diff --git a/Cargo.toml b/Cargo.toml
index 230de6402..24badb1ea 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -27,6 +27,9 @@ unstable = []
 async-task = "1.0.0"
 cfg-if = "0.1.9"
 crossbeam-channel = "0.3.9"
+futures-channel-preview = "0.3.0-alpha.18"
+futures-core-preview = "0.3.0-alpha.18"
+futures-io-preview = "0.3.0-alpha.18"
 futures-timer = "0.3.0"
 lazy_static = "1.3.0"
 log = { version = "0.4.8", features = ["kv_unstable"] }
@@ -37,11 +40,11 @@ num_cpus = "1.10.0"
 pin-utils = "0.1.0-alpha.4"
 slab = "0.4.2"
 
-[dependencies.futures-preview]
-version = "0.3.0-alpha.18"
-features = ["async-await", "nightly"]
-
 [dev-dependencies]
 femme = "1.1.0"
-tempdir = "0.3.7"
 surf = "1.0.1"
+tempdir = "0.3.7"
+
+[dev-dependencies.futures-preview]
+version = "0.3.0-alpha.18"
+features = ["std", "nightly", "async-await"]
diff --git a/docs/src/tutorial/connecting_readers_and_writers.md b/docs/src/tutorial/connecting_readers_and_writers.md
index 31631f880..f3ccf2d98 100644
--- a/docs/src/tutorial/connecting_readers_and_writers.md
+++ b/docs/src/tutorial/connecting_readers_and_writers.md
@@ -20,7 +20,7 @@ The order of events "Bob sends message to Alice" and "Alice joins" is determined
 #     task,
 # };
 # use futures::channel::mpsc;
-# use futures::SinkExt;
+# use futures::sink::SinkExt;
 # use std::sync::Arc;
 #
 # type Result<T> = std::result::Result<T, Box<dyn std::error::Error + Send + Sync>>;
diff --git a/docs/src/tutorial/sending_messages.md b/docs/src/tutorial/sending_messages.md
index 465d67409..80784c2a1 100644
--- a/docs/src/tutorial/sending_messages.md
+++ b/docs/src/tutorial/sending_messages.md
@@ -20,7 +20,7 @@ if Alice and Charley send two messages to Bob at the same time, Bob will see the
 #     prelude::Stream,
 # };
 use futures::channel::mpsc; // 1
-use futures::SinkExt;
+use futures::sink::SinkExt;
 use std::sync::Arc;
 
 # type Result<T> = std::result::Result<T, Box<dyn std::error::Error + Send + Sync>>;
diff --git a/src/fs/dir_entry.rs b/src/fs/dir_entry.rs
index 4e07a3f22..c7928ebd2 100644
--- a/src/fs/dir_entry.rs
+++ b/src/fs/dir_entry.rs
@@ -1,15 +1,12 @@
 use std::ffi::OsString;
 use std::fs;
 use std::path::PathBuf;
-use std::pin::Pin;
-use std::sync::Mutex;
+use std::sync::Arc;
 
 use cfg_if::cfg_if;
-use futures::future::{self, FutureExt, TryFutureExt};
 
-use crate::future::Future;
 use crate::io;
-use crate::task::{blocking, Poll};
+use crate::task::blocking;
 
 /// An entry inside a directory.
 ///
@@ -21,26 +18,11 @@ use crate::task::{blocking, Poll};
 /// [`std::fs::DirEntry`]: https://doc.rust-lang.org/std/fs/struct.DirEntry.html
 #[derive(Debug)]
 pub struct DirEntry {
-    /// The state of the entry.
-    state: Mutex<State>,
-
-    /// The full path to the entry.
-    path: PathBuf,
+    /// The inner synchronous `DirEntry`.
+    inner: Arc<fs::DirEntry>,
 
     #[cfg(unix)]
     ino: u64,
-
-    /// The bare name of the entry without the leading path.
-    file_name: OsString,
-}
-
-/// The state of an asynchronous `DirEntry`.
-///
-/// The `DirEntry` can be either idle or busy performing an asynchronous operation.
-#[derive(Debug)]
-enum State {
-    Idle(Option<fs::DirEntry>),
-    Busy(blocking::JoinHandle<State>),
 }
 
 impl DirEntry {
@@ -48,17 +30,13 @@ impl DirEntry {
     pub(crate) fn new(inner: fs::DirEntry) -> DirEntry {
         #[cfg(unix)]
         let dir_entry = DirEntry {
-            path: inner.path(),
-            file_name: inner.file_name(),
             ino: inner.ino(),
-            state: Mutex::new(State::Idle(Some(inner))),
+            inner: Arc::new(inner),
         };
 
         #[cfg(windows)]
         let dir_entry = DirEntry {
-            path: inner.path(),
-            file_name: inner.file_name(),
-            state: Mutex::new(State::Idle(Some(inner))),
+            inner: Arc::new(inner),
         };
 
         dir_entry
@@ -89,7 +67,7 @@ impl DirEntry {
     /// # Ok(()) }) }
     /// ```
     pub fn path(&self) -> PathBuf {
-        self.path.clone()
+        self.inner.path()
     }
 
     /// Returns the metadata for this entry.
@@ -114,35 +92,8 @@ impl DirEntry {
     /// # Ok(()) }) }
     /// ```
     pub async fn metadata(&self) -> io::Result<fs::Metadata> {
-        future::poll_fn(|cx| {
-            let state = &mut *self.state.lock().unwrap();
-
-            loop {
-                match state {
-                    State::Idle(opt) => match opt.take() {
-                        None => return Poll::Ready(None),
-                        Some(inner) => {
-                            let (s, r) = futures::channel::oneshot::channel();
-
-                            // Start the operation asynchronously.
-                            *state = State::Busy(blocking::spawn(async move {
-                                let res = inner.metadata();
-                                let _ = s.send(res);
-                                State::Idle(Some(inner))
-                            }));
-
-                            return Poll::Ready(Some(r));
-                        }
-                    },
-                    // Poll the asynchronous operation the file is currently blocked on.
-                    State::Busy(task) => *state = futures::ready!(Pin::new(task).poll(cx)),
-                }
-            }
-        })
-        .map(|opt| opt.ok_or_else(|| io_error("invalid state")))
-        .await?
-        .map_err(|_| io_error("blocking task failed"))
-        .await?
+        let inner = self.inner.clone();
+        blocking::spawn(async move { inner.metadata() }).await
     }
 
     /// Returns the file type for this entry.
@@ -167,35 +118,8 @@ impl DirEntry {
     /// # Ok(()) }) }
     /// ```
     pub async fn file_type(&self) -> io::Result<fs::FileType> {
-        future::poll_fn(|cx| {
-            let state = &mut *self.state.lock().unwrap();
-
-            loop {
-                match state {
-                    State::Idle(opt) => match opt.take() {
-                        None => return Poll::Ready(None),
-                        Some(inner) => {
-                            let (s, r) = futures::channel::oneshot::channel();
-
-                            // Start the operation asynchronously.
-                            *state = State::Busy(blocking::spawn(async move {
-                                let res = inner.file_type();
-                                let _ = s.send(res);
-                                State::Idle(Some(inner))
-                            }));
-
-                            return Poll::Ready(Some(r));
-                        }
-                    },
-                    // Poll the asynchronous operation the file is currently blocked on.
-                    State::Busy(task) => *state = futures::ready!(Pin::new(task).poll(cx)),
-                }
-            }
-        })
-        .map(|opt| opt.ok_or_else(|| io_error("invalid state")))
-        .await?
-        .map_err(|_| io_error("blocking task failed"))
-        .await?
+        let inner = self.inner.clone();
+        blocking::spawn(async move { inner.file_type() }).await
     }
 
     /// Returns the bare name of this entry without the leading path.
@@ -218,15 +142,10 @@ impl DirEntry {
     /// # Ok(()) }) }
     /// ```
     pub fn file_name(&self) -> OsString {
-        self.file_name.clone()
+        self.inner.file_name()
     }
 }
 
-/// Creates a custom `io::Error` with an arbitrary error type.
-fn io_error(err: impl Into<Box<dyn std::error::Error + Send + Sync>>) -> io::Error {
-    io::Error::new(io::ErrorKind::Other, err)
-}
-
 cfg_if! {
     if #[cfg(feature = "docs")] {
         use crate::os::unix::fs::DirEntryExt;
diff --git a/src/fs/file.rs b/src/fs/file.rs
index b297181d2..09e2ad64e 100644
--- a/src/fs/file.rs
+++ b/src/fs/file.rs
@@ -7,10 +7,9 @@ use std::pin::Pin;
 use std::sync::Mutex;
 
 use cfg_if::cfg_if;
-use futures::future::{self, FutureExt, TryFutureExt};
-use futures::io::{AsyncRead, AsyncSeek, AsyncWrite, Initializer};
+use futures_io::{AsyncRead, AsyncSeek, AsyncWrite, Initializer};
 
-use crate::future::Future;
+use crate::future::{self, Future};
 use crate::io;
 use crate::task::{blocking, Context, Poll};
 
@@ -234,7 +233,7 @@ impl File {
                     State::Idle(opt) => match opt.take() {
                         None => return Poll::Ready(None),
                         Some(inner) => {
-                            let (s, r) = futures::channel::oneshot::channel();
+                            let (s, r) = futures_channel::oneshot::channel();
 
