      1
      2
      3
      4
      5
      6
      7
      8
      9
     10
     11
     12
     13
     14
     15
     16
     17
     18
     19
     20
     21
     22
     23
     24
     25
     26
     27
     28
     29
     30
     31
     32
     33
     34
     35
     36
     37
     38
     39
     40
     41
     42
     43
     44
     45
     46
     47
     48
     49
     50
     51
     52
     53
     54
     55
     56
     57
     58
     59
     60
     61
     62
     63
     64
     65
     66
     67
     68
     69
     70
     71
     72
     73
     74
     75
     76
     77
     78
     79
     80
     81
     82
     83
     84
     85
     86
     87
     88
     89
     90
     91
     92
     93
     94
     95
     96
     97
     98
     99
    100
    101
    102
    103
    104
    105
    106
    107
    108
    109
    110
    111
    112
    113
    114
    115
    116
    117
    118
    119
    120
    121
    122
    123
    124
    125
    126
    127
    128
    129
    130
    131
    132
    133
    134
    135
    136
    137
    138
    139
    140
    141
    142
    143
    144
    145
    146
    147
    148
    149
    150
    151
    152
    153
    154
    155
    156
    157
    158
    159
    160
    161
    162
    163
    164
    165
    166
    167
    168
    169
    170
    171
    172
    173
    174
    175
    176
    177
    178
    179
    180
    181
    182
    183
    184
    185
    186
    187
    188
    189
    190
    191
    192
    193
    194
    195
    196
    197
    198
    199
    200
    201
    202
    203
    204
    205
    206
    207
    208
    209
    210
    211
    212
    213
    214
    215
    216
    217
    218
    219
    220
    221
    222
    223
    224
    225
    226
    227
    228
    229
    230
    231
    232
    233
    234
    235
    236
    237
    238
    239
    240
    241
    242
    243
    244
    245
    246
    247
    248
    249
    250
    251
    252
    253
    254
    255
    256

    use crate::io::driver::{Direction, Handle, Interest, ReadyEvent, ScheduledIo};
    use crate::util::slab;

    use mio::event::Source;
    use std::io;
    use std::task::{Context, Poll};

    cfg_io_driver! {
        /// Associates an I/O resource with the reactor instance that drives it.
        ///
        /// A registration represents an I/O resource registered with a Reactor such
        /// that it will receive task notifications on readiness. This is the lowest
        /// level API for integrating with a reactor.
        ///
        /// The association between an I/O resource is made by calling [`new`]. Once
        /// the association is established, it remains established until the
        /// registration instance is dropped.
        ///
        /// A registration instance represents two separate readiness streams. One
        /// for the read readiness and one for write readiness. These streams are
        /// independent and can be consumed from separate tasks.
        ///
        /// **Note**: while `Registration` is `Sync`, the caller must ensure that
        /// there are at most two tasks that use a registration instance
        /// concurrently. One task for [`poll_read_ready`] and one task for
        /// [`poll_write_ready`]. While violating this requirement is "safe" from a
        /// Rust memory safety point of view, it will result in unexpected behavior
        /// in the form of lost notifications and tasks hanging.
        ///
        /// ## Platform-specific events
        ///
        /// `Registration` also allows receiving platform-specific `mio::Ready`
        /// events. These events are included as part of the read readiness event
        /// stream. The write readiness event stream is only for `Ready::writable()`
        /// events.
        ///
        /// [`new`]: method@Self::new
        /// [`poll_read_ready`]: method@Self::poll_read_ready`
        /// [`poll_write_ready`]: method@Self::poll_write_ready`
        #[derive(Debug)]
        pub(crate) struct Registration {
            /// Handle to the associated driver.
            handle: Handle,

            /// Reference to state stored by the driver.
            shared: slab::Ref<ScheduledIo>,
        }
    }

    unsafe impl Send for Registration {}
    unsafe impl Sync for Registration {}

    // ===== impl Registration =====

    impl Registration {
        /// Registers the I/O resource with the default reactor, for a specific
        /// `Interest`. `new_with_interest` 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.
        ///
        /// # Return
        ///
        /// - `Ok` if the registration happened successfully
        /// - `Err` if an error was encountered during registration
        pub(crate) fn new_with_interest_and_handle(
            io: &mut impl Source,
            interest: Interest,
            handle: Handle,
        ) -> io::Result<Registration> {
            let shared = if let Some(inner) = handle.inner() {
                inner.add_source(io, interest)?
            } else {
                return Err(io::Error::new(
                    io::ErrorKind::Other,
                    "failed to find event loop",
                ));
            };

            Ok(Registration { handle, shared })
        }

        /// Deregisters the I/O resource from the reactor it is associated with.
        ///
        /// This function must be called before the I/O resource associated with the
        /// registration is dropped.
        ///
        /// Note that deregistering does not guarantee that the I/O resource can be
        /// registered with a different reactor. Some I/O resource types can only be
        /// associated with a single reactor instance for their lifetime.
        ///
        /// # Return
        ///
        /// If the deregistration was successful, `Ok` is returned. Any calls to
        /// `Reactor::turn` that happen after a successful call to `deregister` will
        /// no longer result in notifications getting sent for this registration.
        ///
        /// `Err` is returned if an error is encountered.
        pub(crate) fn deregister(&mut self, io: &mut impl Source) -> io::Result<()> {
            let inner = match self.handle.inner() {
                Some(inner) => inner,
                None => return Err(io::Error::new(io::ErrorKind::Other, "reactor gone")),
            };
            inner.deregister_source(io)
        }

        pub(crate) fn clear_readiness(&self, event: ReadyEvent) {
            self.shared.clear_readiness(event);
        }

