Cache resiliency

msal_extensions/cache_lock.py

@@ -2,6 +2,9 @@
 import os
 import sys
 import errno
+import time
+import logging
+
 import portalocker
 from distutils.version import LooseVersion
 
@@ -25,7 +28,24 @@ def __init__(self, lockfile_path):
             flags=portalocker.LOCK_EX | portalocker.LOCK_NB,
             **open_kwargs)
 
+    def try_to_create_lock_file(self):
+        retries_no = 100
+        retry_delay_milliseconds = 0.150
+        for i in range(retries_no):
+            try:
+                with open(self._lockpath, 'x'):
+                    return True
+            except OSError as err:
+                if err.errno == errno.EEXIST:
+                    time.sleep(retry_delay_milliseconds)
+            except ValueError:
+                logging.warning("Python 2 does not support atomic creation of file")
+                return False
+        return False
+
     def __enter__(self):
+        if not self.try_to_create_lock_file():
+            logging.warning("Failed to create lock file")
         file_handle = self._lock.__enter__()
         file_handle.write('{} {}'.format(os.getpid(), sys.argv[0]).encode('utf-8'))
         return file_handle

tests/test_cache_lock_file_perf.py

@@ -67,7 +67,7 @@ def test_lock_for_high_workload(temp_location):
 
 
 def test_lock_for_timeout(temp_location):
-    num_of_processes = 10
+    num_of_processes = 30
     sleep_interval = 1
     _run_multiple_processes(num_of_processes, temp_location, sleep_interval)
     count = _validate_result_in_cache(temp_location)