                             // Start the operation asynchronously.
                             *state = State::Busy(blocking::spawn(async move {
@@ -247,14 +246,14 @@ impl File {
                         }
                     },
                     // Poll the asynchronous operation the file is currently blocked on.
-                    State::Busy(task) => *state = futures::ready!(Pin::new(task).poll(cx)),
+                    State::Busy(task) => *state = futures_core::ready!(Pin::new(task).poll(cx)),
                 }
             }
         })
-        .map(|opt| opt.ok_or_else(|| io_error("file closed")))
-        .await?
-        .map_err(|_| io_error("blocking task failed"))
-        .await?
+        .await
+        .ok_or_else(|| io_error("file closed"))?
+        .await
+        .map_err(|_| io_error("blocking task failed"))?
     }
 
     /// Similar to [`sync_all`], except that it may not synchronize file metadata.
@@ -289,7 +288,7 @@ impl File {
                     State::Idle(opt) => match opt.take() {
                         None => return Poll::Ready(None),
                         Some(inner) => {
-                            let (s, r) = futures::channel::oneshot::channel();
+                            let (s, r) = futures_channel::oneshot::channel();
 
                             // Start the operation asynchronously.
                             *state = State::Busy(blocking::spawn(async move {
@@ -302,14 +301,14 @@ impl File {
                         }
                     },
                     // Poll the asynchronous operation the file is currently blocked on.
-                    State::Busy(task) => *state = futures::ready!(Pin::new(task).poll(cx)),
+                    State::Busy(task) => *state = futures_core::ready!(Pin::new(task).poll(cx)),
                 }
             }
         })
-        .map(|opt| opt.ok_or_else(|| io_error("file closed")))
-        .await?
-        .map_err(|_| io_error("blocking task failed"))
-        .await?
+        .await
+        .ok_or_else(|| io_error("file closed"))?
+        .await
+        .map_err(|_| io_error("blocking task failed"))?
     }
 
     /// Truncates or extends the underlying file.
@@ -346,7 +345,7 @@ impl File {
                     State::Idle(opt) => match opt.take() {
                         None => return Poll::Ready(None),
                         Some(inner) => {
-                            let (s, r) = futures::channel::oneshot::channel();
+                            let (s, r) = futures_channel::oneshot::channel();
 
                             // Start the operation asynchronously.
                             *state = State::Busy(blocking::spawn(async move {
@@ -359,14 +358,14 @@ impl File {
                         }
                     },
                     // Poll the asynchronous operation the file is currently blocked on.
-                    State::Busy(task) => *state = futures::ready!(Pin::new(task).poll(cx)),
+                    State::Busy(task) => *state = futures_core::ready!(Pin::new(task).poll(cx)),
                 }
             }
         })
-        .map(|opt| opt.ok_or_else(|| io_error("file closed")))
-        .await?
-        .map_err(|_| io_error("blocking task failed"))
-        .await?
+        .await
+        .ok_or_else(|| io_error("file closed"))?
+        .await
+        .map_err(|_| io_error("blocking task failed"))?
     }
 
     /// Queries metadata about the file.
@@ -392,7 +391,7 @@ impl File {
                     State::Idle(opt) => match opt.take() {
                         None => return Poll::Ready(None),
                         Some(inner) => {
-                            let (s, r) = futures::channel::oneshot::channel();
+                            let (s, r) = futures_channel::oneshot::channel();
 
                             // Start the operation asynchronously.
                             *state = State::Busy(blocking::spawn(async move {
@@ -405,14 +404,14 @@ impl File {
                         }
                     },
                     // Poll the asynchronous operation the file is currently blocked on.
-                    State::Busy(task) => *state = futures::ready!(Pin::new(task).poll(cx)),
+                    State::Busy(task) => *state = futures_core::ready!(Pin::new(task).poll(cx)),
                 }
             }
         })
-        .map(|opt| opt.ok_or_else(|| io_error("file closed")))
-        .await?
-        .map_err(|_| io_error("blocking task failed"))
-        .await?
+        .await
+        .ok_or_else(|| io_error("file closed"))?
+        .await
+        .map_err(|_| io_error("blocking task failed"))?
     }
 
     /// Changes the permissions on the underlying file.
@@ -448,7 +447,7 @@ impl File {
                     State::Idle(opt) => match opt.take() {
                         None => return Poll::Ready(None),
                         Some(inner) => {
-                            let (s, r) = futures::channel::oneshot::channel();
+                            let (s, r) = futures_channel::oneshot::channel();
                             let perm = perm.take().unwrap();
 
                             // Start the operation asynchronously.
@@ -462,14 +461,14 @@ impl File {
                         }
                     },
                     // Poll the asynchronous operation the file is currently blocked on.
-                    State::Busy(task) => *state = futures::ready!(Pin::new(task).poll(cx)),
+                    State::Busy(task) => *state = futures_core::ready!(Pin::new(task).poll(cx)),
                 }
             }
         })
-        .map(|opt| opt.ok_or_else(|| io_error("file closed")))
-        .await?
-        .map_err(|_| io_error("blocking task failed"))
-        .await?
+        .await
+        .ok_or_else(|| io_error("file closed"))?
+        .await
+        .map_err(|_| io_error("blocking task failed"))?
     }
 }
 
@@ -543,7 +542,7 @@ impl AsyncRead for &File {
                     }));
                 }
                 // Poll the asynchronous operation the file is currently blocked on.
-                State::Busy(task) => *state = futures::ready!(Pin::new(task).poll(cx)),
+                State::Busy(task) => *state = futures_core::ready!(Pin::new(task).poll(cx)),
             }
         }
     }
@@ -619,7 +618,7 @@ impl AsyncWrite for &File {
                     }
                 }
                 // Poll the asynchronous operation the file is currently blocked on.
-                State::Busy(task) => *state = futures::ready!(Pin::new(task).poll(cx)),
+                State::Busy(task) => *state = futures_core::ready!(Pin::new(task).poll(cx)),
             }
         }
     }
@@ -652,7 +651,7 @@ impl AsyncWrite for &File {
                     }
                 }
                 // Poll the asynchronous operation the file is currently blocked on.
-                State::Busy(task) => *state = futures::ready!(Pin::new(task).poll(cx)),
+                State::Busy(task) => *state = futures_core::ready!(Pin::new(task).poll(cx)),
             }
         }
     }
@@ -677,7 +676,7 @@ impl AsyncWrite for &File {
                     }));
                 }
                 // Poll the asynchronous operation the file is currently blocked on.
-                State::Busy(task) => *state = futures::ready!(Pin::new(task).poll(cx)),
+                State::Busy(task) => *state = futures_core::ready!(Pin::new(task).poll(cx)),
             }
         }
     }
@@ -723,7 +722,7 @@ impl AsyncSeek for &File {
                     }
                 }
                 // Poll the asynchronous operation the file is currently blocked on.
-                State::Busy(task) => *state = futures::ready!(Pin::new(task).poll(cx)),
+                State::Busy(task) => *state = futures_core::ready!(Pin::new(task).poll(cx)),
             }
         }
     }
diff --git a/src/fs/read_dir.rs b/src/fs/read_dir.rs
index dffab3a46..b3771610e 100644
--- a/src/fs/read_dir.rs
+++ b/src/fs/read_dir.rs
@@ -1,7 +1,6 @@
 use std::fs;
 use std::path::Path;
 use std::pin::Pin;
-use std::sync::Mutex;
 
 use super::DirEntry;
 use crate::future::Future;
@@ -64,71 +63,45 @@ pub async fn read_dir<P: AsRef<Path>>(path: P) -> io::Result<ReadDir> {
 /// [`DirEntry`]: struct.DirEntry.html
 /// [`std::fs::ReadDir`]: https://doc.rust-lang.org/std/fs/struct.ReadDir.html
 #[derive(Debug)]
-pub struct ReadDir(Mutex<State>);
+pub struct ReadDir(State);
 
 /// The state of an asynchronous `ReadDir`.
 ///
 /// The `ReadDir` can be either idle or busy performing an asynchronous operation.
 #[derive(Debug)]
 enum State {
-    Idle(Option<Inner>),
-    Busy(blocking::JoinHandle<State>),
-}
-
-/// Inner representation of an asynchronous `DirEntry`.
-#[derive(Debug)]
-struct Inner {
-    /// The blocking handle.
-    read_dir: fs::ReadDir,
-
-    /// The next item in the stream.
-    item: Option<io::Result<DirEntry>>,
+    Idle(Option<fs::ReadDir>),
+    Busy(blocking::JoinHandle<(fs::ReadDir, Option<io::Result<fs::DirEntry>>)>),
 }
 
 impl ReadDir {
     /// Creates an asynchronous `ReadDir` from a synchronous handle.
     pub(crate) fn new(inner: fs::ReadDir) -> ReadDir {
-        ReadDir(Mutex::new(State::Idle(Some(Inner {
-            read_dir: inner,
-            item: None,
-        }))))
+        ReadDir(State::Idle(Some(inner)))
     }
 }
 
-impl futures::Stream for ReadDir {
+impl futures_core::stream::Stream for ReadDir {
     type Item = io::Result<DirEntry>;
 
     fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
-        let state = &mut *self.0.lock().unwrap();
-
         loop {
-            match state {
+            match &mut self.0 {
                 State::Idle(opt) => {
-                    let inner = match opt.as_mut() {
-                        None => return Poll::Ready(None),
-                        Some(inner) => inner,
-                    };
-
-                    // Check if the operation has completed.
-                    if let Some(res) = inner.item.take() {
-                        return Poll::Ready(Some(res));
-                    } else {
-                        let mut inner = opt.take().unwrap();
+                    let mut inner = opt.take().unwrap();
 
