Provide optional features on tokio crate (#808)

Disabling all features means the only dependency is `futures`.

Relevant pieces of the API can then be enabled with the following features:

- `codec`
- `fs`
- `io`
- `reactor`
- `tcp`
- `timer`
- `udp`
- `uds`

This also introduces the beginnings of enabling only certain pieces of the `Runtime`. As a start, the entire default runtime API is enabled via the `rt-full` feature.

12 files changed, 480 insertions, 405 deletions

diff --git a/src/io.rs b/src/io.rs
index 0f1fcbca..1f7ecc28 100644
--- a/src/io.rs
+++ b/src/io.rs
@@ -51,6 +51,7 @@ pub use tokio_io::{
 };
 
 // standard input, output, and error
+#[cfg(feature = "fs")]
 pub use tokio_fs::{
     stdin,
     Stdin,
diff --git a/src/lib.rs b/src/lib.rs
index 401d90f8..23c89ece 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -72,42 +72,72 @@
 //! }
 //! ```
 
-extern crate bytes;
-#[macro_use]
+macro_rules! if_runtime {
+    ($($i:item)*) => ($(
+        #[cfg(any(feature = "rt-full"))]
+        $i
+    )*)
+}
+
+#[cfg_attr(feature = "rt-full", macro_use)]
 extern crate futures;
+
+#[cfg(feature = "io")]
+extern crate bytes;
+#[cfg(feature = "reactor")]
 extern crate mio;
+#[cfg(feature = "rt-full")]
 extern crate num_cpus;
+#[cfg(feature = "rt-full")]
 extern crate tokio_current_thread;
+#[cfg(feature = "io")]
 extern crate tokio_io;
-extern crate tokio_executor;
+#[cfg(feature = "codec")]
 extern crate tokio_codec;
+#[cfg(feature = "fs")]
 extern crate tokio_fs;
+#[cfg(feature = "reactor")]
 extern crate tokio_reactor;
+#[cfg(feature = "rt-full")]
 extern crate tokio_threadpool;
+#[cfg(feature = "timer")]
 extern crate tokio_timer;
+#[cfg(feature = "tcp")]
 extern crate tokio_tcp;
+#[cfg(feature = "udp")]
 extern crate tokio_udp;
 
 #[cfg(feature = "async-await-preview")]
 extern crate tokio_async_await;
 
-#[cfg(unix)]
+#[cfg(all(unix, feature = "uds"))]
 extern crate tokio_uds;
 
+#[cfg(feature = "timer")]
 pub mod clock;
+#[cfg(feature = "codec")]
 pub mod codec;
-pub mod executor;
+#[cfg(feature = "fs")]
 pub mod fs;
+#[cfg(feature = "io")]
 pub mod io;
+#[cfg(any(feature = "tcp", feature = "udp", feature = "uds"))]
 pub mod net;
 pub mod prelude;
+#[cfg(feature = "reactor")]
 pub mod reactor;
-pub mod runtime;
+#[cfg(feature = "timer")]
 pub mod timer;
 pub mod util;
 
-pub use executor::spawn;
-pub use runtime::run;
+if_runtime! {
+    extern crate tokio_executor;
+    pub mod executor;
+    pub mod runtime;
+
+    pub use executor::spawn;
+    pub use runtime::run;
+}
 
 // ===== Experimental async/await support =====
 
diff --git a/src/net.rs b/src/net.rs
index be8612ae..a6b425da 100644
--- a/src/net.rs
+++ b/src/net.rs
@@ -22,6 +22,7 @@
 //! [`UnixDatagram`]: struct.UnixDatagram.html
 //! [`UnixDatagramFramed`]: struct.UnixDatagramFramed.html
 
+#[cfg(feature = "tcp")]
 pub mod tcp {
     //! TCP bindings for `tokio`.
     //!
@@ -42,15 +43,19 @@ pub mod tcp {
     //! [`Incoming`]: struct.Incoming.html
     pub use tokio_tcp::{ConnectFuture, Incoming, TcpListener, TcpStream};
 }
+#[cfg(feature = "tcp")]
 pub use self::tcp::{TcpListener, TcpStream};
 
