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// This implementation is based on the one in the `polling` crate.
// Permission to use this code has been granted by original author:
use std::collections::HashMap;
use std::fmt::{Debug, Formatter};
#[cfg(not(target_os = "hermit"))]
use std::os::fd::{AsRawFd, RawFd};
// can use `std::os::fd` and be merged with the above.
#[cfg(target_os = "hermit")]
use std::os::hermit::io::{AsRawFd, RawFd};
use std::sync::atomic::{AtomicBool, AtomicUsize, Ordering};
use std::sync::{Arc, Condvar, Mutex};
use std::time::Duration;
use std::{cmp, fmt, io};
use crate::sys::unix::waker::Waker as WakerInternal;
use crate::{Interest, Token};
/// Unique id for use as `SelectorId`.
#[cfg(debug_assertions)]
static NEXT_ID: AtomicUsize = AtomicUsize::new(1);
#[derive(Debug)]
pub struct Selector {
state: Arc<SelectorState>,
}
impl Selector {
pub fn new() -> io::Result<Selector> {
let state = SelectorState::new()?;
Ok(Selector {
state: Arc::new(state),
})
}
pub fn try_clone(&self) -> io::Result<Selector> {
let state = self.state.clone();
Ok(Selector { state })
}
pub fn select(&self, events: &mut Events, timeout: Option<Duration>) -> io::Result<()> {
self.state.select(events, timeout)
}
pub fn register(&self, fd: RawFd, token: Token, interests: Interest) -> io::Result<()> {
self.state.register(fd, token, interests)
}
#[allow(dead_code)]
pub(crate) fn register_internal(
&self,
fd: RawFd,
token: Token,
interests: Interest,
) -> io::Result<Arc<RegistrationRecord>> {
self.state.register_internal(fd, token, interests)
}
pub fn reregister(&self, fd: RawFd, token: Token, interests: Interest) -> io::Result<()> {
self.state.reregister(fd, token, interests)
}
pub fn deregister(&self, fd: RawFd) -> io::Result<()> {
self.state.deregister(fd)
}
pub fn wake(&self, token: Token) -> io::Result<()> {
self.state.wake(token)
}
cfg_io_source! {
#[cfg(debug_assertions)]
pub fn id(&self) -> usize {
self.state.id
}
}
}
/// Interface to poll.
#[derive(Debug)]
struct SelectorState {
/// File descriptors to poll.
fds: Mutex<Fds>,
/// File descriptors which will be removed before the next poll call.
///
/// When a file descriptor is deregistered while a poll is running, we need to filter
/// out all removed descriptors after that poll is finished running.
pending_removal: Mutex<Vec<RawFd>>,
/// Token associated with Waker that have recently asked to wake. This will
/// cause a synthetic behaviour where on any wakeup we add all pending tokens
/// to the list of emitted events.
pending_wake_token: Mutex<Option<Token>>,
/// Data is written to this to wake up the current instance of `wait`, which can occur when the
/// user notifies it (in which case `notified` would have been set) or when an operation needs
/// to occur (in which case `waiting_operations` would have been incremented).
notify_waker: WakerInternal,
/// The number of operations (`add`, `modify` or `delete`) that are currently waiting on the
/// mutex to become free. When this is nonzero, `wait` must be suspended until it reaches zero
/// again.
waiting_operations: AtomicUsize,
/// The condition variable that gets notified when `waiting_operations` reaches zero or
/// `notified` becomes true.
///
/// This is used with the `fds` mutex.
operations_complete: Condvar,
/// This selectors id.
#[cfg(debug_assertions)]
#[allow(dead_code)]
id: usize,
}
/// The file descriptors to poll in a `Poller`.
#[derive(Debug, Clone)]
struct Fds {
/// The list of `pollfds` taken by poll.
///
/// The first file descriptor is always present and is used to notify the poller.
poll_fds: Vec<PollFd>,
/// The map of each file descriptor to data associated with it. This does not include the file
/// descriptors created by the internal notify waker.
fd_data: HashMap<RawFd, FdData>,
}
/// Transparent wrapper around `libc::pollfd`, used to support `Debug` derives without adding the
/// `extra_traits` feature of `libc`.
