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use {Direction, Handle, HandlePriv, Task}; use futures::{task, Async, Poll}; use mio::{self, Evented}; use std::cell::UnsafeCell; use std::sync::atomic::AtomicUsize; use std::sync::atomic::Ordering::SeqCst; use std::{io, ptr, usize}; /// 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 [`register`]. /// Once the association is established, it remains established until the /// registration instance is dropped. Subsequent calls to [`register`] are /// no-ops. /// /// 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. /// /// [`register`]: #method.register /// [`poll_read_ready`]: #method.poll_read_ready`] /// [`poll_write_ready`]: #method.poll_write_ready`] #[derive(Debug)] pub struct Registration { /// Stores the handle. Once set, the value is not changed. /// /// Setting this requires acquiring the lock from state. inner: UnsafeCell<Option<Inner>>, /// Tracks the state of the registration. /// /// The least significant 2 bits are used to track the lifecycle of the /// registration. The rest of the `state` variable is a pointer to tasks /// that must be notified once the lock is released. state: AtomicUsize, } #[derive(Debug)] struct Inner { handle: HandlePriv, token: usize, } #[derive(PartialEq)] enum Notify { Yes, No, } /// Tasks waiting on readiness notifications. #[derive(Debug)] struct Node { direction: Direction, task: Task, next: *mut Node, } /// Initial state. The handle is not set and the registration is idle. const INIT: usize = 0; /// A thread locked the state and will associate a handle. const LOCKED: usize = 1; /// A handle has been associated with the registration. const READY: usize = 2; /// Masks the lifecycle state const LIFECYCLE_MASK: usize = 0b11; /// A fake token used to identify error situations const ERROR: usize = usize::MAX; // ===== impl Registration ===== impl Registration { /// Create a new `Registration`. /// /// This registration is not associated with a Reactor instance. Call /// `register` to establish the association. pub fn new() -> Registration { Registration { inner: UnsafeCell::new(None), state: AtomicUsize::new(INIT), } } /// Register the I/O resource with the default reactor. /// /// This function is safe to call concurrently and repeatedly. However, only /// the first call will establish the registration. Subsequent calls will be /// no-ops. /// /// # Return /// /// If the registration happened successfully, `Ok(true)` is returned. /// /// If an I/O resource has previously been successfully registered, /// `Ok(false)` is returned. /// /// If an error is encountered during registration, `Err` is returned. pub fn register<T>(&self, io: &T) -> io::Result<bool> where T: Evented, { self.register2(io, || HandlePriv::try_current()) } /// Deregister 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 fn deregister<T>(&mut self, io: &T) -> io::Result<()> where T: Evented, { // The state does not need to be checked and coordination is not // necessary as this function takes `&mut self`. This guarantees a // single thread is accessing the instance. if let Some(inner) = unsafe { (*self.inner.get()).as_ref() } { inner.deregister(io)?; } Ok(()) } /// Register the I/O resource with the specified reactor. /// /// This function is safe to call concurrently and repeatedly. However, only /// the first call will establish the registration. Subsequent calls will be /// no-ops. /// /// If the registration happened successfully, `Ok(true)` is returned. /// /// If an I/O resource has previously been successfully registered, /// `Ok(false)` is returned. /// /// If an error is encountered during registration, `Err` is returned. pub fn register_with<T>(&self, io: &T, handle: &Handle) -> io::Result<bool> where T: Evented, { self.register2(io, || match handle.as_priv() { Some(handle) => Ok(handle.clone()), None => HandlePriv::try_current(), }) } pub(crate) fn register_with_priv<T>(&self, io: &T, handle: &HandlePriv) -> io::Result<bool> where T: Evented, { self.register2(io, || Ok(handle.clone())) } fn register2<T, F>(&self, io: &T, f: F) -> io::Result<bool> where T: Evented, F: Fn() -> io::Result<HandlePriv>, { let mut state = self.state.load(SeqCst); loop { match state { INIT => { // Registration is currently not associated with a handle. // Get a handle then attempt to lock the