-                        // Start the operation asynchronously.
-                        *state = State::Busy(blocking::spawn(async move {
-                            match inner.read_dir.next() {
-                                None => State::Idle(None),
-                                Some(res) => {
-                                    inner.item = Some(res.map(DirEntry::new));
-                                    State::Idle(Some(inner))
-                                }
-                            }
-                        }));
-                    }
+                    // Start the operation asynchronously.
+                    self.0 = State::Busy(blocking::spawn(async move {
+                        let next = inner.next();
+                        (inner, next)
+                    }));
                 }
                 // Poll the asynchronous operation the file is currently blocked on.
-                State::Busy(task) => *state = futures::ready!(Pin::new(task).poll(cx)),
+                State::Busy(task) => {
+                    let (inner, opt) = futures_core::ready!(Pin::new(task).poll(cx));
+                    self.0 = State::Idle(Some(inner));
+                    return Poll::Ready(opt.map(|res| res.map(DirEntry::new)));
+                }
             }
         }
     }
diff --git a/src/future/mod.rs b/src/future/mod.rs
index 5d510a449..7d88b9031 100644
--- a/src/future/mod.rs
+++ b/src/future/mod.rs
@@ -6,9 +6,11 @@ pub use std::future::Future;
 use cfg_if::cfg_if;
 
 pub use pending::pending;
+pub use poll_fn::poll_fn;
 pub use ready::ready;
 
 mod pending;
+mod poll_fn;
 mod ready;
 
 cfg_if! {
diff --git a/src/future/pending.rs b/src/future/pending.rs
index 41284f54d..aaee70656 100644
--- a/src/future/pending.rs
+++ b/src/future/pending.rs
@@ -1,16 +1,23 @@
+use std::marker::PhantomData;
+use std::pin::Pin;
+
+use crate::future::Future;
+use crate::task::{Context, Poll};
+
 /// Never resolves to a value.
 ///
 /// # Examples
+///
 /// ```
 /// # fn main() { async_std::task::block_on(async {
 /// #
 /// use std::time::Duration;
 ///
-/// use async_std::future::pending;
+/// use async_std::future;
 /// use async_std::io;
 ///
 /// let dur = Duration::from_secs(1);
-/// let fut = pending();
+/// let fut = future::pending();
 ///
 /// let res: io::Result<()> = io::timeout(dur, fut).await;
 /// assert!(res.is_err());
@@ -18,5 +25,20 @@
 /// # }) }
 /// ```
 pub async fn pending<T>() -> T {
-    futures::future::pending::<T>().await
+    let fut = Pending {
+        _marker: PhantomData,
+    };
+    fut.await
+}
+
+struct Pending<T> {
+    _marker: PhantomData<T>,
+}
+
+impl<T> Future for Pending<T> {
+    type Output = T;
+
+    fn poll(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<T> {
+        Poll::Pending
+    }
 }
diff --git a/src/future/poll_fn.rs b/src/future/poll_fn.rs
new file mode 100644
index 000000000..116e71c69
--- /dev/null
+++ b/src/future/poll_fn.rs
@@ -0,0 +1,49 @@
+use std::pin::Pin;
+
+use crate::future::Future;
+use crate::task::{Context, Poll};
+
+/// Creates a new future wrapping around a function returning [`Poll`].
+///
+/// Polling the returned future delegates to the wrapped function.
+///
+/// # Examples
+///
+/// ```
+/// # fn main() { async_std::task::block_on(async {
+/// #
+/// use async_std::future;
+/// use async_std::task::{Context, Poll};
+///
+/// fn poll_greeting(_: &mut Context<'_>) -> Poll<String> {
+///     Poll::Ready("hello world".to_string())
+/// }
+///
+/// assert_eq!(future::poll_fn(poll_greeting).await, "hello world");
+/// #
+/// # }) }
+/// ```
+pub async fn poll_fn<F, T>(f: F) -> T
+where
+    F: FnMut(&mut Context<'_>) -> Poll<T>,
+{
+    let fut = PollFn { f };
+    fut.await
+}
+
+struct PollFn<F> {
+    f: F,
+}
+
+impl<F> Unpin for PollFn<F> {}
+
+impl<T, F> Future for PollFn<F>
+where
+    F: FnMut(&mut Context<'_>) -> Poll<T>,
+{
+    type Output = T;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<T> {
+        (&mut self.f)(cx)
+    }
+}
diff --git a/src/io/buf_read.rs b/src/io/buf_read.rs
index 6b7b9dbb8..b05bf89e8 100644
--- a/src/io/buf_read.rs
+++ b/src/io/buf_read.rs
@@ -3,7 +3,7 @@ use std::pin::Pin;
 use std::str;
 
 use cfg_if::cfg_if;
-use futures::io::AsyncBufRead;
+use futures_io::AsyncBufRead;
 
 use crate::future::Future;
 use crate::io;
@@ -212,7 +212,7 @@ impl<T: AsyncBufRead + Unpin + ?Sized> Future for ReadLineFuture<'_, T> {
         } = &mut *self;
         let reader = Pin::new(reader);
 
-        let ret = futures::ready!(read_until_internal(reader, cx, b'\n', bytes, read));
+        let ret = futures_core::ready!(read_until_internal(reader, cx, b'\n', bytes, read));
         if str::from_utf8(&bytes).is_err() {
             Poll::Ready(ret.and_then(|_| {
                 Err(io::Error::new(
@@ -247,7 +247,7 @@ pub struct Lines<R> {
     read: usize,
 }
 
-impl<R: AsyncBufRead> futures::Stream for Lines<R> {
+impl<R: AsyncBufRead> futures_core::stream::Stream for Lines<R> {
     type Item = io::Result<String>;
 
     fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
@@ -258,7 +258,7 @@ impl<R: AsyncBufRead> futures::Stream for Lines<R> {
             read,
         } = unsafe { self.get_unchecked_mut() };
         let reader = unsafe { Pin::new_unchecked(reader) };
-        let n = futures::ready!(read_line_internal(reader, cx, buf, bytes, read))?;
+        let n = futures_core::ready!(read_line_internal(reader, cx, buf, bytes, read))?;
         if n == 0 && buf.is_empty() {
             return Poll::Ready(None);
         }
@@ -279,7 +279,7 @@ pub fn read_line_internal<R: AsyncBufRead + ?Sized>(
     bytes: &mut Vec<u8>,
     read: &mut usize,
 ) -> Poll<io::Result<usize>> {
-    let ret = futures::ready!(read_until_internal(reader, cx, b'\n', bytes, read));
+    let ret = futures_core::ready!(read_until_internal(reader, cx, b'\n', bytes, read));
     if str::from_utf8(&bytes).is_err() {
         Poll::Ready(ret.and_then(|_| {
             Err(io::Error::new(
@@ -305,7 +305,7 @@ pub fn read_until_internal<R: AsyncBufRead + ?Sized>(
 ) -> Poll<io::Result<usize>> {
     loop {
         let (done, used) = {
-            let available = futures::ready!(reader.as_mut().poll_fill_buf(cx))?;
+            let available = futures_core::ready!(reader.as_mut().poll_fill_buf(cx))?;
             if let Some(i) = memchr::memchr(byte, available) {
                 buf.extend_from_slice(&available[..=i]);
                 (true, i + 1)
diff --git a/src/io/buf_reader.rs b/src/io/buf_reader.rs
index 2ad10cc68..f38307a9b 100644
--- a/src/io/buf_reader.rs
+++ b/src/io/buf_reader.rs
@@ -2,7 +2,7 @@ use std::io::{IoSliceMut, Read as _};
 use std::pin::Pin;
 use std::{cmp, fmt};
 
-use futures::io::{AsyncBufRead, AsyncRead, AsyncSeek, Initializer};
+use futures_io::{AsyncBufRead, AsyncRead, AsyncSeek, Initializer};
 
 use crate::io::{self, SeekFrom};
 use crate::task::{Context, Poll};
@@ -51,7 +51,7 @@ pub struct BufReader<R> {
     cap: usize,
 }
 
