process: add ProcessDriver to handle orphan reaping (#2907)

9 files changed, 327 insertions, 98 deletions

diff --git a/tokio/src/macros/cfg.rs b/tokio/src/macros/cfg.rs
index f245b09e..328f3230 100644
--- a/tokio/src/macros/cfg.rs
+++ b/tokio/src/macros/cfg.rs
@@ -242,6 +242,23 @@ macro_rules! cfg_process {
     }
 }
 
+macro_rules! cfg_process_driver {
+    ($($item:item)*) => {
+        #[cfg(unix)]
+        #[cfg(not(loom))]
+        cfg_process! { $($item)* }
+    }
+}
+
+macro_rules! cfg_not_process_driver {
+    ($($item:item)*) => {
+        $(
+            #[cfg(not(all(unix, not(loom), feature = "process")))]
+            $item
+        )*
+    }
+}
+
 macro_rules! cfg_signal {
     ($($item:item)*) => {
         $(
diff --git a/tokio/src/process/mod.rs b/tokio/src/process/mod.rs
index 7da9783b..ff84428e 100644
--- a/tokio/src/process/mod.rs
+++ b/tokio/src/process/mod.rs
@@ -113,6 +113,11 @@
 #[cfg(unix)]
 mod imp;
 
+#[cfg(unix)]
+pub(crate) mod unix {
+    pub(crate) use super::imp::*;
+}
+
 #[path = "windows.rs"]
 #[cfg(windows)]
 mod imp;
diff --git a/tokio/src/process/unix/driver.rs b/tokio/src/process/unix/driver.rs
new file mode 100644
index 00000000..2eea0043
--- /dev/null
+++ b/tokio/src/process/unix/driver.rs
@@ -0,0 +1,154 @@
+//! Process driver
+
+use crate::park::Park;
+use crate::process::unix::orphan::ReapOrphanQueue;
+use crate::process::unix::GlobalOrphanQueue;
+use crate::signal::unix::driver::Driver as SignalDriver;
+use crate::signal::unix::{signal_with_handle, InternalStream, Signal, SignalKind};
+use crate::sync::mpsc::error::TryRecvError;
+
+use std::io;
+use std::time::Duration;
+
+/// Responsible for cleaning up orphaned child processes on Unix platforms.
+#[derive(Debug)]
+pub(crate) struct Driver {
+    park: SignalDriver,
+    inner: CoreDriver<Signal, GlobalOrphanQueue>,
+}
+
+#[derive(Debug)]
+struct CoreDriver<S, Q> {
+    sigchild: S,
+    orphan_queue: Q,
+}
+
+// ===== impl CoreDriver =====
+
+impl<S, Q> CoreDriver<S, Q>
+where
+    S: InternalStream,
+    Q: ReapOrphanQueue,
+{
+    fn got_signal(&mut self) -> bool {
+        match self.sigchild.try_recv() {
+            Ok(()) => true,
+            Err(TryRecvError::Empty) => false,
+            Err(TryRecvError::Closed) => panic!("signal was deregistered"),
+        }
+    }
+
+    fn process(&mut self) {
+        if self.got_signal() {
+            // Drain all notifications which may have been buffered
+            // so we can try to reap all orphans in one batch
+            while self.got_signal() {}
+
+            self.orphan_queue.reap_orphans();
+        }
+    }
+}
+
+// ===== impl Driver =====
+
+impl Driver {
+    /// Creates a new signal `Driver` instance that delegates wakeups to `park`.
+    pub(crate) fn new(park: SignalDriver) -> io::Result<Self> {
+        let sigchild = signal_with_handle(SignalKind::child(), park.handle())?;
+        let inner = CoreDriver {
+            sigchild,
+            orphan_queue: GlobalOrphanQueue,
+        };
+
+        Ok(Self { park, inner })
+    }
+}
+
+// ===== impl Park for Driver =====
+
+impl Park for Driver {
