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
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
#![cfg_attr(not(feature = "rt"), allow(dead_code))]

mod interest;
#[allow(unreachable_pub)]
pub use interest::Interest;

mod ready;
#[allow(unreachable_pub)]
pub use ready::Ready;

mod registration;
pub(crate) use registration::Registration;

mod scheduled_io;
use scheduled_io::ScheduledIo;

use crate::park::{Park, Unpark};
use crate::util::slab::{self, Slab};
use crate::{loom::sync::Mutex, util::bit};

use std::fmt;
use std::io;
use std::sync::{Arc, Weak};
use std::time::Duration;

/// I/O driver, backed by Mio
pub(crate) struct Driver {
    /// Tracks the number of times `turn` is called. It is safe for this to wrap
    /// as it is mostly used to determine when to call `compact()`
    tick: u8,

    /// Reuse the `mio::Events` value across calls to poll.
    events: Option<mio::Events>,

    /// Primary slab handle containing the state for each resource registered
    /// with this driver. During Drop this is moved into the Inner structure, so
    /// this is an Option to allow it to be vacated (until Drop this is always
    /// Some)
    resources: Option<Slab<ScheduledIo>>,

    /// The system event queue
    poll: mio::Poll,

    /// State shared between the reactor and the handles.
    inner: Arc<Inner>,
}

/// A reference to an I/O driver
#[derive(Clone)]
pub(crate) struct Handle {
    inner: Weak<Inner>,
}

pub(crate) struct ReadyEvent {
    tick: u8,
    pub(crate) ready: Ready,
}

pub(super) struct Inner {
    /// Primary slab handle containing the state for each resource registered
    /// with this driver.
    ///
    /// The ownership of this slab is moved into this structure during
    /// `Driver::drop`, so that `Inner::drop` can notify all outstanding handles
    /// without risking new ones being registered in the meantime.
    resources: Mutex<Option<Slab<ScheduledIo>>>,

    /// Registers I/O resources
    registry: mio::Registry,

    /// Allocates `ScheduledIo` handles when creating new resources.
    pub(super) io_dispatch: slab::Allocator<ScheduledIo>,

    /// Used to wake up the reactor from a call to `turn`
    waker: mio::Waker,
}

#[derive(Debug, Eq, PartialEq, Clone, Copy)]
enum Direction {
    Read,
    Write,
}

enum Tick {
    Set(u8),
    Clear(u8),
}

// TODO: Don't use a fake token. Instead, reserve a slot entry for the wakeup
// token.
const TOKEN_WAKEUP: mio::Token = mio::Token(1 << 31);

const ADDRESS: bit::Pack = bit::Pack::least_significant(24);

// Packs the generation value in the `readiness` field.
//
// The generation prevents a race condition where a slab slot is reused for a
// new socket while the I/O driver is about to apply a readiness event. The
// generaton value is checked when setting new readiness. If the generation do
// not match, then the readiness event is discarded.
const GENERATION: bit::Pack = ADDRESS.then(7);

fn _assert_kinds() {
    fn _assert<T: Send + Sync>() {}

    _assert::<Handle>();
}

// ===== impl Driver =====

impl Driver {
    /// Creates a new event loop, returning any error that happened during the
    /// creation.
    pub(crate) fn new() -> io::Result<Driver> {
        let poll = mio::Poll::new()?;
        let waker = mio::Waker::new(poll.registry(), TOKEN_WAKEUP)?;
        let registry = poll.registry().try_clone()?;

        let slab = Slab::new();
        let allocator = slab.allocator();

        Ok(Driver {
            tick: 0,
            events: Some(mio::Events::with_capacity(1024)),
            poll,
            resources: Some(slab),
            inner: Arc::new(Inner {
                resources: Mutex::new(None),
                registry,
                io_dispatch: allocator,
                waker,
            }),
        })
    }

    /// Returns a handle to this event loop which can be sent across threads
    /// and can be used as a proxy to the event loop itself.
    ///
    /// Handles are cloneable and clones always refer to the same event loop.
    /// This handle is typically passed into functions that create I/O objects
    /// to bind them to this event loop.
    pub(crate) fn handle(&self) -> Handle {
        Handle {
            inner: Arc::downgrade(&self.inner),
        }
    }

    fn turn(&mut self, max_wait: Option<Duration>) -> io::Result<()> {
        // How often to call `compact()` on the resource slab
        const COMPACT_INTERVAL: u8 = 255;

        self.tick = self.tick.wrapping_add(1);

        if self.tick == COMPACT_INTERVAL {
            self.resources.as_mut().unwrap().compact()
        }

        let mut events = self.events.take().expect("i/o driver event store missing");

