Merge lp:~ubuntubmw/intltool/fix-cache-race into lp:intltool

[Bernhard M. Wiedemann]

    Avoid a race where some processes try to use a partial cache file
    that is still being written to.
    Note that we release the lock before load_cache,
    because if we got the lock, the cache is already completely written
    and it is OK to have multiple parallel readers

    Without this patch, translation files would randomly miss translations
    for some or all languages.

    fixes bug #1687644
    maybe also bug #986897

[Данило Шеган (danilo)]

Looks good, thanks for the fix!

review: Approve

=== modified file 'intltool-merge.in'
--- intltool-merge.in	2014-11-24 02:37:01 +0000
+++ intltool-merge.in	2017-05-18 19:19:33 +0000
@@ -43,6 +43,7 @@
 use Text::Wrap;
 use File::Basename;
 use Encode;
+use Fcntl qw(:flock);
 
 my $must_end_tag      = -1;
 my $last_depth        = -1;
@@ -392,11 +393,14 @@
 
 sub get_cached_translation_database
 {
+    open(my $lockfh, ">", "$cache_file.lock") or die $!;
+    flock($lockfh, LOCK_EX) or die "Could not lock '$cache_file.lock' - $!";
     my $cache_file_age = -M $cache_file;
     if (defined $cache_file_age) 
     {
         if ($cache_file_age <= &get_newest_po_age) 
         {
+            close($lockfh);
             &load_cache;
             return;
         }
@@ -404,6 +408,7 @@
     }
 
     &create_cache;
+    close($lockfh);
 }
 
 sub add_translation