diff --git a/crates/wasi-common/tokio/Cargo.toml b/crates/wasi-common/tokio/Cargo.toml
index f480de0635..d67fc72914 100644
--- a/crates/wasi-common/tokio/Cargo.toml
+++ b/crates/wasi-common/tokio/Cargo.toml
@@ -22,6 +22,15 @@ cap-time-ext = "0.13.7"
 fs-set-times = "0.3.1"
 unsafe-io = "0.6.2"
 system-interface = { version = "0.6.3", features = ["cap_std_impls"] }
+tracing = "0.1.19"
+bitflags = "1.2"
+
+[target.'cfg(unix)'.dependencies]
+libc = "0.2"
+
+[target.'cfg(windows)'.dependencies]
+winapi = "0.3"
+lazy_static = "1.4"
 
 [dev-dependencies]
 tempfile = "3.1.0"
diff --git a/crates/wasi-common/tokio/src/lib.rs b/crates/wasi-common/tokio/src/lib.rs
index 7ae8849259..a5ff5f8ca7 100644
--- a/crates/wasi-common/tokio/src/lib.rs
+++ b/crates/wasi-common/tokio/src/lib.rs
@@ -1,5 +1,6 @@
 mod dir;
 mod file;
+mod sched;
 
 use std::cell::RefCell;
 use std::path::Path;
@@ -7,27 +8,7 @@ use std::rc::Rc;
 pub use wasi_cap_std_sync::{clocks_ctx, random_ctx, Dir};
 use wasi_common::{Error, Table, WasiCtx};
 
-pub fn sched_ctx() -> Box<dyn wasi_common::WasiSched> {
-    use wasi_common::sched::{Duration, Poll, WasiSched};
-    struct AsyncSched;
-
-    #[wiggle::async_trait]
-    impl WasiSched for AsyncSched {
-        async fn poll_oneoff<'a>(&self, _poll: &'_ Poll<'a>) -> Result<(), Error> {
-            todo!()
-        }
-        async fn sched_yield(&self) -> Result<(), Error> {
-            tokio::task::yield_now().await;
-            Ok(())
-        }
-        async fn sleep(&self, duration: Duration) -> Result<(), Error> {
-            tokio::time::sleep(duration).await;
-            Ok(())
-        }
-    }
-
-    Box::new(AsyncSched)
-}
+use crate::sched::sched_ctx;
 
 pub struct WasiCtxBuilder(wasi_common::WasiCtxBuilder);
 
diff --git a/crates/wasi-common/tokio/src/sched.rs b/crates/wasi-common/tokio/src/sched.rs
new file mode 100644
index 0000000000..fd41f32996
--- /dev/null
+++ b/crates/wasi-common/tokio/src/sched.rs
@@ -0,0 +1,35 @@
+#[cfg(unix)]
+mod unix;
+#[cfg(unix)]
+use unix::poll_oneoff;
+
+#[cfg(windows)]
+mod windows;
+#[cfg(windows)]
+use windows::poll_oneoff;
+
+use wasi_common::{
+    sched::{Duration, Poll, WasiSched},
+    Error,
+};
+
+pub fn sched_ctx() -> Box<dyn wasi_common::WasiSched> {
+    struct AsyncSched;
+
+    #[wiggle::async_trait]
+    impl WasiSched for AsyncSched {
+        async fn poll_oneoff<'a>(&self, poll: &'_ Poll<'a>) -> Result<(), Error> {
+            poll_oneoff(poll).await
+        }
+        async fn sched_yield(&self) -> Result<(), Error> {
+            tokio::task::yield_now().await;
+            Ok(())
+        }
+        async fn sleep(&self, duration: Duration) -> Result<(), Error> {
+            tokio::time::sleep(duration).await;
+            Ok(())
+        }
+    }
+
+    Box::new(AsyncSched)
+}
diff --git a/crates/wasi-common/tokio/src/sched/unix.rs b/crates/wasi-common/tokio/src/sched/unix.rs
new file mode 100644
index 0000000000..83ddb2c839
--- /dev/null
+++ b/crates/wasi-common/tokio/src/sched/unix.rs
@@ -0,0 +1,176 @@
+use cap_std::time::Duration;
+use std::convert::TryInto;
+use std::ops::Deref;
+use std::os::unix::io::{AsRawFd, RawFd};
+use wasi_common::{
+    file::WasiFile,
+    sched::{
+        subscription::{RwEventFlags, Subscription},
+        Poll,
+    },
+    Error, ErrorExt,
+};
+
+use poll::{PollFd, PollFlags};
+
+pub async fn poll_oneoff<'a>(poll: &'_ Poll<'a>) -> Result<(), Error> {
+    if poll.is_empty() {
+        return Ok(());
+    }
+    let mut pollfds = Vec::new();
+    let timeout = poll.earliest_clock_deadline();
+    for s in poll.rw_subscriptions() {
+        match s {
+            Subscription::Read(f) => {
+                let raw_fd = wasi_file_raw_fd(f.file.deref()).ok_or(
+                    Error::invalid_argument().context("read subscription fd downcast failed"),
+                )?;
+                pollfds.push(unsafe { PollFd::new(raw_fd, PollFlags::POLLIN) });
+            }
+
+            Subscription::Write(f) => {
+                let raw_fd = wasi_file_raw_fd(f.file.deref()).ok_or(
+                    Error::invalid_argument().context("write subscription fd downcast failed"),
+                )?;
+                pollfds.push(unsafe { PollFd::new(raw_fd, PollFlags::POLLOUT) });
+            }
+            Subscription::MonotonicClock { .. } => unreachable!(),
+        }
+    }
+
+    let ready = loop {
+        let poll_timeout = if let Some(t) = timeout {
+            let duration = t.duration_until().unwrap_or(Duration::from_secs(0));
+            (duration.as_millis() + 1) // XXX try always rounding up?
