Optimize the single book add/save case by using a spare pool

src/calibre/gui2/actions/add.py

@@ -159,7 +159,8 @@ class AddAction(InterfaceAction):
 
     def do_add_recursive(self, root, single):
         from calibre.gui2.add2 import Adder
-        Adder(root, single_book_per_directory=single, db=self.gui.current_db, callback=self._files_added, parent=self.gui)
+        Adder(root, single_book_per_directory=single, db=self.gui.current_db,
+              callback=self._files_added, parent=self.gui, pool=self.gui.spare_pool())
 
     def add_recursive_single(self, *args):
         '''
@@ -362,7 +363,8 @@ class AddAction(InterfaceAction):
         if not paths:
             return
         from calibre.gui2.add2 import Adder
-        Adder(paths, db=None if to_device else self.gui.current_db, parent=self.gui, callback=partial(self._files_added, on_card=on_card))
+        Adder(paths, db=None if to_device else self.gui.current_db,
+              parent=self.gui, callback=partial(self._files_added, on_card=on_card), pool=self.gui.spare_pool())
 
     def _files_added(self, adder, on_card=None):
         if adder.items:
@@ -485,4 +487,4 @@ class AddAction(InterfaceAction):
         if ok_paths:
             from calibre.gui2.add2 import Adder
             callback = partial(self._add_from_device_adder, on_card=None, model=view.model())
-            Adder(ok_paths, db=None, parent=self.gui, callback=callback)
+            Adder(ok_paths, db=None, parent=self.gui, callback=callback, pool=self.gui.spare_pool())

src/calibre/gui2/actions/save_to_disk.py

@@ -113,7 +113,7 @@ class SaveToDiskAction(InterfaceAction):
             if save_cover is not None:
                 opts.save_cover = save_cover
             book_ids = set(map(self.gui.library_view.model().id, rows))
-            Saver(book_ids, self.gui.current_db, opts, path, parent=self.gui)
+            Saver(book_ids, self.gui.current_db, opts, path, parent=self.gui, pool=self.gui.spare_pool())
         else:
             paths = self.gui.current_view().model().paths(rows)
             self.gui.device_manager.save_books(

src/calibre/gui2/add2.py

@@ -55,7 +55,7 @@ class Adder(QObject):
 
     do_one_signal = pyqtSignal()
 
-    def __init__(self, source, single_book_per_directory=True, db=None, parent=None, callback=None):
+    def __init__(self, source, single_book_per_directory=True, db=None, parent=None, callback=None, pool=None):
         if not validate_source(source, parent):
             raise ValueError('Bad source')
         QObject.__init__(self, parent)
@@ -64,7 +64,7 @@ class Adder(QObject):
         self.add_formats_to_existing = prefs['add_formats_to_existing']
         self.do_one_signal.connect(self.tick, type=Qt.QueuedConnection)
         self.tdir = PersistentTemporaryDirectory('_add_books')
-        self.pool = None
+        self.pool = pool
         self.pd = ProgressDialog(_('Adding books...'), _('Scanning for files...'), min=0, max=0, parent=parent, icon='add_book.png')
         self.db = getattr(db, 'new_api', None)
         if self.db is not None:

src/calibre/gui2/save.py

@@ -72,7 +72,7 @@ class Saver(QObject):
 
     do_one_signal = pyqtSignal()
 
-    def __init__(self, book_ids, db, opts, root, parent=None):
+    def __init__(self, book_ids, db, opts, root, parent=None, pool=None):
         QObject.__init__(self, parent)
         self.db = db.new_api
         self.plugboards = self.db.pref('plugboards', {})
@@ -87,7 +87,7 @@ class Saver(QObject):
         self.do_one = self.do_one_collect
         self.ids_to_collect = iter(self.all_book_ids)
         self.tdir = PersistentTemporaryDirectory('_save_to_disk')
-        self.pool = None
+        self.pool = pool
 
         self.pd.show()
         self.root, self.opts, self.path_length = sanitize_args(root, opts)

src/calibre/gui2/ui.py

@@ -20,10 +20,10 @@ from PyQt5.Qt import (
     Qt, QTimer, QAction, QMenu, QIcon, pyqtSignal, QUrl, QFont, QDialog,
     QApplication, QSystemTrayIcon)
 
