Ubic::AtomicFile module

lib/Ubic.pm

@@ -50,6 +50,7 @@ use Ubic::Multiservice::Dir;
 use Ubic::AccessGuard;
 use Ubic::Credentials;
 use Ubic::Persistent;
+use Ubic::AtomicFile;
 use Ubic::SingletonLock;
 use Ubic::Settings;
 
@@ -727,12 +728,9 @@ sub forked_call {
         };
 
         try {
-            open my $fh, '>', "$tmp_file.tmp" or die "Can't write to '$tmp_file.tmp: $!";
-            print {$fh} freeze($result);
-            close $fh or die "Can't close $tmp_file.tmp: $!";
+            Ubic::AtomicFile::store( freeze($result) => $tmp_file );
             STDOUT->flush;
             STDERR->flush;
-            rename "$tmp_file.tmp", $tmp_file;
             POSIX::_exit(0); # don't allow to lock to be released - this process was forked from unknown environment, don't want to run unknown destructors
         }
         catch {

lib/Ubic/Admin/Setup.pm

@@ -23,6 +23,7 @@ use Getopt::Long 2.33;
 use Carp;
 use IPC::Open3;
 
+use Ubic::AtomicFile;
 use Ubic::Settings;
 use Ubic::Settings::ConfigFile;
 
@@ -299,9 +300,7 @@ sub setup {
             print "Installing ubic.$name service...\n";
 
             my $file = "$service_dir/ubic/$name";
-            open my $fh, '>', $file or die "Can't write to '$file': $!";
-            print {$fh} $content or die "Can't write to '$file': $!";
-            close $fh or die "Can't close '$file': $!";
+            Ubic::AtomicFile::store($content => $file);
         };
 
         $add_service->(

lib/Ubic/AtomicFile.pm

@@ -0,0 +1,40 @@
+package Ubic::AtomicFile;
+
+use strict;
+use warnings;
+
+# ABSTRACT: atomic file operations
+
+=head1 SYNOPSIS
+
+    use Ubic::AtomicFile;
+
+    Ubic::AtomicFile::store("blah\n" => "/var/lib/blah");
+
+=head1 FUNCTIONS
+
+=over
+
+=item B<store($data, $file)>
+
+Store C<$data> into C<$file> atomically. Temporary C<$file.new> will be created and then renamed to C<$file>.
+
+=cut
+sub store($$) {
+    my ($data, $file) = @_;
+
+    my $new_file = "$file.new";
+
+    # here is an interesting link explaining why we need to do it this way:
+    # https://bugs.launchpad.net/ubuntu/+source/linux/+bug/317781/comments/54
+    open my $fh, '>', $new_file or die "Can't open '$new_file' for writing: $!";
+    print {$fh} $data or die "Can't print to '$new_file': $!";
+    $fh->flush or die "Can't flush '$new_file': $!";
+    close $fh or die "Can't close '$new_file': $!";
+    rename $new_file => $file or die "Can't rename '$new_file' to '$file': $!";
+}
+=back
+
+=cut
+
+1;

lib/Ubic/Daemon/PidState.pm

@@ -13,6 +13,7 @@ use warnings;
 
 use Params::Validate qw(:all);
 use Ubic::Lockf;
+use Ubic::AtomicFile;
 
 use overload '""' => sub {
     my $self = shift;
@@ -176,13 +177,13 @@ sub write {
 
     my ($pid, $guid) = @$params{qw/ pid guid /};
     my $self_pid = $$;
-    open my $fh, '>', "$dir/pid.new" or die "Can't write '$dir/pid.new': $!";
-    print {$fh} "pid $self_pid\n";
-    print {$fh} "guid $guid\n";
-    print {$fh} "daemon $pid\n";
-    $fh->flush;
-    close $fh or die "Can't close '$dir/pid.new': $!";
-    rename "$dir/pid.new" => "$dir/pid" or die "Can't commit pidfile $dir: $!";
+
+    Ubic::AtomicFile::store(
+        "pid $self_pid\n".
+        "guid $guid\n".
+        "daemon $pid\n"
+        => "$dir/pid"
+    );
 }
 
 =back

lib/Ubic/Persistent.pm

@@ -22,6 +22,7 @@ use warnings;
 
 use JSON;
 use Ubic::Lockf;
+use Ubic::AtomicFile;
 
 {
     # JSON.pm v2 incompatibility with v1 is really, really annoying.
@@ -92,11 +93,8 @@ Write data back on disk.
 sub commit {
     my $self = shift;
     my $fname = $meta->{$self}{fname};
-    open my $tmp_fh, '>', "$fname.new" or die "Can't write '$fname.new': $!";
 
-    print {$tmp_fh} objToJson({ %$self });
-    close $tmp_fh or die "Can't write to '$fname.new': $!";
-    rename "$fname.new" => $fname or die "Can't rename '$fname.new' to '$fname': $!";
+    Ubic::AtomicFile::store(objToJson({ %$self }) => $fname);
 }
 
 sub DESTROY {