+#[cfg(feature = "tcp")]
 #[deprecated(note = "use `tokio::net::tcp::ConnectFuture` instead")]
 #[doc(hidden)]
 pub type ConnectFuture = self::tcp::ConnectFuture;
+#[cfg(feature = "tcp")]
 #[deprecated(note = "use `tokio::net::tcp::Incoming` instead")]
 #[doc(hidden)]
 pub type Incoming = self::tcp::Incoming;
 
+#[cfg(feature = "udp")]
 pub mod udp {
     //! UDP bindings for `tokio`.
     //!
@@ -68,16 +73,19 @@ pub mod udp {
     //! [`framed`]: struct.UdpSocket.html#method.framed
     pub use tokio_udp::{RecvDgram, SendDgram, UdpFramed, UdpSocket};
 }
+#[cfg(feature = "udp")]
 pub use self::udp::{UdpFramed, UdpSocket};
 
+#[cfg(feature = "udp")]
 #[deprecated(note = "use `tokio::net::udp::RecvDgram` instead")]
 #[doc(hidden)]
 pub type RecvDgram<T> = self::udp::RecvDgram<T>;
+#[cfg(feature = "udp")]
 #[deprecated(note = "use `tokio::net::udp::SendDgram` instead")]
 #[doc(hidden)]
 pub type SendDgram<T> = self::udp::SendDgram<T>;
 
-#[cfg(unix)]
+#[cfg(all(unix, feature = "uds"))]
 pub mod unix {
     //! Unix domain socket bindings for `tokio` (only available on unix systems).
 
@@ -86,5 +94,5 @@ pub mod unix {
         UnixListener, UnixStream,
     };
 }
-#[cfg(unix)]
+#[cfg(all(unix, feature = "uds"))]
 pub use self::unix::{UnixDatagram, UnixDatagramFramed, UnixListener, UnixStream};
diff --git a/src/prelude.rs b/src/prelude.rs
index ecd82fe4..5ca20399 100644
--- a/src/prelude.rs
+++ b/src/prelude.rs
@@ -10,6 +10,7 @@
 //!
 //! The prelude may grow over time as additional items see ubiquitous use.
 
+#[cfg(feature = "io")]
 pub use tokio_io::{
     AsyncRead,
     AsyncWrite,
diff --git a/src/runtime/current_thread/mod.rs b/src/runtime/current_thread/mod.rs
index dca41711..45dc4efe 100644
--- a/src/runtime/current_thread/mod.rs
+++ b/src/runtime/current_thread/mod.rs
@@ -90,3 +90,18 @@ where
     r.run().expect("failed to resolve remaining futures");
     Ok(v)
 }
+
+/// Start a current-thread runtime using the supplied future to bootstrap execution.
+///
+/// # Panics
+///
+/// This function panics if called from the context of an executor.
+pub fn run<F>(future: F)
+where
+    F: Future<Item = (), Error = ()> + 'static,
+{
+
+    let mut r = Runtime::new().expect("failed to start runtime on current thread");
+    r.spawn(future);
+    r.run().expect("failed to resolve remaining futures");
+}
diff --git a/src/runtime/mod.rs b/src/runtime/mod.rs
index 2ea0d548..9e7b700c 100644
--- a/src/runtime/mod.rs
+++ b/src/runtime/mod.rs
@@ -112,399 +112,14 @@
 //! [`tokio::spawn`]: ../executor/fn.spawn.html
 //! [`Timer`]: https://docs.rs/tokio-timer/0.2/tokio_timer/timer/struct.Timer.html
 
-mod builder;
 pub mod current_thread;
-mod shutdown;
-mod task_executor;
+mod threadpool;
 
-pub use self::builder::Builder;
-pub use self::shutdown::Shutdown;
-pub use self::task_executor::TaskExecutor;
+pub use self::threadpool::{
+    Builder,
+    Runtime,
+    Shutdown,
+    TaskExecutor,
+    run,
+};
 
