commit 3cbec5453ba92d1f6def57f958b2b8bb14da1ce3
author Pieter Noordhuis <pcnoordhuis@gmail.com> Mon Sep 17 21:47:00 2018 -0700
committer Facebook Github Bot <facebook-github-bot@users.noreply.github.com> Mon Sep 17 21:58:15 2018 -0700
tree 7c34650d5355c36d6cec0992e999e124c766c66f
parent a7cbcb1bb9f1b8244f2441a0fcc8d491677c988b

Reorder statements for readability (#11764)

Summary:
I was reading this a couple times before figuring out it's also the entry point for the MPI_COMM_WORLD.

Reordered statements and added comment to clarify.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/11764

Differential Revision: D9882834

Pulled By: pietern

fbshipit-source-id: a9282d55368815925fd695a2541354e5aec599da

torch/lib/c10d/ProcessGroupMPI.cpp

diff --git a/torch/lib/c10d/ProcessGroupMPI.cpp b/torch/lib/c10d/ProcessGroupMPI.cpp
index 0369996..63846b4 100644
--- a/torch/lib/c10d/ProcessGroupMPI.cpp
+++ b/torch/lib/c10d/ProcessGroupMPI.cpp
@@ -253,33 +253,30 @@
   MPI_CHECK(MPI_Comm_size(MPI_COMM_WORLD, &size));
   MPI_CHECK(MPI_Comm_rank(MPI_COMM_WORLD, &rank));
 
-  globalLock.unlock();
-
   if (rank < 0 || size < 0) {
     throw std::runtime_error("Failed to get the world_size / rank");
   }
 
+  // If no ranks are specified, assume we're creating the root group
   if (ranks.empty()) {
-    return std::make_shared<ProcessGroupMPI>(rank, size, MPI_COMM_WORLD);
-  } else {
-    std::unique_lock<std::mutex> globalLock(pgGlobalMutex_);
-
-    MPI_Group worldGroup;
-    MPI_CHECK(MPI_Comm_group(MPI_COMM_WORLD, &worldGroup));
-
-    MPI_Group ranksGroup;
-    MPI_CHECK(
-        MPI_Group_incl(worldGroup, ranks.size(), ranks.data(), &ranksGroup));
-
-    MPI_Comm groupComm;
-    MPI_CHECK(MPI_Comm_create(MPI_COMM_WORLD, ranksGroup, &groupComm));
-
-    MPI_CHECK(MPI_Group_free(&worldGroup));
-    MPI_CHECK(MPI_Group_free(&ranksGroup));
-
     globalLock.unlock();
-    return std::make_shared<ProcessGroupMPI>(rank, size, groupComm);
+    return std::make_shared<ProcessGroupMPI>(rank, size, MPI_COMM_WORLD);
   }
+
+  MPI_Group worldGroup;
+  MPI_CHECK(MPI_Comm_group(MPI_COMM_WORLD, &worldGroup));
+
+  MPI_Group ranksGroup;
+  MPI_CHECK(MPI_Group_incl(worldGroup, ranks.size(), ranks.data(), &ranksGroup));
+
+  MPI_Comm groupComm;
+  MPI_CHECK(MPI_Comm_create(MPI_COMM_WORLD, ranksGroup, &groupComm));
+
+  MPI_CHECK(MPI_Group_free(&worldGroup));
+  MPI_CHECK(MPI_Group_free(&ranksGroup));
+
+  globalLock.unlock();
+  return std::make_shared<ProcessGroupMPI>(rank, size, groupComm);
 }
 
 ProcessGroupMPI::ProcessGroupMPI(int rank, int size, MPI_Comm pgComm)