[fotobilder] r1442: internal

U   trunk/lib/FotoBilder/Auth/LiveJournal.pm

Modified: trunk/lib/FotoBilder/Auth/LiveJournal.pm
===================================================================
--- trunk/lib/FotoBilder/Auth/LiveJournal.pm	2011-04-13 06:49:17 UTC (rev 1441)
+++ trunk/lib/FotoBilder/Auth/LiveJournal.pm	2011-05-24 03:38:38 UTC (rev 1442)
@@ -154,27 +154,34 @@
              "AND timemade < UNIX_TIMESTAMP() - 60*15");
 
     # now, see if we have at least one buffered challenge to return
-    $dbu->do("LOCK TABLES domainchalbuffer WRITE");
-    my $ch = $dbu->selectrow_hashref(qq{
-        SELECT challenge, resp FROM domainchalbuffer
-        WHERE userid=$u->{userid} LIMIT 1
-    });
-    if ($ch) {
-        # we got one, so delete it.
-        $dbu->do("DELETE FROM domainchalbuffer WHERE userid=$u->{userid} ".
-                 "AND challenge=? AND resp=?", undef,
-                 $ch->{'challenge'}, $ch->{'resp'});
+    # warning: other processes may access table "domainchalbuffer" concurently
+    GET_CHALLENGE: 
+    {
+        my $ch = $dbu->selectrow_hashref(qq{
+            SELECT challenge, resp FROM domainchalbuffer
+            WHERE userid=$u->{userid} LIMIT 1
+        });
+        if ($ch) {
+            # we got one, so delete it.
+            my $is_deleted = $dbu->do("DELETE FROM domainchalbuffer WHERE userid=$u->{userid} ".
+                     "AND challenge=? AND resp=?", undef,
+                     $ch->{'challenge'}, $ch->{'resp'});
+            if ($is_deleted) {
+                # if we just got a buffered one, put it in challenges table and return it
+                $dbu->do("INSERT INTO challenges (userid, timecreate, challenge, resp) ".
+                    "VALUES (?,UNIX_TIMESTAMP(),?,?)", undef, $u->{'userid'}, $ch->{'challenge'},
+                    $ch->{'resp'});
+                return $ch->{'challenge'};
+            } else {
+                # if we can't delete, then other process did it before us
+                redo GET_CHALLENGE;
+            }
+        } else {
+            # no challenges left in domainchalbuffer table
+            last GET_CHALLENGE;
+        }
     }
-    $dbu->do("UNLOCK TABLES");
 
-    # if we just got a buffered one, put it in challenges table and return it
-    if ($ch) {
-        $dbu->do("INSERT INTO challenges (userid, timecreate, challenge, resp) ".
-                 "VALUES (?,UNIX_TIMESTAMP(),?,?)", undef, $u->{'userid'}, $ch->{'challenge'},
-                 $ch->{'resp'});
-        return $ch->{'challenge'};
-    }
-
     # time to buffer a batch from the remote LJ server.  we'll make
     # 20, since they're probably needing the challenges to upload
     # a bunch of pictures.