+    type Unpark = <SignalDriver as Park>::Unpark;
+    type Error = io::Error;
+
+    fn unpark(&self) -> Self::Unpark {
+        self.park.unpark()
+    }
+
+    fn park(&mut self) -> Result<(), Self::Error> {
+        self.park.park()?;
+        self.inner.process();
+        Ok(())
+    }
+
+    fn park_timeout(&mut self, duration: Duration) -> Result<(), Self::Error> {
+        self.park.park_timeout(duration)?;
+        self.inner.process();
+        Ok(())
+    }
+
+    fn shutdown(&mut self) {
+        self.park.shutdown()
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+    use crate::process::unix::orphan::test::MockQueue;
+    use crate::sync::mpsc::error::TryRecvError;
+    use std::task::{Context, Poll};
+
+    struct MockStream {
+        total_try_recv: usize,
+        values: Vec<Option<()>>,
+    }
+
+    impl MockStream {
+        fn new(values: Vec<Option<()>>) -> Self {
+            Self {
+                total_try_recv: 0,
+                values,
+            }
+        }
+    }
+
+    impl InternalStream for MockStream {
+        fn poll_recv(&mut self, _cx: &mut Context<'_>) -> Poll<Option<()>> {
+            unimplemented!();
+        }
+
+        fn try_recv(&mut self) -> Result<(), TryRecvError> {
+            self.total_try_recv += 1;
+            match self.values.remove(0) {
+                Some(()) => Ok(()),
+                None => Err(TryRecvError::Empty),
+            }
+        }
+    }
+
+    #[test]
+    fn no_reap_if_no_signal() {
+        let mut driver = CoreDriver {
+            sigchild: MockStream::new(vec![None]),
+            orphan_queue: MockQueue::<()>::new(),
+        };
+
+        driver.process();
+
+        assert_eq!(1, driver.sigchild.total_try_recv);
+        assert_eq!(0, driver.orphan_queue.total_reaps.get());
+    }
+
+    #[test]
+    fn coalesce_signals_before_reaping() {
+        let mut driver = CoreDriver {
+            sigchild: MockStream::new(vec![Some(()), Some(()), None]),
+            orphan_queue: MockQueue::<()>::new(),
+        };
+
+        driver.process();
+
+        assert_eq!(3, driver.sigchild.total_try_recv);
+        assert_eq!(1, driver.orphan_queue.total_reaps.get());
+    }
+}
diff --git a/tokio/src/process/unix/mod.rs b/tokio/src/process/unix/mod.rs
index 46f1d790..db9d592c 100644
--- a/tokio/src/process/unix/mod.rs
+++ b/tokio/src/process/unix/mod.rs
@@ -21,8 +21,10 @@
 //! processes in general aren't scalable (e.g. millions) so it shouldn't be that
 //! bad in theory...
 
-mod orphan;
-use orphan::{OrphanQueue, OrphanQueueImpl, Wait};
+pub(crate) mod driver;
+
+pub(crate) mod orphan;
+use orphan::{OrphanQueue, OrphanQueueImpl, ReapOrphanQueue, Wait};
 
 mod reap;
 use reap::Reaper;
@@ -39,11 +41,11 @@ use std::future::Future;
 use std::io;
 use std::os::unix::io::{AsRawFd, RawFd};
 use std::pin::Pin;
-use std::process::ExitStatus;
+use std::process::{Child as StdChild, ExitStatus};
 use std::task::Context;
 use std::task::Poll;
 
-impl Wait for std::process::Child {
+impl Wait for StdChild {
     fn id(&self) -> u32 {
         self.id()
     }
@@ -53,17 +55,17 @@ impl Wait for std::process::Child {
     }
 }
 
