[Bugfix] Handle case where process has no elements to update, in NCCL communicator (#3035)

Co-authored-by: Minjie Wang <wmjlyjemaine@gmail.com>

[Bugfix] Handle case where process has no elements to update, in NCCL communicator (#3035)
Co-authored-by: Minjie Wang <wmjlyjemaine@gmail.com>
7415eaa5 · nv-dlasalle · GitHub · cb2327d4 · 7415eaa5
Unverified Commit 7415eaa5 authored Jun 23, 2021 by nv-dlasalle Committed by GitHub Jun 23, 2021
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src/runtime/cuda/nccl_api.cu src/runtime/cuda/nccl_api.cu +1 -1

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--- a/src/runtime/cuda/nccl_api.cu
+++ b/src/runtime/cuda/nccl_api.cu
@@ -176,7 +176,7 @@ std::pair<IdArray, NDArray> SparsePush(
  Workspace<DType> send_value(device, ctx, num_in*num_feat);
  // permute the indices and values
-  {
+  if (num_in > 0) {
    const dim3 block(256);
    const dim3 grid((num_in+block.x-1)/block.x);