If anyone is ever blocked, you are doing it wrong. When performed on git branches, you can easily branch off you current feature branch, keep going and rebase to master when the original branch has been merged. Continuous integration is with you all the time and helps the reviewer by annotating the diff with code coverage, cyclomatic complexity and other metrics. A good review culture emphasizes design feedback over low level issues. In addition, plenty of positive feedback is as important as finding issues.