Fix failing to acquire lock in case of parallel runs (#1524)

Signed-off-by: Bernat Gabor <[email protected]>

docs/changelog/1516.bugfix.rst

@@ -0,0 +1 @@
+Creating virtual environments in parallel fail with cannot acquire lock within app data - by ``gaborbernat``.

src/virtualenv/util/lock.py

@@ -2,12 +2,13 @@
 from __future__ import absolute_import, unicode_literals
 
 import logging
+import os
 from contextlib import contextmanager
 from threading import Lock
 
 from filelock import FileLock, Timeout
 
-from virtualenv.util.path import Path, ensure_dir
+from virtualenv.util.path import Path
 
 
 class _CountedFileLock(FileLock):
@@ -72,11 +73,17 @@ def __exit__(self, exc_type, exc_val, exc_tb):
         self._release(self._lock)
 
     def _lock_file(self, lock):
-        ensure_dir(self.path)
+        # multiple processes might be trying to get a first lock... so we cannot check if this directory exist without
+        # a lock, but that lock might then become expensive, and it's not clear where that lock should live.
+        # Instead here we just ignore if we fail to create the directory.
+        try:
+            os.makedirs(str(self.path))
+        except OSError:
+            pass
         try:
             lock.acquire(0.0001)
         except Timeout:
-            logging.debug("lock file %s present, will block until released", self._lock.lock_file)
+            logging.debug("lock file %s present, will block until released", lock.lock_file)
             lock.release()  # release the acquire try from above
             lock.acquire()
 

tests/unit/create/test_creator.py

@@ -5,8 +5,10 @@
 import logging
 import os
 import stat
+import subprocess
 import sys
 from itertools import product
+from threading import Thread
 
 import pytest
 import six
@@ -275,3 +277,16 @@ def test_cross_major(cross_python, coverage_env, tmp_path, current_fastest):
     coverage_env()
     env = PythonInfo.from_exe(str(result.creator.exe))
     assert env.version_info.major != CURRENT.version_info.major
+
+
+def test_create_parallel(tmp_path, monkeypatch):
+    monkeypatch.setenv(str("_VIRTUALENV_OVERRIDE_APP_DATA"), str(tmp_path))
+
+    def create(count):
+        subprocess.check_call([sys.executable, "-m", "virtualenv", str(tmp_path / "venv{}".format(count))])
+
+    threads = [Thread(target=create, args=(i,)) for i in range(1, 4)]
+    for thread in threads:
+        thread.start()
+    for thread in threads:
+        thread.join()