[jhbuild] terminal: Avoid passing invalid arguments if ionice/chrt are too old

[Colin Walters <walters src gnome org>]

commit aac1075a6ccddd92241c044db87b684da0469d35
Author: Colin Walters <walters verbum org>
Date:   Thu Mar 1 15:28:46 2012 -0500

    terminal: Avoid passing invalid arguments if ionice/chrt are too old
    
    https://bugzilla.gnome.org/show_bug.cgi?id=671162

 jhbuild/frontends/buildscript.py |   16 +++++++++++++---
 1 files changed, 13 insertions(+), 3 deletions(-)
---
diff --git a/jhbuild/frontends/buildscript.py b/jhbuild/frontends/buildscript.py
index 66570d3..d4e9845 100644
--- a/jhbuild/frontends/buildscript.py
+++ b/jhbuild/frontends/buildscript.py
@@ -20,6 +20,7 @@
 
 import os
 import logging
+import subprocess
 
 from jhbuild.utils import trigger
 from jhbuild.utils import cmds
@@ -60,13 +61,22 @@ class BuildScript:
 
         self.subprocess_nice_args = []
         if config.nice_build:
-            if cmds.has_command('chrt'):
-                self.subprocess_nice_args.extend(['chrt', '--idle', '0'])
+            chrt_args = ['chrt', '--idle', '0']
+            devnull = open(os.devnull, 'w')
+            if (cmds.has_command('chrt') and
+                subprocess.call(chrt_args + ['true'], stdout=devnull, stderr=devnull) == 0):
+                self.subprocess_nice_args.extend(chrt_args)
+
             elif cmds.has_command('nice'):
                 self.subprocess_nice_args.append('nice')
                 
+            ionice_args = ['ionice', '-c', '3', '-t']
             if cmds.has_command('ionice'):
-                self.subprocess_nice_args.extend(['ionice', '-c', '3', '-t'])
+                subproc = subprocess.Popen(ionice_args + ['true'], stdout=devnull,
+                                           stderr=subprocess.PIPE)
+                stderr_val = subproc.communicate()[1]
+                if subproc.returncode == 0 and len(stderr_val) == 0:
+                    self.subprocess_nice_args.extend(ionice_args)
 
     def _prepare_execute(self, command):
         if self.subprocess_nice_args: