Do not scan system for fonts in viewer processes and on multiple calibre invocations

src/calibre/gui2/__init__.py

@@ -764,7 +764,7 @@ qt_app = None
 class Application(QApplication):
 
     def __init__(self, args, force_calibre_style=False,
-            override_program_name=None, scan_for_fonts=False):
+            override_program_name=None):
         self.file_event_hook = None
         if override_program_name:
             args = [override_program_name] + args[1:]
@@ -780,7 +780,6 @@ class Application(QApplication):
         qt_app = self
         self._file_open_paths = []
         self._file_open_lock = RLock()
-        self.load_builtin_fonts(scan_for_fonts=scan_for_fonts)
         self.setup_styles(force_calibre_style)
 
     if DEBUG:

src/calibre/gui2/main.py

@@ -95,7 +95,7 @@ def init_qt(args):
     QCoreApplication.setOrganizationName(ORG_NAME)
     QCoreApplication.setApplicationName(APP_UID)
     override = 'calibre-gui' if islinux else None
-    app = Application(args, override_program_name=override, scan_for_fonts=True)
+    app = Application(args, override_program_name=override)
     actions = tuple(Main.create_application_menubar())
     app.setWindowIcon(QIcon(I('lt.png')))
     return app, opts, args, actions
@@ -291,6 +291,7 @@ def run_in_debug_mode(logpath=None):
 
 def run_gui(opts, args, actions, listener, app, gui_debug=None):
     initialize_file_icon_provider()
+    app.load_builtin_fonts(scan_for_fonts=True)
     if not dynamic.get('welcome_wizard_was_run', False):
         from calibre.gui2.wizard import wizard
         wizard().exec_()

src/calibre/gui2/viewer/main.py

@@ -1137,6 +1137,7 @@ def main(args=sys.argv):
     if pid <= 0:
         override = 'calibre-ebook-viewer' if islinux else None
         app = Application(args, override_program_name=override)
+        app.load_builtin_fonts()
         app.setWindowIcon(QIcon(I('viewer.png')))
         QApplication.setOrganizationName(ORG_NAME)
         QApplication.setApplicationName(APP_UID)