural support for threading:
      • CPUs have cores as well as hardware threads
      • Consider Oracle SPARC T4 with 8 cores, and 8 hardware threads per core

    Concurrency vs. Parallelism

    • Concurrent execution: on a single-core system
    • Parallelism: on a multi-core system

    Single and Multithreaded Processes

    • Single-threaded process: only one thread of execution
    • Multithreaded process: multiple threads of execution

    Amdahl's Law

    • Identifies performance gains: from adding additional cores to an application that has both serial and parallel components
    • S is serial portion: N processing cores
    • Formula: Speedup = (1 - S) / (1 - S + S/N)
    • Serial portion: has a disproportionate effect on performance gained by adding additional cores

    User Threads and Kernel Threads

    • User threads: management done by user-level threads library
    • Three primary thread libraries:
      • POSIX Pthreads
      • Windows threads
      • Java threads
    • Kernel threads: supported by the Kernel
    • Examples:
      • Windows
      • Solaris
      • Linux
      • Tru64 UNIX
      • Mac OS X

    Multithreading Models

    • Many-to-One: many user-level threads mapped to single kernel thread
    • One-to-One: each user-level thread maps to kernel thread
    • Many-to-Many: many user-level threads mapped to many kernel threads
    • Two-level Model: similar to many-to-many, except that it allows a user thread to be bound to kernel thread

    Thread Libraries

    • Provides programmer with API: for creating and managing threads
    • Two primary ways of implementing:
      • Library entirely in user space
      • Kernel-level library supported by the OS

    Pthreads

    • May be provided: either as user-level or kernel-level
    • A POSIX standard: API for thread creation and synchronization
    • Specification, not implementation: API specifies behavior of the thread library, implementation is up to development of the library
    • Common in UNIX operating systems: Solaris, Linux, Mac OS X

    Windows Multithreaded C Program

    • Example of creating threads: using Windows API

    Java Threads

    • Managed by the JVM: typically implemented using the threads model provided by underlying OS
    • Java threads may be created by:
      • Extending Thread class
      • Implementing the Runnable interface

    Implicit Threading

    • Growing in popularity: as numbers of threads increase, program correctness more difficult with explicit threads
    • Creation and management of threads: done by compilers and run-time libraries rather than programmers
    • Three methods explored:
      • Thread Pools
      • OpenMP
      • Grand Central Dispatch
    • Other methods: Microsoft Threading Building Blocks (TBB), java.util.concurrent package

    Thread Pools

    • Create a number of threads: in a pool where they await work
    • Advantages:
      • Usually slightly faster to service a request with an existing thread than create a new thread
      • Allows the number of threads in the application(s) to be bound to the size of the pool
      • Separating task to be performed from mechanics of creating task allows different strategies for running task

    OpenMP

    • Set of compiler directives: and an API for C, C++, FORTRAN
    • Provides support for parallel programming: in shared-memory environments
    • Identifies parallel regions: blocks of code that can run in parallel
    • Examples: #pragma omp parallel, #pragma omp parallel for

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    Learn about threads, a fundamental unit of CPU utilization, and how they form the basis of multithreaded computer systems. Understand the motivation behind multithreading and its benefits.

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