-use reactor::{Handle, Reactor};
-
-use std::io;
-use std::sync::Mutex;
-
-use tokio_executor::enter;
-use tokio_threadpool as threadpool;
-
-use futures;
-use futures::future::Future;
-
-/// Handle to the Tokio runtime.
-///
-/// The Tokio runtime includes a reactor as well as an executor for running
-/// tasks.
-///
-/// Instances of `Runtime` can be created using [`new`] or [`Builder`]. However,
-/// most users will use [`tokio::run`], which uses a `Runtime` internally.
-///
-/// See [module level][mod] documentation for more details.
-///
-/// [mod]: index.html
-/// [`new`]: #method.new
-/// [`Builder`]: struct.Builder.html
-/// [`tokio::run`]: fn.run.html
-#[derive(Debug)]
-pub struct Runtime {
-    inner: Option<Inner>,
-}
-
-#[derive(Debug)]
-struct Inner {
-    /// A handle to the reactor in the background thread.
-    reactor_handle: Handle,
-
-    // TODO: This should go away in 0.2
-    reactor: Mutex<Option<Reactor>>,
-
-    /// Task execution pool.
-    pool: threadpool::ThreadPool,
-}
-
-// ===== impl Runtime =====
-
-/// Start the Tokio runtime using the supplied future to bootstrap execution.
-///
-/// This function is used to bootstrap the execution of a Tokio application. It
-/// does the following:
-///
-/// * Start the Tokio runtime using a default configuration.
-/// * Spawn the given future onto the thread pool.
-/// * Block the current thread until the runtime shuts down.
-///
-/// Note that the function will not return immediately once `future` has
-/// completed. Instead it waits for the entire runtime to become idle.
-///
-/// See the [module level][mod] documentation for more details.
-///
-/// # Examples
-///
-/// ```rust
-/// # extern crate tokio;
-/// # extern crate futures;
-/// # use futures::{Future, Stream};
-/// use tokio::net::TcpListener;
-///
-/// # fn process<T>(_: T) -> Box<Future<Item = (), Error = ()> + Send> {
-/// # unimplemented!();
-/// # }
-/// # fn dox() {
-/// # let addr = "127.0.0.1:8080".parse().unwrap();
-/// let listener = TcpListener::bind(&addr).unwrap();
-///
-/// let server = listener.incoming()
-///     .map_err(|e| println!("error = {:?}", e))
-///     .for_each(|socket| {
-///         tokio::spawn(process(socket))
-///     });
-///
-/// tokio::run(server);
-/// # }
-/// # pub fn main() {}
-/// ```
-///
-/// # Panics
-///
-/// This function panics if called from the context of an executor.
-///
-/// [mod]: ../index.html
-pub fn run<F>(future: F)
-where F: Future<Item = (), Error = ()> + Send + 'static,
-{
-    // Check enter before creating a new Runtime...
-    let mut entered = enter().expect("nested tokio::run");
-    let mut runtime = Runtime::new().expect("failed to start new Runtime");
-    runtime.spawn(future);
-    entered
-        .block_on(runtime.shutdown_on_idle())
-        .expect("shutdown cannot error")
-}
-
-impl Runtime {
-    /// Create a new runtime instance with default configuration values.
-    ///
-    /// This results in a reactor, thread pool, and timer being initialized. The
-    /// thread pool will not spawn any worker threads until it needs to, i.e.
-    /// tasks are scheduled to run.
-    ///
-    /// Most users will not need to call this function directly, instead they
-    /// will use [`tokio::run`](fn.run.html).
-    ///
-    /// See [module level][mod] documentation for more details.
-    ///
-    /// # Examples
-    ///
-    /// Creating a new `Runtime` with default configuration values.
-    ///
-    /// ```
-    /// use tokio::runtime::Runtime;
-    /// use tokio::prelude::*;
-    ///
-    /// let rt = Runtime::new()
-    ///     .unwrap();
-    ///
-    /// // Use the runtime...
-    ///
-    /// // Shutdown the runtime
-    /// rt.shutdown_now()
-    ///     .wait().unwrap();
-    /// ```
-    ///
-    /// [mod]: index.html
-    pub fn new() -> io::Result<Self> {
-        Builder::new().build()
-    }
-
-    #[deprecated(since = "0.1.5", note = "use `reactor` instead")]
-    #[doc(hidden)]
-    pub fn handle(&self) -> &Handle {
-        #[allow(deprecated)]
-        self.reactor()
-    }
-
-    /// Return a reference to the reactor handle for this runtime instance.
