settings: avoid syncing when cola.sync is configured to false

We can now inhibit the use of `os.sync()` using `git config`:

    git config --global cola.sync false

Resolves: #1305
Reported-by: @installgentoo via github
Signed-off-by: David Aguilar <davvid@gmail.com>

CHANGES.rst

@@ -34,6 +34,11 @@ Fixes
   (`#1385 <https://github.com/git-cola/git-cola/issues/1385>`_)
   (`#1388 <https://github.com/git-cola/git-cola/pull/1388>`_)
 
+* Git Cola syncs the OS-level filesystem when windows are closed, which can
+  cause performance issues. The `cola.sync` configuration variable can
+  be configured to `false` to avoid this behavior.
+  (`#1305 <https://github.com/git-cola/git-cola/issues/1305>`_)
+
 
 .. _v4.6.1:
 

cola/settings.py

@@ -165,7 +165,7 @@ def rename_recent(self, path, name, new_name):
     def path(self):
         return self.config_path
 
-    def save(self):
+    def save(self, sync=True):
         """Write settings robustly to avoid losing data during a forced shutdown.
 
         To save robustly we take these steps:
@@ -190,7 +190,8 @@ def save(self):
         if not rename_path(path_tmp, path):
             return
         # Flush the data to disk.
-        core.sync()
+        if sync:
+            core.sync()
         # Delete the .bak file.
         if core.exists(path_bak):
             remove_path(path_bak)
@@ -276,11 +277,11 @@ def asdict(self, path=None):
             entry['path'] = normalize(entry['path'])
         return values
 
-    def save_gui_state(self, gui):
+    def save_gui_state(self, gui, sync=True):
         """Saves settings for a cola view"""
         name = gui.name()
         self.gui_state[name] = mkdict(gui.export_state())
-        self.save()
+        self.save(sync=sync)
 
     def get_gui_state(self, gui):
         """Returns the saved state for a gui"""

cola/widgets/standard.py

@@ -63,14 +63,16 @@ def name(self):
 
     def save_state(self, settings=None):
         save = True
+        sync = True
         context = getattr(self, 'context', None)
         if context:
             cfg = context.cfg
             save = cfg.get('cola.savewindowsettings', default=True)
+            sync = cfg.get('cola.sync', default=True)
         if save:
             if settings is None:
                 settings = Settings.read()
-            settings.save_gui_state(self)
+            settings.save_gui_state(self, sync=sync)
 
     def restore_state(self, settings=None):
         if settings is None:

docs/git-cola.rst

@@ -855,6 +855,12 @@ cola.statusshowtotals
 Set to `true` to display files counts in the Status widget's category titles.
 Defaults to `false`.
 
+cola.sync
+---------
+Set to `false` to disable calling `os.sync()` when saving settings.
+Defaults to `true`, which means that `os.sync()` is called when windows are closed
+and their settings are saved.
+
 cola.tabwidth
 -------------
 The number of columns occupied by a tab character.  Defaults to 8.