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Introduce the Tokio runtime: Reactor + Threadpool (#141)

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This patch is an intial implementation of the Tokio runtime. The Tokio
runtime provides an out of the box configuration for running I/O heavy
asynchronous applications.

As of now, the Tokio runtime is a combination of a work-stealing thread
pool as well as a background reactor to drive I/O resources.

This patch also includes tokio-executor, a hopefully short lived crate
that is based on the futures 0.2 executor RFC.

* Implement `Park` for `Reactor`

This enables the reactor to be used as the thread parker for executors.
This also adds an `Error` component to `Park`. With this change, a
`Reactor` and a `CurrentThread` can be combined to achieve the
capabilities of tokio-core.
This commit is contained in:
Carl Lerche
2018-02-21 07:42:22 -08:00
committed by GitHub
parent e0d95aa037
commit fe14e7b127
32 changed files with 6344 additions and 966 deletions
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tokio-threadpool/src/task.rs
+429
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use Notifier;
use futures::{future, Future, Async};
use futures::executor::{self, Spawn};
use std::{fmt, mem, ptr};
use std::cell::Cell;
use std::sync::Arc;
use std::sync::atomic::{self, AtomicUsize, AtomicPtr};
use std::sync::atomic::Ordering::{AcqRel, Acquire, Release, Relaxed};
pub(crate) struct Task {
ptr: *mut Inner,
}
#[derive(Debug)]
pub(crate) struct Queue {
head: AtomicPtr<Inner>,
tail: Cell<*mut Inner>,
stub: Box<Inner>,
}
#[derive(Debug)]
pub(crate) enum Poll {
Empty,
Inconsistent,
Data(Task),
}
#[derive(Debug)]
pub(crate) enum Run {
Idle,
Schedule,
Complete,
}
struct Inner {
// Next pointer in the queue that submits tasks to a worker.
next: AtomicPtr<Inner>,
// Task state
state: AtomicUsize,
// Number of outstanding references to the task
ref_count: AtomicUsize,
// Store the future at the head of the struct
//
// The future is dropped immediately when it transitions to Complete
future: Option<Spawn<BoxFuture>>,
}
#[derive(Debug, Clone, Copy, Eq, PartialEq)]
enum State {
/// Task is currently idle
Idle,
/// Task is currently running
Running,
/// Task is currently running, but has been notified that it must run again.
Notified,
/// Task has been scheduled
Scheduled,
/// Task is complete
Complete,
}
type BoxFuture = Box<Future<Item = (), Error = ()> + Send + 'static>;
// ===== impl Task =====
impl Task {
/// Create a new task handle
pub fn new(future: BoxFuture) -> Task {
let inner = Box::new(Inner {
next: AtomicPtr::new(ptr::null_mut()),
state: AtomicUsize::new(State::new().into()),
ref_count: AtomicUsize::new(1),
future: Some(executor::spawn(future)),
});
Task { ptr: Box::into_raw(inner) }
}
/// Transmute a u64 to a Task
pub unsafe fn from_notify_id(unpark_id: usize) -> Task {
mem::transmute(unpark_id)
}
/// Transmute a u64 to a task ref
pub unsafe fn from_notify_id_ref<'a>(unpark_id: &'a usize) -> &'a Task {
mem::transmute(unpark_id)
}
/// Execute the task returning `Run::Schedule` if the task needs to be
/// scheduled again.
pub fn run(&self, unpark: &Arc<Notifier>) -> Run {
use self::State::*;
// Transition task to running state. At this point, the task must be
// scheduled.
let actual: State = self.inner().state.compare_and_swap(
Scheduled.into(), Running.into(), AcqRel).into();
trace!("running; state={:?}", actual);
match actual {
Scheduled => {},
_ => panic!("unexpected task state; {:?}", actual),
}
trace!("Task::run; state={:?}", State::from(self.inner().state.load(Relaxed)));
let res = self.inner_mut().future.as_mut().unwrap()
.poll_future_notify(unpark, self.ptr as usize);
match res {
Ok(Async::Ready(_)) | Err(_) => {
trace!(" -> task complete");
// Drop the future
self.inner_mut().drop_future();
// Transition to the completed state
self.inner().state.store(State::Complete.into(), Release);
Run::Complete
}
_ => {
trace!(" -> not ready");
// Attempt to transition from Running -> Idle, if successful,
// then the task does not need to be scheduled again. If the CAS
// fails, then the task has been unparked concurrent to running,
// in which case it transitions immediately back to scheduled
// and we return `true`.
let prev: State = self.inner().state.compare_and_swap(
Running.into(), Idle.into(), AcqRel).into();
match prev {
Running => Run::Idle,
Notified => {
self.inner().state.store(Scheduled.into(), Release);
Run::Schedule
}
_ => unreachable!(),
}
}
}
}
/// Transition the task state to scheduled.
///
/// Returns `true` if the caller is permitted to schedule the task.
pub fn schedule(&self) -> bool {
use self::State::*;
loop {
let actual = self.inner().state.compare_and_swap(
Idle.into(),
Scheduled.into(),
Relaxed).into();
match actual {
Idle => return true,
Running => {
let actual = self.inner().state.compare_and_swap(
Running.into(), Notified.into(), Relaxed).into();
match actual {
Idle => continue,
_ => return false,
}
}
Complete | Notified | Scheduled => return false,
}
}
}
#[inline]
fn inner(&self) -> &Inner {
unsafe { &*self.ptr }
}
#[inline]
fn inner_mut(&self) -> &mut Inner {
unsafe { &mut *self.ptr }
}
}
impl fmt::Debug for Task {
fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
fmt.debug_struct("Task")
.field("inner", self.inner())
.finish()
}
}
impl Clone for Task {
fn clone(&self) -> Task {
use std::isize;