        // Block waiting for an event to happen, peeling out how many events
        // happened.
        match self.poll.poll(&mut events, max_wait) {
            Ok(_) => {}
            Err(ref e) if e.kind() == io::ErrorKind::Interrupted => {}
            Err(e) => return Err(e),
        }

        // Process all the events that came in, dispatching appropriately
        for event in events.iter() {
            let token = event.token();

            if token != TOKEN_WAKEUP {
                self.dispatch(token, Ready::from_mio(event));
            }
        }

        self.events = Some(events);

        Ok(())
    }

    fn dispatch(&mut self, token: mio::Token, ready: Ready) {
        let addr = slab::Address::from_usize(ADDRESS.unpack(token.0));

        let resources = self.resources.as_mut().unwrap();

        let io = match resources.get(addr) {
            Some(io) => io,
            None => return,
        };

        let res = io.set_readiness(Some(token.0), Tick::Set(self.tick), |curr| curr | ready);

        if res.is_err() {
            // token no longer valid!
            return;
        }

        io.wake(ready);
    }
}

impl Drop for Driver {
    fn drop(&mut self) {
        (*self.inner.resources.lock()) = self.resources.take();
    }
}

impl Drop for Inner {
    fn drop(&mut self) {
        let resources = self.resources.lock().take();

        if let Some(mut slab) = resources {
            slab.for_each(|io| {
                // If a task is waiting on the I/O resource, notify it. The task
                // will then attempt to use the I/O resource and fail due to the
                // driver being shutdown.
                io.shutdown();
            });
        }
    }
}

impl Park for Driver {
    type Unpark = Handle;
    type Error = io::Error;

    fn unpark(&self) -> Self::Unpark {
        self.handle()
    }

    fn park(&mut self) -> io::Result<()> {
        self.turn(None)?;
        Ok(())
    }

    fn park_timeout(&mut self, duration: Duration) -> io::Result<()> {
        self.turn(Some(duration))?;
        Ok(())
    }

    fn shutdown(&mut self) {}
}

impl fmt::Debug for Driver {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "Driver")
    }
}

// ===== impl Handle =====

cfg_rt! {
    impl Handle {
        /// Returns a handle to the current reactor
        ///
        /// # Panics
        ///
        /// This function panics if there is no current reactor set and `rt` feature
        /// flag is not enabled.
        pub(super) fn current() -> Self {
            crate::runtime::context::io_handle()
                .expect("there is no reactor running, must be called from the context of a Tokio 0.3.x runtime")
        }
    }
}

cfg_not_rt! {
    impl Handle {
        /// Returns a handle to the current reactor
        ///
        /// # Panics
        ///
        /// This function panics if there is no current reactor set, or if the `rt`
        /// feature flag is not enabled.
        pub(super) fn current() -> Self {
            panic!("there is no reactor running, must be called from the context of a Tokio 0.3.x runtime with `rt` enabled.")
        }
    }
}

impl Handle {
    /// Forces a reactor blocked in a call to `turn` to wakeup, or otherwise
    /// makes the next call to `turn` return immediately.
    ///
    /// This method is intended to be used in situations where a notification
    /// needs to otherwise be sent to the main reactor. If the reactor is
    /// currently blocked inside of `turn` then it will wake up and soon return
    /// after this method has been called. If the reactor is not currently
    /// blocked in `turn`, then the next call to `turn` will not block and
    /// return immediately.
    fn wakeup(&self) {
        if let Some(inner) = self.inner() {
            inner.waker.wake().expect("failed to wake I/O driver");
        }
    }

    pub(super) fn inner(&self) -> Option<Arc<Inner>> {
        self.inner.upgrade()
    }
}

impl Unpark for Handle {
    fn unpark(&self) {
        self.wakeup();
    }
}

impl fmt::Debug for Handle {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "Handle")
    }
}

// ===== impl Inner =====

impl Inner {
    /// 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: &mut impl mio::event::Source,
        interest: Interest,
    ) -> io::Result<slab::Ref<ScheduledIo>> {
        let (address, shared) = self.io_dispatch.allocate().ok_or_else(|| {
            io::Error::new(
                io::ErrorKind::Other,
                "reactor at max registered I/O resources",
            )
        })?;

        let token = GENERATION.pack(shared.generation(), ADDRESS.pack(address.as_usize(), 0));

        self.registry
            .register(source, mio::Token(token), interest.to_mio())?;

        Ok(shared)
    }

    /// Deregisters an I/O resource from the reactor.
    pub(super) fn deregister_source(&self, source: &mut impl mio::event::Source) -> io::Result<()> {
        self.registry.deregister(source)
    }
}

impl Direction {
    pub(super) fn mask(self) -> Ready {
        match self {
            Direction::Read => Ready::READABLE | Ready::READ_CLOSED,
            Direction::Write => Ready::WRITABLE | Ready::WRITE_CLOSED,
        }
    }
}