Hotfix race condition in mutex creation/deletion

On my machine TestHeaderChange.testDirect() fails

    with cache.lock, cache.statistics as stats:
  File "C:\Users\hesse\code\clcache\clcache.py", line 211, in __enter__
    self.acquire()
  File "C:\Users\hesse\code\clcache\clcache.py", line 227, in acquire
    raise CacheLockException(errorString)
__main__.CacheLockException: Error! WaitForSingleObject returns -1, last error 6

Author: Hubert Hesse

clcache.py

@@ -20,6 +20,7 @@
 import multiprocessing
 import re
 
+
 VERSION = "3.2.0-dev"
 
 HashAlgorithm = hashlib.md5
@@ -198,17 +199,21 @@ class CacheLock(object):
     can be used in 'with' statements. """
     INFINITE = 0xFFFFFFFF
     WAIT_ABANDONED_CODE = 0x00000080
+    INVALID_HANDLE = 0x00000006
 
     def __init__(self, mutexName, timeoutMs):
-        mutexName = 'Local\\' + mutexName
-        self._mutex = windll.kernel32.CreateMutexW(
-            wintypes.INT(0),
-            wintypes.INT(0),
-            mutexName)
+        self.mutexName = 'Local\\' + mutexName
+        self.createMutex()
         self._timeoutMs = timeoutMs
         self._acquired = False
         assert self._mutex
 
+    def createMutex(self):
+        self._mutex = windll.kernel32.CreateMutexW(
+            wintypes.INT(0),
+            wintypes.BOOLEAN(False),
+            self.mutexName)
+
     def __enter__(self):
         if not self._acquired:
             self.acquire()
@@ -224,10 +229,15 @@ def acquire(self):
         result = windll.kernel32.WaitForSingleObject(
             self._mutex, wintypes.INT(self._timeoutMs))
         if result not in [0, self.WAIT_ABANDONED_CODE]:
+            error = windll.kernel32.GetLastError()
             errorString = 'Error! WaitForSingleObject returns {result}, last error {error}'.format(
                 result=result,
-                error=windll.kernel32.GetLastError())
-            raise CacheLockException(errorString)
+                error=error)
+            if error == self.INVALID_HANDLE:
+                self.createMutex()
+                self.acquire()
+            else:
+                raise CacheLockException(errorString)
         self._acquired = True
 
     def release(self):