+                .try_into()
+                .map_err(|_| Error::overflow().context("poll timeout"))?
+        } else {
+            libc::c_int::max_value()
+        };
+        tracing::debug!(
+            poll_timeout = tracing::field::debug(poll_timeout),
+            poll_fds = tracing::field::debug(&pollfds),
+            "poll"
+        );
+        match poll::poll(&mut pollfds, poll_timeout) {
+            Ok(ready) => break ready,
+            Err(_) => {
+                let last_err = std::io::Error::last_os_error();
+                if last_err.raw_os_error().unwrap() == libc::EINTR {
+                    continue;
+                } else {
+                    return Err(last_err.into());
+                }
+            }
+        }
+    };
+    if ready > 0 {
+        for (rwsub, pollfd) in poll.rw_subscriptions().zip(pollfds.into_iter()) {
+            if let Some(revents) = pollfd.revents() {
+                let (nbytes, rwsub) = match rwsub {
+                    Subscription::Read(sub) => {
+                        let ready = sub.file.num_ready_bytes().await?;
+                        (std::cmp::max(ready, 1), sub)
+                    }
+                    Subscription::Write(sub) => (0, sub),
+                    _ => unreachable!(),
+                };
+                if revents.contains(PollFlags::POLLNVAL) {
+                    rwsub.error(Error::badf());
+                } else if revents.contains(PollFlags::POLLERR) {
+                    rwsub.error(Error::io());
+                } else if revents.contains(PollFlags::POLLHUP) {
+                    rwsub.complete(nbytes, RwEventFlags::HANGUP);
+                } else {
+                    rwsub.complete(nbytes, RwEventFlags::empty());
+                };
+            }
+        }
+    } else {
+        timeout
+            .expect("timed out")
+            .result()
+            .expect("timer deadline is past")
+            .unwrap()
+    }
+    Ok(())
+}
+
+fn wasi_file_raw_fd(f: &dyn WasiFile) -> Option<RawFd> {
+    let a = f.as_any();
+    if a.is::<crate::file::File>() {
+        Some(a.downcast_ref::<crate::file::File>().unwrap().as_raw_fd())
+    } else if a.is::<crate::stdio::Stdin>() {
+        Some(a.downcast_ref::<crate::stdio::Stdin>().unwrap().as_raw_fd())
+    } else if a.is::<crate::stdio::Stdout>() {
+        Some(
+            a.downcast_ref::<crate::stdio::Stdout>()
+                .unwrap()
+                .as_raw_fd(),
+        )
+    } else if a.is::<crate::stdio::Stderr>() {
+        Some(
+            a.downcast_ref::<crate::stdio::Stderr>()
+                .unwrap()
+                .as_raw_fd(),
+        )
+    } else {
+        None
+    }
+}
+
+mod poll {
+    use bitflags::bitflags;
+    use std::convert::TryInto;
+    use std::os::unix::io::RawFd;
+
+    bitflags! {
+        pub struct PollFlags: libc::c_short {
+            const POLLIN = libc::POLLIN;
+            const POLLPRI = libc::POLLPRI;
+            const POLLOUT = libc::POLLOUT;
+            const POLLRDNORM = libc::POLLRDNORM;
+            const POLLWRNORM = libc::POLLWRNORM;
+            const POLLRDBAND = libc::POLLRDBAND;
+            const POLLWRBAND = libc::POLLWRBAND;
+            const POLLERR = libc::POLLERR;
+            const POLLHUP = libc::POLLHUP;
+            const POLLNVAL = libc::POLLNVAL;
+        }
+    }
+
+    #[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
+    #[repr(C)]
+    pub struct PollFd(libc::pollfd);
+
+    impl PollFd {
+        pub unsafe fn new(fd: RawFd, events: PollFlags) -> Self {
+            Self(libc::pollfd {
+                fd,
+                events: events.bits(),
+                revents: PollFlags::empty().bits(),
+            })
+        }
+
+        pub fn revents(self) -> Option<PollFlags> {
+            PollFlags::from_bits(self.0.revents)
+        }
+    }
+
+    pub fn poll(fds: &mut [PollFd], timeout: libc::c_int) -> Result<usize, std::io::Error> {
+        let nready = unsafe {
+            libc::poll(
+                fds.as_mut_ptr() as *mut libc::pollfd,
+                fds.len() as libc::nfds_t,
+                timeout,
+            )
+        };
+        if nready == -1 {
+            Err(std::io::Error::last_os_error())
+        } else {
+            // When poll doesn't fail, its return value is a non-negative int, which will
+            // always be convertable to usize, so we can unwrap() here.
