exclude mpi run from auto-detection of horovod (#8610)

Lightning-AI · Jul 30, 2021 · b6ea637 · b6ea637
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -70,7 +70,7 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 
 
 
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+- Fixed horovod auto-detection when horovod is not installed and the launcher is `mpirun` ([#8610](https://github.com/PyTorchLightning/pytorch-lightning/pull/8610))
 
 ### Fixed
 

diff --git a/pytorch_lightning/trainer/connectors/accelerator_connector.py b/pytorch_lightning/trainer/connectors/accelerator_connector.py
@@ -857,7 +857,7 @@ def check_horovod(self):
     @staticmethod
     def has_horovodrun() -> bool:
         """Returns True if running with `horovodrun` using Gloo or OpenMPI."""
-        return "OMPI_COMM_WORLD_RANK" in os.environ or "HOROVOD_RANK" in os.environ
+        return _HOROVOD_AVAILABLE and ("OMPI_COMM_WORLD_RANK" in os.environ or "HOROVOD_RANK" in os.environ)
 
     def update_device_type_if_ipu_plugin(self) -> None:
         # This allows the poptorch.Options that are passed into the IPUPlugin to be the source of truth,