handle test folder cleanup being unable to create a cleanup lock

changelog/4181.bugfix.rst

@@ -0,0 +1 @@
+Handle race condition between creation and deletion of temporary folders.

src/_pytest/pathlib.py

@@ -182,9 +182,15 @@ def register_cleanup_lock_removal(lock_path, register=atexit.register):
     return register(cleanup_on_exit)
 
 
-def delete_a_numbered_dir(path):
-    """removes a numbered directory"""
+def maybe_delete_a_numbered_dir(path):
+    """removes a numbered directory if its lock can be obtained"""
+    try:
         create_cleanup_lock(path)
+    except (OSError, EnvironmentError):
+        #  known races:
+        #  * other process did a cleanup at the same time
+        #  * deletable folder was found
+        return
     parent = path.parent
 
     garbage = parent.joinpath("garbage-{}".format(uuid.uuid4()))
@@ -214,7 +220,7 @@ def ensure_deletable(path, consider_lock_dead_if_created_before):
 def try_cleanup(path, consider_lock_dead_if_created_before):
     """tries to cleanup a folder if we can ensure its deletable"""
     if ensure_deletable(path, consider_lock_dead_if_created_before):
-        delete_a_numbered_dir(path)
+        maybe_delete_a_numbered_dir(path)
 
 
 def cleanup_candidates(root, prefix, keep):

testing/test_tmpdir.py

@@ -4,6 +4,7 @@ import sys
 import six
 
 import pytest
+from _pytest import pathlib
 from _pytest.pathlib import Path
 
 
@@ -284,11 +285,17 @@ class TestNumberedDir(object):
         rmtree(adir, force=True)
         assert not adir.exists()
 
-    def test_cleanup_symlink(self, tmp_path):
+    def test_cleanup_ignores_symlink(self, tmp_path):
         the_symlink = tmp_path / (self.PREFIX + "current")
         attempt_symlink_to(the_symlink, tmp_path / (self.PREFIX + "5"))
         self._do_cleanup(tmp_path)
 
+    def test_removal_accepts_lock(self, tmp_path):
+        folder = pathlib.make_numbered_dir(root=tmp_path, prefix=self.PREFIX)
+        pathlib.create_cleanup_lock(folder)
+        pathlib.maybe_delete_a_numbered_dir(folder)
+        assert folder.is_dir()
+
 
 def attempt_symlink_to(path, to_path):
     """Try to make a symlink from "path" to "to_path", skipping in case this platform