In Upsource, a typical code review process involves two or more participants which can be divided into the following roles:
Requester (author) initiates a review and invites other participants — reviewers and watchers — to examine and watch the changes he has committed. See Requesting a Code Review for an author’s workflow.
Reviewer is expected to examine the changes committed by Requester and leave feedback. He can discuss specific lines, or add general comments; he can also mark the review as complete as soon as he’s OK with the changes. See Reviewing a Teammate’s Changes for a reviewer’s workflow.
Watcher is not expected to take part in the review process. He is just kept updated of the project’s status whenever an important change is made. See Monitoring Changes Introduced by Teammates for a watcher’s workflow.