Move waker cfg attributes to sys::unix module

Same as what we did for the selector.

But for the waker it's a little more complicated due to the poll(2)
implementation. That needs to wrap the Waker type to use it's internal
waker, compared to kqueue and epoll which just reexport the Waker
directly.

This logical of what waker to use is now moved to the selector module.
For kqueue and epoll it's a simple export, for poll it's a special type
that call the internal waker. This special poll waker used to be the
fdbased waker.

All these changes (hopefully) add up to no changes at all. All the
supported targets should continue to work with all configurations.
However it should be easier to port to new targets without having to
deal with the clusterfuck that was the old sys::unix::waker module.

src/sys/unix/mod.rs

@@ -53,6 +53,18 @@ cfg_os_poll! {
 
     #[cfg_attr(all(
         not(mio_unsupported_force_waker_pipe),
+        any(
+            target_os = "android",
+            target_os = "espidf",
+            target_os = "fuchsia",
+            target_os = "hermit",
+            target_os = "illumos",
+            target_os = "linux",
+        )
+    ), path = "waker/eventfd.rs")]
+    #[cfg_attr(all(
+        not(mio_unsupported_force_waker_pipe),
+        not(mio_unsupported_force_poll_poll), // `kqueue(2)` based waker doesn't work with `poll(2)`.
         any(
             target_os = "freebsd",
             target_os = "ios",
@@ -62,8 +74,34 @@ cfg_os_poll! {
             target_os = "watchos",
         )
     ), path = "waker/kqueue.rs")]
+    #[cfg_attr(any(
+        // NOTE: also add to the list list for the `pipe` module below.
+        mio_unsupported_force_waker_pipe,
+        all(
+            // `kqueue(2)` based waker doesn't work with `poll(2)`.
+            mio_unsupported_force_poll_poll,
+            any(
+                target_os = "freebsd",
+                target_os = "ios",
+                target_os = "macos",
+                target_os = "tvos",
+                target_os = "visionos",
+                target_os = "watchos",
+            ),
+        ),
+        target_os = "aix",
+        target_os = "dragonfly",
+        target_os = "haiku",
+        target_os = "netbsd",
+        target_os = "nto",
+        target_os = "openbsd",
+        target_os = "redox",
+        target_os = "solaris",
+        target_os = "vita",
+    ), path = "waker/pipe.rs")]
     mod waker;
-    pub(crate) use self::waker::Waker;
+    // NOTE: the `Waker` type is expected in the selector module as the
+    // `poll(2)` implementation needs to do some special stuff.
 
     mod sourcefd;
     #[cfg(feature = "os-ext")]
@@ -83,10 +121,22 @@ cfg_os_poll! {
         all(feature = "os-ext", not(target_os = "hermit")),
         // For the `Waker` type based on a pipe.
         mio_unsupported_force_waker_pipe,
+        all(
+            // `kqueue(2)` based waker doesn't work with `poll(2)`.
+            mio_unsupported_force_poll_poll,
+            any(
+                target_os = "freebsd",
+                target_os = "ios",
+                target_os = "macos",
+                target_os = "tvos",
+                target_os = "visionos",
+                target_os = "watchos",
+            ),
+        ),
+        // NOTE: also add to the list list for the `pipe` module below.
         target_os = "aix",
         target_os = "dragonfly",
         target_os = "haiku",
-        target_os = "illumos",
         target_os = "netbsd",
         target_os = "nto",
         target_os = "openbsd",

src/sys/unix/selector/epoll.rs

@@ -222,6 +222,9 @@ pub mod event {
     }
 }
 
+// No special requirement from the implementation around waking.
+pub(crate) use crate::sys::unix::waker::Waker;
+
 cfg_io_source! {
     mod stateless_io_source;
     pub(crate) use stateless_io_source::IoSourceState;

src/sys/unix/selector/kqueue.rs

@@ -868,6 +868,9 @@ pub mod event {
     }
 }
 
+// No special requirement from the implementation around waking.
+pub(crate) use crate::sys::unix::waker::Waker;
+
 cfg_io_source! {
     mod stateless_io_source;
     pub(crate) use stateless_io_source::IoSourceState;

src/sys/unix/selector/poll.rs

@@ -16,7 +16,7 @@ use std::sync::{Arc, Condvar, Mutex};
 use std::time::Duration;
 use std::{cmp, fmt, io};
 
-use crate::sys::unix::waker::WakerInternal;
+use crate::sys::unix::waker::Waker as WakerInternal;
 use crate::{Interest, Token};
 
 /// Unique id for use as `SelectorId`.
@@ -161,7 +161,7 @@ struct FdData {
 
 impl SelectorState {
     pub fn new() -> io::Result<SelectorState> {
-        let notify_waker = WakerInternal::new()?;
+        let notify_waker = WakerInternal::new_unregistered()?;
 
         Ok(Self {
             fds: Mutex::new(Fds {
@@ -625,6 +625,25 @@ pub mod event {
     }
 }
 
+#[derive(Debug)]
+pub(crate) struct Waker {
+    selector: Selector,
+    token: Token,
+}
+
+impl Waker {
+    pub(crate) fn new(selector: &Selector, token: Token) -> io::Result<Waker> {
+        Ok(Waker {
+            selector: selector.try_clone()?,
+            token,
+        })
+    }
+
+    pub(crate) fn wake(&self) -> io::Result<()> {
+        self.selector.wake(self.token)
+    }
+}
+
 cfg_io_source! {
     use crate::Registry;
 

src/sys/unix/waker/eventfd.rs

@@ -22,6 +22,7 @@ pub(crate) struct Waker {
 }
 
 impl Waker {
+    #[allow(dead_code)] // Not used by the `poll(2)` implementation.
     pub(crate) fn new(selector: &Selector, token: Token) -> io::Result<Waker> {
         let waker = Waker::new_unregistered()?;
         selector.register(waker.fd.as_raw_fd(), token, Interest::READABLE)?;
@@ -54,12 +55,7 @@ impl Waker {
         }
     }
 
-    #[cfg(any(
-        mio_unsupported_force_poll_poll,
-        target_os = "espidf",
-        target_os = "fuchsia",
-        target_os = "hermit",
-    ))]
+    #[allow(dead_code)] // Only used by the `poll(2)` implementation.
     pub(crate) fn ack_and_reset(&self) {
         let _ = self.reset();
     }

src/sys/unix/waker/pipe.rs

@@ -22,9 +22,10 @@ pub(crate) struct Waker {
 }
 
 impl Waker {
+    #[allow(dead_code)] // Not used by the `poll(2)` implementation.
     pub(crate) fn new(selector: &Selector, token: Token) -> io::Result<Waker> {
         let waker = Waker::new_unregistered()?;
-        selector.register(waker.fd.as_raw_fd(), token, Interest::READABLE)?;
+        selector.register(waker.receiver.as_raw_fd(), token, Interest::READABLE)?;
         Ok(waker)
     }
 
@@ -55,14 +56,7 @@ impl Waker {
         }
     }
 
-    #[cfg(any(
-        mio_unsupported_force_poll_poll,
-        target_os = "espidf",
-        target_os = "haiku",
-        target_os = "nto",
-        target_os = "solaris",
-        target_os = "vita",
-    ))]
+    #[allow(dead_code)] // Only used by the `poll(2)` implementation.
     pub(crate) fn ack_and_reset(&self) {
         self.empty();
     }