Copy illumos waker pipe work around to eventfd

It seems the same behaviour we seen for pipe waker implementation is
also true for eventfd. Work around this by resetting the waker before
writing to it.

src/sys/unix/waker/eventfd.rs

@@ -42,6 +42,13 @@ impl Waker {
 
     #[allow(clippy::unused_io_amount)] // Don't care about partial writes.
     pub(crate) fn wake(&self) -> io::Result<()> {
+        // The epoll emulation on some illumos systems currently requires
+        // the eventfd to be read before an edge-triggered read event is
+        // generated.
+        // See https://www.illumos.org/issues/16700.
+        #[cfg(target_os = "illumos")]
+        self.reset();
+
         let buf: [u8; 8] = 1u64.to_ne_bytes();
         match (&self.fd).write(&buf) {
             Ok(_) => Ok(()),

src/sys/unix/waker/pipe.rs

@@ -40,6 +40,7 @@ impl Waker {
         // The epoll emulation on some illumos systems currently requires
         // the pipe buffer to be completely empty for an edge-triggered
         // wakeup on the pipe read side.
+        // See https://www.illumos.org/issues/16700.
         #[cfg(target_os = "illumos")]
         self.empty();