OSX and Linux: Add a setting in Preferences->Behavior to control the priority with which calibre worker processes run. Fixes #741231 (calibre-parallel process priority)

src/calibre/gui2/preferences/behavior.py

@@ -31,9 +31,11 @@ class ConfigWidget(ConfigWidgetBase, Ui_Form):
         db = gui.library_view.model().db
 
         r = self.register
-
-        r('worker_process_priority', prefs, choices=
-                [(_('Low'), 'low'), (_('Normal'), 'normal'), (_('High'), 'high')])
+        choices = [(_('Low'), 'low'), (_('Normal'), 'normal'), (_('High'),
+            'high')] if iswindows else \
+                    [(_('Normal'), 'normal'), (_('Low'), 'low'), (_('Very low'),
+                        'high')]
+        r('worker_process_priority', prefs, choices=choices)
 
         r('network_timeout', prefs)
 
@@ -60,9 +62,6 @@ class ConfigWidget(ConfigWidgetBase, Ui_Form):
             signal = getattr(self.opt_internally_viewed_formats, 'item'+signal)
             signal.connect(self.internally_viewed_formats_changed)
 
-        self.settings['worker_process_priority'].gui_obj.setVisible(iswindows)
-        self.priority_label.setVisible(iswindows)
-
 
     def initialize(self):
         ConfigWidgetBase.initialize(self)

src/calibre/utils/ipc/launch.py

@@ -7,6 +7,7 @@ __copyright__ = '2009, Kovid Goyal <kovid@kovidgoyal.net>'
 __docformat__ = 'restructuredtext en'
 
 import subprocess, os, sys, time, binascii, cPickle
+from functools import partial
 
 from calibre.constants import iswindows, isosx, isfrozen
 from calibre.utils.config import prefs
@@ -19,6 +20,12 @@ if iswindows:
     except:
         raise RuntimeError('NUL %r file missing in windows'%os.devnull)
 
+def renice(niceness):
+    try:
+        os.nice(niceness)
+    except:
+        pass
+
 class Worker(object):
     '''
     Platform independent object for launching child processes. All processes
@@ -144,6 +151,13 @@ class Worker(object):
                     'normal' : win32process.NORMAL_PRIORITY_CLASS,
                     'low'    : win32process.IDLE_PRIORITY_CLASS}[priority]
             args['creationflags'] = win32process.CREATE_NO_WINDOW|priority
+        else:
+            niceness = {
+                    'normal' : 0,
+                    'low'    : 10,
+                    'high'   : 20,
+            }[priority]
+            args['preexec_fn'] = partial(renice, niceness)
         ret = None
         if redirect_output:
             self._file = PersistentTemporaryFile('_worker_redirect.log')