Chapter 6: MPI Case Study, and Pthread

Pthread

• POSIX standard: Unix, Linux, BSD, etc.
• Thread library for POSIX Operating Systems
• Code
  • pthread.h header file
  • -lpthread linking flag for gcc
• Types
  • pthread_t thread handle object used to refer to a thread
• Function as parameter
  • declaration like void *function_name (void * arg);
  • parameter declared like void *(*function_name)(void)
• API
  • pthread-create create a thread, run the function, return a pthread_t object
  • pthread-join wait for the thread to finish
• Compilation with gcc
  • -pthread flag, preferred
  • -lpthread old flag, retiring, should put at the very end of the gcc command line

Case Studies

Odd-even transportation sort

• Modified bubble sort to adapt to parallelization
• Assuming size N, parallelized on P processes
• Serial version
  • Phase 0: compare and swap between even element with its right neighbor
  • Phase 1: compare and swap between even element with its left neighbor
  • N rounds to finish
• Parallelized with MPI
  • Sort the local section first
  • Phase 0: compare and exchange between even process with its right neighbor
  • Phase 1: compare and swap between even process with its left neighbor

N-body MPI

• Decide the data structure
  • each process stores a whole array of masses
  • computes physical metrics of its share of local particles
  • allgether to collect local position array to global position array