A retractable awning is provided, comprising a support arm forming a longitudinally extending channel, a roller, and a canopy configured to be rolled and unrolled about the roller. A rafter arm is operatively attached to the support arm and is sized to be longitudinally nestable in the channel of the support arm. A self-engaging and self-releasing locking device includes an engagement device configured to selectively engage the support arm to selectively lock a position of a slide member within the longitudinally extending channel. In addition or alternatively, the retractable awning can include a pair of support mechanisms, each support mechanism comprising a support arm, a rafter arm, and a locking device. In addition or alternatively, the retractable awning can include a control link configured to selectively disengage the engagement device from the support arm to release the position of the slide member within the longitudinally extending channel.