-    ///
-    /// The returned handle reference can be cloned in order to get an owned
-    /// value of the handle. This handle can be used to initialize I/O resources
-    /// (like TCP or UDP sockets) that will not be used on the runtime.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use tokio::runtime::Runtime;
-    ///
-    /// let rt = Runtime::new()
-    ///     .unwrap();
-    ///
-    /// let reactor_handle = rt.reactor().clone();
-    ///
-    /// // use `reactor_handle`
-    /// ```
-    #[deprecated(since = "0.1.11", note = "there is now a reactor per worker thread")]
-    pub fn reactor(&self) -> &Handle {
-        let mut reactor = self.inner().reactor.lock().unwrap();
-        if let Some(reactor) = reactor.take() {
-            if let Ok(background) = reactor.background() {
-                background.forget();
-            }
-        }
-
-        &self.inner().reactor_handle
-    }
-
-    /// Return a handle to the runtime's executor.
-    ///
-    /// The returned handle can be used to spawn tasks that run on this runtime.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use tokio::runtime::Runtime;
-    ///
-    /// let rt = Runtime::new()
-    ///     .unwrap();
-    ///
-    /// let executor_handle = rt.executor();
-    ///
-    /// // use `executor_handle`
-    /// ```
-    pub fn executor(&self) -> TaskExecutor {
-        let inner = self.inner().pool.sender().clone();
-        TaskExecutor { inner }
-    }
-
-    /// Spawn a future onto the Tokio runtime.
-    ///
-    /// This spawns the given future onto the runtime's executor, usually a
-    /// thread pool. The thread pool is then responsible for polling the future
-    /// until it completes.
-    ///
-    /// See [module level][mod] documentation for more details.
-    ///
-    /// [mod]: index.html
-    ///
-    /// # Examples
-    ///
-    /// ```rust
-    /// # extern crate tokio;
-    /// # extern crate futures;
-    /// # use futures::{future, Future, Stream};
-    /// use tokio::runtime::Runtime;
-    ///
-    /// # fn dox() {
-    /// // Create the runtime
-    /// let mut rt = Runtime::new().unwrap();
-    ///
-    /// // Spawn a future onto the runtime
-    /// rt.spawn(future::lazy(|| {
-    ///     println!("now running on a worker thread");
-    ///     Ok(())
-    /// }));
-    /// # }
-    /// # pub fn main() {}
-    /// ```
-    ///
-    /// # Panics
-    ///
-    /// This function panics if the spawn fails. Failure occurs if the executor
-    /// is currently at capacity and is unable to spawn a new future.
-    pub fn spawn<F>(&mut self, future: F) -> &mut Self
-    where F: Future<Item = (), Error = ()> + Send + 'static,
-    {
-        self.inner_mut().pool.sender().spawn(future).unwrap();
-        self
-    }
-
-    /// Run a future to completion on the Tokio runtime.
-    ///
-    /// This runs the given future on the runtime, blocking until it is
-    /// complete, and yielding its resolved result. Any tasks or timers which
-    /// the future spawns internally will be executed on the runtime.
-    ///
-    /// This method should not be called from an asynchronous context.
-    ///
-    /// # Panics
-    ///
-    /// This function panics if the executor is at capacity, if the provided
-    /// future panics, or if called within an asynchronous execution context.
-    pub fn block_on<F, R, E>(&mut self, future: F) -> Result<R, E>
-    where
-        F: Send + 'static + Future<Item = R, Error = E>,
-        R: Send + 'static,
-        E: Send + 'static,
-    {
-        let mut entered = enter().expect("nested block_on");
-        let (tx, rx) = futures::sync::oneshot::channel();
-        self.spawn(future.then(move |r| tx.send(r).map_err(|_| unreachable!())));
-        entered.block_on(rx).unwrap()
-    }
-
-    /// Run a future to completion on the Tokio runtime, then wait for all
-    /// background futures to complete too.
-    ///
-    /// This runs the given future on the runtime, blocking until it is
-    /// complete, waiting for background futures to complete, and yielding
