What is the test for dismissing a complaint sua sponte?

Under Rule 4, if the plaintiff fails to show good cause as to why service was not made within the required period, the action "shall be dismissed as to that defendant without prejudice upon the court's own initiative with notice such party or on motion." (emphasis added). District courts have wide discretion to dismiss a complaint sua sponte if a plaintiff has failed to serve process within 120 days without good cause. See Wei v. State of Hawaii, 763 F.2d 370, 372 (9th Cir.1985). The district court exercised that power in this case.