-impl Kill for std::process::Child {
+impl Kill for StdChild {
     fn kill(&mut self) -> io::Result<()> {
         self.kill()
     }
 }
 
 lazy_static::lazy_static! {
-    static ref ORPHAN_QUEUE: OrphanQueueImpl<std::process::Child> = OrphanQueueImpl::new();
+    static ref ORPHAN_QUEUE: OrphanQueueImpl<StdChild> = OrphanQueueImpl::new();
 }
 
-struct GlobalOrphanQueue;
+pub(crate) struct GlobalOrphanQueue;
 
 impl fmt::Debug for GlobalOrphanQueue {
     fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
@@ -71,19 +73,21 @@ impl fmt::Debug for GlobalOrphanQueue {
     }
 }
 
-impl OrphanQueue<std::process::Child> for GlobalOrphanQueue {
-    fn push_orphan(&self, orphan: std::process::Child) {
-        ORPHAN_QUEUE.push_orphan(orphan)
-    }
-
+impl ReapOrphanQueue for GlobalOrphanQueue {
     fn reap_orphans(&self) {
         ORPHAN_QUEUE.reap_orphans()
     }
 }
 
+impl OrphanQueue<StdChild> for GlobalOrphanQueue {
+    fn push_orphan(&self, orphan: StdChild) {
+        ORPHAN_QUEUE.push_orphan(orphan)
+    }
+}
+
 #[must_use = "futures do nothing unless polled"]
 pub(crate) struct Child {
-    inner: Reaper<std::process::Child, GlobalOrphanQueue, Signal>,
+    inner: Reaper<StdChild, GlobalOrphanQueue, Signal>,
 }
 
 impl fmt::Debug for Child {
diff --git a/tokio/src/process/unix/orphan.rs b/tokio/src/process/unix/orphan.rs
index 6c449a90..8a1e1278 100644
--- a/tokio/src/process/unix/orphan.rs
+++ b/tokio/src/process/unix/orphan.rs
@@ -20,23 +20,29 @@ impl<T: Wait> Wait for &mut T {
     }
 }
 
-/// An interface for queueing up an orphaned process so that it can be reaped.
-pub(crate) trait OrphanQueue<T> {
-    /// Adds an orphan to the queue.
-    fn push_orphan(&self, orphan: T);
+/// An interface for reaping a set of orphaned processes.
+pub(crate) trait ReapOrphanQueue {
     /// Attempts to reap every process in the queue, ignoring any errors and
     /// enqueueing any orphans which have not yet exited.
     fn reap_orphans(&self);
 }
 
+impl<T: ReapOrphanQueue> ReapOrphanQueue for &T {
+    fn reap_orphans(&self) {
+        (**self).reap_orphans()
+    }
+}
+
+/// An interface for queueing up an orphaned process so that it can be reaped.
+pub(crate) trait OrphanQueue<T>: ReapOrphanQueue {
+    /// Adds an orphan to the queue.
+    fn push_orphan(&self, orphan: T);
+}
+
 impl<T, O: OrphanQueue<T>> OrphanQueue<T> for &O {
     fn push_orphan(&self, orphan: T) {
         (**self).push_orphan(orphan);
     }
-
-    fn reap_orphans(&self) {
-        (**self).reap_orphans()
-    }
 }
 
 /// An implementation of `OrphanQueue`.
@@ -62,42 +68,62 @@ impl<T: Wait> OrphanQueue<T> for OrphanQueueImpl<T> {
     fn push_orphan(&self, orphan: T) {
         self.queue.lock().unwrap().push(orphan)
     }
+}
 
+impl<T: Wait> ReapOrphanQueue for OrphanQueueImpl<T> {
     fn reap_orphans(&self) {
         let mut queue = self.queue.lock().unwrap();
         let queue = &mut *queue;
 