-    /// its resolved result. Any tasks or timers which the future spawns
-    /// internally will be executed on the runtime and waited for completion.
-    ///
-    /// This method should not be called from an asynchronous context.
-    ///
-    /// # Panics
-    ///
-    /// This function panics if the executor is at capacity, if the provided
-    /// future panics, or if called within an asynchronous execution context.
-    pub fn block_on_all<F, R, E>(mut self, future: F) -> Result<R, E>
-    where
-        F: Send + 'static + Future<Item = R, Error = E>,
-        R: Send + 'static,
-        E: Send + 'static,
-    {
-        let mut entered = enter().expect("nested block_on_all");
-        let (tx, rx) = futures::sync::oneshot::channel();
-        self.spawn(future.then(move |r| tx.send(r).map_err(|_| unreachable!())));
-        let block = rx
-            .map_err(|_| unreachable!())
-            .and_then(move |r| {
-                self.shutdown_on_idle()
-                    .map(move |()| r)
-            });
-        entered.block_on(block).unwrap()
-    }
-
-    /// Signals the runtime to shutdown once it becomes idle.
-    ///
-    /// Returns a future that completes once the shutdown operation has
-    /// completed.
-    ///
-    /// This function can be used to perform a graceful shutdown of the runtime.
-    ///
-    /// The runtime enters an idle state once **all** of the following occur.
-    ///
-    /// * The thread pool has no tasks to execute, i.e., all tasks that were
-    ///   spawned have completed.
-    /// * The reactor is not managing any I/O resources.
-    ///
-    /// See [module level][mod] documentation for more details.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use tokio::runtime::Runtime;
-    /// use tokio::prelude::*;
-    ///
-    /// let rt = Runtime::new()
-    ///     .unwrap();
-    ///
-    /// // Use the runtime...
-    ///
-    /// // Shutdown the runtime
-    /// rt.shutdown_on_idle()
-    ///     .wait().unwrap();
-    /// ```
-    ///
-    /// [mod]: index.html
-    pub fn shutdown_on_idle(mut self) -> Shutdown {
-        let inner = self.inner.take().unwrap();
-        let inner = inner.pool.shutdown_on_idle();
-        Shutdown { inner }
-    }
-
-    /// Signals the runtime to shutdown immediately.
-    ///
-    /// Returns a future that completes once the shutdown operation has
-    /// completed.
-    ///
-    /// This function will forcibly shutdown the runtime, causing any
-    /// in-progress work to become canceled. The shutdown steps are:
-    ///
-    /// * Drain any scheduled work queues.
-    /// * Drop any futures that have not yet completed.
-    /// * Drop the reactor.
-    ///
-    /// Once the reactor has dropped, any outstanding I/O resources bound to
-    /// that reactor will no longer function. Calling any method on them will
-    /// result in an error.
-    ///
-    /// See [module level][mod] documentation for more details.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use tokio::runtime::Runtime;
-    /// use tokio::prelude::*;
-    ///
-    /// let rt = Runtime::new()
-    ///     .unwrap();
-    ///
-    /// // Use the runtime...
-    ///
-    /// // Shutdown the runtime
-    /// rt.shutdown_now()
-    ///     .wait().unwrap();
-    /// ```
-    ///
-    /// [mod]: index.html
-    pub fn shutdown_now(mut self) -> Shutdown {
-        let inner = self.inner.take().unwrap();
-        Shutdown::shutdown_now(inner)
-    }
-
-    fn inner(&self) -> &Inner {
-        self.inner.as_ref().unwrap()
-    }
-
-    fn inner_mut(&mut self) -> &mut Inner {
-        self.inner.as_mut().unwrap()
-    }
-}
-
-impl Drop for Runtime {
-    fn drop(&mut self) {
-        if let Some(inner) = self.inner.take() {
-            let shutdown = Shutdown::shutdown_now(inner);
-            let _ = shutdown.wait();
-        }
-    }
-}
diff --git a/src/runtime/builder.rs b/src/runtime/threadpool/builder.rs
index 8a5dca77..f7af4493 100644
--- a/src/runtime/builder.rs
+++ b/src/runtime/threadpool/builder.rs
@@ -1,4 +1,4 @@
-use runtime::{Inner, Runtime};
+use super::{Inner, Runtime};
 
