Fix race condition in luigi.lock.acquire_for (spotify#2357) (spotify#…

…2477)

luigi/lock.py

@@ -21,6 +21,7 @@
 """
 from __future__ import print_function
 
+import errno
 import hashlib
 import os
 import sys
@@ -102,10 +103,14 @@ def acquire_for(pid_dir, num_available=1, kill_signal=None):
 
  my_pid, my_cmd, pid_file = get_info(pid_dir)
 
- # Check if there is a pid file corresponding to this name
- if not os.path.exists(pid_dir):
+ # Create a pid file if it does not exist
+ try:
  os.mkdir(pid_dir)
  os.chmod(pid_dir, 0o777)
+ except OSError as exc:
+ if exc.errno != errno.EEXIST:
+ raise
+ pass
 
  # Let variable "pids" be all pids who exist in the .pid-file who are still
  # about running the same command.