#[repr(transparent)]
#[derive(Clone)]
struct PollFd(libc::pollfd);
impl Debug for PollFd {
fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
f.debug_struct("pollfd")
.field("fd", &self.0.fd)
.field("events", &self.0.events)
.field("revents", &self.0.revents)
.finish()
}
}
/// Data associated with a file descriptor in a poller.
#[derive(Debug, Clone)]
struct FdData {
/// The index into `poll_fds` this file descriptor is.
poll_fds_index: usize,
/// The key of the `Event` associated with this file descriptor.
token: Token,
/// Used to communicate with IoSourceState when we need to internally deregister
/// based on a closed fd.
shared_record: Arc<RegistrationRecord>,
}
impl SelectorState {
pub fn new() -> io::Result<SelectorState> {
let notify_waker = WakerInternal::new_unregistered()?;
Ok(Self {
fds: Mutex::new(Fds {
poll_fds: vec![PollFd(libc::pollfd {
fd: notify_waker.as_raw_fd(),
events: libc::POLLIN,
revents: 0,
})],
fd_data: HashMap::new(),
}),
pending_removal: Mutex::new(Vec::new()),
pending_wake_token: Mutex::new(None),
notify_waker,
waiting_operations: AtomicUsize::new(0),
operations_complete: Condvar::new(),
#[cfg(debug_assertions)]
id: NEXT_ID.fetch_add(1, Ordering::Relaxed),
})
}
pub fn select(&self, events: &mut Events, timeout: Option<Duration>) -> io::Result<()> {
events.clear();
let mut fds = self.fds.lock().unwrap();
// Keep track of fds that receive POLLHUP or POLLERR (i.e. won't receive further
// events) and internally deregister them before they are externally deregister'd. See
// IoSourceState below to track how the external deregister call will be handled
// when this state occurs.
let mut closed_raw_fds = Vec::new();
loop {
// Complete all current operations.
loop {
if self.waiting_operations.load(Ordering::SeqCst) == 0 {
break;
}
fds = self.operations_complete.wait(fds).unwrap();
}
// Perform the poll.
trace!("Polling on {:?}", &fds);
let num_events = poll(&mut fds.poll_fds, timeout)?;
trace!("Poll finished: {:?}", &fds);
if num_events == 0 {
return Ok(());
}
let waker_events = fds.poll_fds[0].0.revents;
let notified = waker_events != 0;
let mut num_fd_events = if notified { num_events - 1 } else { num_events };
let pending_wake_token = self.pending_wake_token.lock().unwrap().take();
if notified {
self.notify_waker.ack_and_reset();
if pending_wake_token.is_some() {
num_fd_events += 1;
}
}
// We now check whether this poll was performed with descriptors which were pending
// for removal and filter out any matching.
let mut pending_removal_guard = self.pending_removal.lock().unwrap();
let mut pending_removal = std::mem::replace(pending_removal_guard.as_mut(), Vec::new());
drop(pending_removal_guard);
// Store the events if there were any.
if num_fd_events > 0 {
let fds = &mut *fds;
events.reserve(num_fd_events);
// Add synthetic events we picked up from calls to wake()
if let Some(pending_wake_token) = pending_wake_token {
events.push(Event {
token: pending_wake_token,
events: waker_events,
});
}
for fd_data in fds.fd_data.values_mut() {
let PollFd(poll_fd) = &mut fds.poll_fds[fd_data.poll_fds_index];
if pending_removal.contains(&poll_fd.fd) {
// Fd was removed while poll was running
continue;
}
if poll_fd.revents != 0 {
// Store event
events.push(Event {
token: fd_data.token,
events: poll_fd.revents,
});
if poll_fd.revents & (libc::POLLHUP | libc::POLLERR) != 0 {
pending_removal.push(poll_fd.fd);
closed_raw_fds.push(poll_fd.fd);
}
// Remove the interest which just got triggered the IoSourceState's do_io
// wrapper used with this selector will add back the interest using
// reregister.
poll_fd.events &= !poll_fd.revents;
// Minor optimization to potentially avoid looping n times where n is the
// number of input fds (i.e. we might loop between m and n times where m is
// the number of fds with revents != 0).
if events.len() == num_fd_events {
break;
}
}
}
break; // No more polling.
}
// If we didn't break above it means we got woken up internally (for example for adding an fd), so we poll again.
