Speed up subprocess launch (#15738)

src/lightning_lite/strategies/launchers/subprocess_script.py

@@ -14,10 +14,8 @@
 import os
 import subprocess
 import sys
-from time import sleep
 from typing import Any, Callable, Sequence
 
-import numpy as np
 from lightning_utilities.core.imports import RequirementCache
 
 from lightning_lite.plugins.environments.cluster_environment import ClusterEnvironment
@@ -126,11 +124,6 @@ def _call_children_scripts(self) -> None:
                 command = _basic_subprocess_cmd()
             subprocess.Popen(command, env=env_copy)
 
-            # starting all processes at once can cause issues
-            # with dataloaders delay between 1-10 seconds
-            delay = np.random.uniform(1, 5, 1)[0]
-            sleep(delay)
-
     def _check_can_spawn_children(self) -> None:
         if self.cluster_environment.local_rank() != 0:
             raise RuntimeError(

src/pytorch_lightning/strategies/launchers/subprocess_script.py

@@ -13,10 +13,8 @@
 # limitations under the License.
 import os
 import subprocess
-from time import sleep
 from typing import Any, Callable, Optional
 
-import numpy as np
 from lightning_utilities.core.imports import RequirementCache
 
 import pytorch_lightning as pl
@@ -123,11 +121,6 @@ def _call_children_scripts(self) -> None:
 
             subprocess.Popen(command, env=env_copy)
 
-            # starting all processes at once can cause issues
-            # with dataloaders delay between 1-10 seconds
-            delay = np.random.uniform(1, 5, 1)[0]
-            sleep(delay)
-
     def _check_can_spawn_children(self) -> None:
         if self.cluster_environment.local_rank() != 0:
             raise RuntimeError(

tests/tests_lite/strategies/launchers/test_subprocess_script.py

@@ -47,9 +47,8 @@ def test_subprocess_script_launcher_external_processes(popen_mock):
     popen_mock.assert_not_called()
 
 
-@mock.patch("lightning_lite.strategies.launchers.subprocess_script.sleep")
 @mock.patch("lightning_lite.strategies.launchers.subprocess_script.subprocess.Popen")
-def test_subprocess_script_launcher_launch_processes(popen_mock, _):
+def test_subprocess_script_launcher_launch_processes(popen_mock):
     cluster_env = Mock()
     cluster_env.creates_processes_externally = False
     cluster_env.local_rank.return_value = 0