Use custom DummyLock class rather than dummy_threading.RLock

dummy_threading is not safe to use in the presence of actual threads.

fs/__init__.py

@@ -15,7 +15,7 @@ implementations of this interface such as:
 
 """
 
-__version__ = "0.2.0a3"
+__version__ = "0.2.0a4"
 __author__ = "Will McGugan (will@willmcgugan.com)"
 
 #  'base' imports * from 'path' and 'errors', so their

fs/base.py

@@ -18,12 +18,30 @@ try:
     import threading
 except ImportError:
     import dummy_threading as threading
-import dummy_threading
 
 from fs.path import *
 from fs.errors import *
 
 
+class DummyLock:
+    """A dummy lock object that doesn't do anything.
+
+    This is used as a placeholder when locking is disabled.  We can't
+    directly use the Lock class from the dummy_threading module, since
+    it attempts to sanity-check the sequence of acquire/release calls
+    in a way that breaks when real threading is available.
+    """
+
+    def acquire(self,blocking=1):
+        """Acquiring a DummyLock always succeeds."""
+        return 1
+
+    def release(self):
+        """Releasing a DummyLock always succeeds."""
+        pass
+
+
+
 def silence_fserrors(f, *args, **kwargs):
     """Perform a function call and return None if FSError is thrown
 
@@ -139,7 +157,7 @@ class FS(object):
         if thread_synchronize:
             self._lock = threading.RLock()
         else:
-            self._lock = dummy_threading.RLock()
+            self._lock = DummyLock()
 
 
     def __getstate__(self):
@@ -163,7 +181,7 @@ class FS(object):
             if lock:
                 self._lock = threading.RLock()
             else:
-                self._lock = dummy_threading.RLock()
+                self._lock = DummyLock()
 
 
     def getsyspath(self, path, allow_none=False):