        // Uses the poll path, requiring the caller to ensure mutual exclusion for
        // correctness. Only the last task to call this function is notified.
        pub(crate) fn poll_read_ready(&self, cx: &mut Context<'_>) -> Poll<io::Result<ReadyEvent>> {
            self.poll_ready(cx, Direction::Read)
        }

        // Uses the poll path, requiring the caller to ensure mutual exclusion for
        // correctness. Only the last task to call this function is notified.
        pub(crate) fn poll_write_ready(&self, cx: &mut Context<'_>) -> Poll<io::Result<ReadyEvent>> {
            self.poll_ready(cx, Direction::Write)
        }

        // Uses the poll path, requiring the caller to ensure mutual exclusion for
        // correctness. Only the last task to call this function is notified.
        pub(crate) fn poll_read_io<R>(
            &self,
            cx: &mut Context<'_>,
            f: impl FnMut() -> io::Result<R>,
        ) -> Poll<io::Result<R>> {
            self.poll_io(cx, Direction::Read, f)
        }

        // Uses the poll path, requiring the caller to ensure mutual exclusion for
        // correctness. Only the last task to call this function is notified.
        pub(crate) fn poll_write_io<R>(
            &self,
            cx: &mut Context<'_>,
            f: impl FnMut() -> io::Result<R>,
        ) -> Poll<io::Result<R>> {
            self.poll_io(cx, Direction::Write, f)
        }

        /// Polls for events on the I/O resource's `direction` readiness stream.
        ///
        /// If called with a task context, notify the task when a new event is
        /// received.
        fn poll_ready(
            &self,
            cx: &mut Context<'_>,
            direction: Direction,
        ) -> Poll<io::Result<ReadyEvent>> {
            // Keep track of task budget
            let coop = ready!(crate::coop::poll_proceed(cx));
            let ev = ready!(self.shared.poll_readiness(cx, direction));

            if self.handle.inner().is_none() {
                return Poll::Ready(Err(gone()));
            }

            coop.made_progress();
            Poll::Ready(Ok(ev))
        }

        fn poll_io<R>(
            &self,
            cx: &mut Context<'_>,
            direction: Direction,
            mut f: impl FnMut() -> io::Result<R>,
        ) -> Poll<io::Result<R>> {
            loop {
                let ev = ready!(self.poll_ready(cx, direction))?;

                match f() {
                    Ok(ret) => {
                        return Poll::Ready(Ok(ret));
                    }
                    Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
                        self.clear_readiness(ev);
                    }
                    Err(e) => return Poll::Ready(Err(e)),
                }
            }
        }

        pub(crate) fn try_io<R>(
            &self,
            interest: Interest,
            f: impl FnOnce() -> io::Result<R>,
        ) -> io::Result<R> {
            let ev = self.shared.ready_event(interest);

            // Don't attempt the operation if the resource is not ready.
            if ev.ready.is_empty() {
                return Err(io::ErrorKind::WouldBlock.into());
            }

            match f() {
                Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
                    self.clear_readiness(ev);
                    Err(io::ErrorKind::WouldBlock.into())
                }
                res => res,
            }
        }
    }

    impl Drop for Registration {
        fn drop(&mut self) {
            // It is possible for a cycle to be created between wakers stored in
            // `ScheduledIo` instances and `Arc<driver::Inner>`. To break this
            // cycle, wakers are cleared. This is an imperfect solution as it is
            // possible to store a `Registration` in a waker. In this case, the
            // cycle would remain.
            //
            // See tokio-rs/tokio#3481 for more details.
            self.shared.clear_wakers();
        }
    }

    fn gone() -> io::Error {
        io::Error::new(io::ErrorKind::Other, "IO driver has terminated")
    }

    cfg_io_readiness! {
        impl Registration {
            pub(crate) async fn readiness(&self, interest: Interest) -> io::Result<ReadyEvent> {
                use std::future::Future;
                use std::pin::Pin;

                let fut = self.shared.readiness(interest);
                pin!(fut);

                crate::future::poll_fn(|cx| {
                    if self.handle.inner().is_none() {
                        return Poll::Ready(Err(io::Error::new(io::ErrorKind::Other, "reactor gone")));
                    }

                    Pin::new(&mut fut).poll(cx).map(Ok)
                }).await
            }

            pub(crate) async fn async_io<R>(&self, interest: Interest, mut f: impl FnMut() -> io::Result<R>) -> io::Result<R> {
                loop {
                    let event = self.readiness(interest).await?;

                    match f() {
                        Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
                            self.clear_readiness(event);
                        }
                        x => return x,
                    }
                }
            }
        }
    }