}
drop(fds);
let _ = self.deregister_all(&closed_raw_fds);
Ok(())
}
pub fn register(&self, fd: RawFd, token: Token, interests: Interest) -> io::Result<()> {
self.register_internal(fd, token, interests).map(|_| ())
}
pub fn register_internal(
&self,
fd: RawFd,
token: Token,
interests: Interest,
) -> io::Result<Arc<RegistrationRecord>> {
#[cfg(debug_assertions)]
if fd == self.notify_waker.as_raw_fd() {
return Err(io::Error::from(io::ErrorKind::InvalidInput));
}
// We must handle the unlikely case that the following order of operations happens:
//
// register(1 as RawFd)
// deregister(1 as RawFd)
// register(1 as RawFd)
// <poll happens>
//
// Fd's pending removal only get cleared when poll has been run. It is possible that
// between registering and deregistering and then _again_ registering the file descriptor
// poll never gets called, thus the fd stays stuck in the pending removal list.
//
// To avoid this scenario we remove an fd from pending removals when registering it.
let mut pending_removal = self.pending_removal.lock().unwrap();
if let Some(idx) = pending_removal.iter().position(|&pending| pending == fd) {
pending_removal.swap_remove(idx);
}
drop(pending_removal);
self.modify_fds(|fds| {
if fds.fd_data.contains_key(&fd) {
return Err(io::Error::new(
io::ErrorKind::AlreadyExists,
"I/O source already registered this `Registry` \
(an old file descriptor might have been closed without deregistration)",
));
}
let poll_fds_index = fds.poll_fds.len();
let record = Arc::new(RegistrationRecord::new());
fds.fd_data.insert(
fd,
FdData {
poll_fds_index,
token,
shared_record: record.clone(),
},
);
fds.poll_fds.push(PollFd(libc::pollfd {
fd,
events: interests_to_poll(interests),
revents: 0,
}));
Ok(record)
})
}
pub fn reregister(&self, fd: RawFd, token: Token, interests: Interest) -> io::Result<()> {
self.modify_fds(|fds| {
let data = fds.fd_data.get_mut(&fd).ok_or(io::ErrorKind::NotFound)?;
data.token = token;
let poll_fds_index = data.poll_fds_index;
fds.poll_fds[poll_fds_index].0.events = interests_to_poll(interests);
Ok(())
})
}
pub fn deregister(&self, fd: RawFd) -> io::Result<()> {
self.deregister_all(&[fd])
.map_err(|_| io::ErrorKind::NotFound)?;
Ok(())
}
/// Perform a modification on `fds`, interrupting the current caller of `wait` if it's running.
fn modify_fds<T>(&self, f: impl FnOnce(&mut Fds) -> T) -> T {
self.waiting_operations.fetch_add(1, Ordering::SeqCst);
// Wake up the current caller of `wait` if there is one.
let sent_notification = self.notify_waker.wake().is_ok();
let mut fds = self.fds.lock().unwrap();
// If there was no caller of `wait` our notification was not removed from the pipe.
if sent_notification {
self.notify_waker.ack_and_reset();
}
let res = f(&mut *fds);
if self.waiting_operations.fetch_sub(1, Ordering::SeqCst) == 1 {
self.operations_complete.notify_one();
}
res
}
/// Special optimized version of [Self::deregister] which handles multiple removals
/// at once. Ok result if all removals were performed, Err if any entries
/// were not found.
fn deregister_all(&self, targets: &[RawFd]) -> Result<(), ()> {
if targets.is_empty() {
return Ok(());
}
let mut pending_removal = self.pending_removal.lock().unwrap();
pending_removal.extend(targets);
drop(pending_removal);
self.modify_fds(|fds| {
let mut all_successful = true;
for target in targets {
match fds.fd_data.remove(target).ok_or(()) {
Ok(data) => {
data.shared_record.mark_unregistered();
fds.poll_fds.swap_remove(data.poll_fds_index);
if let Some(swapped_pollfd) = fds.poll_fds.get(data.poll_fds_index) {
fds.fd_data
.get_mut(&swapped_pollfd.0.fd)
.unwrap()
.poll_fds_index = data.poll_fds_index;
}
}
Err(_) => all_successful = false,
}
}
if all_successful {
Ok(())
} else {
Err(())
}
})
}
pub fn wake(&self, token: Token) -> io::Result<()> {
self.pending_wake_token.lock().unwrap().replace(token);
self.notify_waker.wake()
}
}
/// Shared record between IoSourceState and SelectorState that allows us to internally
/// deregister partially or fully closed fds (i.e. when we get POLLHUP or PULLERR) without
/// confusing IoSourceState and trying to deregister twice. This isn't strictly
/// required as technically deregister is idempotent but it is confusing
/// when trying to debug behaviour as we get imbalanced calls to register/deregister and
/// superfluous NotFound errors.