 use reactor::Reactor;
 
diff --git a/src/runtime/threadpool/mod.rs b/src/runtime/threadpool/mod.rs
new file mode 100644
index 00000000..77d89498
--- /dev/null
+++ b/src/runtime/threadpool/mod.rs
@@ -0,0 +1,395 @@
+mod builder;
+mod shutdown;
+mod task_executor;
+
+pub use self::builder::Builder;
+pub use self::shutdown::Shutdown;
+pub use self::task_executor::TaskExecutor;
+
+use reactor::{Handle, Reactor};
+
+use std::io;
+use std::sync::Mutex;
+
+use tokio_executor::enter;
+use tokio_threadpool as threadpool;
+
+use futures;
+use futures::future::Future;
+
+/// Handle to the Tokio runtime.
+///
+/// The Tokio runtime includes a reactor as well as an executor for running
+/// tasks.
+///
+/// Instances of `Runtime` can be created using [`new`] or [`Builder`]. However,
+/// most users will use [`tokio::run`], which uses a `Runtime` internally.
+///
+/// See [module level][mod] documentation for more details.
+///
+/// [mod]: index.html
+/// [`new`]: #method.new
+/// [`Builder`]: struct.Builder.html
+/// [`tokio::run`]: fn.run.html
+#[derive(Debug)]
+pub struct Runtime {
+    inner: Option<Inner>,
+}
+
+#[derive(Debug)]
+struct Inner {
+    /// A handle to the reactor in the background thread.
+    reactor_handle: Handle,
+
+    // TODO: This should go away in 0.2
+    reactor: Mutex<Option<Reactor>>,
+
+    /// Task execution pool.
+    pool: threadpool::ThreadPool,
+}
+
+// ===== impl Runtime =====
+
+/// Start the Tokio runtime using the supplied future to bootstrap execution.
+///
+/// This function is used to bootstrap the execution of a Tokio application. It
+/// does the following:
+///
+/// * Start the Tokio runtime using a default configuration.
+/// * Spawn the given future onto the thread pool.
+/// * Block the current thread until the runtime shuts down.
+///
+/// Note that the function will not return immediately once `future` has
+/// completed. Instead it waits for the entire runtime to become idle.
+///
+/// See the [module level][mod] documentation for more details.
+///
+/// # Examples
+///
+/// ```rust
+/// # extern crate tokio;
+/// # extern crate futures;
+/// # use futures::{Future, Stream};
+/// use tokio::net::TcpListener;
+///
+/// # fn process<T>(_: T) -> Box<Future<Item = (), Error = ()> + Send> {
+/// # unimplemented!();
+/// # }
+/// # fn dox() {
+/// # let addr = "127.0.0.1:8080".parse().unwrap();
+/// let listener = TcpListener::bind(&addr).unwrap();
+///
+/// let server = listener.incoming()
+///     .map_err(|e| println!("error = {:?}", e))
+///     .for_each(|socket| {
+///         tokio::spawn(process(socket))
+///     });
+///
+/// tokio::run(server);
+/// # }
+/// # pub fn main() {}
+/// ```
+///
+/// # Panics
+///
+/// This function panics if called from the context of an executor.
+///
+/// [mod]: ../index.html
+pub fn run<F>(future: F)
+where F: Future<Item = (), Error = ()> + Send + 'static,
+{
+    // Check enter before creating a new Runtime...
+    let mut entered = enter().expect("nested tokio::run");
+    let mut runtime = Runtime::new().expect("failed to start new Runtime");
+    runtime.spawn(future);
+    entered
+        .block_on(runtime.shutdown_on_idle())
+        .expect("shutdown cannot error")
+}
+
+impl Runtime {
+    /// Create a new runtime instance with default configuration values.
+    ///
+    /// This results in a reactor, thread pool, and timer being initialized. The
+    /// thread pool will not spawn any worker threads until it needs to, i.e.
+    /// tasks are scheduled to run.
+    ///
+    /// Most users will not need to call this function directly, instead they
+    /// will use [`tokio::run`](fn.run.html).
+    ///
+    /// See [module level][mod] documentation for more details.
+    ///
+    /// # Examples
+    ///
+    /// Creating a new `Runtime` with default configuration values.
+    ///
+    /// ```
+    /// use tokio::runtime::Runtime;
+    /// use tokio::prelude::*;
+    ///
+    /// let rt = Runtime::new()
+    ///     .unwrap();
+    ///
+    /// // Use the runtime...
+    ///
