io: add mio::Ready argument to PollEvented (#2419)

Add additional methods to allow PollEvented to be created with an appropriate
mio::Ready state, so that it can be properly registered with the reactor.

Fixes #2413

tokio/src/io/driver/mod.rs

@@ -237,10 +237,14 @@ impl fmt::Debug for Handle {
 // ===== impl Inner =====
 
 impl Inner {
-    /// Registers an I/O resource with the reactor.
+    /// Registers an I/O resource with the reactor for a given `mio::Ready` state.
     ///
     /// The registration token is returned.
-    pub(super) fn add_source(&self, source: &dyn Evented) -> io::Result<Address> {
+    pub(super) fn add_source(
+        &self,
+        source: &dyn Evented,
+        ready: mio::Ready,
+    ) -> io::Result<Address> {
         let address = self.io_dispatch.alloc().ok_or_else(|| {
             io::Error::new(
                 io::ErrorKind::Other,
@@ -253,7 +257,7 @@ impl Inner {
         self.io.register(
             source,
             mio::Token(address.to_usize()),
-            mio::Ready::all(),
+            ready,
             mio::PollOpt::edge(),
         )?;
 
@@ -339,12 +343,12 @@ mod tests {
             let inner = reactor.inner;
             let inner2 = inner.clone();
 
-            let token_1 = inner.add_source(&NotEvented).unwrap();
+            let token_1 = inner.add_source(&NotEvented, mio::Ready::all()).unwrap();
             let thread = thread::spawn(move || {
                 inner2.drop_source(token_1);
             });
 
-            let token_2 = inner.add_source(&NotEvented).unwrap();
+            let token_2 = inner.add_source(&NotEvented, mio::Ready::all()).unwrap();
             thread.join().unwrap();
 
             assert!(token_1 != token_2);
@@ -360,15 +364,15 @@ mod tests {
             // add sources to fill up the first page so that the dropped index
             // may be reused.
             for _ in 0..31 {
-                inner.add_source(&NotEvented).unwrap();
+                inner.add_source(&NotEvented, mio::Ready::all()).unwrap();
             }
 
-            let token_1 = inner.add_source(&NotEvented).unwrap();
+            let token_1 = inner.add_source(&NotEvented, mio::Ready::all()).unwrap();
             let thread = thread::spawn(move || {
                 inner2.drop_source(token_1);
             });
 
-            let token_2 = inner.add_source(&NotEvented).unwrap();
+            let token_2 = inner.add_source(&NotEvented, mio::Ready::all()).unwrap();
             thread.join().unwrap();
 
             assert!(token_1 != token_2);
@@ -383,11 +387,11 @@ mod tests {
             let inner2 = inner.clone();
 
             let thread = thread::spawn(move || {
-                let token_2 = inner2.add_source(&NotEvented).unwrap();
+                let token_2 = inner2.add_source(&NotEvented, mio::Ready::all()).unwrap();
                 token_2
             });
 
-            let token_1 = inner.add_source(&NotEvented).unwrap();
+            let token_1 = inner.add_source(&NotEvented, mio::Ready::all()).unwrap();
             let token_2 = thread.join().unwrap();
 
             assert!(token_1 != token_2);

tokio/src/io/poll_evented.rs

@@ -175,7 +175,35 @@ where
     /// from a future driven by a tokio runtime, otherwise runtime can be set
     /// explicitly with [`Handle::enter`](crate::runtime::Handle::enter) function.
     pub fn new(io: E) -> io::Result<Self> {
-        let registration = Registration::new(&io)?;
+        PollEvented::new_with_ready(io, mio::Ready::all())
+    }
+
+    /// Creates a new `PollEvented` associated with the default reactor, for specific `mio::Ready`
+    /// state. `new_with_ready` should be used over `new` when you need control over the readiness
+    /// state, such as when a file descriptor only allows reads. This does not add `hup` or `error`
+    /// so if you are interested in those states, you will need to add them to the readiness state
+    /// passed to this function.
+    ///
+    /// An example to listen to read only
+    ///
+    /// ```rust
+    /// ##[cfg(unix)]
+    ///     mio::Ready::from_usize(
+    ///         mio::Ready::readable().as_usize()
+    ///         | mio::unix::UnixReady::error().as_usize()
+    ///         | mio::unix::UnixReady::hup().as_usize()
+    ///     );
+    /// ```
+    ///
+    /// # Panics
+    ///
+    /// This function panics if thread-local runtime is not set.
+    ///
+    /// The runtime is usually set implicitly when this function is called
+    /// from a future driven by a tokio runtime, otherwise runtime can be set
+    /// explicitly with [`Handle::enter`](crate::runtime::Handle::enter) function.
+    pub fn new_with_ready(io: E, ready: mio::Ready) -> io::Result<Self> {
+        let registration = Registration::new_with_ready(&io, ready)?;
         Ok(Self {
             io: Some(io),
             inner: Inner {

tokio/src/io/registration.rs

@@ -63,12 +63,49 @@ impl Registration {
     /// from a future driven by a tokio runtime, otherwise runtime can be set
     /// explicitly with [`Handle::enter`](crate::runtime::Handle::enter) function.
     pub fn new<T>(io: &T) -> io::Result<Registration>
+    where
+        T: Evented,
+    {
+        Registration::new_with_ready(io, mio::Ready::all())
+    }
+
+    /// Registers the I/O resource with the default reactor, for a specific `mio::Ready` state.
+    /// `new_with_ready` should be used over `new` when you need control over the readiness state,
+    /// such as when a file descriptor only allows reads. This does not add `hup` or `error` so if
+    /// you are interested in those states, you will need to add them to the readiness state passed
+    /// to this function.
+    ///
+    /// An example to listen to read only
+    ///
+    /// ```rust
+    /// ##[cfg(unix)]
+    ///     mio::Ready::from_usize(
+    ///         mio::Ready::readable().as_usize()
+    ///         | mio::unix::UnixReady::error().as_usize()
+    ///         | mio::unix::UnixReady::hup().as_usize()
+    ///     );
+    /// ```
+    ///
+    /// # Return
+    ///
+    /// - `Ok` if the registration happened successfully
+    /// - `Err` if an error was encountered during registration
+    ///
+    ///
+    /// # Panics
+    ///
+    /// This function panics if thread-local runtime is not set.
+    ///
+    /// The runtime is usually set implicitly when this function is called
+    /// from a future driven by a tokio runtime, otherwise runtime can be set
+    /// explicitly with [`Handle::enter`](crate::runtime::Handle::enter) function.
+    pub fn new_with_ready<T>(io: &T, ready: mio::Ready) -> io::Result<Registration>
     where
         T: Evented,
     {
         let handle = Handle::current();
         let address = if let Some(inner) = handle.inner() {
-            inner.add_source(io)?
+            inner.add_source(io, ready)?
         } else {
             return Err(io::Error::new(
                 io::ErrorKind::Other,