SERVER-6931 Don't attempt to look up a cursor using an invalid id. Pr…

…events an occasional incorrect warning message.

jstests/cursorb.js

@@ -0,0 +1,17 @@
+// The 'cursor not found in map -1' warning is not logged when get more exhausts a client cursor.
+// SERVER-6931
+
+t = db.jstests_cursorb;
+t.drop();
+
+// Exhaust a client cursor in get more.
+for( i = 0; i < 200; ++i ) {
+    t.save( { a:i } );
+}
+t.find().itcount();
+
+// Check that the 'cursor not found in map -1' message is not printed.  This message indicates an
+// attempt to look up a cursor with an invalid id and should never appear in the log.
+log = db.adminCommand( { getLog:'global' } ).log
+log.forEach( function( line ) { assert( !line.match( /cursor not found in map -1 / ),
+                                        'Cursor map lookup with id -1.' ); } );

src/mongo/db/clientcursor.cpp

@@ -792,7 +792,7 @@ namespace mongo {
         if ( ! cc().getAuthenticationInfo()->isAuthorizedReads( nsToDatabase( cursor->ns() ) ) )
             return false;
 
-        // mustn't have an active ClientCursor::Pointer
+        // Must not have an active ClientCursor::Pin.
         massert( 16089,
                 str::stream() << "Cannot kill active cursor " << id,
                 cursor->_pinValue < 100 );

src/mongo/db/clientcursor.h

@@ -100,6 +100,9 @@ namespace mongo {
                 }
             }
             void release() {
+                if ( _cursorid == INVALID_CURSOR_ID ) {
+                    return;
+                }
                 ClientCursor *cursor = c();
                 _cursorid = INVALID_CURSOR_ID;
                 if ( cursor ) {