tokio_reactor/registration.rs
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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);
}
}