Added exception handlers to take care of the bugs with the file and db backends

(refs #515).  Eugene, I'm going to leave #515 open; can you check the bug fixes
in this revision and mark the ticket as closed if you're satisfied?  I don't 
run Django in a threaded environment, so I'm having issues reproducing your 
errors.


git-svn-id: http://code.djangoproject.com/svn/django/trunk@699 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/core/cache.py

@@ -289,10 +289,7 @@ class _FileCache(_SimpleCache):
     def __init__(self, dir, params):
         self._dir = dir
         if not os.path.exists(self._dir):
-            try:
-                os.makedirs(self._dir)
-            except OSError:
-                raise EnvironmentError, "Cache directory '%s' does not exist and could not be created'" % self._dir
+            self._createdir()
         _SimpleCache.__init__(self, dir, params)
         del self._cache
         del self._expire_info
@@ -316,7 +313,10 @@ class _FileCache(_SimpleCache):
         fname = self._key_to_file(key)
         if timeout is None:
             timeout = self.default_timeout
+        try:
             filelist = os.listdir(self._dir)
+        except (IOError, OSError):
+            self._createdir()
         if len(filelist) > self._max_entries:
             self._cull(filelist)
         try:
@@ -347,6 +347,12 @@ class _FileCache(_SimpleCache):
             except (IOError, OSError):
                 pass
 
+    def _createdir(self):    
+        try:
+            os.makedirs(self._dir)
+        except OSError:
+            raise EnvironmentError, "Cache directory '%s' does not exist and could not be created'" % self._dir
+
     def _key_to_file(self, key):
         return os.path.join(self._dir, urllib.quote_plus(key))
 
@@ -355,7 +361,7 @@ class _FileCache(_SimpleCache):
 #############
 
 import base64
-from django.core.db import db
+from django.core.db import db, DatabaseError
 from datetime import datetime
 
 class _DBCache(_Cache):
@@ -400,10 +406,15 @@ class _DBCache(_Cache):
             self._cull(cursor, now)
         encoded = base64.encodestring(pickle.dumps(value, 2)).strip()
         cursor.execute("SELECT cache_key FROM %s WHERE cache_key = %%s" % self._table, [key])
+        try:
             if cursor.fetchone():
                 cursor.execute("UPDATE %s SET value = %%s, expires = %%s WHERE cache_key = %%s" % self._table, [encoded, str(exp), key])
             else:
                 cursor.execute("INSERT INTO %s (cache_key, value, expires) VALUES (%%s, %%s, %%s)" % self._table, [key, encoded, str(exp)])
+        except DatabaseError:
+            # To be threadsafe, updates/inserts are allowed to fail silently
+            pass
+        else:
             db.commit()
         
     def delete(self, key):