const MAX_REFCOUNT: usize = (isize::MAX) as usize;
// Using a relaxed ordering is alright here, as knowledge of the
// original reference prevents other threads from erroneously deleting
// the object.
//
// As explained in the [Boost documentation][1], Increasing the
// reference counter can always be done with memory_order_relaxed: New
// references to an object can only be formed from an existing
// reference, and passing an existing reference from one thread to
// another must already provide any required synchronization.
//
// [1]: (www.boost.org/doc/libs/1_55_0/doc/html/atomic/usage_examples.html)
let old_size = self.inner().ref_count.fetch_add(1, Relaxed);
// However we need to guard against massive refcounts in case someone
// is `mem::forget`ing Arcs. If we don't do this the count can overflow
// and users will use-after free. We racily saturate to `isize::MAX` on
// the assumption that there aren't ~2 billion threads incrementing
// the reference count at once. This branch will never be taken in
// any realistic program.
//
// We abort because such a program is incredibly degenerate, and we
// don't care to support it.
if old_size > MAX_REFCOUNT {
// TODO: abort
panic!();
}
Task { ptr: self.ptr }
}
}
impl Drop for Task {
fn drop(&mut self) {
// Because `fetch_sub` is already atomic, we do not need to synchronize
// with other threads unless we are going to delete the object. This
// same logic applies to the below `fetch_sub` to the `weak` count.
if self.inner().ref_count.fetch_sub(1, Release) != 1 {
return;
}
// This fence is needed to prevent reordering of use of the data and
// deletion of the data. Because it is marked `Release`, the decreasing
// of the reference count synchronizes with this `Acquire` fence. This
// means that use of the data happens before decreasing the reference
// count, which happens before this fence, which happens before the
// deletion of the data.
//
// As explained in the [Boost documentation][1],
//
// > It is important to enforce any possible access to the object in one
// > thread (through an existing reference) to *happen before* deleting
// > the object in a different thread. This is achieved by a "release"
// > operation after dropping a reference (any access to the object
// > through this reference must obviously happened before), and an
// > "acquire" operation before deleting the object.
//
// [1]: (www.boost.org/doc/libs/1_55_0/doc/html/atomic/usage_examples.html)
atomic::fence(Acquire);
unsafe {
let _ = Box::from_raw(self.ptr);
}
}
}
unsafe impl Send for Task {}
// ===== impl Inner =====
impl Inner {
fn stub() -> Inner {
Inner {
next: AtomicPtr::new(ptr::null_mut()),
state: AtomicUsize::new(State::stub().into()),
ref_count: AtomicUsize::new(0),
future: Some(executor::spawn(Box::new(future::empty()))),
}
}
fn drop_future(&mut self) {
let _ = self.future.take();
}
}
impl Drop for Inner {
fn drop(&mut self) {
self.drop_future();
}
}
impl fmt::Debug for Inner {
fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
fmt.debug_struct("Inner")
.field("next", &self.next)
.field("state", &self.state)
.field("ref_count", &self.ref_count)
.field("future", &"Spawn<BoxFuture>")
.finish()
}
}
// ===== impl Queue =====
impl Queue {
pub fn new() -> Queue {
let stub = Box::new(Inner::stub());
let ptr = &*stub as *const _ as *mut _;
Queue {
head: AtomicPtr::new(ptr),
tail: Cell::new(ptr),
stub: stub,
}
}
pub fn push(&self, handle: Task) {
unsafe {
self.push2(handle.ptr);
// Forgetting the handle is necessary to avoid the ref dec
mem::forget(handle);
}
}
unsafe fn push2(&self, handle: *mut Inner) {
// Set the next pointer. This does not require an atomic operation as
// this node is not accessible. The write will be flushed with the next
// operation
(*handle).next = AtomicPtr::new(ptr::null_mut());
// Update the head to point to the new node. We need to see the previous
// node in order to update the next pointer as well as release `handle`
// to any other threads calling `push`.
let prev = self.head.swap(handle, AcqRel);
// Release `handle` to the consume end.
(*prev).next.store(handle, Release);
}
pub unsafe fn poll(&self) -> Poll {
let mut tail = self.tail.get();
let mut next = (*tail).next.load(Acquire);
let stub = &*self.stub as *const _ as *mut _;
if tail == stub {
if next.is_null() {
return Poll::Empty;
}
self.tail.set(next);
tail = next;
next = (*next).next.load(Acquire);
}
if !next.is_null() {
self.tail.set(next);
// No ref_count inc is necessary here as this poll is paired
// with a `push` which "forgets" the handle.
return Poll::Data(Task {
ptr: tail,
});
}
if self.head.load(Acquire) != tail {
return Poll::Inconsistent;
}
self.push2(stub);
next = (*tail).next.load(Acquire);
if !next.is_null() {
self.tail.set(next);
return Poll::Data(Task {
ptr: tail,
});
}
Poll::Inconsistent
}
}
// ===== impl State =====
impl State {
/// Returns the initial task state.
///
/// Tasks start in the scheduled state as they are immediately scheduled on
/// creation.
fn new() -> State {
State::Scheduled
}
fn stub() -> State {
State::Idle
}
}
impl From<usize> for State {
fn from(src: usize) -> Self {
use self::State::*;
match src {
0 => Idle,
1 => Running,
2 => Notified,
3 => Scheduled,
4 => Complete,
_ => unreachable!(),
}
}
}
impl From<State> for usize {
fn from(src: State) -> Self {
use self::State::*;
match src {
Idle => 0,
Running => 1,
Notified => 2,
Scheduled => 3,
Complete => 4,
}
}
}