--- a/src/parallel_execution/generate_context.pl	Thu Mar 18 10:34:06 2021 +0900
+++ b/src/parallel_execution/generate_context.pl	Thu Mar 18 10:49:58 2021 +0900
@@ -92,8 +92,17 @@
   $project  = $projects{$opt_project};
 }
 
-if ($opt_D || ! -f "context.h") {
-  generateContextHeader($opt_w, $opt_o, $project, @ARGV);
+if (! $opt_w) {
+      generateContextHeader("stdout", $opt_o, $project, @ARGV);
+} elsif (-f  "context.h") {
+      generateContextHeader("context.h-new", $opt_o, $project, @ARGV);
+      if (system("cmp -s context.h context.h-new")) {
+          rename "context.h-new","context.h";
+      } else {
+          unlink "context.h-new";
+      }
+} else  {
+      generateContextHeader("context.h", $opt_o, $project, @ARGV);
 }
 
 
@@ -331,9 +340,7 @@
 }
 
 sub generateContextHeader {
-  my ($opt_w, $opt_o, $project, @argv) = @_;
-
-  my $output     = $opt_w ? "context.h" : "stdout";
+  my ($output, $opt_o, $project, @argv) = @_;
 
 
   my @cbc_files = map { File::Spec->rel2abs($_) }  @argv;