Add a LibraryClosed plugin type that is called when the library is closed (new_api). Add a way to provide a message during shutdown.

src/calibre/customize/__init__.py

@@ -781,3 +781,25 @@ class EditBookToolPlugin(Plugin):  # {{{
 
 # }}}
 
+class LibraryClosedPlugin(Plugin):  # {{{
+    '''
+    LibraryClosedPlugins are run when a library is closed, either at shutdown,
+    when the library is changed, or when a library is used in some other way.
+    At the moment these plugins won't be called by the CLI functions.
+    '''
+    type = _('Library Closed')
+
+    # minimum version 2 because it requires the new db
+    minimum_calibre_version = (2, 0, 0)
+
+    def run(self, db):
+        '''
+        The db will be a reference to the new_api (db.cache.py).
+
+        The plugin must run to completion. It must not use the GUI, threads, or
+        any signals.
+        '''
+        raise NotImplementedError('LibraryClosedPlugin '
+                'run method must be overridden in subclass')
+# }}}
+

src/calibre/customize/ui.py

@@ -9,7 +9,8 @@ from calibre.customize import (CatalogPlugin, FileTypePlugin, PluginNotFound,
                               MetadataReaderPlugin, MetadataWriterPlugin,
                               InterfaceActionBase as InterfaceAction,
                               PreferencesPlugin, platform, InvalidPlugin,
-                              StoreBase as Store, ViewerPlugin, EditBookToolPlugin)
+                              StoreBase as Store, ViewerPlugin, EditBookToolPlugin,
+                              LibraryClosedPlugin)
 from calibre.customize.conversion import InputFormatPlugin, OutputFormatPlugin
 from calibre.customize.zipplugin import loader
 from calibre.customize.profiles import InputProfile, OutputProfile
@@ -246,6 +247,16 @@ def preferences_plugins():
                 yield plugin
 # }}}
 
+# Library Closed Plugins # {{{
+def available_library_closed_plugins():
+    customization = config['plugin_customization']
+    for plugin in _initialized_plugins:
+        if isinstance(plugin, LibraryClosedPlugin):
+            if not is_disabled(plugin):
+                plugin.site_customization = customization.get(plugin.name, '')
+                yield plugin
+# }}}
+
 # Store Plugins # {{{
 
 def store_plugins():

src/calibre/db/cache.py

@@ -2013,6 +2013,13 @@ class Cache(object):
 
     @write_api
     def close(self):
+        from calibre.customize.ui import available_library_closed_plugins
+        for plugin in available_library_closed_plugins():
+            try:
+                plugin.run(self)
+            except:
+                import traceback
+                traceback.print_exc()
         self.backend.close()
 
     @write_api

src/calibre/gui2/layout.py

@@ -8,7 +8,7 @@ __docformat__ = 'restructuredtext en'
 from functools import partial
 
 from PyQt5.Qt import (QIcon, Qt, QWidget, QSize,
-    pyqtSignal, QToolButton, QMenu, QAction,
+    pyqtSignal, QToolButton, QMenu, QAction, QCoreApplication,
     QObject, QVBoxLayout, QSizePolicy, QLabel, QHBoxLayout, QActionGroup)
 
 
@@ -306,8 +306,34 @@ class MainWindowMixin(object):  # {{{
         l = self.centralwidget.layout()
         l.addWidget(self.search_bar)
 
+
+
+    def show_shutdown_message(self, message):
+        msgs = getattr(self, 'shutdown_messages', None)
+        if msgs is None:
+            msgs = self.shutdown_messages = []
+        msgs.append(message)
+
+        smw = QWidget()
+        sml = QVBoxLayout()
+        smw.setLayout(sml)
+
+        # Construct the widget containing all the messages to date. Add stretch
+        # to make it vertically centered.
+        sml.addStretch()
+        for msg in msgs:
+            sml.addWidget(QLabel(msg), alignment=Qt.AlignHCenter)
+        sml.addStretch()
+
+        # The next line is needed to prevent the main widget from being garbage
+        # collected just in case more processing is required (and it is). As we
+        # are shutting down, the memory leak isn't of concern
+        if getattr(self, 'saved_central_widget', None) is None:
+            self.saved_central_widget = self.centralWidget
+
+        # Show the shutdown messages
+        self.setCentralWidget(smw)
+        # Force processing the events needed to show the message
+        QCoreApplication.processEvents()
+
 # }}}
-
-
-
-

src/calibre/gui2/ui.py

@@ -878,7 +878,15 @@ class Main(MainWindow, MainWindowMixin, DeviceMixin, EmailMixin,  # {{{
         return True
 
     def shutdown(self, write_settings=True):
+        get_gui().show_shutdown_message(_('Shutting down'))
+
+        from calibre.customize.ui import available_library_closed_plugins
+        if available_library_closed_plugins():
+            get_gui().show_shutdown_message(
+                _('Running database shutdown plugins. This could take a few seconds...'))
+
         self.grid_view.shutdown()
+        db = None
         try:
             db = self.library_view.model().db
             cf = db.clean
@@ -908,10 +916,20 @@ class Main(MainWindow, MainWindowMixin, DeviceMixin, EmailMixin,  # {{{
         if mb is not None:
             mb.stop()
 
-        self.hide_windows()
+        if db is not None:
+            db.close()
+
+        # This happens again later. Don't do it here because it hides the
+        # shutdown messages
+        # self.hide_windows()
         try:
             try:
                 if self.content_server is not None:
+                    # If the content server has any sockets being closed then
+                    # this can take quite a long time (minutes). Tell the user that it is
+                    # happening.
+                    get_gui().show_shutdown_message(
+                        _('Shutting down the content server. This could take a while ...'))
                     s = self.content_server
                     self.content_server = None
                     s.exit()