diff --git a/src/calibre/gui2/__init__.py b/src/calibre/gui2/__init__.py
index ae25dead4e..f69788e849 100644
--- a/src/calibre/gui2/__init__.py
+++ b/src/calibre/gui2/__init__.py
@@ -271,6 +271,9 @@ class Dispatcher(QObject):
     Convenience class to use Qt signals with arbitrary python callables.
     By default, ensures that a function call always happens in the
     thread this Dispatcher was created in.
+
+    Note that if you create the Dispatcher in a thread without an event loop of
+    its own, the function call will happen in the GUI thread (I think).
     '''
     dispatch_signal = pyqtSignal(object, object)
 
@@ -292,11 +295,20 @@ class FunctionDispatcher(QObject):
     '''
     Convenience class to use Qt signals with arbitrary python functions.
     By default, ensures that a function call always happens in the
-    thread this Dispatcher was created in.
+    thread this FunctionDispatcher was created in.
+
+    Note that you must create FunctionDispatcher objects in the GUI thread.
     '''
     dispatch_signal = pyqtSignal(object, object, object)
 
     def __init__(self, func, queued=True, parent=None):
+        global gui_thread
+        if gui_thread is None:
+            gui_thread = QThread.currentThread()
+        if not is_gui_thread():
+            raise ValueError(
+                'You can only create a FunctionDispatcher in the GUI thread')
+
         QObject.__init__(self, parent)
         self.func = func
         typ = Qt.QueuedConnection
@@ -305,10 +317,9 @@ class FunctionDispatcher(QObject):
         self.dispatch_signal.connect(self.dispatch, type=typ)
         self.q = Queue.Queue()
         self.lock = threading.Lock()
-        self.calling_thread = QThread.currentThread()
 
     def __call__(self, *args, **kwargs):
-        if self.calling_thread == QThread.currentThread():
+        if is_gui_thread():
             return self.func(*args, **kwargs)
         with self.lock:
             self.dispatch_signal.emit(self.q, args, kwargs)
diff --git a/src/calibre/gui2/device.py b/src/calibre/gui2/device.py
index eb35e937c0..ab02a183c6 100644
--- a/src/calibre/gui2/device.py
+++ b/src/calibre/gui2/device.py
@@ -6,18 +6,18 @@ __copyright__ = '2008, Kovid Goyal <kovid at kovidgoyal.net>'
 import os, traceback, Queue, time, cStringIO, re, sys
 from threading import Thread
 
-from PyQt4.Qt import QMenu, QAction, QActionGroup, QIcon, SIGNAL, \
-                     Qt, pyqtSignal, QDialog, QObject
+from PyQt4.Qt import (QMenu, QAction, QActionGroup, QIcon, SIGNAL,
+                     Qt, pyqtSignal, QDialog, QObject)
 
-from calibre.customize.ui import available_input_formats, available_output_formats, \
-    device_plugins
+from calibre.customize.ui import (available_input_formats, available_output_formats,
+    device_plugins)
 from calibre.devices.interface import DevicePlugin
 from calibre.devices.errors import UserFeedback, OpenFeedback
 from calibre.gui2.dialogs.choose_format_device import ChooseFormatDeviceDialog
 from calibre.utils.ipc.job import BaseJob
 from calibre.devices.scanner import DeviceScanner
-from calibre.gui2 import config, error_dialog, Dispatcher, dynamic, \
-        warning_dialog, info_dialog, choose_dir, FunctionDispatcher
+from calibre.gui2 import (config, error_dialog, Dispatcher, dynamic,
+        warning_dialog, info_dialog, choose_dir, FunctionDispatcher)
 from calibre.ebooks.metadata import authors_to_string
 from calibre import preferred_encoding, prints, force_unicode, as_unicode
 from calibre.utils.filenames import ascii_filename
@@ -35,8 +35,9 @@ class DeviceJob(BaseJob): # {{{
 
     def __init__(self, func, done, job_manager, args=[], kwargs={},
             description=''):
-        BaseJob.__init__(self, description, done=done)
+        BaseJob.__init__(self, description)
         self.func = func
+        self.callback_on_done = done
         self.args, self.kwargs = args, kwargs
         self.exception = None
         self.job_manager = job_manager
@@ -50,6 +51,10 @@ class DeviceJob(BaseJob): # {{{
     def job_done(self):
         self.duration = time.time() - self.start_time
         self.percent = 1
+        try:
+            self.callback_on_done(self)
+        except:
+            pass
         self.job_manager.changed_queue.put(self)
 
     def report_progress(self, percent, msg=''):
diff --git a/src/calibre/gui2/email.py b/src/calibre/gui2/email.py
index c8adeb7d31..4b4c920a7e 100644
--- a/src/calibre/gui2/email.py
+++ b/src/calibre/gui2/email.py
@@ -11,8 +11,8 @@ from binascii import unhexlify
 from functools import partial
 from itertools import repeat
 
-from calibre.utils.smtp import compose_mail, sendmail, extract_email_address, \
-        config as email_config
+from calibre.utils.smtp import (compose_mail, sendmail, extract_email_address,
+        config as email_config)
 from calibre.utils.filenames import ascii_filename
 from calibre.customize.ui import available_input_formats, available_output_formats
 from calibre.ebooks.metadata import authors_to_string
@@ -67,8 +67,8 @@ class Sendmail(object):
             from_ = opts.from_
             if not from_:
                 from_ = 'calibre <calibre@'+socket.getfqdn()+'>'
-            msg = compose_mail(from_, to, text, subject, open(attachment, 'rb'),
-                    aname)
+            with lopen(attachment, 'rb') as f:
+                msg = compose_mail(from_, to, text, subject, f, aname)
             efrom, eto = map(extract_email_address, (from_, to))
             eto = [eto]
             sendmail(msg, efrom, eto, localhost=None,