gistfile1.m

    __weak typeof (self) wself = self;
    [self runRequest:request handler:^(NSError *err) {
      __strong typeof (wself) sself = wself;
      __weak typeof(sself) wself2 = sself;
      [sself runSecondRequest:data handler:^(NSError *err) {
        __strong typeof (wself2) sself2 = wself2;
        [sself2 doStuff];
      }];
    }];