#[derive(Debug)]
pub(crate) struct RegistrationRecord {
is_unregistered: AtomicBool,
}
impl RegistrationRecord {
pub fn new() -> Self {
Self {
is_unregistered: AtomicBool::new(false),
}
}
pub fn mark_unregistered(&self) {
self.is_unregistered.store(true, Ordering::Relaxed);
}
#[allow(dead_code)]
pub fn is_registered(&self) -> bool {
!self.is_unregistered.load(Ordering::Relaxed)
}
}
#[cfg(target_os = "linux")]
const POLLRDHUP: libc::c_short = libc::POLLRDHUP;
#[cfg(not(target_os = "linux"))]
const POLLRDHUP: libc::c_short = 0;
const READ_EVENTS: libc::c_short = libc::POLLIN | POLLRDHUP;
const WRITE_EVENTS: libc::c_short = libc::POLLOUT;
const PRIORITY_EVENTS: libc::c_short = libc::POLLPRI;
/// Get the input poll events for the given event.
fn interests_to_poll(interest: Interest) -> libc::c_short {
let mut kind = 0;
if interest.is_readable() {
kind |= READ_EVENTS;
}
if interest.is_writable() {
kind |= WRITE_EVENTS;
}
if interest.is_priority() {
kind |= PRIORITY_EVENTS;
}
kind
}
/// Helper function to call poll.
fn poll(fds: &mut [PollFd], timeout: Option<Duration>) -> io::Result<usize> {
loop {
// A bug in kernels < 2.6.37 makes timeouts larger than LONG_MAX / CONFIG_HZ
// (approx. 30 minutes with CONFIG_HZ=1200) effectively infinite on 32 bits
// architectures. The magic number is the same constant used by libuv.
#[cfg(target_pointer_width = "32")]
const MAX_SAFE_TIMEOUT: u128 = 1789569;
#[cfg(not(target_pointer_width = "32"))]
const MAX_SAFE_TIMEOUT: u128 = libc::c_int::MAX as u128;
let timeout = timeout
.map(|to| {
// `Duration::as_millis` truncates, so round up. This avoids
// turning sub-millisecond timeouts into a zero timeout, unless
// the caller explicitly requests that by specifying a zero
// timeout.
let to_ms = to
.checked_add(Duration::from_nanos(999_999))
.unwrap_or(to)
.as_millis();
cmp::min(MAX_SAFE_TIMEOUT, to_ms) as libc::c_int
})
.unwrap_or(-1);
let res = syscall!(poll(
fds.as_mut_ptr() as *mut libc::pollfd,
fds.len() as libc::nfds_t,
timeout,
));
match res {
Ok(num_events) => break Ok(num_events as usize),
// poll returns EAGAIN if we can retry it.
Err(e) if e.raw_os_error() == Some(libc::EAGAIN) => continue,
Err(e) => return Err(e),
}
}
}
#[derive(Debug, Clone)]
pub struct Event {
token: Token,
events: libc::c_short,
}
pub type Events = Vec<Event>;
pub mod event {
use std::fmt;
use crate::sys::Event;
use crate::Token;
use super::POLLRDHUP;
pub fn token(event: &Event) -> Token {
event.token
}
pub fn is_readable(event: &Event) -> bool {
(event.events & libc::POLLIN) != 0 || (event.events & libc::POLLPRI) != 0
}
pub fn is_writable(event: &Event) -> bool {
(event.events & libc::POLLOUT) != 0
}
pub fn is_error(event: &Event) -> bool {
(event.events & libc::POLLERR) != 0
}
pub fn is_read_closed(event: &Event) -> bool {
// Both halves of the socket have closed
(event.events & libc::POLLHUP) != 0
// Socket has received FIN or called shutdown(SHUT_RD)
|| (event.events & POLLRDHUP) != 0
}
pub fn is_write_closed(event: &Event) -> bool {
// Both halves of the socket have closed
(event.events & libc::POLLHUP) != 0
// Unix pipe write end has closed
|| ((event.events & libc::POLLOUT) != 0 && (event.events & libc::POLLERR) != 0)
// The other side (read end) of a Unix pipe has closed.
