Fix locking thread safe log objects' exception()

Also fix the default stream ignoring the stream parameter to its
constructor.

Change RLock to Lock for better performance, since locking recursion is
not needed

src/calibre/utils/logging.py

@@ -12,18 +12,17 @@ ERROR = 3
 
 import sys, traceback, cStringIO
 from functools import partial
-from threading import RLock
+from threading import Lock
 
-from calibre import isbytestring, force_unicode, as_unicode
+from calibre import isbytestring, force_unicode, as_unicode, prints
 
 class Stream(object):
 
     def __init__(self, stream=None):
-        from calibre import prints
-        self._prints = partial(prints, safe_encode=True)
         if stream is None:
             stream = cStringIO.StringIO()
         self.stream = stream
+        self._prints = partial(prints, safe_encode=True, file=stream)
 
     def flush(self):
         self.stream.flush()
@@ -53,7 +52,6 @@ class FileStream(Stream):
         Stream.__init__(self, stream)
 
     def prints(self, level, *args, **kwargs):
-        kwargs['file'] = self.stream
         self._prints(*args, **kwargs)
 
 class HTMLStream(Stream):
@@ -171,18 +169,24 @@ class ThreadSafeLog(Log):
 
     def __init__(self, level=Log.INFO):
         Log.__init__(self, level=level)
-        self._lock = RLock()
+        self._lock = Lock()
 
     def prints(self, *args, **kwargs):
         with self._lock:
             Log.prints(self, *args, **kwargs)
 
+    def exception(self, *args, **kwargs):
+        limit = kwargs.pop('limit', None)
+        with self._lock:
+            Log.prints(self, ERROR, *args, **kwargs)
+            Log.prints(self, DEBUG, traceback.format_exc(limit))
+
 class ThreadSafeWrapper(Log):
 
     def __init__(self, other_log):
         Log.__init__(self, level=other_log.filter_level)
         self.outputs = list(other_log.outputs)
-        self._lock = RLock()
+        self._lock = Lock()
 
     def prints(self, *args, **kwargs):
         with self._lock: