code example
MPI-2 message passing interface, version 2
one-sided communication defined in MPI-2
TBB boost threads
part of the C++ boost library
AltiVec PowerPC SIMD instructions

#include <mpi.h>
#include <boost/thread/thread.hpp>
using namespace boost;
#include <altivec.h>

#define PROC (8)

struct thread1 {
 float *x, *y, *ep;
 int i0, i1, p;
 thread1(float *xx, float *yy, float *ee, int pp, int ii0, int ii1) :
  x(xx), y(yy), ep(ee), p(pp), i0(ii0), i1(ii1) {}
 void operator()() {
  // do computation
  float ve[4] = {0, 0, 0, 0};
  float e = 0;
  for (int i=i0; i<i1; i+=4) {
   float* yp = &y[i+1], y0 = &y[i], ym = &y[i-1];
   vec_st(vec_madd(
    vec_splats(.5),
    vec_add(
     vec_perm(vec_ld(0,ym), vec_ld(16,ym),
      vec_lvsl(0,ym)),
     vec_perm(vec_ld(0,yp), vec_ld(16,yp),
      vec_lvsl(0,yp))),
    vec_splats(0.)),
    0, &x[i]);
   vec_st(vec_add(
    vec_ld(0,&ve[0]),vec_madd(
     vec_ld(0,y0),
     vec_ld(0,y0),
     vec_splats(0.))),
    0, &ve[0]);
  }
  e += ve[0] + ve[1] + ve[2] + ve[3];
  *ep = e;
 }
};

int main(int argc, char *argv[]) {
  int n = ...;
  MPI_Init(&argc, &argv);
  int numproc, me;
  MPI_Comm_size(MPI_COMM_WORLD, &numproc);
  MPI_Comm_rank(MPI_COMM_WORLD, &me);
  int p_left = -1, p_right = -1;
  if (me > 0)
   p_left = me-1;
  if (me < numproc-1)
   p_right = me+1;
  int n_local0 = 1 + (me * (n-1)) / numproc;
  int n_local1 = 1 + ((me+1) * (n-1)) / numproc;
  // allocate only local part + ghost zone of the arrays x,y
  float *x, *y;
  MPI_Alloc_mem(sizeof(float) * (n_local1 - n_local0 + 2),
   MPI_INFO_NULL, &x);
  MPI_Alloc_mem(sizeof(float) * (n_local1 - n_local0 + 2),
   MPI_INFO_NULL, &y);
  x -= (n_local0 - 1);
  y -= (n_local0 - 1);
  MPI_Win win;
  MPI_Win_create(&y[n_local0], sizeof(float) * (n_local1-n_local0+2),
   sizeof(float), MPI_INFO_NULL, MPI_COMM_WORLD, &win);

  ... // fill x, y

  // fill ghost zone
  MPI_Win_fence(0, win);
  if (p_left != -1)
   MPI_Put(&y[n_local0], 1, MPI_FLOAT, p_left,
   n_local1-n_local0+1, 1, MPI_FLOAT, win);
  if (p_right != -1)
   MPI_Put(&y[n_local1-1], 1, MPI_FLOAT, p_right,
   0, 1, MPI_FLOAT, win);
  MPI_Win_fence(0, win);

  float e = 0;
  float e_vec[PROC];
  thread_group grp;
  // start threads and wait for termination
  for (int i=0; i<PROC; ++i) {
   thread1 t(x, y, &e_vec[i], i,
     n_local0+((n_local1-n_local0)*i)/PROC, n_local0+((n_local1-n_local0)*(i+1))/PROC);
   grp.create_thread(t);
  }
  grp.join_all();
  for (int i=0; i<PROC; ++i)
   e += e_vec[i];

  float e_local = e;
  MPI_Allreduce(&e_local, &e, 1, MPI_FLOAT, MPI_SUM, MPI_COMM_WORLD);

  ... // output x, e

  MPI_Win_free(&win);
  x += (n_local0 - 1);
  y += (n_local0 - 1);
  MPI_Free_mem(y);
  MPI_Free_mem(x);
  MPI_Finalize();
  return 0;
}

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