Pthreads for Parallel Applications

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?

To wait for a thread to terminate Signup and view all the answers

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

-lpthread Signup and view all the answers

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

To define the thread object reference Signup and view all the answers

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

By dividing the iterations evenly among threads Signup and view all the answers

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

To pass a function argument to the thread Signup and view all the answers

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

The main thread waits for the specified thread to terminate Signup and view all the answers

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

POSIX-compliant Signup and view all the answers

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

To invoke functions from the library Signup and view all the answers

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

void* Signup and view all the answers

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

Thread rank and iteration counts Signup and view all the answers

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

To divide the work among threads Signup and view all the answers

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

They divide the iteration range among threads Signup and view all the answers

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

To link the Pthreads library during compilation Signup and view all the answers

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

pthread_t Signup and view all the answers

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

To store the number of iterations Signup and view all the answers

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

To store the global sum value 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.