import torch hangs when running in subprocess with preexec_fn=os.setpgrp, python >=3.13, conda env #159645
Description
🐛 Describe the bug
Trying to import torch in a subprocess after setting preexec_fn=os.setpgrp in a conda env with Python >= 3.13 causes the code execution to hang indefinitely.
If any of the above is changed, torch import as expected.
See detailed repro here.
Snippet to Repro:
import subprocess
import sys
import os
TIMEOUT_SEC = 20
def test_yes_setpgrp_no_import_torch():
print("Testing YES preexec_fn=os.setpgrp, NO import torch...")
try:
proc = subprocess.Popen(
[
sys.executable,
"-c",
"print('=== SUCCESS: YES os.setpgrp, NO torch import')",
],
preexec_fn=os.setpgrp,
)
stdout, stderr = proc.communicate(timeout=TIMEOUT_SEC)
print("PASS")
except Exception as e:
print(f"ERROR: {e}")
def test_no_setpgrp_yes_torch_import():
print("Testing NO preexec_fn=os.setpgrp, YES import torch...")
try:
proc = subprocess.Popen(
[
sys.executable,
"-c",
"import torch; print('=== SUCCESS: NO os.setpgrp, YES import torch')",
]
)
stdout, stderr = proc.communicate(timeout=TIMEOUT_SEC)
print("PASS")
except Exception as e:
print(f"ERROR: {e}")
def test_yes_setpgrp_yes_torch_import():
print("Testing YES preexec_fn=os.setpgrp, YES import torch...")
try:
proc = subprocess.Popen(
[
sys.executable,
"-c",
"import torch; print('=== SUCCESS: YES os.setpgrp, YES import torch')",
],
preexec_fn=os.setpgrp,
)
# Wait with timeout
try:
stdout, stderr = proc.communicate(timeout=TIMEOUT_SEC)
print("PASS")
except subprocess.TimeoutExpired:
print(f"FAIL: Process timed out after {TIMEOUT_SEC} seconds")
proc.kill()
except Exception as e:
print(f"ERROR: {e}")
if __name__ == "__main__":
test_yes_setpgrp_no_import_torch()
test_no_setpgrp_yes_torch_import()
test_yes_setpgrp_yes_torch_import()Versions
torch==2.7.1
python==3.13.5
conda==25.3.1