-impl<R: AsyncRead> BufReader<R> {
+impl<R: io::Read> BufReader<R> {
     /// Creates a buffered reader with default buffer capacity.
     ///
     /// The default capacity is currently 8 KB, but may change in the future.
@@ -87,17 +87,11 @@ impl<R: AsyncRead> BufReader<R> {
     /// # Ok(()) }) }
     /// ```
     pub fn with_capacity(capacity: usize, inner: R) -> BufReader<R> {
-        unsafe {
-            let mut buffer = Vec::with_capacity(capacity);
-            buffer.set_len(capacity);
-            inner.initializer().initialize(&mut buffer);
-
-            BufReader {
-                inner,
-                buf: buffer.into_boxed_slice(),
-                pos: 0,
-                cap: 0,
-            }
+        BufReader {
+            inner,
+            buf: vec![0; capacity].into_boxed_slice(),
+            pos: 0,
+            cap: 0,
         }
     }
 }
@@ -209,11 +203,11 @@ impl<R: AsyncRead> AsyncRead for BufReader<R> {
         // (larger than our internal buffer), bypass our internal buffer
         // entirely.
         if self.pos == self.cap && buf.len() >= self.buf.len() {
-            let res = futures::ready!(self.as_mut().inner().poll_read(cx, buf));
+            let res = futures_core::ready!(self.as_mut().inner().poll_read(cx, buf));
             self.discard_buffer();
             return Poll::Ready(res);
         }
-        let mut rem = futures::ready!(self.as_mut().poll_fill_buf(cx))?;
+        let mut rem = futures_core::ready!(self.as_mut().poll_fill_buf(cx))?;
         let nread = rem.read(buf)?;
         self.consume(nread);
         Poll::Ready(Ok(nread))
@@ -226,11 +220,11 @@ impl<R: AsyncRead> AsyncRead for BufReader<R> {
     ) -> Poll<io::Result<usize>> {
         let total_len = bufs.iter().map(|b| b.len()).sum::<usize>();
         if self.pos == self.cap && total_len >= self.buf.len() {
-            let res = futures::ready!(self.as_mut().inner().poll_read_vectored(cx, bufs));
+            let res = futures_core::ready!(self.as_mut().inner().poll_read_vectored(cx, bufs));
             self.discard_buffer();
             return Poll::Ready(res);
         }
-        let mut rem = futures::ready!(self.as_mut().poll_fill_buf(cx))?;
+        let mut rem = futures_core::ready!(self.as_mut().poll_fill_buf(cx))?;
         let nread = rem.read_vectored(bufs)?;
         self.consume(nread);
         Poll::Ready(Ok(nread))
@@ -261,7 +255,7 @@ impl<R: AsyncRead> AsyncBufRead for BufReader<R> {
         // to tell the compiler that the pos..cap slice is always valid.
         if *pos >= *cap {
             debug_assert!(*pos == *cap);
-            *cap = futures::ready!(inner.as_mut().poll_read(cx, buf))?;
+            *cap = futures_core::ready!(inner.as_mut().poll_read(cx, buf))?;
             *pos = 0;
         }
         Poll::Ready(Ok(&buf[*pos..*cap]))
@@ -272,7 +266,7 @@ impl<R: AsyncRead> AsyncBufRead for BufReader<R> {
     }
 }
 
-impl<R: AsyncRead + fmt::Debug> fmt::Debug for BufReader<R> {
+impl<R: io::Read + fmt::Debug> fmt::Debug for BufReader<R> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         f.debug_struct("BufReader")
             .field("reader", &self.inner)
@@ -316,25 +310,26 @@ impl<R: AsyncSeek> AsyncSeek for BufReader<R> {
             // support seeking by i64::min_value() so we need to handle underflow when subtracting
             // remainder.
             if let Some(offset) = n.checked_sub(remainder) {
-                result = futures::ready!(
+                result = futures_core::ready!(
                     self.as_mut()
                         .inner()
                         .poll_seek(cx, SeekFrom::Current(offset))
                 )?;
             } else {
                 // seek backwards by our remainder, and then by the offset
-                futures::ready!(
+                futures_core::ready!(
                     self.as_mut()
                         .inner()
                         .poll_seek(cx, SeekFrom::Current(-remainder))
                 )?;
                 self.as_mut().discard_buffer();
-                result =
-                    futures::ready!(self.as_mut().inner().poll_seek(cx, SeekFrom::Current(n)))?;
+                result = futures_core::ready!(
+                    self.as_mut().inner().poll_seek(cx, SeekFrom::Current(n))
+                )?;
             }
         } else {
             // Seeking with Start/End doesn't care about our buffer length.
-            result = futures::ready!(self.as_mut().inner().poll_seek(cx, pos))?;
+            result = futures_core::ready!(self.as_mut().inner().poll_seek(cx, pos))?;
         }
         self.discard_buffer();
         Poll::Ready(Ok(result))
diff --git a/src/io/copy.rs b/src/io/copy.rs
index 961c8264b..ccc6bc829 100644
--- a/src/io/copy.rs
+++ b/src/io/copy.rs
@@ -1,6 +1,10 @@
-use futures::io::{AsyncRead, AsyncReadExt, AsyncWrite};
+use std::pin::Pin;
 
-use crate::io;
+use futures_io::{AsyncBufRead, AsyncRead, AsyncWrite};
+
+use crate::future::Future;
+use crate::io::{self, BufReader};
+use crate::task::{Context, Poll};
 
 /// Copies the entire contents of a reader into a writer.
 ///
@@ -44,6 +48,55 @@ where
     R: AsyncRead + Unpin + ?Sized,
     W: AsyncWrite + Unpin + ?Sized,
 {
-    let bytes_read = reader.copy_into(writer).await?;
-    Ok(bytes_read)
+    pub struct CopyFuture<'a, R, W: ?Sized> {
+        reader: R,
+        writer: &'a mut W,
+        amt: u64,
+    }
+
+    impl<R, W: Unpin + ?Sized> CopyFuture<'_, R, W> {
+        fn project(self: Pin<&mut Self>) -> (Pin<&mut R>, Pin<&mut W>, &mut u64) {
+            unsafe {
+                let this = self.get_unchecked_mut();
+                (
+                    Pin::new_unchecked(&mut this.reader),
+                    Pin::new(&mut *this.writer),
+                    &mut this.amt,
+                )
+            }
+        }
+    }
+
+    impl<R, W> Future for CopyFuture<'_, R, W>
+    where
+        R: AsyncBufRead,
+        W: AsyncWrite + Unpin + ?Sized,
+    {
+        type Output = io::Result<u64>;
+
+        fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+            let (mut reader, mut writer, amt) = self.project();
+            loop {
+                let buffer = futures_core::ready!(reader.as_mut().poll_fill_buf(cx))?;
+                if buffer.is_empty() {
+                    futures_core::ready!(writer.as_mut().poll_flush(cx))?;
+                    return Poll::Ready(Ok(*amt));
+                }
+
+                let i = futures_core::ready!(writer.as_mut().poll_write(cx, buffer))?;
+                if i == 0 {
+                    return Poll::Ready(Err(io::ErrorKind::WriteZero.into()));
+                }
+                *amt += i as u64;
+                reader.as_mut().consume(i);
+            }
+        }
+    }
+
+    let future = CopyFuture {
+        reader: BufReader::new(reader),
+        writer,
+        amt: 0,
+    };
+    future.await
 }
diff --git a/src/io/empty.rs b/src/io/empty.rs
index a832677db..35ed732bc 100644
--- a/src/io/empty.rs
+++ b/src/io/empty.rs
@@ -1,7 +1,7 @@
 use std::fmt;
 use std::pin::Pin;
 
-use futures::io::{AsyncBufRead, AsyncRead, Initializer};
+use futures_io::{AsyncBufRead, AsyncRead, Initializer};
 
 use crate::io;
 use crate::task::{Context, Poll};
diff --git a/src/io/read.rs b/src/io/read.rs
index cf3732f74..4b6bb1fb2 100644
--- a/src/io/read.rs
+++ b/src/io/read.rs
@@ -4,7 +4,7 @@ use std::pin::Pin;
 use std::str;
 
 use cfg_if::cfg_if;
-use futures::io::AsyncRead;
+use futures_io::AsyncRead;
 
 use crate::future::Future;
 use crate::io;
@@ -290,7 +290,7 @@ impl<T: AsyncRead + Unpin + ?Sized> Future for ReadToStringFuture<'_, T> {
         } = &mut *self;
         let reader = Pin::new(reader);
 
-        let ret = futures::ready!(read_to_end_internal(reader, cx, bytes, *start_len));
+        let ret = futures_core::ready!(read_to_end_internal(reader, cx, bytes, *start_len));
         if str::from_utf8(&bytes).is_err() {
             Poll::Ready(ret.and_then(|_| {
                 Err(io::Error::new(
@@ -321,7 +321,7 @@ impl<T: AsyncRead + Unpin + ?Sized> Future for ReadExactFuture<'_, T> {
         let Self { reader, buf } = &mut *self;
 
         while !buf.is_empty() {
-            let n = futures::ready!(Pin::new(&mut *reader).poll_read(cx, buf))?;
+            let n = futures_core::ready!(Pin::new(&mut *reader).poll_read(cx, buf))?;
             let (_, rest) = mem::replace(buf, &mut []).split_at_mut(n);
             *buf = rest;
 
@@ -377,7 +377,7 @@ pub fn read_to_end_internal<R: AsyncRead + ?Sized>(
             }
         }
 
-        match futures::ready!(rd.as_mut().poll_read(cx, &mut g.buf[g.len..])) {
+        match futures_core::ready!(rd.as_mut().poll_read(cx, &mut g.buf[g.len..])) {
             Ok(0) => {
                 ret = Poll::Ready(Ok(g.len - start_len));
                 break;
diff --git a/src/io/seek.rs b/src/io/seek.rs
index 9250faaf8..61a5d9c5e 100644
--- a/src/io/seek.rs
+++ b/src/io/seek.rs
@@ -1,7 +1,7 @@
 use std::pin::Pin;
 
 use cfg_if::cfg_if;
-use futures::io::AsyncSeek;
+use futures_io::AsyncSeek;
 
 use crate::future::Future;
 use crate::io::{self, SeekFrom};
diff --git a/src/io/sink.rs b/src/io/sink.rs
index ec38431c0..fba563340 100644
--- a/src/io/sink.rs
+++ b/src/io/sink.rs
@@ -1,7 +1,7 @@
 use std::fmt;
 use std::pin::Pin;
 