-        let mut i = 0;
-        while i < queue.len() {
+        for i in (0..queue.len()).rev() {
             match queue[i].try_wait() {
-                Ok(Some(_)) => {}
-                Err(_) => {
-                    // TODO: bubble up error some how. Is this an internal bug?
-                    // Shoudl we panic? Is it OK for this to be silently
-                    // dropped?
-                }
-                // Still not done yet
-                Ok(None) => {
-                    i += 1;
-                    continue;
+                Ok(None) => {}
+                Ok(Some(_)) | Err(_) => {
+                    // The stdlib handles interruption errors (EINTR) when polling a child process.
+                    // All other errors represent invalid inputs or pids that have already been
+                    // reaped, so we can drop the orphan in case an error is raised.
+                    queue.swap_remove(i);
                 }
             }
-
-            queue.remove(i);
         }
     }
 }
 
 #[cfg(all(test, not(loom)))]
-mod test {
-    use super::Wait;
-    use super::{OrphanQueue, OrphanQueueImpl};
-    use std::cell::Cell;
+pub(crate) mod test {
+    use super::*;
+    use std::cell::{Cell, RefCell};
     use std::io;
     use std::os::unix::process::ExitStatusExt;
     use std::process::ExitStatus;
     use std::rc::Rc;
 
+    pub(crate) struct MockQueue<W> {
+        pub(crate) all_enqueued: RefCell<Vec<W>>,
+        pub(crate) total_reaps: Cell<usize>,
+    }
+
+    impl<W> MockQueue<W> {
+        pub(crate) fn new() -> Self {
+            Self {
+                all_enqueued: RefCell::new(Vec::new()),
+                total_reaps: Cell::new(0),
+            }
+        }
+    }
+
+    impl<W> OrphanQueue<W> for MockQueue<W> {
+        fn push_orphan(&self, orphan: W) {
+            self.all_enqueued.borrow_mut().push(orphan);
+        }
+    }
+
+    impl<W> ReapOrphanQueue for MockQueue<W> {
+        fn reap_orphans(&self) {
+            self.total_reaps.set(self.total_reaps.get() + 1);
+        }
+    }
+
     struct MockWait {
         total_waits: Rc<Cell<usize>>,
         num_wait_until_status: usize,
diff --git a/tokio/src/process/unix/reap.rs b/tokio/src/process/unix/reap.rs
index c51a20b9..de483c44 100644
--- a/tokio/src/process/unix/reap.rs
+++ b/tokio/src/process/unix/reap.rs
@@ -1,6 +1,6 @@
 use crate::process::imp::orphan::{OrphanQueue, Wait};
 use crate::process::kill::Kill;
-use crate::signal::unix::Signal;
+use crate::signal::unix::InternalStream;
 
 use std::future::Future;
 use std::io;
@@ -23,17 +23,6 @@ where
     signal: S,
 }
 
-// Work around removal of `futures_core` dependency
-pub(crate) trait Stream: Unpin {
-    fn poll_recv(&mut self, cx: &mut Context<'_>) -> Poll<Option<()>>;
-}
-
-impl Stream for Signal {
-    fn poll_recv(&mut self, cx: &mut Context<'_>) -> Poll<Option<()>> {
-        Signal::poll_recv(self, cx)
-    }
-}
-
 impl<W, Q, S> Deref for Reaper<W, Q, S>
 where
     W: Wait + Unpin,
@@ -72,7 +61,7 @@ impl<W, Q, S> Future for Reaper<W, Q, S>
 where
     W: Wait + Unpin,
     Q: OrphanQueue<W> + Unpin,
-    S: Stream,
+    S: InternalStream,
 {
     type Output = io::Result<ExitStatus>;
 
@@ -80,10 +69,8 @@ where
         loop {
             // If the child hasn't exited yet, then it's our responsibility to
             // ensure the current task gets notified when it might be able to
-            // make progress.
-            //
-            // As described in `spawn` above, we just indicate that we can
-            // next make progress once a SIGCHLD is received.
+            // make progress. We can use the delivery of a SIGCHLD signal as a
+            // sign that we can potentially make progress.
             //
             // However, we will register for a notification on the next signal
             // BEFORE we poll the child. Otherwise it is possible that the child
@@ -99,7 +86,6 @@ where
             // should not cause significant issues with parent futures.
             let registered_interest = self.signal.poll_recv(cx).is_pending();
 
