add broadcast

guide/broadcast.cc

@@ -0,0 +1,16 @@
+#include <rabit.h>
+using namespace rabit;
+const int N = 3;
+int main(int argc, char *argv[]) {
+  rabit::Init(argc, argv);
+  std::string s;
+  if (rabit::GetRank() == 0) s = "hello world";
+  printf("@node[%d] before-broadcast: s=\"%s\"\n",
+         rabit::GetRank(), s.c_str());
+  // broadcast s from node 0 to all other nodes
+  rabit::Broadcast(&s, 0);
+  printf("@node[%d] after-broadcast: s=\"%s\"\n",
+         rabit::GetRank(), s.c_str());
+  rabit::Finalize();
+  return 0;
+}