-use futures::io::AsyncWrite;
+use futures_io::AsyncWrite;
 
 use crate::io;
 use crate::task::{Context, Poll};
diff --git a/src/io/stderr.rs b/src/io/stderr.rs
index 73b64ce44..bb2318fad 100644
--- a/src/io/stderr.rs
+++ b/src/io/stderr.rs
@@ -3,7 +3,7 @@ use std::pin::Pin;
 use std::sync::Mutex;
 
 use cfg_if::cfg_if;
-use futures::io::AsyncWrite;
+use futures_io::AsyncWrite;
 
 use crate::future::Future;
 use crate::task::{blocking, Context, Poll};
@@ -125,7 +125,7 @@ impl AsyncWrite for Stderr {
                     }
                 }
                 // Poll the asynchronous operation the stderr is currently blocked on.
-                State::Busy(task) => *state = futures::ready!(Pin::new(task).poll(cx)),
+                State::Busy(task) => *state = futures_core::ready!(Pin::new(task).poll(cx)),
             }
         }
     }
@@ -153,7 +153,7 @@ impl AsyncWrite for Stderr {
                     }
                 }
                 // Poll the asynchronous operation the stderr is currently blocked on.
-                State::Busy(task) => *state = futures::ready!(Pin::new(task).poll(cx)),
+                State::Busy(task) => *state = futures_core::ready!(Pin::new(task).poll(cx)),
             }
         }
     }
diff --git a/src/io/stdin.rs b/src/io/stdin.rs
index bd4c1118d..9fe432d01 100644
--- a/src/io/stdin.rs
+++ b/src/io/stdin.rs
@@ -3,10 +3,9 @@ use std::pin::Pin;
 use std::sync::Mutex;
 
 use cfg_if::cfg_if;
-use futures::future;
-use futures::io::{AsyncRead, Initializer};
+use futures_io::{AsyncRead, Initializer};
 
-use crate::future::Future;
+use crate::future::{self, Future};
 use crate::task::{blocking, Context, Poll};
 
 /// Constructs a new handle to the standard input of the current process.
@@ -130,7 +129,7 @@ impl Stdin {
                         }
                     }
                     // Poll the asynchronous operation the stdin is currently blocked on.
-                    State::Busy(task) => *state = futures::ready!(Pin::new(task).poll(cx)),
+                    State::Busy(task) => *state = futures_core::ready!(Pin::new(task).poll(cx)),
                 }
             }
         })
@@ -182,7 +181,7 @@ impl AsyncRead for Stdin {
                     }
                 }
                 // Poll the asynchronous operation the stdin is currently blocked on.
-                State::Busy(task) => *state = futures::ready!(Pin::new(task).poll(cx)),
+                State::Busy(task) => *state = futures_core::ready!(Pin::new(task).poll(cx)),
             }
         }
     }
diff --git a/src/io/stdout.rs b/src/io/stdout.rs
index 5045d1124..f62f3df37 100644
--- a/src/io/stdout.rs
+++ b/src/io/stdout.rs
@@ -3,7 +3,7 @@ use std::pin::Pin;
 use std::sync::Mutex;
 
 use cfg_if::cfg_if;
-use futures::io::AsyncWrite;
+use futures_io::AsyncWrite;
 
 use crate::future::Future;
 use crate::task::{blocking, Context, Poll};
@@ -125,7 +125,7 @@ impl AsyncWrite for Stdout {
                     }
                 }
                 // Poll the asynchronous operation the stdout is currently blocked on.
-                State::Busy(task) => *state = futures::ready!(Pin::new(task).poll(cx)),
+                State::Busy(task) => *state = futures_core::ready!(Pin::new(task).poll(cx)),
             }
         }
     }
@@ -153,7 +153,7 @@ impl AsyncWrite for Stdout {
                     }
                 }
                 // Poll the asynchronous operation the stdout is currently blocked on.
-                State::Busy(task) => *state = futures::ready!(Pin::new(task).poll(cx)),
+                State::Busy(task) => *state = futures_core::ready!(Pin::new(task).poll(cx)),
             }
         }
     }
diff --git a/src/io/write.rs b/src/io/write.rs
index 0fba81bcd..d332eec39 100644
--- a/src/io/write.rs
+++ b/src/io/write.rs
@@ -3,7 +3,7 @@ use std::mem;
 use std::pin::Pin;
 
 use cfg_if::cfg_if;
-use futures::io::AsyncWrite;
+use futures_io::AsyncWrite;
 
 use crate::future::Future;
 use crate::io;
@@ -201,7 +201,7 @@ impl<T: AsyncWrite + Unpin + ?Sized> Future for WriteAllFuture<'_, T> {
         let Self { writer, buf } = &mut *self;
 
         while !buf.is_empty() {
-            let n = futures::ready!(Pin::new(&mut **writer).poll_write(cx, buf))?;
+            let n = futures_core::ready!(Pin::new(&mut **writer).poll_write(cx, buf))?;
             let (_, rest) = mem::replace(buf, &[]).split_at(n);
             *buf = rest;
 
diff --git a/src/net/addr.rs b/src/net/addr.rs
index 39dba52df..71f43a5c0 100644
--- a/src/net/addr.rs
+++ b/src/net/addr.rs
@@ -1,15 +1,14 @@
+use std::marker::PhantomData;
 use std::net::{IpAddr, Ipv4Addr, Ipv6Addr};
 use std::net::{SocketAddr, SocketAddrV4, SocketAddrV6};
 use std::pin::Pin;
 
 use cfg_if::cfg_if;
-use futures::future::{ready, Ready};
 
 use crate::future::Future;
 use crate::io;
 use crate::task::blocking;
 use crate::task::{Context, Poll};
-use std::marker::PhantomData;
 
 cfg_if! {
     if #[cfg(feature = "docs")] {
@@ -47,19 +46,22 @@ pub trait ToSocketAddrs {
 
 #[doc(hidden)]
 #[allow(missing_debug_implementations)]
-pub enum ToSocketAddrsFuture<'a, I: Iterator<Item = SocketAddr>> {
+pub enum ToSocketAddrsFuture<'a, I> {
     Phantom(PhantomData<&'a ()>),
     Join(blocking::JoinHandle<io::Result<I>>),
-    Ready(Ready<io::Result<I>>),
+    Ready(Option<io::Result<I>>),
 }
 
 impl<I: Iterator<Item = SocketAddr>> Future for ToSocketAddrsFuture<'_, I> {
     type Output = io::Result<I>;
 
     fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
-        match self.get_mut() {
+        match unsafe { self.get_unchecked_mut() } {
             ToSocketAddrsFuture::Join(f) => Pin::new(&mut *f).poll(cx),
-            ToSocketAddrsFuture::Ready(f) => Pin::new(&mut *f).poll(cx),
+            ToSocketAddrsFuture::Ready(res) => {
+                let res = res.take().expect("polled a completed future");
+                Poll::Ready(res)
+            }
             _ => unreachable!(),
         }
     }
@@ -69,7 +71,7 @@ impl ToSocketAddrs for SocketAddr {
     type Iter = std::option::IntoIter<SocketAddr>;
 
     fn to_socket_addrs(&self) -> ret!('_, ToSocketAddrsFuture, Self::Iter) {
-        ToSocketAddrsFuture::Ready(ready(std::net::ToSocketAddrs::to_socket_addrs(self)))
+        ToSocketAddrsFuture::Ready(Some(std::net::ToSocketAddrs::to_socket_addrs(self)))
     }
 }
 
@@ -77,7 +79,7 @@ impl ToSocketAddrs for SocketAddrV4 {
     type Iter = std::option::IntoIter<SocketAddr>;
 
     fn to_socket_addrs(&self) -> ret!('_, ToSocketAddrsFuture, Self::Iter) {
-        ToSocketAddrsFuture::Ready(ready(std::net::ToSocketAddrs::to_socket_addrs(self)))
+        ToSocketAddrsFuture::Ready(Some(std::net::ToSocketAddrs::to_socket_addrs(self)))
     }
 }
 
@@ -85,7 +87,7 @@ impl ToSocketAddrs for SocketAddrV6 {
     type Iter = std::option::IntoIter<SocketAddr>;
 
     fn to_socket_addrs(&self) -> ret!('_, ToSocketAddrsFuture, Self::Iter) {
-        ToSocketAddrsFuture::Ready(ready(std::net::ToSocketAddrs::to_socket_addrs(self)))
+        ToSocketAddrsFuture::Ready(Some(std::net::ToSocketAddrs::to_socket_addrs(self)))
     }
 }
 
@@ -93,7 +95,7 @@ impl ToSocketAddrs for (IpAddr, u16) {
     type Iter = std::option::IntoIter<SocketAddr>;
 
     fn to_socket_addrs(&self) -> ret!('_, ToSocketAddrsFuture, Self::Iter) {
-        ToSocketAddrsFuture::Ready(ready(std::net::ToSocketAddrs::to_socket_addrs(self)))
+        ToSocketAddrsFuture::Ready(Some(std::net::ToSocketAddrs::to_socket_addrs(self)))
     }
 }
 