-            self.orphan_queue.reap_orphans();
             if let Some(status) = self.inner_mut().try_wait()? {
                 return Poll::Ready(Ok(status));
             }
@@ -147,8 +133,9 @@ where
 mod test {
     use super::*;
 
+    use crate::process::unix::orphan::test::MockQueue;
+    use crate::sync::mpsc::error::TryRecvError;
     use futures::future::FutureExt;
-    use std::cell::{Cell, RefCell};
     use std::os::unix::process::ExitStatusExt;
     use std::process::ExitStatus;
     use std::task::Context;
@@ -211,7 +198,7 @@ mod test {
         }
     }
 
-    impl Stream for MockStream {
+    impl InternalStream for MockStream {
         fn poll_recv(&mut self, _cx: &mut Context<'_>) -> Poll<Option<()>> {
             self.total_polls += 1;
             match self.values.remove(0) {
@@ -219,29 +206,9 @@ mod test {
                 None => Poll::Pending,
             }
         }
-    }
 
-    struct MockQueue<W> {
-        all_enqueued: RefCell<Vec<W>>,
-        total_reaps: Cell<usize>,
-    }
-
-    impl<W> MockQueue<W> {
-        fn new() -> Self {
-            Self {
-                all_enqueued: RefCell::new(Vec::new()),
-                total_reaps: Cell::new(0),
-            }
-        }
-    }
-
-    impl<W: Wait> OrphanQueue<W> for MockQueue<W> {
-        fn push_orphan(&self, orphan: W) {
-            self.all_enqueued.borrow_mut().push(orphan);
-        }
-
-        fn reap_orphans(&self) {
-            self.total_reaps.set(self.total_reaps.get() + 1);
+        fn try_recv(&mut self) -> Result<(), TryRecvError> {
+            unimplemented!();
         }
     }
 
@@ -262,7 +229,7 @@ mod test {
         assert!(grim.poll_unpin(&mut context).is_pending());
         assert_eq!(1, grim.signal.total_polls);
         assert_eq!(1, grim.total_waits);
-        assert_eq!(1, grim.orphan_queue.total_reaps.get());
+        assert_eq!(0, grim.orphan_queue.total_reaps.get());
         assert!(grim.orphan_queue.all_enqueued.borrow().is_empty());
 
         // Not yet exited, couldn't register interest the first time
@@ -270,7 +237,7 @@ mod test {
         assert!(grim.poll_unpin(&mut context).is_pending());
         assert_eq!(3, grim.signal.total_polls);
         assert_eq!(3, grim.total_waits);
-        assert_eq!(3, grim.orphan_queue.total_reaps.get());
+        assert_eq!(0, grim.orphan_queue.total_reaps.get());
         assert!(grim.orphan_queue.all_enqueued.borrow().is_empty());
 
         // Exited
@@ -283,7 +250,7 @@ mod test {
         }
         assert_eq!(4, grim.signal.total_polls);
         assert_eq!(4, grim.total_waits);
-        assert_eq!(4, grim.orphan_queue.total_reaps.get());
+        assert_eq!(0, grim.orphan_queue.total_reaps.get());
         assert!(grim.orphan_queue.all_enqueued.borrow().is_empty());
     }
 
diff --git a/tokio/src/runtime/driver.rs b/tokio/src/runtime/driver.rs
index 148e0b16..af8e17a3 100644
--- a/tokio/src/runtime/driver.rs
+++ b/tokio/src/runtime/driver.rs
@@ -38,6 +38,7 @@ cfg_not_io_driver! {
 }
 
 // ===== signal driver =====
+
 macro_rules! cfg_signal_internal_and_unix {
     ($($item:item)*) => {
         #[cfg(unix)]
@@ -73,10 +74,37 @@ cfg_not_signal_internal! {
     }
 }
 
