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Correct CWD for ddp subprocesses when using Hydra #2719

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merged 3 commits into from
Jul 28, 2020
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Correct CWD for ddp subprocesses when using Hydra #2719

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8fc9f6e
when hydra is enabled, set the cwd of subprocesses to the original cw…
yukw777 Jul 27, 2020
0170fbe
move imports up
yukw777 Jul 27, 2020
71317b8
clean up imports
yukw777 Jul 27, 2020
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10 changes: 8 additions & 2 deletions pytorch_lightning/trainer/distrib_data_parallel.py
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Original file line number Diff line number Diff line change
Expand Up @@ -162,7 +162,8 @@ def train_fx(trial_hparams, cluster_manager, _):


try:
from hydra.utils import to_absolute_path
from hydra.utils import to_absolute_path, get_original_cwd
from hydra.core.hydra_config import HydraConfig
except ImportError:
HYDRA_AVAILABLE = False
else:
Expand Down Expand Up @@ -464,7 +465,12 @@ def spawn_ddp_children(self, model):
env_copy['LOCAL_RANK'] = f'{local_rank}'

# start process
proc = subprocess.Popen(command, env=env_copy)
# if hydra is available and initialized, make sure to set the cwd correctly
cwd: Optional[str] = None
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this will break for non hydra users... no?
shouldn't cwd be set to something for non hydra people?

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None is the default value for cwd (https://docs.python.org/3/library/subprocess.html#subprocess.Popen). If None, it just uses whatever the current value for cwd is.

If cwd is not None, the function changes the working directory to cwd before executing the child. cwd can be a string, bytes or path-like object. In particular, the function looks for executable (or for the first item in args) relative to cwd if the executable path is a relative path.

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So currently, we're setting cwd to None for everyone, hence the problem for Hydra scripts.

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can we pull the cwd correctly then and also use it for non hydra users?

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sure, but what should we set it to for non hydra users? do you think we need to save the original cwd and then use that? I feel like that's going down the slippery slope b/c we can't possibly anticipate how a script will change the cwd... for hydra scripts we can be sure b/c of the way it operates...

if HYDRA_AVAILABLE:
if HydraConfig.initialized():
cwd = get_original_cwd()
proc = subprocess.Popen(command, env=env_copy, cwd=cwd)
self.interactive_ddp_procs.append(proc)

# starting all processes at once can cause issues
Expand Down