+            Ok(nready.try_into().unwrap())
+        }
+    }
+}
diff --git a/crates/wasi-common/tokio/src/sched/windows.rs b/crates/wasi-common/tokio/src/sched/windows.rs
new file mode 100644
index 0000000000..a3c15f3c2f
--- /dev/null
+++ b/crates/wasi-common/tokio/src/sched/windows.rs
@@ -0,0 +1,242 @@
+use anyhow::Context;
+use std::ops::Deref;
+use std::os::windows::io::{AsRawHandle, RawHandle};
+use std::sync::mpsc::{self, Receiver, RecvTimeoutError, Sender, TryRecvError};
+use std::sync::Mutex;
+use std::thread;
+use std::time::Duration;
+use wasi_common::{
+    file::WasiFile,
+    sched::{
+        subscription::{RwEventFlags, Subscription},
+        Poll,
+    },
+    Error, ErrorExt,
+};
+pub async fn poll_oneoff<'a>(poll: &'_ Poll<'a>) -> Result<(), Error> {
+    if poll.is_empty() {
+        return Ok(());
+    }
+
+    let mut ready = false;
+    let timeout = poll.earliest_clock_deadline();
+
+    let mut stdin_read_subs = Vec::new();
+    let mut immediate_subs = Vec::new();
+    for s in poll.rw_subscriptions() {
+        match s {
+            Subscription::Read(r) if r.file.as_any().is::<crate::stdio::Stdin>() => {
+                stdin_read_subs.push(r);
+            }
+            Subscription::Read(rw) | Subscription::Write(rw) => {
+                if wasi_file_raw_handle(rw.file.deref()).is_some() {
+                    immediate_subs.push(s);
+                } else {
+                    return Err(Error::invalid_argument()
+                        .context("read/write subscription fd downcast failed"));
+                }
+            }
+            Subscription::MonotonicClock { .. } => unreachable!(),
+        }
+    }
+
+    if !stdin_read_subs.is_empty() {
+        let waitmode = if let Some(t) = timeout {
+            if let Some(duration) = t.duration_until() {
+                WaitMode::Timeout(duration)
+            } else {
+                WaitMode::Immediate
+            }
+        } else {
+            if ready {
+                WaitMode::Immediate
+            } else {
+                WaitMode::Infinite
+            }
+        };
+        let state = STDIN_POLL
+            .lock()
+            .map_err(|_| Error::trap("failed to take lock of STDIN_POLL"))?
+            .poll(waitmode)?;
+        for readsub in stdin_read_subs.into_iter() {
+            match state {
+                PollState::Ready => {
+                    readsub.complete(1, RwEventFlags::empty());
+                    ready = true;
+                }
+                PollState::NotReady | PollState::TimedOut => {}
+                PollState::Error(ref e) => {
+                    // Unfortunately, we need to deliver the Error to each of the
+                    // subscriptions, but there is no Clone on std::io::Error. So, we convert it to the
+                    // kind, and then back to std::io::Error, and finally to anyhow::Error.
+                    // When its time to turn this into an errno elsewhere, the error kind will
+                    // be inspected.
+                    let ekind = e.kind();
+                    let ioerror = std::io::Error::from(ekind);
+                    readsub.error(ioerror.into());
+                    ready = true;
+                }
+            }
+        }
+    }
+    for sub in immediate_subs {
+        match sub {
+            Subscription::Read(r) => {
+                // XXX This doesnt strictly preserve the behavior in the earlier
+                // implementation, which would always do complete(0) for reads from
+                // stdout/err.
+                match r.file.num_ready_bytes().await {
+                    Ok(ready_bytes) => {
+                        r.complete(ready_bytes, RwEventFlags::empty());
+                        ready = true;
+                    }
+                    Err(e) => {
+                        r.error(e);
+                        ready = true;
+                    }
+                }
+            }
+            Subscription::Write(w) => {
+                // Everything is always ready for writing, apparently?