+// ===== process driver =====
+
+cfg_process_driver! {
+    type ProcessDriver = crate::park::Either<crate::process::unix::driver::Driver, SignalDriver>;
+
+    fn create_process_driver(signal_driver: SignalDriver) -> io::Result<ProcessDriver> {
+        use crate::park::Either;
+
+        // Enable the signal driver if IO is also enabled
+        match signal_driver {
+            Either::A(signal_driver) => {
+                let driver = crate::process::unix::driver::Driver::new(signal_driver)?;
+                Ok(Either::A(driver))
+            }
+            Either::B(_) => Ok(Either::B(signal_driver)),
+        }
+    }
+}
+
+cfg_not_process_driver! {
+    type ProcessDriver = SignalDriver;
+
+    fn create_process_driver(signal_driver: SignalDriver) -> io::Result<ProcessDriver> {
+        Ok(signal_driver)
+    }
+}
+
 // ===== time driver =====
 
 cfg_time! {
-    type TimeDriver = crate::park::Either<crate::time::driver::Driver<SignalDriver>, SignalDriver>;
+    type TimeDriver = crate::park::Either<crate::time::driver::Driver<ProcessDriver>, ProcessDriver>;
 
     pub(crate) type Clock = crate::time::Clock;
     pub(crate) type TimeHandle = Option<crate::time::driver::Handle>;
@@ -87,24 +115,24 @@ cfg_time! {
 
     fn create_time_driver(
         enable: bool,
-        signal_driver: SignalDriver,
+        process_driver: ProcessDriver,
         clock: Clock,
     ) -> (TimeDriver, TimeHandle) {
         use crate::park::Either;
 
         if enable {
-            let driver = crate::time::driver::Driver::new(signal_driver, clock);
+            let driver = crate::time::driver::Driver::new(process_driver, clock);
             let handle = driver.handle();
 
             (Either::A(driver), Some(handle))
         } else {
-            (Either::B(signal_driver), None)
+            (Either::B(process_driver), None)
         }
     }
 }
 
 cfg_not_time! {
-    type TimeDriver = SignalDriver;
+    type TimeDriver = ProcessDriver;
 
     pub(crate) type Clock = ();
     pub(crate) type TimeHandle = ();
@@ -115,10 +143,10 @@ cfg_not_time! {
 
     fn create_time_driver(
         _enable: bool,
-        signal_driver: SignalDriver,
+        process_driver: ProcessDriver,
         _clock: Clock,
     ) -> (TimeDriver, TimeHandle) {
-        (signal_driver, ())
+        (process_driver, ())
     }
 }
 
@@ -147,8 +175,9 @@ impl Driver {
 
         let (io_driver, io_handle) = create_io_driver(cfg.enable_io)?;
         let (signal_driver, signal_handle) = create_signal_driver(io_driver)?;
+        let process_driver = create_process_driver(signal_driver)?;
         let (time_driver, time_handle) =
-            create_time_driver(cfg.enable_time, signal_driver, clock.clone());
+            create_time_driver(cfg.enable_time, process_driver, clock.clone());
 
         Ok((
             Self { inner: time_driver },
diff --git a/tokio/src/signal/unix.rs b/tokio/src/signal/unix.rs
index 77f300bb..aaaa75ed 100644
--- a/tokio/src/signal/unix.rs
+++ b/tokio/src/signal/unix.rs
@@ -6,6 +6,7 @@
 #![cfg(unix)]
 
 use crate::signal::registry::{globals, EventId, EventInfo, Globals, Init, Storage};
+use crate::sync::mpsc::error::TryRecvError;
 use crate::sync::mpsc::{channel, Receiver};
 
 use libc::c_int;
@@ -17,6 +18,7 @@ use std::sync::Once;
 use std::task::{Context, Poll};
 
 pub(crate) mod driver;
+use self::driver::Handle;
 
 pub(crate) type OsStorage = Vec<SignalInfo>;
 
