Merge rabit

rabit/guide/lazy_allreduce.cc

@@ -0,0 +1,34 @@
+/*!
+ *  Copyright (c) 2014 by Contributors
+ * \file basic.cc
+ * \brief This is an example demonstrating what is Allreduce
+ *
+ * \author Tianqi Chen
+ */
+#include <rabit/rabit.h>
+
+using namespace rabit;
+const int N = 3;
+int main(int argc, char *argv[]) {
+  int a[N] = {0};
+  rabit::Init(argc, argv);
+  // lazy preparation function
+  auto prepare = [&]() {
+    printf("@node[%d] run prepare function\n", rabit::GetRank());
+    for (int i = 0; i < N; ++i) {
+      a[i] = rabit::GetRank() + i;
+    }
+  };
+  printf("@node[%d] before-allreduce: a={%d, %d, %d}\n",
+         rabit::GetRank(), a[0], a[1], a[2]);
+  // allreduce take max of each elements in all processes
+  Allreduce<op::Max>(&a[0], N, prepare);
+  printf("@node[%d] after-allreduce-sum: a={%d, %d, %d}\n",
+         rabit::GetRank(), a[0], a[1], a[2]);
+  // rum second allreduce
+  Allreduce<op::Sum>(&a[0], N);
+  printf("@node[%d] after-allreduce-max: a={%d, %d, %d}\n",
+         rabit::GetRank(), a[0], a[1], a[2]);
+  rabit::Finalize();
+  return 0;
+}