SERVER-4712 check that query results are valid before using in case of conn error

1 files changed, 3 insertions, 0 deletions

diff --git a/client/distlock.cpp b/client/distlock.cpp
index 595fc38197c..73ee1304f0e 100644
--- a/client/distlock.cpp
+++ b/client/distlock.cpp
@@ -111,6 +111,9 @@ namespace mongo {
                     // replace it for a quite a while)
                     // if the lock is taken, the take-over mechanism should handle the situation
                     auto_ptr<DBClientCursor> c = conn->query( DistributedLock::locksNS , BSONObj() );
+                    // TODO:  Would be good to make clear whether query throws or returns empty on errors
+                    uassert( 16060, str::stream() << "cannot query locks collection on config server " << conn.getHost(), c.get() );
+
                     set<string> pids;
                     while ( c->more() ) {
                         BSONObj lock = c->next();