@@ -220,7 +222,7 @@ fn action(globals: Pin<&'static Globals>, signal: c_int) {
 ///
 /// This will register the signal handler if it hasn't already been registered,
 /// returning any error along the way if that fails.
-fn signal_enable(signal: c_int) -> io::Result<()> {
+fn signal_enable(signal: c_int, handle: Handle) -> io::Result<()> {
     if signal < 0 || signal_hook_registry::FORBIDDEN.contains(&signal) {
         return Err(Error::new(
             ErrorKind::Other,
@@ -229,7 +231,7 @@ fn signal_enable(signal: c_int) -> io::Result<()> {
     }
 
     // Check that we have a signal driver running
-    driver::Handle::current().check_inner()?;
+    handle.check_inner()?;
 
     let globals = globals();
     let siginfo = match globals.storage().get(signal as EventId) {
@@ -349,10 +351,14 @@ pub struct Signal {
 /// * If the signal is one of
 ///   [`signal_hook::FORBIDDEN`](fn@signal_hook_registry::register#panics)
 pub fn signal(kind: SignalKind) -> io::Result<Signal> {
+    signal_with_handle(kind, Handle::current())
+}
+
+pub(crate) fn signal_with_handle(kind: SignalKind, handle: Handle) -> io::Result<Signal> {
     let signal = kind.0;
 
     // Turn the signal delivery on once we are ready for it
-    signal_enable(signal)?;
+    signal_enable(signal, handle)?;
 
     // One wakeup in a queue is enough, no need for us to buffer up any
     // more.
@@ -394,6 +400,11 @@ impl Signal {
     pub(crate) fn poll_recv(&mut self, cx: &mut Context<'_>) -> Poll<Option<()>> {
         self.rx.poll_recv(cx)
     }
+
+    /// Try to receive a signal notification without blocking or registering a waker.
+    pub(crate) fn try_recv(&mut self) -> Result<(), TryRecvError> {
+        self.rx.try_recv()
+    }
 }
 
 cfg_stream! {
@@ -406,6 +417,22 @@ cfg_stream! {
     }
 }
 
+// Work around for abstracting streams internally
+pub(crate) trait InternalStream: Unpin {
+    fn poll_recv(&mut self, cx: &mut Context<'_>) -> Poll<Option<()>>;
+    fn try_recv(&mut self) -> Result<(), TryRecvError>;
+}
+
+impl InternalStream for Signal {
+    fn poll_recv(&mut self, cx: &mut Context<'_>) -> Poll<Option<()>> {
+        self.poll_recv(cx)
+    }
+
+    fn try_recv(&mut self) -> Result<(), TryRecvError> {
+        self.try_recv()
+    }
+}
+
 pub(crate) fn ctrl_c() -> io::Result<Signal> {
     signal(SignalKind::interrupt())
 }
@@ -416,11 +443,11 @@ mod tests {
 
     #[test]
     fn signal_enable_error_on_invalid_input() {
-        signal_enable(-1).unwrap_err();
+        signal_enable(-1, Handle::default()).unwrap_err();
     }
 
     #[test]
     fn signal_enable_error_on_forbidden_input() {
-        signal_enable(signal_hook_registry::FORBIDDEN[0]).unwrap_err();
+        signal_enable(signal_hook_registry::FORBIDDEN[0], Handle::default()).unwrap_err();
     }
 }
diff --git a/tokio/src/signal/unix/driver.rs b/tokio/src/signal/unix/driver.rs
index ae60c22f..d0615312 100644
--- a/tokio/src/signal/unix/driver.rs
+++ b/tokio/src/signal/unix/driver.rs
@@ -30,7 +30,7 @@ pub(crate) struct Driver {
     inner: Arc<Inner>,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Default)]
 pub(crate) struct Handle {
     inner: Weak<Inner>,
 }