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use pool::Pool;
use sender::Sender;

use futures::{Future, Poll, Async};

/// Future that resolves when the thread pool is shutdown.
///
/// A `ThreadPool` is shutdown once all the worker have drained their queues and
/// shutdown their threads.
///
/// `Shutdown` is returned by [`shutdown`], [`shutdown_on_idle`], and
/// [`shutdown_now`].
///
/// [`shutdown`]: struct.ThreadPool.html#method.shutdown
/// [`shutdown_on_idle`]: struct.ThreadPool.html#method.shutdown_on_idle
/// [`shutdown_now`]: struct.ThreadPool.html#method.shutdown_now
#[derive(Debug)]
pub struct Shutdown {
    pub(crate) inner: Sender,
}

impl Shutdown {
    fn inner(&self) -> &Pool {
        &*self.inner.inner
    }
}

impl Future for Shutdown {
    type Item = ();
    type Error = ();

    fn poll(&mut self) -> Poll<(), ()> {
        use futures::task;

        self.inner().shutdown_task.task.register_task(task::current());

        if !self.inner().is_shutdown() {
            return Ok(Async::NotReady);
        }

        Ok(().into())
    }
}