LazyFS: lazy-creation code factored out of ConnectionManagerFS

fs/remote.py

@@ -22,7 +22,7 @@ import time
 import copy
 
 from fs.base import FS, threading
-from fs.wrapfs import WrapFS, wrap_fs_methods
+from fs.wrapfs import WrapFS, LazyFS, wrap_fs_methods
 from fs.path import *
 from fs.errors import *
 
@@ -156,7 +156,7 @@ class RemoteFileBuffer(object):
             self._lock.release()
 
 
-class ConnectionManagerFS(WrapFS):
+class ConnectionManagerFS(LazyFS):
     """FS wrapper providing simple connection management of a remote FS.
 
     The ConnectionManagerFS class is designed to wrap a remote FS object
@@ -174,9 +174,9 @@ class ConnectionManagerFS(WrapFS):
     operating-system integration may be added.
 
     Since some remote FS classes can raise RemoteConnectionError during
-    initialisation, this class also provides a simple "lazy initialisation"
-    facility.  The remote FS can be specified as an FS instance, an FS
-    subclass, or a (class,args) or (class,args,kwds) tuple. For example:
+    initialisation, this class makes use of lazy initialization. The
+    remote FS can be specified as an FS instance, an FS subclass, or a
+    (class,args) or (class,args,kwds) tuple. For example:
 
         >>> fs = ConnectionManagerFS(MyRemoteFS("http://www.example.com/"))
         Traceback (most recent call last):
@@ -200,41 +200,6 @@ class ConnectionManagerFS(WrapFS):
         self._poll_sleeper = threading.Event()
         self.connected = connected
 
-    def _get_wrapped_fs(self):
-        try:
-            return self.__dict__["wrapped_fs"]
-        except KeyError:
-            self._connection_cond.acquire()
-            try:
-                try:
-                    return self.__dict__["wrapped_fs"]
-                except KeyError:
-                    fs = self._fsclass(*self._fsargs,**self._fskwds)
-                    self.__dict__["wrapped_fs"] = fs
-                    return fs
-            finally:
-                self._connection_cond.release()
-
-    def _set_wrapped_fs(self,fs):
-        if isinstance(fs,FS):
-            self.__dict__["wrapped_fs"] = fs
-        elif isinstance(fs,type):
-            self._fsclass = fs
-            self._fsargs = []
-            self._fskwds = {}
-        else:
-            self._fsclass = fs[0]
-            try:
-                self._fsargs = fs[1]
-            except IndexError:
-                self._fsargs = []
-            try:
-                self._fskwds = fs[2]
-            except IndexError:
-                self._fskwds = {}
-
-    wrapped_fs = property(_get_wrapped_fs,_set_wrapped_fs)
-
     def setcontents(self,path,data):
         self.wrapped_fs.setcontents(path,data)
 

fs/tests/__init__.py

@@ -512,6 +512,7 @@ class FSTestCases:
         fs3 = pickle.loads(pickle.dumps(self.fs,-1))
         self.assert_(fs3.isfile("test1"))
 
+
     def test_big_file(self):
         chunk_size = 1024 * 256
         num_chunks = 4

fs/wrapfs.py

@@ -233,6 +233,7 @@ class WrapFS(FS):
             self.wrapped_fs.close()
         super(WrapFS,self).close()
 
+
 def wrap_fs_methods(decorator,cls=None,exclude=[]):
     """Apply the given decorator to all FS methods on the given class.
 
@@ -270,6 +271,73 @@ def wrap_fs_methods(decorator,cls=None,exclude=[]):
         return apply_decorator
 
 
+class LazyFS(WrapFS):
+    """Simple 'lazy initialization' for FS objects.
+
+    This FS wrapper can be created with an FS instance, an FS class, or a
+    (class,args,kwds) tuple.  The actual FS instance will be created on demand
+    the first time it is accessed.
+    """
+
+    def __init__(self,fs):
+        super(LazyFS,self).__init__(fs)
+        self._lazy_creation_lock = threading.RLock()
+
+    def __getstate__(self):
+        state = super(LazyFS,self).__getstate__()
+        del state["_lazy_creation_lock"]
+        return state
+
+    def __setstate__(self,state):
+        self.__dict__.update(state)
+        self._lazy_creation_lock = threading.RLock()
+
+    def _get_wrapped_fs(self):
+        """Obtain the wrapped FS instance, created it if necessary."""
+        try:
+            return self.__dict__["wrapped_fs"]
+        except KeyError:
+            self._lazy_creation_lock.acquire()
+            try:
+                try:
+                    return self.__dict__["wrapped_fs"]
+                except KeyError:
+                    fs = self._fsclass(*self._fsargs,**self._fskwds)
+                    self.__dict__["wrapped_fs"] = fs
+                    return fs
+            finally:
+                self._lazy_creation_lock.release()
+
+    def _set_wrapped_fs(self,fs):
+        if isinstance(fs,FS):
+            self.__dict__["wrapped_fs"] = fs
+        elif isinstance(fs,type):
+            self._fsclass = fs
+            self._fsargs = []
+            self._fskwds = {}
+        else:
+            self._fsclass = fs[0]
+            try:
+                self._fsargs = fs[1]
+            except IndexError:
+                self._fsargs = []
+            try:
+                self._fskwds = fs[2]
+            except IndexError:
+                self._fskwds = {}
+
+    wrapped_fs = property(_get_wrapped_fs,_set_wrapped_fs)
+
+
+    def close(self):
+        if not self.closed:
+            #  If it was never initialized, create a fake one to close.
+            if "wrapped_fs" not in self.__dict__:
+                self.__dict__["wrapped_fs"] = FS()
+            super(LazyFS,self).close()
+
+
+
 class HideDotFiles(WrapFS):
     """FS wrapper class that hides dot-files in directory listings.