@synchronized doesn't retain monitored object under MRC

gistfile1.m

    __block id foo = [MyObject new];
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        NSLog(@"block entering synchronized");
        @synchronized(foo) {
            NSLog(@"running in synchronized");
            sleep(10);
            NSLog(@"running [foo self]");
            [foo self];
            NSLog(@"ran [foo self]");
        }
        NSLog(@"block exited synchronized");
    });
    sleep(1);
    NSLog(@"running at top level, releasing foo");
    [foo release];
    NSLog(@"running at top level, released foo");

2012-07-07 00:44:23.115 Synchronized[39663:11e03] block entering synchronized
2012-07-07 00:44:23.116 Synchronized[39663:11e03] running in synchronized
2012-07-07 00:44:24.116 Synchronized[39663:fb03] running at top level, releasing foo
2012-07-07 00:44:24.117 Synchronized[39663:fb03] releasing MyObject
2012-07-07 00:44:24.117 Synchronized[39663:fb03] running at top level, released foo
2012-07-07 00:44:24.119 Synchronized[39663:fb03] Application windows are expected to have a root view controller at the end of application launch
2012-07-07 00:44:33.118 Synchronized[39663:11e03] running [foo self]
(lldb)

Does this mean you should retain foo before @synchronized(foo) and release afterwards? Does that mean you need to wrap all of that in a try/catch in case it does throw so that foo can be released in that case too?