+    /// // Shutdown the runtime
+    /// rt.shutdown_now()
+    ///     .wait().unwrap();
+    /// ```
+    ///
+    /// [mod]: index.html
+    pub fn new() -> io::Result<Self> {
+        Builder::new().build()
+    }
+
+    #[deprecated(since = "0.1.5", note = "use `reactor` instead")]
+    #[doc(hidden)]
+    pub fn handle(&self) -> &Handle {
+        #[allow(deprecated)]
+        self.reactor()
+    }
+
+    /// Return a reference to the reactor handle for this runtime instance.
+    ///
+    /// The returned handle reference can be cloned in order to get an owned
+    /// value of the handle. This handle can be used to initialize I/O resources
+    /// (like TCP or UDP sockets) that will not be used on the runtime.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::runtime::Runtime;
+    ///
+    /// let rt = Runtime::new()
+    ///     .unwrap();
+    ///
+    /// let reactor_handle = rt.reactor().clone();
+    ///
+    /// // use `reactor_handle`
+    /// ```
+    #[deprecated(since = "0.1.11", note = "there is now a reactor per worker thread")]
+    pub fn reactor(&self) -> &Handle {
+        let mut reactor = self.inner().reactor.lock().unwrap();
+        if let Some(reactor) = reactor.take() {
+            if let Ok(background) = reactor.background() {
+                background.forget();
+            }
+        }
+
+        &self.inner().reactor_handle
+    }
+
+    /// Return a handle to the runtime's executor.
+    ///
+    /// The returned handle can be used to spawn tasks that run on this runtime.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::runtime::Runtime;
+    ///
+    /// let rt = Runtime::new()
+    ///     .unwrap();
+    ///
+    /// let executor_handle = rt.executor();
+    ///
+    /// // use `executor_handle`
+    /// ```
+    pub fn executor(&self) -> TaskExecutor {
+        let inner = self.inner().pool.sender().clone();
+        TaskExecutor { inner }
+    }
+
+    /// Spawn a future onto the Tokio runtime.
+    ///
+    /// This spawns the given future onto the runtime's executor, usually a
+    /// thread pool. The thread pool is then responsible for polling the future
+    /// until it completes.
+    ///
+    /// See [module level][mod] documentation for more details.
+    ///
+    /// [mod]: index.html
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// # extern crate tokio;
+    /// # extern crate futures;
+    /// # use futures::{future, Future, Stream};
+    /// use tokio::runtime::Runtime;
+    ///
+    /// # fn dox() {
+    /// // Create the runtime
+    /// let mut rt = Runtime::new().unwrap();
+    ///
+    /// // Spawn a future onto the runtime
+    /// rt.spawn(future::lazy(|| {
+    ///     println!("now running on a worker thread");
+    ///     Ok(())
+    /// }));
+    /// # }
+    /// # pub fn main() {}
+    /// ```
+    ///
+    /// # Panics
+    ///
+    /// This function panics if the spawn fails. Failure occurs if the executor
+    /// is currently at capacity and is unable to spawn a new future.
+    pub fn spawn<F>(&mut self, future: F) -> &mut Self
+    where F: Future<Item = (), Error = ()> + Send + 'static,
+    {
+        self.inner_mut().pool.sender().spawn(future).unwrap();
+        self
+    }
+
+    /// Run a future to completion on the Tokio runtime.
+    ///
+    /// This runs the given future on the runtime, blocking until it is
+    /// complete, and yielding its resolved result. Any tasks or timers which
+    /// the future spawns internally will be executed on the runtime.
+    ///
+    /// This method should not be called from an asynchronous context.
+    ///
+    /// # Panics
+    ///
+    /// This function panics if the executor is at capacity, if the provided
+    /// future panics, or if called within an asynchronous execution context.
+    pub fn block_on<F, R, E>(&mut self, future: F) -> Result<R, E>
+    where
+        F: Send + 'static + Future<Item = R, Error = E>,
+        R: Send + 'static,
+        E: Send + 'static,
+    {
