From 0d6cdc0c6d484ff87fbf9067ad57a3ce538f6ccd Mon Sep 17 00:00:00 2001
From: noobpwnftw <noobpwnftw@users.noreply.github.com>
Date: Mon, 16 Jul 2018 04:27:44 +0800
Subject: [PATCH] Implement yielding loop while waiting for input

Some MPI implementations use busy-wait pooling, which will turn MPI_Bcast into busy-wait loop, workaround with our own yielding loop.
---
 src/cluster.cpp | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/src/cluster.cpp b/src/cluster.cpp
index 44a830b0..940a8ee9 100644
--- a/src/cluster.cpp
+++ b/src/cluster.cpp
@@ -124,6 +124,23 @@ bool getline(std::istream& input, std::string& str) {
       vec.assign(str.begin(), str.end());
       size = vec.size();
   }
+
+  // Some MPI implementations use busy-wait pooling, while we need yielding
+  static MPI_Request reqInput = MPI_REQUEST_NULL;
+  MPI_Ibarrier(InputComm, &reqInput);
+  if (is_root())
+      MPI_Wait(&reqInput, MPI_STATUS_IGNORE);
+  else {
+      while (true) {
+          static int flag;
+          MPI_Test(&reqInput, &flag, MPI_STATUS_IGNORE);
+          if (flag)
+              break;
+          else
+              std::this_thread::sleep_for(std::chrono::milliseconds(10));
+      }
+  }
+
   MPI_Bcast(&size, 1, MPI_UNSIGNED_LONG, 0, InputComm);
   if (!is_root())
       vec.resize(size);