Support push notification of repository changes

External machines can now notify Hydra that it should check a
repository by sending a GET or PUSH request to /api/push, providing a
list of jobsets to be checked and/or a list of repository URLs.  In
the latter case, all jobsets that have any of the specified
repositories as an input will be checked.

For instance, you can configure GitHub or BitBucket to send a request
to the URL

  http://hydra.example.org/api/push?repos=git://github.com/NixOS/nixpkgs.git

to trigger evaluation of all jobsets that have
git://github.com/NixOS/nixpkgs.git as an input, or to the URL

  http://hydra.example.org/api/push?jobsets=patchelf:trunk,nixpkgs:trunk

to trigger evaluation of just the specified jobsets.

src/script/hydra-evaluator

@@ -21,7 +21,7 @@ my $db = Hydra::Model::DB->new();
 my $config = getHydraConfig();
 
 # Don't check a jobset more than once every five minutes.
-my $minCheckInterval = 1;
+my $minCheckInterval = 5 * 60;
 
 
 
@@ -232,6 +232,8 @@ sub checkJobset {
           ? " (last checked " . (time() - $jobset->lastcheckedtime) . "s ago)\n"
           : " (never checked)\n";
 
+    my $triggerTime = $jobset->triggertime;
+
     eval {
         checkJobsetWrapped($jobset);
     };
@@ -244,15 +246,35 @@ sub checkJobset {
             setJobsetError($jobset, $msg);
         });
     }
+
+    if (defined $triggerTime) {
+        txn_do($db, sub {
+            # Only clear the trigger time if the jobset hasn't been
+            # triggered in the meantime.  In that case, we need to
+            # evaluate again.
+            my $new = $jobset->get_from_storage();
+            $jobset->update({ triggertime => undef })
+                if $new->triggertime == $triggerTime;
+        });
+    }
 }
 
 
-# Check the jobset that hasn't been checked for the longest time.
 sub checkSomeJobset {
+    # If any jobset has been triggered by a push, check it.
     my ($jobset) = $db->resultset('Jobsets')->search(
-        { 'project.enabled' => 1, 'me.enabled' => 1
+        { 'project.enabled' => 1, 'me.enabled' => 1, 'triggertime' => { '!=', undef },
         , -or => [ 'lastcheckedtime' => undef, 'lastcheckedtime' => { '<', time() - $minCheckInterval } ] },
-        { join => 'project', order_by => [ 'lastcheckedtime nulls first' ], rows => 1 });
+        { join => 'project', order_by => [ 'triggertime' ], rows => 1 });
+
+    # Otherwise, check the jobset that hasn't been checked for the
+    # longest time (but don't check more often than the minimal check
+    # interval).
+    ($jobset) = $db->resultset('Jobsets')->search(
+        { 'project.enabled' => 1, 'me.enabled' => 1,
+        , -or => [ 'lastcheckedtime' => undef, 'lastcheckedtime' => { '<', time() - $minCheckInterval } ] },
+        { join => 'project', order_by => [ 'lastcheckedtime nulls first' ], rows => 1 })
+        unless defined $jobset;
 
     return 0 unless defined $jobset;