Add mpi_gossip for prototype

scripts/mpi_gossip.cc

@@ -0,0 +1,71 @@
+// A pure C++ mpi win ops to implement simple gossip algorithm.
+// Compile and run with
+//   mpicxx -o mpi_gossip mpi_gossip.cc -std=c++11 && bfrun -np 8 mpi_gossip
+#include <mpi.h>
+#include <stdio.h>
+
+#include <cassert>
+#include <thread>
+
+void AvgTwo(void* invec, void* inoutvec, int* len,
+                    MPI_Datatype* datatype) {
+  if (*datatype == MPI_DOUBLE) {
+    double* invec_d = (double*)invec;
+    double* inoutvec_d = (double*)inoutvec;
+    for (int i = 0; i < *len; i++) {
+      inoutvec_d[i] += invec_d[i];
+      inoutvec_d[i] /= 2.0;
+    }
+  } else if (*datatype == MPI_FLOAT) {
+    float* invec_d = (float*)invec;
+    float* inoutvec_d = (float*)inoutvec;
+    for (int i = 0; i < *len; i++) {
+      inoutvec_d[i] += invec_d[i];
+      inoutvec_d[i] /= 2.0;
+    }
+  }
+}
+
+int main(int argc, char** argv) {
+  int rank, nproc;
+  int mpi_threads_provided;
+  MPI_Init_thread(&argc, &argv, 1, &mpi_threads_provided);
+  // MPI_Init(&argc, &argv);
+  MPI_Comm_rank(MPI_COMM_WORLD, &rank);
+  MPI_Comm_size(MPI_COMM_WORLD, &nproc);
+  assert(nproc % 2 == 0);
+
+  const int win_size = 10;
+  double array[win_size];
+  double recv_array[win_size];
+  for (int i = 0; i < win_size; i++) {
+    array[i] = rank;
+    recv_array[i] = 0.0;
+  }
+
+  MPI_Op MPI_AVG_TWO;
+  MPI_Op_create((MPI_User_function*)AvgTwo, true, &MPI_AVG_TWO);
+
+  MPI_Win win;
+  MPI_Win_create(array, win_size * sizeof(double), sizeof(double),
+                 MPI_INFO_NULL, MPI_COMM_WORLD, &win);
+  for (int i = 0; i < 100; i++) {
+    if (rank % 2 == 1) continue;  // passive worker
+    int target_rank = (rank + 1 + 2*i) % nproc;
+    MPI_Win_lock(MPI_LOCK_EXCLUSIVE, target_rank, MPI_MODE_NOCHECK, win);
+    MPI_Fetch_and_op(array, recv_array, MPI_DOUBLE, target_rank, 0, MPI_AVG_TWO,
+                     win);
+    auto temp_type = MPI_DOUBLE;
+    AvgTwo(recv_array, array, (int*)&win_size, &temp_type);
+    MPI_Win_unlock(target_rank, win);
+  }
+
+  MPI_Barrier(MPI_COMM_WORLD);
+  printf("Rank %d: %f, %f\t", rank, array[0], recv_array[0]);
+
+  printf("Done\n");
+  MPI_Win_free(&win);
+
+  MPI_Finalize();
+  return 0;
+}