文档中的注释
// Wait atomically unlocks c.L and suspends execution
// of the calling goroutine. After later resuming execution,
// Wait locks c.L before returning. Unlike in other systems,
// Wait cannot return unless awoken by Broadcast or Signal.
//
// Because c.L is not locked while Wait is waiting, the caller
// typically cannot assume that the condition is true when
// Wait returns. Instead, the caller should Wait in a loop: