From fdae87aa6effa80ef317794292b48f90c9ec9ba6 Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Fri, 9 Oct 2020 22:53:21 +0530
Subject: [PATCH] When restarting detect actual parent process death instead of
 sleeping for two seconds

This should hopefully fix the issue with restarts not working on some
Windows machines because the parent process takes longer than two
seconds to die.
---
 src/calibre/gui2/main.py | 40 +++++++++++++++++++++++++++++++++++-----
 1 file changed, 35 insertions(+), 5 deletions(-)

diff --git a/src/calibre/gui2/main.py b/src/calibre/gui2/main.py
index a0fa608fae..e0ee88296f 100644
--- a/src/calibre/gui2/main.py
+++ b/src/calibre/gui2/main.py
@@ -353,12 +353,20 @@ class GuiRunner(QObject):
         self.initialize_db()
 
 
+def set_restarting_env_var():
+    if iswindows:
+        ctime = plugins['winutil'][0].get_process_times(None)[0]
+        os.environ['CALIBRE_RESTARTING_FROM_GUI'] = str(ctime)
+    else:
+        os.environ['CALIBRE_RESTARTING_FROM_GUI'] = str(os.getpid())
+
+
 def run_in_debug_mode():
     from calibre.debug import run_calibre_debug
     import tempfile, subprocess
     fd, logpath = tempfile.mkstemp('.txt')
     os.close(fd)
-    os.environ['CALIBRE_RESTARTING_FROM_GUI'] = environ_item('1')
+    set_restarting_env_var()
     run_calibre_debug(
         '--gui-debug', logpath, stdout=lopen(logpath, 'wb'),
         stderr=subprocess.STDOUT, stdin=lopen(os.devnull, 'rb'))
@@ -403,8 +411,8 @@ def run_gui(opts, args, listener, app, gui_debug=None):
                 run_calibre_debug('-c', 'import sys, os, time; time.sleep(3); os.execlp("open", "open", sys.argv[-1])', app)
             else:
                 import subprocess
-                os.environ['CALIBRE_RESTARTING_FROM_GUI'] = environ_item('1')
-                if iswindows and hasattr(winutil, 'prepare_for_restart'):
+                set_restarting_env_var()
+                if iswindows:
                     winutil.prepare_for_restart()
                 if hasattr(sys, 'run_local'):
                     cmd = [sys.run_local]
@@ -514,9 +522,31 @@ def create_listener():
     return Listener(address=gui_socket_address())
 
 
+def wait_for_parent_to_die(ppid, max_wait=10):
+    ppid = int(ppid)
+    if iswindows:
+        get_process_times = plugins['winutil'][0].get_process_times
+
+        def parent_done():
+            try:
+                ctime = get_process_times(os.getppid())[0]
+            except Exception:
+                return True
+            return ctime > ppid
+
+    else:
+        def parent_done():
+            return os.getppid() != ppid
+
+    st = time.monotonic()
+    while not parent_done() and time.monotonic() - st < max_wait:
+        time.sleep(0.1)
+
+
 def main(args=sys.argv):
-    if os.environ.pop('CALIBRE_RESTARTING_FROM_GUI', None) == environ_item('1'):
-        time.sleep(2)  # give the parent process time to cleanup and close
+    ppid = os.environ.pop('CALIBRE_RESTARTING_FROM_GUI', None)
+    if ppid is not None:
+        wait_for_parent_to_die(ppid)
     if iswindows and 'CALIBRE_REPAIR_CORRUPTED_DB' in os.environ:
         windows_repair()
         return 0