|| (event.events == libc::POLLERR)
}
pub fn is_priority(event: &Event) -> bool {
(event.events & libc::POLLPRI) != 0
}
pub fn is_aio(_: &Event) -> bool {
// Not supported in the kernel, only in libc.
false
}
pub fn is_lio(_: &Event) -> bool {
// Not supported.
false
}
pub fn debug_details(f: &mut fmt::Formatter<'_>, event: &Event) -> fmt::Result {
#[allow(clippy::trivially_copy_pass_by_ref)]
fn check_events(got: &libc::c_short, want: &libc::c_short) -> bool {
(*got & want) != 0
}
debug_detail!(
EventsDetails(libc::c_short),
check_events,
libc::POLLIN,
libc::POLLPRI,
libc::POLLOUT,
libc::POLLRDNORM,
libc::POLLRDBAND,
libc::POLLWRNORM,
libc::POLLWRBAND,
libc::POLLERR,
libc::POLLHUP,
);
f.debug_struct("poll_event")
.field("token", &event.token)
.field("events", &EventsDetails(event.events))
.finish()
}
}
#[derive(Debug)]
pub(crate) struct Waker {
selector: Selector,
token: Token,
}
impl Waker {
pub(crate) fn new(selector: &Selector, token: Token) -> io::Result<Waker> {
Ok(Waker {
selector: selector.try_clone()?,
token,
})
}
pub(crate) fn wake(&self) -> io::Result<()> {
self.selector.wake(self.token)
}
}
cfg_io_source! {
use crate::Registry;
struct InternalState {
selector: Selector,
token: Token,
interests: Interest,
fd: RawFd,
shared_record: Arc<RegistrationRecord>,
}
impl Drop for InternalState {
fn drop(&mut self) {
if self.shared_record.is_registered() {
let _ = self.selector.deregister(self.fd);
}
}
}
pub(crate) struct IoSourceState {
inner: Option<Box<InternalState>>,
}
impl IoSourceState {
pub fn new() -> IoSourceState {
IoSourceState { inner: None }
}
pub fn do_io<T, F, R>(&self, f: F, io: &T) -> io::Result<R>
where
F: FnOnce(&T) -> io::Result<R>,
{
let result = f(io);
if let Err(err) = &result {
if err.kind() == io::ErrorKind::WouldBlock {
self.inner.as_ref().map_or(Ok(()), |state| {
state
.selector
.reregister(state.fd, state.token, state.interests)
})?;
}
}
result
}
pub fn register(
&mut self,
registry: &Registry,
token: Token,
interests: Interest,
fd: RawFd,
) -> io::Result<()> {
if self.inner.is_some() {
Err(io::ErrorKind::AlreadyExists.into())
} else {
let selector = registry.selector().try_clone()?;
selector.register_internal(fd, token, interests).map(move |shared_record| {
let state = InternalState {
selector,
token,
interests,
fd,
shared_record,
};
self.inner = Some(Box::new(state));
})
}
}
pub fn reregister(
&mut self,
registry: &Registry,
token: Token,
interests: Interest,
fd: RawFd,
) -> io::Result<()> {
match self.inner.as_mut() {
Some(state) => registry
.selector()
.reregister(fd, token, interests)
.map(|()| {
state.token = token;
state.interests = interests;
}),
None => Err(io::ErrorKind::NotFound.into()),
}
}
pub fn deregister(&mut self, registry: &Registry, fd: RawFd) -> io::Result<()> {
if let Some(state) = self.inner.take() {
// Marking unregistered will short circuit the drop behaviour of calling
// deregister so the call to deregister below is strictly required.
state.shared_record.mark_unregistered();
}
registry.selector().deregister(fd)
}
}
}