Pthreads for Parallel Applications
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Questions and Answers

What is the primary assumption of Pthreads library?

  • A multi-core processor
  • A cluster of computers
  • A distributed memory architecture
  • A POSIX-compliant operating system (correct)

    • What is the purpose of the pthread_attr_t argument in the pthread_create function?

  • To pass a function argument to the thread
  • To set the thread's scheduling priority
  • To define the thread's creation attributes (correct)
  • To specify the thread's stack size

    • What is the return type of the start_routine function in Pthreads?

  • void
  • void* (correct)
  • int
  • long long

    • What is the purpose of the pthread_join function?

    <p>To wait for a thread to terminate</p> Signup and view all the answers

    What is the linker option required to compile a Pthreads program?

    <p>-lpthread</p> Signup and view all the answers

    What is the purpose of the thread_p argument in the pthread_create function?

    <p>To define the thread object reference</p> Signup and view all the answers

    How does the Increment function in the example application divide the work among threads?

    <p>By dividing the iterations evenly among threads</p> Signup and view all the answers

    What is the purpose of the arg_p argument in the pthread_create function?

    <p>To pass a function argument to the thread</p> Signup and view all the answers

    What is the effect of calling pthread_join on the main thread?

    <p>The main thread waits for the specified thread to terminate</p> Signup and view all the answers

    What is the common operating system requirement for Pthreads to work?

    <p>POSIX-compliant</p> Signup and view all the answers

    What is the purpose of including the library headers in a Pthreads program?

    <p>To invoke functions from the library</p> Signup and view all the answers

    What is the type of the 'start_routine' function argument in the pthread_create function?

    <p>void*</p> Signup and view all the answers

    What is the output of the 'printf' statement in the 'Increment' function?

    <p>Thread rank and iteration counts</p> Signup and view all the answers

    What is the purpose of the 'my_n' variable in the 'Increment' function?

    <p>To divide the work among threads</p> Signup and view all the answers

    What is the effect of the 'my_first_i' and 'my_last_i' variables in the 'Increment' function?

    <p>They divide the iteration range among threads</p> Signup and view all the answers

    What is the purpose of the 'gcc -lpthread hello.c -o hello' command?

    <p>To link the Pthreads library during compilation</p> Signup and view all the answers

    What is the type of the 'thread_p' argument in the pthread_create function?

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

    What is the purpose of the 'n' variable in the example application?

    <p>To store the number of iterations</p> Signup and view all the answers

    What is the purpose of the 'sum' variable in the example application?

    <p>To store the global sum value</p> Signup and view all the answers

    Study Notes

    Introduction to Pthreads

    • Pthreads is a library for developing parallel applications using shared memory.
    • It assumes a POSIX-compliant operating system as its base.
    • The library can be embedded in any programming language, usually C.

    Compilation and Execution of Pthreads Programs

    • To compile a Pthreads program, include the library headers using #include .
    • Use the linker option -lpthread to link the program with the Pthreads library.
    • Example compilation command: gcc -lpthread hello.c -o hello.

    Pthread API to Create and Join Threads

    • The pthread_create function is used to create a new thread:
      • pthread_t* thread_p: thread object reference
      • const pthread_attr_t* attr_p: creation attributes (can be NULL)
      • void* (*start_routine)(void*): function to execute
      • void* arg_p: function argument
    • The pthread_join function is used to wait for a thread to finish:
      • pthread_t thread: thread to wait for
      • void** ret_val_p: return value of the thread

    Thread Function Header

    • The header for a thread function is void* start_routine(void* args_p);.

    Example Incremental Application

    • The example application uses global variables:
      • long long n: number of iterations
      • long long thread_count: number of threads
      • long long sum: global sum value
    • The Increment function is executed by each thread:
      • void* Increment(void* rank): function to increment the global sum
      • The function calculates its own range of iteration based on the thread rank and number of threads.

    Pthreads Overview

    • Pthreads is a library for developing parallel applications using shared memory.
    • It assumes a POSIX-compliant operating system as its base.
    • The library can be embedded in any programming language, usually C.

    Compilation and Execution of Pthreads Programs

    • To compile a Pthreads program, include the library headers with #include .
    • Use the linker option -lpthread to link the program.
    • Example compilation command: gcc -lpthread hello.c -o hello.

    Pthread API

    Thread Creation

    • The pthread_create function creates a new thread:
      • pthread_t* thread_p: thread object reference
      • const pthread_attr_t* attr_p: creation attributes (can be NULL)
      • void* (*start_routine)(void*): function to execute
      • void* arg_p: function argument
    • Generic function header for the start_routine: void* start_routine(void* args_p);

    Thread Joining

    • The pthread_join function waits for a thread to terminate:
      • pthread_t thread: thread to join
      • void** ret_val_p: return value of the thread (can be NULL)

    Example Incremental Application

    • The example application demonstrates thread creation and synchronization.
    • Global variables:
      • long long n: number of iterations
      • long long thread_count: number of threads
      • long long sum: global sum value
    • The Increment function is the thread operation:
      • Each thread calculates its range of iterations based on its rank.
      • The thread prints its range and then increments the global sum.

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