.. highlight:: c++
  :linenothreshold: 5

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Module 6: MPI Case Study, and Pthread
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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