@@ -101,7 +103,7 @@ impl ToSocketAddrs for (Ipv4Addr, u16) {
     type Iter = std::option::IntoIter<SocketAddr>;
 
     fn to_socket_addrs(&self) -> ret!('_, ToSocketAddrsFuture, Self::Iter) {
-        ToSocketAddrsFuture::Ready(ready(std::net::ToSocketAddrs::to_socket_addrs(self)))
+        ToSocketAddrsFuture::Ready(Some(std::net::ToSocketAddrs::to_socket_addrs(self)))
     }
 }
 
@@ -109,7 +111,7 @@ impl ToSocketAddrs for (Ipv6Addr, u16) {
     type Iter = std::option::IntoIter<SocketAddr>;
 
     fn to_socket_addrs(&self) -> ret!('_, ToSocketAddrsFuture, Self::Iter) {
-        ToSocketAddrsFuture::Ready(ready(std::net::ToSocketAddrs::to_socket_addrs(self)))
+        ToSocketAddrsFuture::Ready(Some(std::net::ToSocketAddrs::to_socket_addrs(self)))
     }
 }
 
@@ -141,7 +143,7 @@ impl<'a> ToSocketAddrs for &'a [SocketAddr] {
     type Iter = std::iter::Cloned<std::slice::Iter<'a, SocketAddr>>;
 
     fn to_socket_addrs(&self) -> ret!('_, ToSocketAddrsFuture, Self::Iter) {
-        ToSocketAddrsFuture::Ready(ready(std::net::ToSocketAddrs::to_socket_addrs(self)))
+        ToSocketAddrsFuture::Ready(Some(std::net::ToSocketAddrs::to_socket_addrs(self)))
     }
 }
 
diff --git a/src/net/driver/mod.rs b/src/net/driver/mod.rs
index 4002254d8..04ab4bb6f 100644
--- a/src/net/driver/mod.rs
+++ b/src/net/driver/mod.rs
@@ -4,7 +4,7 @@ use std::pin::Pin;
 use std::sync::atomic::{AtomicUsize, Ordering};
 use std::sync::{Arc, Mutex};
 
-use futures::io::{AsyncRead, AsyncWrite};
+use futures_io::{AsyncRead, AsyncWrite};
 use lazy_static::lazy_static;
 use mio::{self, Evented};
 use slab::Slab;
@@ -303,7 +303,7 @@ impl<T: Evented + std::io::Read + Unpin> AsyncRead for IoHandle<T> {
         cx: &mut Context<'_>,
         buf: &mut [u8],
     ) -> Poll<io::Result<usize>> {
-        futures::ready!(Pin::new(&mut *self).poll_readable(cx)?);
+        futures_core::ready!(Pin::new(&mut *self).poll_readable(cx)?);
 
         match self.source.read(buf) {
             Err(ref err) if err.kind() == io::ErrorKind::WouldBlock => {
@@ -324,7 +324,7 @@ where
         cx: &mut Context<'_>,
         buf: &mut [u8],
     ) -> Poll<io::Result<usize>> {
-        futures::ready!(Pin::new(&mut *self).poll_readable(cx)?);
+        futures_core::ready!(Pin::new(&mut *self).poll_readable(cx)?);
 
         match (&self.source).read(buf) {
             Err(ref err) if err.kind() == io::ErrorKind::WouldBlock => {
@@ -342,7 +342,7 @@ impl<T: Evented + std::io::Write + Unpin> AsyncWrite for IoHandle<T> {
         cx: &mut Context<'_>,
         buf: &[u8],
     ) -> Poll<io::Result<usize>> {
-        futures::ready!(self.poll_writable(cx)?);
+        futures_core::ready!(self.poll_writable(cx)?);
 
         match self.source.write(buf) {
             Err(ref err) if err.kind() == io::ErrorKind::WouldBlock => {
@@ -354,7 +354,7 @@ impl<T: Evented + std::io::Write + Unpin> AsyncWrite for IoHandle<T> {
     }
 
     fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
-        futures::ready!(self.poll_writable(cx)?);
+        futures_core::ready!(self.poll_writable(cx)?);
 
         match self.source.flush() {
             Err(ref err) if err.kind() == io::ErrorKind::WouldBlock => {
@@ -379,7 +379,7 @@ where
         cx: &mut Context<'_>,
         buf: &[u8],
     ) -> Poll<io::Result<usize>> {
-        futures::ready!(self.poll_writable(cx)?);
+        futures_core::ready!(self.poll_writable(cx)?);
 
         match (&self.source).write(buf) {
             Err(ref err) if err.kind() == io::ErrorKind::WouldBlock => {
@@ -391,7 +391,7 @@ where
     }
 
     fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
-        futures::ready!(self.poll_writable(cx)?);
+        futures_core::ready!(self.poll_writable(cx)?);
 
         match (&self.source).flush() {
             Err(ref err) if err.kind() == io::ErrorKind::WouldBlock => {
diff --git a/src/net/tcp/listener.rs b/src/net/tcp/listener.rs
index ac18387a7..67a486500 100644
--- a/src/net/tcp/listener.rs
+++ b/src/net/tcp/listener.rs
@@ -2,10 +2,9 @@ use std::net::SocketAddr;
 use std::pin::Pin;
 
 use cfg_if::cfg_if;
-use futures::future;
 
 use super::TcpStream;
-use crate::future::Future;
+use crate::future::{self, Future};
 use crate::io;
 use crate::net::driver::IoHandle;
 use crate::net::ToSocketAddrs;
@@ -129,7 +128,7 @@ impl TcpListener {
     /// ```
     pub async fn accept(&self) -> io::Result<(TcpStream, SocketAddr)> {
         future::poll_fn(|cx| {
-            futures::ready!(self.io_handle.poll_readable(cx)?);
+            futures_core::ready!(self.io_handle.poll_readable(cx)?);
 
             match self.io_handle.get_ref().accept_std() {
                 Ok((io, addr)) => {
@@ -225,14 +224,14 @@ impl TcpListener {
 #[derive(Debug)]
 pub struct Incoming<'a>(&'a TcpListener);
 
-impl<'a> futures::Stream for Incoming<'a> {
+impl<'a> futures_core::stream::Stream for Incoming<'a> {
     type Item = io::Result<TcpStream>;
 
     fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
         let future = self.0.accept();
         pin_utils::pin_mut!(future);
 
-        let (socket, _) = futures::ready!(future.poll(cx))?;
+        let (socket, _) = futures_core::ready!(future.poll(cx))?;
         Poll::Ready(Some(Ok(socket)))
     }
 }
diff --git a/src/net/tcp/stream.rs b/src/net/tcp/stream.rs
index 5ea181f25..b63b7f2e4 100644
--- a/src/net/tcp/stream.rs
+++ b/src/net/tcp/stream.rs
@@ -4,9 +4,9 @@ use std::net::SocketAddr;
 use std::pin::Pin;
 
 use cfg_if::cfg_if;
-use futures::future;
-use futures::io::{AsyncRead, AsyncWrite};
+use futures_io::{AsyncRead, AsyncWrite};
 
+use crate::future;
 use crate::io;
 use crate::net::driver::IoHandle;
 use crate::net::ToSocketAddrs;
@@ -259,7 +259,7 @@ impl TcpStream {
     /// ```
     pub async fn peek(&self, buf: &mut [u8]) -> io::Result<usize> {
         let res = future::poll_fn(|cx| {
-            futures::ready!(self.io_handle.poll_readable(cx)?);
+            futures_core::ready!(self.io_handle.poll_readable(cx)?);
 
             match self.io_handle.get_ref().peek(buf) {
                 Ok(len) => Poll::Ready(Ok(len)),
diff --git a/src/net/udp/mod.rs b/src/net/udp/mod.rs
index 19119a562..23024274d 100644
--- a/src/net/udp/mod.rs
+++ b/src/net/udp/mod.rs
@@ -2,9 +2,9 @@ use std::io;
 use std::net::SocketAddr;
 
 use cfg_if::cfg_if;
-use futures::future;
 use std::net::{Ipv4Addr, Ipv6Addr};
 
+use crate::future;
 use crate::net::driver::IoHandle;
 use crate::net::ToSocketAddrs;
 use crate::task::Poll;
@@ -165,7 +165,7 @@ impl UdpSocket {
         };
 
         future::poll_fn(|cx| {
-            futures::ready!(self.io_handle.poll_writable(cx)?);
+            futures_core::ready!(self.io_handle.poll_writable(cx)?);
 
             match self.io_handle.get_ref().send_to(buf, &addr) {
                 Ok(n) => Poll::Ready(Ok(n)),
@@ -200,7 +200,7 @@ impl UdpSocket {
     /// ```
     pub async fn recv_from(&self, buf: &mut [u8]) -> io::Result<(usize, SocketAddr)> {
         future::poll_fn(|cx| {
-            futures::ready!(self.io_handle.poll_readable(cx)?);
+            futures_core::ready!(self.io_handle.poll_readable(cx)?);
 
             match self.io_handle.get_ref().recv_from(buf) {
                 Ok(n) => Poll::Ready(Ok(n)),
@@ -282,7 +282,7 @@ impl UdpSocket {
     /// ```
     pub async fn send(&self, buf: &[u8]) -> io::Result<usize> {
         future::poll_fn(|cx| {
-            futures::ready!(self.io_handle.poll_writable(cx)?);
+            futures_core::ready!(self.io_handle.poll_writable(cx)?);
 
             match self.io_handle.get_ref().send(buf) {
                 Ok(n) => Poll::Ready(Ok(n)),
@@ -317,7 +317,7 @@ impl UdpSocket {
     /// ```
     pub async fn recv(&self, buf: &mut [u8]) -> io::Result<usize> {
         future::poll_fn(|cx| {
-            futures::ready!(self.io_handle.poll_readable(cx)?);
+            futures_core::ready!(self.io_handle.poll_readable(cx)?);
 
             match self.io_handle.get_ref().recv(buf) {
                 Ok(n) => Poll::Ready(Ok(n)),
diff --git a/src/os/unix/net/datagram.rs b/src/os/unix/net/datagram.rs
index 62debc4ce..fb5b5f16f 100644
--- a/src/os/unix/net/datagram.rs
+++ b/src/os/unix/net/datagram.rs
@@ -4,10 +4,10 @@ use std::fmt;
 use std::net::Shutdown;
 use std::path::Path;
 