state. let handle = f()?; let actual = self.state.compare_and_swap(INIT, LOCKED, SeqCst); if actual != state { state = actual; continue; } // Create the actual registration let (inner, res) = Inner::new(io, handle); unsafe { *self.inner.get() = Some(inner); } // Transition out of the locked state. This acquires the // current value, potentially having a list of tasks that // are pending readiness notifications. let actual = self.state.swap(READY, SeqCst); // Consume the stack of nodes let mut read = false; let mut write = false; let mut ptr = (actual & !LIFECYCLE_MASK) as *mut Node; let inner = unsafe { (*self.inner.get()).as_ref().unwrap() }; while !ptr.is_null() { let node = unsafe { Box::from_raw(ptr) }; let node = *node; let Node { direction, task, next, } = node; let flag = match direction { Direction::Read => &mut read, Direction::Write => &mut write, }; if !*flag { *flag = true; inner.register(direction, task); } ptr = next; } return res.map(|_| true); } _ => return Ok(false), } } } /// Poll for events on the I/O resource's read readiness stream. /// /// If the I/O resource receives a new read readiness event since the last /// call to `poll_read_ready`, it is returned. If it has not, the current /// task is notified once a new event is received. /// /// All events except `HUP` are [edge-triggered]. Once `HUP` is returned, /// the function will always return `Ready(HUP)`. This should be treated as /// the end of the readiness stream. /// /// Ensure that [`register`] has been called first. /// /// # Return value /// /// There are several possible return values: /// /// * `Ok(Async::Ready(readiness))` means that the I/O resource has received /// a new readiness event. The readiness value is included. /// /// * `Ok(NotReady)` means that no new readiness events have been received /// since the last call to `poll_read_ready`. /// /// * `Err(err)` means that the registration has encountered an error. This /// error either represents a permanent internal error **or** the fact /// that [`register`] was not called first. /// /// [`register`]: #method.register /// [edge-triggered]: https://docs.rs/mio/0.6/mio/struct.Poll.html#edge-triggered-and-level-triggered /// /// # Panics /// /// This function will panic if called from outside of a task context. pub fn poll_read_ready(&self) -> Poll<mio::Ready, io::Error> { self.poll_ready(Direction::Read, Notify::Yes) .map(|v| match v { Some(v) => Async::Ready(v), _ => Async::NotReady, }) } /// Consume any pending read readiness event. /// /// This function is identical to [`poll_read_ready`] **except** that it /// will not notify the current task when a new event is received. As such, /// it is safe to call this function from outside of a task context. /// /// [`poll_read_ready`]: #method.poll_read_ready pub fn take_read_ready(&self) -> io::Result<Option<mio::Ready>> { self.poll_ready(Direction::Read, Notify::No) } /// Poll for events on the I/O resource's write readiness stream. /// /// If the I/O resource receives a new write readiness event since the last /// call to `poll_write_ready`, it is returned. If it has not, the current /// task is notified once a new event is received. /// /// All events except `HUP` are [edge-triggered]. Once `HUP` is returned, /// the function will always return `Ready(HUP)`. This should be treated as /// the end of the readiness stream. /// /// Ensure that [`register`] has been called first. /// /// # Return value /// /// There are several possible return values: /// /// * `Ok(Async::Ready(readiness))` means that the I/O resource has received /// a new readiness event. The readiness value is included. /// /// * `Ok(NotReady)` means that no new readiness events have been received /// since the last call to `poll_write_ready`. /// /// * `Err(err)` means that the registration has encountered an error. This /// error either represents a permanent internal error **or** the fact /// that [`register`] was not called first. /// /// [`register`]: #method.register /// [edge-triggered]: https://docs.rs/mio/0.6/mio/struct.Poll.html#edge-triggered-and-level-triggered /// /// # Panics /// /// This function will panic if called from outside of a task context. pub fn poll_write_ready(&self) -> Poll<mio::Ready, io::Error> { self.poll_ready(Direction::Write, Notify::Yes) .map(|v| match v { Some(v) => Async::Ready(v), _ => Async::NotReady, }) } /// Consume any pending write readiness event. /// /// This function is identical to [`poll_write_ready`] **except** that it /// will not notify the current task when a new event is received. As such, /// it is safe to call this function from outside of a task context. /// /// [`poll_write_ready`]: #method.poll_write_ready pub fn take_write_ready(&self) -> io::Result<Option<mio::Ready>> { self.poll_ready(Direction::Write, Notify::No) } fn poll_ready(&self, direction: Direction, notify: Notify) -> io::Result<Option<mio::Ready>> { let mut state = self.state.load(SeqCst); // Cache the node pointer let mut node = None; loop { match state { INIT => { return Err(io::Error::new( io::ErrorKind::Other, "must call `register` before poll_read_ready", )); } READY => { let inner = unsafe { (*self.inner.get()).as_ref().unwrap() }; return inner.poll_ready(direction, notify); } LOCKED => { if let Notify::No = notify { // Skip the notification tracking junk. return Ok(None); } let next_ptr = (state & !LIFECYCLE_MASK) as *mut Node; let task = task::current(); // Get the node let mut n = node.take().unwrap_or_else(|| { Box::new(Node { direction, task: task, next: ptr::null_mut(), }) }); n.next = next_ptr; let node_ptr = Box::into_raw(n); let next = node_ptr as usize | (state & LIFECYCLE_MASK); let actual = self.state.compare_and_swap(state, next, SeqCst); if actual != state { // Back out of the node boxing let n = unsafe { Box::from_raw(node_ptr) }; // Save this for next loop node = Some(n); state = actual; continue; } return Ok(None); } _ => unreachable!(), } } } } unsafe impl Send for Registration {} unsafe impl Sync for Registration {} // ===== impl Inner ===== impl Inner { fn new<T>(io: &T, handle: HandlePriv) -> (Self, io::Result<()>) where T: Evented, { let mut res = Ok(()); let token = match handle.inner() { Some(inner) => match inner.add_source(io) { Ok(token) => token, Err(e) => { res = Err(e); ERROR } }, None => { res = Err(io::Error::new(io::ErrorKind::Other, "event loop gone")); ERROR } }; let inner = Inner { handle, token }; (inner, res) } fn register(&self, direction: Direction, task: Task) { if self.token == ERROR { task.notify(); return; } let inner = match self.handle.inner() { Some(inner) => inner, None => { task.notify(); return; } }; inner.register(self.token, direction, task); } fn deregister<E: Evented>(&self, io: &E) -> io::Result<()> { if self.token == ERROR { return Err(io::Error::new( io::ErrorKind::Other, "failed to associate with reactor", )); } let inner = match self.handle.inner() { Some(inner) => inner, None => return Err(io::Error::new(io::ErrorKind::Other, "reactor gone")), }; inner.deregister_source(io) } fn poll_ready(&self, direction: Direction, notify: Notify) -> io::Result<Option<mio::Ready>> { if self.token == ERROR { return Err(io::Error::new( io::ErrorKind::Other, "failed to associate with reactor", )); } let inner = match self.handle.inner() { Some(inner) => inner, None => return Err(io::Error::new(io::ErrorKind::Other, "reactor gone")), }; let mask = direction.mask(); let mask_no_hup = (mask - ::platform::hup()).as_usize(); let io_dispatch = inner.io_dispatch.read(); let sched = &io_dispatch[self.token]; // This consumes the current readiness state **except** for HUP. HUP is // excluded because a) it is a final state and never transitions out of // HUP and b) both the read AND the write directions need to be able to // observe this state. // // If HUP were to be cleared when `direction` is `Read`, then when // `poll_ready` is called again with a _`direction` of `Write`, the HUP // state would not be visible. let mut ready = mask & mio::Ready::from_usize(sched.readiness.fetch_and(!mask_no_hup, SeqCst)); if ready.is_empty() && notify == Notify::Yes { debug!("scheduling {:?} for: {}", direction, self.token); // Update the task info match direction { Direction::Read => sched.reader.register(), Direction::Write => sched.writer.register(), } // Try again ready = mask & mio::Ready::from_usize(sched.readiness.fetch_and(!mask_no_hup, SeqCst)); } if ready.is_empty() { Ok(None) } else { Ok(Some(ready)) } } } impl Drop for Inner { fn drop(&mut self) { if self.token == ERROR { return; } let inner = match self.handle.inner() { Some(inner) => inner, None => return, }; inner.drop_source(self.token); } }