-from calibre import prints, force_unicode
+from calibre import prints, force_unicode, detect_ncpus
 from calibre.constants import __appname__, isosx, filesystem_encoding, DEBUG
 from calibre.utils.config import prefs, dynamic
-from calibre.utils.ipc.server import Server
+from calibre.utils.ipc.pool import Pool
 from calibre.db.legacy import LibraryDatabase
 from calibre.customize.ui import interface_actions, available_store_plugins
 from calibre.gui2 import (error_dialog, GetMetadata, open_url,
@@ -213,7 +213,7 @@ class Main(MainWindow, MainWindowMixin, DeviceMixin, EmailMixin,  # {{{
         self.preferences_action, self.quit_action = actions
         self.library_path = library_path
         self.content_server = None
-        self.spare_servers = []
+        self._spare_pool = None
         self.must_restart_before_config = False
         self.listener = Listener(listener)
         self.check_messages_timer = QTimer()
@@ -312,7 +312,7 @@ class Main(MainWindow, MainWindowMixin, DeviceMixin, EmailMixin,  # {{{
         self.alt_esc_action.triggered.connect(self.clear_additional_restriction)
 
         # ###################### Start spare job server ########################
-        QTimer.singleShot(1000, self.add_spare_server)
+        QTimer.singleShot(1000, self.create_spare_pool)
 
         # ###################### Location Manager ########################
         self.location_manager.location_selected.connect(self.location_selected)
@@ -472,21 +472,15 @@ class Main(MainWindow, MainWindowMixin, DeviceMixin, EmailMixin,  # {{{
         MainWindow.resizeEvent(self, ev)
         self.search.setMaximumWidth(self.width()-150)
 
-    def add_spare_server(self, *args):
-        self.spare_servers.append(Server(limit=int(config['worker_limit']/2.0)))
+    def create_spare_pool(self, *args):
+        if self._spare_pool is None:
+            num = min(detect_ncpus(), int(config['worker_limit']/2.0))
+            self._spare_pool = Pool(max_workers=num, name='GUIPool')
 
-    @property
-    def spare_server(self):
-        # Because of the use of the property decorator, we're called one
-        # extra time. Ignore.
-        if not hasattr(self, '__spare_server_property_limiter'):
-            self.__spare_server_property_limiter = True
-            return None
-        try:
-            QTimer.singleShot(1000, self.add_spare_server)
-            return self.spare_servers.pop()
-        except:
-            pass
+    def spare_pool(self):
+        ans, self._spare_pool = self._spare_pool, None
+        QTimer.singleShot(1000, self.create_spare_pool)
+        return ans
 
     def do_proceed(self, func, payload):
         if callable(func):
@@ -893,8 +887,6 @@ class Main(MainWindow, MainWindowMixin, DeviceMixin, EmailMixin,  # {{{
         self.listener.close()
         self.job_manager.server.close()
         self.job_manager.threaded_server.close()
-        while self.spare_servers:
-            self.spare_servers.pop().close()
         self.device_manager.keep_going = False
         self.auto_adder.stop()
         mb = self.library_view.model().metadata_backup
@@ -912,6 +904,8 @@ class Main(MainWindow, MainWindowMixin, DeviceMixin, EmailMixin,  # {{{
                 pass
         except KeyboardInterrupt:
             pass
+        if self._spare_pool is not None:
+            self._spare_pool.shutdown()
         from calibre.db.delete_service import shutdown
         shutdown()
         time.sleep(2)

src/calibre/utils/ipc/pool.py

@@ -122,12 +122,12 @@ class Pool(Thread):
         else:
             join_with_timeout(self.tracker, timeout)
 
-    def shutdown(self):
+    def shutdown(self, wait_time=0.1):
         ''' Shutdown this pool, terminating all worker process. The pool cannot
         be used after a shutdown. '''
         self.shutting_down = True
         self.events.put(None)
-        self.shutdown_workers()
+        self.shutdown_workers(wait_time=wait_time)
 
     def create_worker(self):
         from calibre.utils.ipc.simple_worker import start_pipe_worker