-use futures::future;
 use mio_uds;
 
 use super::SocketAddr;
+use crate::future;
 use crate::io;
 use crate::net::driver::IoHandle;
 use crate::os::unix::io::{AsRawFd, FromRawFd, IntoRawFd, RawFd};
@@ -203,7 +203,7 @@ impl UnixDatagram {
     /// ```
     pub async fn recv_from(&self, buf: &mut [u8]) -> io::Result<(usize, SocketAddr)> {
         future::poll_fn(|cx| {
-            futures::ready!(self.io_handle.poll_readable(cx)?);
+            futures_core::ready!(self.io_handle.poll_readable(cx)?);
 
             match self.io_handle.get_ref().recv_from(buf) {
                 Ok(n) => Poll::Ready(Ok(n)),
@@ -236,7 +236,7 @@ impl UnixDatagram {
     /// ```
     pub async fn recv(&self, buf: &mut [u8]) -> io::Result<usize> {
         future::poll_fn(|cx| {
-            futures::ready!(self.io_handle.poll_writable(cx)?);
+            futures_core::ready!(self.io_handle.poll_writable(cx)?);
 
             match self.io_handle.get_ref().recv(buf) {
                 Ok(n) => Poll::Ready(Ok(n)),
@@ -268,7 +268,7 @@ impl UnixDatagram {
     /// ```
     pub async fn send_to<P: AsRef<Path>>(&self, buf: &[u8], path: P) -> io::Result<usize> {
         future::poll_fn(|cx| {
-            futures::ready!(self.io_handle.poll_writable(cx)?);
+            futures_core::ready!(self.io_handle.poll_writable(cx)?);
 
             match self.io_handle.get_ref().send_to(buf, path.as_ref()) {
                 Ok(n) => Poll::Ready(Ok(n)),
@@ -301,7 +301,7 @@ impl UnixDatagram {
     /// ```
     pub async fn send(&self, buf: &[u8]) -> io::Result<usize> {
         future::poll_fn(|cx| {
-            futures::ready!(self.io_handle.poll_writable(cx)?);
+            futures_core::ready!(self.io_handle.poll_writable(cx)?);
 
             match self.io_handle.get_ref().send(buf) {
                 Ok(n) => Poll::Ready(Ok(n)),
diff --git a/src/os/unix/net/listener.rs b/src/os/unix/net/listener.rs
index 74b0a28d5..61df25176 100644
--- a/src/os/unix/net/listener.rs
+++ b/src/os/unix/net/listener.rs
@@ -4,12 +4,11 @@ use std::fmt;
 use std::path::Path;
 use std::pin::Pin;
 
-use futures::future;
 use mio_uds;
 
 use super::SocketAddr;
 use super::UnixStream;
-use crate::future::Future;
+use crate::future::{self, Future};
 use crate::io;
 use crate::net::driver::IoHandle;
 use crate::os::unix::io::{AsRawFd, FromRawFd, IntoRawFd, RawFd};
@@ -97,7 +96,7 @@ impl UnixListener {
     /// ```
     pub async fn accept(&self) -> io::Result<(UnixStream, SocketAddr)> {
         future::poll_fn(|cx| {
-            futures::ready!(self.io_handle.poll_readable(cx)?);
+            futures_core::ready!(self.io_handle.poll_readable(cx)?);
 
             match self.io_handle.get_ref().accept_std() {
                 Ok(Some((io, addr))) => {
@@ -198,14 +197,14 @@ impl fmt::Debug for UnixListener {
 #[derive(Debug)]
 pub struct Incoming<'a>(&'a UnixListener);
 
-impl futures::Stream for Incoming<'_> {
+impl futures_core::stream::Stream for Incoming<'_> {
     type Item = io::Result<UnixStream>;
 
     fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
         let future = self.0.accept();
-        futures::pin_mut!(future);
+        pin_utils::pin_mut!(future);
 
-        let (socket, _) = futures::ready!(future.poll(cx))?;
+        let (socket, _) = futures_core::ready!(future.poll(cx))?;
         Poll::Ready(Some(Ok(socket)))
     }
 }
diff --git a/src/os/unix/net/stream.rs b/src/os/unix/net/stream.rs
index 74afdeebd..389720e4a 100644
--- a/src/os/unix/net/stream.rs
+++ b/src/os/unix/net/stream.rs
@@ -6,11 +6,11 @@ use std::net::Shutdown;
 use std::path::Path;
 use std::pin::Pin;
 
-use futures::future;
-use futures::io::{AsyncRead, AsyncWrite};
+use futures_io::{AsyncRead, AsyncWrite};
 use mio_uds;
 
 use super::SocketAddr;
+use crate::future;
 use crate::io;
 use crate::net::driver::IoHandle;
 use crate::os::unix::io::{AsRawFd, FromRawFd, IntoRawFd, RawFd};
@@ -81,7 +81,7 @@ impl UnixStream {
         future::poll_fn(|cx| {
             match &mut state {
                 State::Waiting(stream) => {
-                    futures::ready!(stream.io_handle.poll_writable(cx)?);
+                    futures_core::ready!(stream.io_handle.poll_writable(cx)?);
 
                     if let Some(err) = stream.io_handle.get_ref().take_error()? {
                         return Poll::Ready(Err(err));
diff --git a/src/stream/empty.rs b/src/stream/empty.rs
index 4445e4351..f4cf55253 100644
--- a/src/stream/empty.rs
+++ b/src/stream/empty.rs
@@ -35,7 +35,7 @@ pub struct Empty<T> {
     _marker: PhantomData<T>,
 }
 
-impl<T> futures::Stream for Empty<T> {
+impl<T> futures_core::stream::Stream for Empty<T> {
     type Item = T;
 
     fn poll_next(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Option<Self::Item>> {
diff --git a/src/stream/once.rs b/src/stream/once.rs
index 160d6cf47..09811d8f6 100644
--- a/src/stream/once.rs
+++ b/src/stream/once.rs
@@ -33,7 +33,7 @@ pub struct Once<T> {
     value: Option<T>,
 }
 
-impl<T: Unpin> futures::Stream for Once<T> {
+impl<T: Unpin> futures_core::stream::Stream for Once<T> {
     type Item = T;
 
     fn poll_next(mut self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Option<T>> {
diff --git a/src/stream/repeat.rs b/src/stream/repeat.rs
index d42b7271c..c2ee97ae7 100644
--- a/src/stream/repeat.rs
+++ b/src/stream/repeat.rs
@@ -36,7 +36,7 @@ pub struct Repeat<T> {
     item: T,
 }
 
-impl<T: Clone> futures::Stream for Repeat<T> {
+impl<T: Clone> futures_core::stream::Stream for Repeat<T> {
     type Item = T;
 
     fn poll_next(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Option<Self::Item>> {
diff --git a/src/stream/stream.rs b/src/stream/stream.rs
index 7a127b092..698eb320b 100644
--- a/src/stream/stream.rs
+++ b/src/stream/stream.rs
@@ -233,8 +233,8 @@ pub trait Stream {
     }
 }
 
-impl<T: futures::Stream + Unpin + ?Sized> Stream for T {
-    type Item = <Self as futures::Stream>::Item;
+impl<T: futures_core::stream::Stream + Unpin + ?Sized> Stream for T {
+    type Item = <Self as futures_core::stream::Stream>::Item;
 
     fn next(&mut self) -> ret!('_, NextFuture, Option<Self::Item>)
     where
@@ -250,7 +250,7 @@ pub struct NextFuture<'a, T: Unpin + ?Sized> {
     stream: &'a mut T,
 }
 
-impl<T: futures::Stream + Unpin + ?Sized> Future for NextFuture<'_, T> {
+impl<T: futures_core::stream::Stream + Unpin + ?Sized> Future for NextFuture<'_, T> {
     type Output = Option<T::Item>;
 
     fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
@@ -267,19 +267,19 @@ pub struct Take<S> {
 
 impl<S: Unpin> Unpin for Take<S> {}
 
-impl<S: futures::Stream> Take<S> {
+impl<S: futures_core::stream::Stream> Take<S> {
     pin_utils::unsafe_pinned!(stream: S);
     pin_utils::unsafe_unpinned!(remaining: usize);
 }
 