+        let mut entered = enter().expect("nested block_on");
+        let (tx, rx) = futures::sync::oneshot::channel();
+        self.spawn(future.then(move |r| tx.send(r).map_err(|_| unreachable!())));
+        entered.block_on(rx).unwrap()
+    }
+
+    /// Run a future to completion on the Tokio runtime, then wait for all
+    /// background futures to complete too.
+    ///
+    /// This runs the given future on the runtime, blocking until it is
+    /// complete, waiting for background futures to complete, and yielding
+    /// its resolved result. Any tasks or timers which the future spawns
+    /// internally will be executed on the runtime and waited for completion.
+    ///
+    /// This method should not be called from an asynchronous context.
+    ///
+    /// # Panics
+    ///
+    /// This function panics if the executor is at capacity, if the provided
+    /// future panics, or if called within an asynchronous execution context.
+    pub fn block_on_all<F, R, E>(mut self, future: F) -> Result<R, E>
+    where
+        F: Send + 'static + Future<Item = R, Error = E>,
+        R: Send + 'static,
+        E: Send + 'static,
+    {
+        let mut entered = enter().expect("nested block_on_all");
+        let (tx, rx) = futures::sync::oneshot::channel();
+        self.spawn(future.then(move |r| tx.send(r).map_err(|_| unreachable!())));
+        let block = rx
+            .map_err(|_| unreachable!())
+            .and_then(move |r| {
+                self.shutdown_on_idle()
+                    .map(move |()| r)
+            });
+        entered.block_on(block).unwrap()
+    }
+
+    /// Signals the runtime to shutdown once it becomes idle.
+    ///
+    /// Returns a future that completes once the shutdown operation has
+    /// completed.
+    ///
+    /// This function can be used to perform a graceful shutdown of the runtime.
+    ///
+    /// The runtime enters an idle state once **all** of the following occur.
+    ///
+    /// * The thread pool has no tasks to execute, i.e., all tasks that were
+    ///   spawned have completed.
+    /// * The reactor is not managing any I/O resources.
+    ///
+    /// See [module level][mod] documentation for more details.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::runtime::Runtime;
+    /// use tokio::prelude::*;
+    ///
+    /// let rt = Runtime::new()
+    ///     .unwrap();
+    ///
+    /// // Use the runtime...
+    ///
+    /// // Shutdown the runtime
+    /// rt.shutdown_on_idle()
+    ///     .wait().unwrap();
+    /// ```
+    ///
+    /// [mod]: index.html
+    pub fn shutdown_on_idle(mut self) -> Shutdown {
+        let inner = self.inner.take().unwrap();
+        let inner = inner.pool.shutdown_on_idle();
+        Shutdown { inner }
+    }
+
+    /// Signals the runtime to shutdown immediately.
+    ///
+    /// Returns a future that completes once the shutdown operation has
+    /// completed.
+    ///
+    /// This function will forcibly shutdown the runtime, causing any
+    /// in-progress work to become canceled. The shutdown steps are:
+    ///
+    /// * Drain any scheduled work queues.
+    /// * Drop any futures that have not yet completed.
+    /// * Drop the reactor.
+    ///
+    /// Once the reactor has dropped, any outstanding I/O resources bound to
+    /// that reactor will no longer function. Calling any method on them will
+    /// result in an error.
+    ///
+    /// See [module level][mod] documentation for more details.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::runtime::Runtime;
+    /// use tokio::prelude::*;
+    ///
+    /// let rt = Runtime::new()
+    ///     .unwrap();
+    ///
+    /// // Use the runtime...
+    ///
+    /// // Shutdown the runtime
+    /// rt.shutdown_now()
+    ///     .wait().unwrap();
+    /// ```
+    ///
+    /// [mod]: index.html
+    pub fn shutdown_now(mut self) -> Shutdown {
+        let inner = self.inner.take().unwrap();
+        Shutdown::shutdown_now(inner)
+    }
+
+    fn inner(&self) -> &Inner {
+        self.inner.as_ref().unwrap()