Possible fix for crash on some linux systems in Qt 5 with --detach

Do the fork() before loading any Qt modules.

src/calibre/gui2/__init__.py

@@ -874,23 +874,6 @@ def setup_gui_option_parser(parser):
         parser.add_option('--detach', default=False, action='store_true',
                           help=_('Detach from the controlling terminal, if any (linux only)'))
 
-def do_detach(fork=True, setsid=True, redirect=True):
-    if fork:
-        # Detach from the controlling process.
-        if os.fork() != 0:
-            raise SystemExit(0)
-    if setsid:
-        os.setsid()
-    if redirect:
-        try:
-            plugins['speedup'][0].detach(os.devnull)
-        except AttributeError:
-            pass  # people running from source without updated binaries
-
-def detach_gui():
-    if islinux and not DEBUG:
-        do_detach()
-
 class Application(QApplication):
 
     def __init__(self, args, force_calibre_style=False, override_program_name=None, headless=False):

src/calibre/gui2/main.py

@@ -13,7 +13,7 @@ from calibre.constants import (iswindows, __appname__, isosx, DEBUG, islinux,
 from calibre.utils.ipc import gui_socket_address, RC
 from calibre.gui2 import (
     ORG_NAME, APP_UID, initialize_file_icon_provider, Application, choose_dir,
-    error_dialog, question_dialog, gprefs, detach_gui, setup_gui_option_parser)
+    error_dialog, question_dialog, gprefs, setup_gui_option_parser)
 from calibre.gui2.main_window import option_parser as _option_parser
 from calibre.gui2.splash import SplashScreen
 from calibre.utils.config import prefs, dynamic
@@ -86,8 +86,6 @@ def find_portable_library():
 def init_qt(args):
     parser = option_parser()
     opts, args = parser.parse_args(args)
-    if getattr(opts, 'detach', False):
-        detach_gui()
     find_portable_library()
     if opts.with_library is not None:
         libpath = os.path.expanduser(opts.with_library)

src/calibre/gui2/tweak_book/main.py

@@ -11,7 +11,7 @@ import sys, os, importlib, time
 from PyQt5.Qt import QIcon
 
 from calibre.constants import islinux, iswindows
-from calibre.gui2 import Application, ORG_NAME, APP_UID, setup_gui_option_parser, detach_gui, decouple
+from calibre.gui2 import Application, ORG_NAME, APP_UID, setup_gui_option_parser, decouple
 from calibre.ptempfile import reset_base_dir
 from calibre.utils.config import OptionParser
 
@@ -51,8 +51,6 @@ def _run(args, notify=None):
 
     parser = option_parser()
     opts, args = parser.parse_args(args)
-    if getattr(opts, 'detach', False):
-        detach_gui()
     decouple('edit-book-')
     override = 'calibre-edit-book' if islinux else None
     app = Application(args, override_program_name=override)

src/calibre/gui2/viewer/main.py

@@ -15,7 +15,7 @@ from calibre.gui2.viewer.toc import TOC
 from calibre.gui2.widgets import ProgressIndicator
 from calibre.gui2 import (
     Application, ORG_NAME, APP_UID, choose_files, info_dialog, error_dialog,
-    open_url, setup_gui_option_parser, detach_gui)
+    open_url, setup_gui_option_parser)
 from calibre.ebooks.oeb.iterator.book import EbookIterator
 from calibre.ebooks import DRMError
 from calibre.constants import islinux, filesystem_encoding
@@ -991,8 +991,6 @@ def main(args=sys.argv):
 
     parser = option_parser()
     opts, args = parser.parse_args(args)
-    if getattr(opts, 'detach', False):
-        detach_gui()
     open_at = float(opts.open_at.replace(',', '.')) if opts.open_at else None
     override = 'calibre-ebook-viewer' if islinux else None
     app = Application(args, override_program_name=override)

src/calibre/gui_launch.py

@@ -0,0 +1,51 @@
+#!/usr/bin/env python
+# vim:fileencoding=utf-8
+from __future__ import (unicode_literals, division, absolute_import,
+                        print_function)
+
+__license__ = 'GPL v3'
+__copyright__ = '2014, Kovid Goyal <kovid at kovidgoyal.net>'
+
+import os, sys
+
+# For some reason Qt 5 crashes on some linux systems if the fork() is done
+# after the Qt modules are loaded in calibre.gui2. We also cannot do a fork()
+# while python is importing a module. So we use this simple launcher module to
+# launch all the GUI apps, forking before Qt is loaded and not during a
+# python import.
+
+def do_detach(fork=True, setsid=True, redirect=True):
+    if fork:
+        # Detach from the controlling process.
+        if os.fork() != 0:
+            raise SystemExit(0)
+    if setsid:
+        os.setsid()
+    if redirect:
+        from calibre.constants import plugins
+        try:
+            plugins['speedup'][0].detach(os.devnull)
+        except AttributeError:
+            pass  # people running from source without updated binaries
+
+def detach_gui():
+    from calibre.constants import islinux, isbsd, DEBUG
+    if (islinux or isbsd) and not DEBUG and '--detach' in sys.argv:
+        do_detach()
+
+
+def calibre():
+    detach_gui()
+    from calibre.gui2.main import main
+    main()
+
+def ebook_viewer():
+    detach_gui()
+    from calibre.gui2.viewer.main import main
+    main()
+
+def ebook_edit():
+    detach_gui()
+    from calibre.gui2.tweak_book.main import main
+    main()
+

src/calibre/linux.py

@@ -34,11 +34,11 @@ entry_points = {
              'calibre-smtp = calibre.utils.smtp:main',
         ],
         'gui_scripts' : [
-            __appname__+' = calibre.gui2.main:main',
+            __appname__+' = calibre.gui_launch:calibre',
             'lrfviewer    = calibre.gui2.lrf_renderer.main:main',
-            'ebook-viewer = calibre.gui2.viewer.main:main',
+            'ebook-viewer = calibre.gui_launch:ebook_viewer',
-            'ebook-edit   = calibre.gui2.tweak_book.main:main',
+            'ebook-edit   = calibre.gui_launch:ebook_edit',
-                            ],
+        ],
       }
 
 class PreserveMIMEDefaults(object):