-impl<S: futures::Stream> futures::Stream for Take<S> {
+impl<S: futures_core::stream::Stream> futures_core::stream::Stream for Take<S> {
     type Item = S::Item;
 
     fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<S::Item>> {
         if self.remaining == 0 {
             Poll::Ready(None)
         } else {
-            let next = futures::ready!(self.as_mut().stream().poll_next(cx));
+            let next = futures_core::ready!(self.as_mut().stream().poll_next(cx));
             match next {
                 Some(_) => *self.as_mut().remaining() -= 1,
                 None => *self.as_mut().remaining() = 0,
@@ -311,14 +311,14 @@ where
 
 impl<S, F> Future for AllFuture<'_, S, F, S::Item>
 where
-    S: futures::Stream + Unpin + Sized,
+    S: futures_core::stream::Stream + Unpin + Sized,
     F: FnMut(S::Item) -> bool,
 {
     type Output = bool;
 
     fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
-        use futures::Stream;
-        let next = futures::ready!(self.as_mut().stream().poll_next(cx));
+        use futures_core::stream::Stream;
+        let next = futures_core::ready!(self.as_mut().stream().poll_next(cx));
         match next {
             Some(v) => {
                 let result = (self.as_mut().f())(v);
@@ -358,14 +358,14 @@ where
 
 impl<S, F> Future for AnyFuture<'_, S, F, S::Item>
 where
-    S: futures::Stream + Unpin + Sized,
+    S: futures_core::stream::Stream + Unpin + Sized,
     F: FnMut(S::Item) -> bool,
 {
     type Output = bool;
 
     fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
-        use futures::Stream;
-        let next = futures::ready!(self.as_mut().stream().poll_next(cx));
+        use futures_core::stream::Stream;
+        let next = futures_core::ready!(self.as_mut().stream().poll_next(cx));
         match next {
             Some(v) => {
                 let result = (self.as_mut().f())(v);
diff --git a/src/task/block_on.rs b/src/task/block_on.rs
new file mode 100644
index 000000000..92c4b5178
--- /dev/null
+++ b/src/task/block_on.rs
@@ -0,0 +1,135 @@
+use std::cell::UnsafeCell;
+use std::mem::{self, ManuallyDrop};
+use std::panic::{self, AssertUnwindSafe, UnwindSafe};
+use std::pin::Pin;
+use std::sync::Arc;
+use std::task::{RawWaker, RawWakerVTable};
+use std::thread::{self, Thread};
+
+use super::pool;
+use super::Builder;
+use crate::future::Future;
+use crate::task::{Context, Poll, Waker};
+
+/// Spawns a task and blocks the current thread on its result.
+///
+/// Calling this function is similar to [spawning] a thread and immediately [joining] it, except an
+/// asynchronous task will be spawned.
+///
+/// [spawning]: https://doc.rust-lang.org/std/thread/fn.spawn.html
+/// [joining]: https://doc.rust-lang.org/std/thread/struct.JoinHandle.html#method.join
+///
+/// # Examples
+///
+/// ```no_run
+/// use async_std::task;
+///
+/// fn main() {
+///     task::block_on(async {
+///         println!("Hello, world!");
+///     })
+/// }
+/// ```
+pub fn block_on<F, T>(future: F) -> T
+where
+    F: Future<Output = T> + Send,
+    T: Send,
+{
+    unsafe {
+        // A place on the stack where the result will be stored.
+        let out = &mut UnsafeCell::new(None);
+
+        // Wrap the future into one that stores the result into `out`.
+        let future = {
+            let out = out.get();
+
+            async move {
+                let future = CatchUnwindFuture {
+                    future: AssertUnwindSafe(future),
+                };
+                *out = Some(future.await);
+            }
+        };
+
+        // Pin the future onto the stack.
+        pin_utils::pin_mut!(future);
+
+        // Transmute the future into one that is static and sendable.
+        let future = mem::transmute::<
+            Pin<&mut dyn Future<Output = ()>>,
+            Pin<&'static mut (dyn Future<Output = ()> + Send)>,
+        >(future);
+
+        // Spawn the future and wait for it to complete.
+        block(pool::spawn_with_builder(Builder::new(), future, "block_on"));
+
+        // Take out the result.
+        match (*out.get()).take().unwrap() {
+            Ok(v) => v,
+            Err(err) => panic::resume_unwind(err),
+        }
+    }
+}
+
+struct CatchUnwindFuture<F> {
+    future: F,
+}
+
+impl<F> CatchUnwindFuture<F> {
+    pin_utils::unsafe_pinned!(future: F);
+}
+
+impl<F: Future + UnwindSafe> Future for CatchUnwindFuture<F> {
+    type Output = thread::Result<F::Output>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        panic::catch_unwind(AssertUnwindSafe(|| self.future().poll(cx)))?.map(Ok)
+    }
+}
+
+fn block<F: Future>(f: F) -> F::Output {
+    thread_local! {
+        static ARC_THREAD: Arc<Thread> = Arc::new(thread::current());
+    }
+
+    pin_utils::pin_mut!(f);
+
+    ARC_THREAD.with(|arc_thread: &Arc<Thread>| {
+        let ptr = (&**arc_thread as *const Thread) as *const ();
+        let vt = vtable();
+
+        let waker = unsafe { ManuallyDrop::new(Waker::from_raw(RawWaker::new(ptr, vt))) };
+        let cx = &mut Context::from_waker(&waker);
+
+        loop {
+            if let Poll::Ready(t) = f.as_mut().poll(cx) {
+                return t;
+            }
+            thread::park();
+        }
+    })
+}
+
+fn vtable() -> &'static RawWakerVTable {
+    unsafe fn clone_raw(ptr: *const ()) -> RawWaker {
+        let arc = ManuallyDrop::new(Arc::from_raw(ptr as *const Thread));
+        mem::forget(arc.clone());
+        RawWaker::new(ptr, vtable())
+    }
+
+    unsafe fn wake_raw(ptr: *const ()) {
+        let arc = Arc::from_raw(ptr as *const Thread);
+        arc.unpark();
+    }
+
+    unsafe fn wake_by_ref_raw(ptr: *const ()) {
+        let arc = ManuallyDrop::new(Arc::from_raw(ptr as *const Thread));
+        arc.unpark();
+    }
+
+    unsafe fn drop_raw(ptr: *const ()) {
+        drop(Arc::from_raw(ptr as *const Thread))
+    }
+
+    &RawWakerVTable::new(clone_raw, wake_raw, wake_by_ref_raw, drop_raw)
+}
diff --git a/src/task/mod.rs b/src/task/mod.rs
index 42b7e0883..eef72846a 100644
--- a/src/task/mod.rs
+++ b/src/task/mod.rs
@@ -24,11 +24,13 @@
 #[doc(inline)]
 pub use std::task::{Context, Poll, Waker};
 
+pub use block_on::block_on;
 pub use local::{AccessError, LocalKey};
-pub use pool::{block_on, current, spawn, Builder};
+pub use pool::{current, spawn, Builder};
 pub use sleep::sleep;
 pub use task::{JoinHandle, Task, TaskId};
 
+mod block_on;
 mod local;
 mod pool;
 mod sleep;
diff --git a/src/task/pool.rs b/src/task/pool.rs
index ab09ffbb2..3640909fd 100644
--- a/src/task/pool.rs
+++ b/src/task/pool.rs
@@ -1,13 +1,10 @@
-use std::cell::{Cell, UnsafeCell};
+use std::cell::Cell;
 use std::fmt::Arguments;
 use std::mem;
-use std::panic::{self, AssertUnwindSafe};
-use std::pin::Pin;
 use std::ptr;
 use std::thread;
 
 use crossbeam_channel::{unbounded, Sender};
-use futures::future::FutureExt;
 use lazy_static::lazy_static;
 
 use super::task;
@@ -70,63 +67,6 @@ where
     spawn_with_builder(Builder::new(), future, "spawn")
 }
 
-/// Spawns a task and blocks the current thread on its result.
-///
-/// Calling this function is similar to [spawning] a thread and immediately [joining] it, except an
-/// asynchronous task will be spawned.
-///
-/// [spawning]: https://doc.rust-lang.org/std/thread/fn.spawn.html
-/// [joining]: https://doc.rust-lang.org/std/thread/struct.JoinHandle.html#method.join
-///
-/// # Examples
-///
-/// ```no_run
-/// use async_std::task;
-///
-/// fn main() {
-///     task::block_on(async {
-///         println!("Hello, world!");
-///     })
-/// }
-/// ```
-pub fn block_on<F, T>(future: F) -> T
-where
-    F: Future<Output = T> + Send,
-    T: Send,
-{
-    unsafe {
-        // A place on the stack where the result will be stored.
-        let out = &mut UnsafeCell::new(None);
-
-        // Wrap the future into one that stores the result into `out`.
-        let future = {
-            let out = out.get();
-            async move {
-                let v = AssertUnwindSafe(future).catch_unwind().await;
-                *out = Some(v);
-            }
-        };
-
-        // Pin the future onto the stack.
-        futures::pin_mut!(future);
-
-        // Transmute the future into one that is static and sendable.
-        let future = mem::transmute::<
-            Pin<&mut dyn Future<Output = ()>>,
-            Pin<&'static mut (dyn Future<Output = ()> + Send)>,
-        >(future);
-
-        // Spawn the future and wait for it to complete.
-        futures::executor::block_on(spawn_with_builder(Builder::new(), future, "block_on"));
-
-        // Take out the result.
-        match (*out.get()).take().unwrap() {
-            Ok(v) => v,
-            Err(err) => panic::resume_unwind(err),
-        }
-    }
-}
-
 /// Task builder that configures the settings of a new task.
 #[derive(Debug)]
 pub struct Builder {