+                w.complete(0, RwEventFlags::empty());
+                ready = true;
+            }
+            Subscription::MonotonicClock { .. } => unreachable!(),
+        }
+    }
+
+    if !ready {
+        if let Some(t) = timeout {
+            if let Some(duration) = t.duration_until() {
+                thread::sleep(duration);
+            }
+        }
+    }
+
+    Ok(())
+}
+
+fn wasi_file_raw_handle(f: &dyn WasiFile) -> Option<RawHandle> {
+    let a = f.as_any();
+    if a.is::<crate::file::File>() {
+        Some(
+            a.downcast_ref::<crate::file::File>()
+                .unwrap()
+                .as_raw_handle(),
+        )
+    } else if a.is::<crate::stdio::Stdin>() {
+        Some(
+            a.downcast_ref::<crate::stdio::Stdin>()
+                .unwrap()
+                .as_raw_handle(),
+        )
+    } else if a.is::<crate::stdio::Stdout>() {
+        Some(
+            a.downcast_ref::<crate::stdio::Stdout>()
+                .unwrap()
+                .as_raw_handle(),
+        )
+    } else if a.is::<crate::stdio::Stderr>() {
+        Some(
+            a.downcast_ref::<crate::stdio::Stderr>()
+                .unwrap()
+                .as_raw_handle(),
+        )
+    } else {
+        None
+    }
+}
+
+enum PollState {
+    Ready,
+    NotReady, // Not ready, but did not wait
+    TimedOut, // Not ready, waited until timeout
+    Error(std::io::Error),
+}
+
+enum WaitMode {
+    Timeout(Duration),
+    Infinite,
+    Immediate,
+}
+
+struct StdinPoll {
+    request_tx: Sender<()>,
+    notify_rx: Receiver<PollState>,
+}
+
+lazy_static::lazy_static! {
+    static ref STDIN_POLL: Mutex<StdinPoll> = StdinPoll::new();
+}
+
+impl StdinPoll {
+    pub fn new() -> Mutex<Self> {
+        let (request_tx, request_rx) = mpsc::channel();
+        let (notify_tx, notify_rx) = mpsc::channel();
+        thread::spawn(move || Self::event_loop(request_rx, notify_tx));
+        Mutex::new(StdinPoll {
+            request_tx,
+            notify_rx,
+        })
+    }
+
+    // This function should not be used directly.
+    // Correctness of this function crucially depends on the fact that
+    // mpsc::Receiver is !Sync.
+    fn poll(&self, wait_mode: WaitMode) -> Result<PollState, Error> {
+        match self.notify_rx.try_recv() {
+            // Clean up possibly unread result from previous poll.
+            Ok(_) | Err(TryRecvError::Empty) => {}
+            Err(TryRecvError::Disconnected) => {
+                return Err(Error::trap("StdinPoll notify_rx channel closed"))
+            }
+        }
+
+        // Notify the worker thread to poll stdin
+        self.request_tx
+            .send(())
+            .context("request_tx channel closed")?;
+
+        // Wait for the worker thread to send a readiness notification
+        match wait_mode {
+            WaitMode::Timeout(timeout) => match self.notify_rx.recv_timeout(timeout) {
+                Ok(r) => Ok(r),
+                Err(RecvTimeoutError::Timeout) => Ok(PollState::TimedOut),
+                Err(RecvTimeoutError::Disconnected) => {
+                    Err(Error::trap("StdinPoll notify_rx channel closed"))
+                }
+            },
+            WaitMode::Infinite => self
+                .notify_rx
+                .recv()
+                .context("StdinPoll notify_rx channel closed"),
+            WaitMode::Immediate => match self.notify_rx.try_recv() {
+                Ok(r) => Ok(r),
+                Err(TryRecvError::Empty) => Ok(PollState::NotReady),
+                Err(TryRecvError::Disconnected) => {
+                    Err(Error::trap("StdinPoll notify_rx channel closed"))
+                }
+            },
+        }
+    }
+
+    fn event_loop(request_rx: Receiver<()>, notify_tx: Sender<PollState>) -> ! {
+        use std::io::BufRead;
+        loop {
+            // Wait on a request:
+            request_rx.recv().expect("request_rx channel");
+            // Wait for data to appear in stdin. If fill_buf returns any slice, it means
+            // that either:
+            // (a) there is some data in stdin, if non-empty,
+            // (b) EOF was recieved, if its empty
+            // Linux returns `POLLIN` in both cases, so we imitate this behavior.
+            let resp = match std::io::stdin().lock().fill_buf() {
+                Ok(_) => PollState::Ready,
+                Err(e) => PollState::Error(e),
+            };
+            // Notify about data in stdin. If the read on this channel has timed out, the
+            // next poller will have to clean the channel.
+            notify_tx.send(resp).expect("notify_tx channel");
+        }
+    }
+}