Make communication with toc editor process more robust

A crash on dialog close no longer affects writing the result. And avoid
using the racy lock files for ipc.

src/calibre/gui2/actions/toc_edit.py

@@ -152,37 +152,31 @@ class ToCEditAction(InterfaceAction):
         self.check_for_completions()
 
     def check_for_completions(self):
-        from calibre.utils.lock import lock_file
+        from calibre.utils.filenames import retry_on_fail
         for job in tuple(self.jobs):
-            lock_path = job['path'] + '.lock'
-            if job['started']:
-                if not os.path.exists(lock_path):
-                    self.jobs.remove(job)
-                    continue
-                try:
-                    lf = lock_file(lock_path, timeout=0.01, sleep_time=0.005)
-                except EnvironmentError:
-                    continue
-                else:
-                    self.jobs.remove(job)
-                    ret = int(lf.read().decode('ascii'))
-                    lf.close()
-                    os.remove(lock_path)
-                    if ret == 0:
-                        db = self.gui.current_db
-                        if db.new_api.library_id != job['library_id']:
-                            error_dialog(self.gui, _('Library changed'), _(
-                                'Cannot save changes made to {0} by the ToC editor as'
-                                ' the calibre library has changed.').format(job['title']), show=True)
-                        else:
-                            db.new_api.add_format(job['book_id'], job['fmt'], job['path'], run_hooks=False)
-                    os.remove(job['path'])
+            started_path = job['path'] + '.started'
+            result_path = job['path'] + '.result'
+            if job['started'] and os.path.exists(result_path):
+                self.jobs.remove(job)
+                with open(result_path) as f:
+                    ret = int(f.read().strip())
+                retry_on_fail(os.remove, result_path)
+                if ret == 0:
+                    db = self.gui.current_db
+                    if db.new_api.library_id != job['library_id']:
+                        error_dialog(self.gui, _('Library changed'), _(
+                            'Cannot save changes made to {0} by the ToC editor as'
+                            ' the calibre library has changed.').format(job['title']), show=True)
+                    else:
+                        db.new_api.add_format(job['book_id'], job['fmt'], job['path'], run_hooks=False)
+                os.remove(job['path'])
             else:
                 if monotonic() - job['start_time'] > 10:
                     self.jobs.remove(job)
                     continue
-                if os.path.exists(lock_path):
+                if os.path.exists(started_path):
                     job['started'] = True
+                    retry_on_fail(os.remove, started_path)
         if self.jobs:
             QTimer.singleShot(100, self.check_for_completions)
 

src/calibre/gui2/toc/main.py

@@ -5,6 +5,7 @@
 
 import os
 import sys
+import tempfile
 import textwrap
 from functools import partial
 from qt.core import (
@@ -29,7 +30,7 @@ from calibre.gui2.progress_indicator import ProgressIndicator
 from calibre.gui2.toc.location import ItemEdit
 from calibre.ptempfile import reset_base_dir
 from calibre.utils.config import JSONConfig
-from calibre.utils.lock import ExclusiveFile
+from calibre.utils.filenames import atomic_rename
 from calibre.utils.logging import GUILog
 from polyglot.builtins import map, range, unicode_type
 
@@ -985,8 +986,9 @@ class TOCEditor(QDialog):  # {{{
     explode_done = pyqtSignal(object)
     writing_done = pyqtSignal(object)
 
-    def __init__(self, pathtobook, title=None, parent=None, prefs=None):
+    def __init__(self, pathtobook, title=None, parent=None, prefs=None, write_result_to=None):
         QDialog.__init__(self, parent)
+        self.write_result_to = write_result_to
         self.prefs = prefs or te_prefs
         self.pathtobook = pathtobook
         self.working = True
@@ -1071,7 +1073,7 @@ class TOCEditor(QDialog):  # {{{
                   ' more information.')%self.book_title, det_msg=tb, show=True)
             super(TOCEditor, self).reject()
             return
-
+        self.write_result(0)
         super(TOCEditor, self).accept()
 
     def reject(self):
@@ -1083,8 +1085,17 @@ class TOCEditor(QDialog):  # {{{
         else:
             self.working = False
             self.prefs['toc_editor_window_geom'] = bytearray(self.saveGeometry())
+            self.write_result(1)
             super(TOCEditor, self).reject()
 
+    def write_result(self, res):
+        if self.write_result_to:
+            with tempfile.NamedTemporaryFile(dir=os.path.dirname(self.write_result_to), delete=False) as f:
+                src = f.name
+                f.write(str(res).encode('utf-8'))
+                f.flush()
+            atomic_rename(src, self.write_result_to)
+
     def start(self):
         t = Thread(target=self.explode)
         t.daemon = True
@@ -1140,15 +1151,15 @@ def main(path=None, title=None):
         # launched from within calibre, as both use calibre-parallel.exe
         set_app_uid(TOC_DIALOG_APP_UID)
 
-    with ExclusiveFile(path + '.lock') as wf:
-        override = 'calibre-gui' if islinux else None
-        app = Application([], override_program_name=override)
-        d = TOCEditor(path, title=title)
-        d.start()
-        ret = 1
-        if d.exec_() == QDialog.DialogCode.Accepted:
-            ret = 0
-        wf.write('{}'.format(ret).encode('ascii'))
+    with open(path + '.started', 'w'):
+        pass
+    override = 'calibre-gui' if islinux else None
+    app = Application([], override_program_name=override)
+    d = TOCEditor(path, title=title, write_result_to=path + '.result')
+    d.start()
+    ret = 1
+    if d.exec_() == QDialog.DialogCode.Accepted:
+        ret = 0
     del d
     del app
     raise SystemExit(ret)