Integrate timers with runtime. (#266)

This patch integrate the new timer implementation with the runtime by
initializing a timer per worker thread. This allows minimizing the
amount of synchronization needed for using timers.

src/util/future.rs

@@ -0,0 +1,61 @@
+use tokio_timer::Deadline;
+
+use futures::Future;
+
+use std::time::Instant;
+
+
+/// An extension trait for `Future` that provides a variety of convenient
+/// combinator functions.
+///
+/// Currently, there only is a [`deadline`] function, but this will increase
+/// over time.
+///
+/// Users are not expected to implement this trait. All types that implement
+/// `Future` already implement `FutureExt`.
+///
+/// This trait can be imported directly or via the Tokio prelude: `use
+/// tokio::prelude::*`.
+///
+/// [`deadline`]: #method.deadline
+pub trait FutureExt: Future {
+
+    /// Creates a new future which allows `self` until `deadline`.
+    ///
+    /// This combinator creates a new future which wraps the receiving future
+    /// with a deadline. The returned future is allowed to execute until it
+    /// completes or `deadline` is reached, whicheever happens first.
+    ///
+    /// If the future completes before `deadline` then the future will resolve
+    /// with that item. Otherwise the future will resolve to an error once
+    /// `deadline` is reached.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # extern crate tokio;
+    /// # extern crate futures;
+    /// use tokio::prelude::*;
+    /// use std::time::{Duration, Instant};
+    /// # use futures::future::{self, FutureResult};
+    ///
+    /// # fn long_future() -> FutureResult<(), ()> {
+    /// #   future::ok(())
+    /// # }
+    /// #
+    /// # fn main() {
+    /// let future = long_future()
+    ///     .deadline(Instant::now() + Duration::from_secs(1))
+    ///     .map_err(|e| println!("error = {:?}", e));
+    ///
+    /// tokio::run(future);
+    /// # }
+    /// ```
+    fn deadline(self, deadline: Instant) -> Deadline<Self>
+    where Self: Sized,
+    {
+        Deadline::new(self, deadline)
+    }
+}
+
+impl<T: ?Sized> FutureExt for T where T: Future {}

src/util/mod.rs

@@ -0,0 +1,9 @@
+//! Utilities for working with Tokio.
+//!
+//! This module contains utilities that are useful for working with Tokio.
+//! Currently, this only includes [`FutureExt`][FutureExt]. However, this will
+//! include over time.
+
+mod future;
+
+pub use self::future::FutureExt;