use alloc::sync::Arc;
use core::mem;
-use core::time::Duration;
use sync::{Condvar, Mutex};
use prelude::*;
#[cfg(any(test, feature = "std"))]
-use std::time::Instant;
+use std::time::{Duration, Instant};
use core::future::Future as StdFuture;
use core::task::{Context, Poll};