Pthreads for Parallel Applications

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.