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//! A backend module for implementing the iterator like
//! [`iterator`][crate::iterator] module and the asynchronous
//! adapter crates.
//!
//! This module contains generic types which abstract over the concrete
//! IO type for the self-pipe. The motivation for having this abstraction
//! are the adapter crates for different asynchronous runtimes. The runtimes
//! provide their own wrappers for [`std::os::unix::net::UnixStream`]
//! which should be used as the internal self pipe. But large parts of the
//! remaining functionality doesn't depend directly onto the IO type and can
//! be reused.
//!
//! See also the [`SignalDelivery::with_pipe`] method for more information
//! about requirements the IO types have to fulfill.
//!
//! As a regular user you shouldn't need to use the types in this module.
//! Use the [`Signals`][crate::iterator::Signals] struct or one of the types
//! contained in the adapter libraries instead.
use std::borrow::{Borrow, BorrowMut};
use std::fmt::{Debug, Formatter, Result as FmtResult};
use std::io::Error;
use std::mem::MaybeUninit;
use std::os::unix::io::AsRawFd;
use std::ptr;
use std::sync::atomic::{AtomicBool, Ordering};
use std::sync::{Arc, Mutex};
use libc::{self, c_int};
use super::exfiltrator::Exfiltrator;
use crate::low_level::pipe::{self, WakeMethod};
use crate::SigId;
/// Maximal signal number we support.
const MAX_SIGNUM: usize = 128;
trait SelfPipeWrite: Debug + Send + Sync {
fn wake_readers(&self);
}
impl<W: AsRawFd + Debug + Send + Sync> SelfPipeWrite for W {
fn wake_readers(&self) {
pipe::wake(self.as_raw_fd(), WakeMethod::Send);
}
}
#[derive(Debug)]
struct DeliveryState {
closed: AtomicBool,
registered_signal_ids: Mutex<Vec<Option<SigId>>>,
}
impl DeliveryState {
fn new() -> Self {
let ids = (0..MAX_SIGNUM).map(|_| None).collect();
Self {
closed: AtomicBool::new(false),
registered_signal_ids: Mutex::new(ids),
}
}
}
impl Drop for DeliveryState {
fn drop(&mut self) {
let lock = self.registered_signal_ids.lock().unwrap();
for id in lock.iter().filter_map(|s| *s) {
crate::low_level::unregister(id);
}
}
}
struct PendingSignals<E: Exfiltrator> {
exfiltrator: E,
slots: [E::Storage; MAX_SIGNUM],
}
impl<E: Exfiltrator> PendingSignals<E> {
fn new(exfiltrator: E) -> Self {
// Unfortunately, Default is not implemented for long arrays :-(
//
// Note that if the default impl panics, the already existing instances are leaked.
let mut slots = MaybeUninit::<[E::Storage; MAX_SIGNUM]>::uninit();
for i in 0..MAX_SIGNUM {
unsafe {
let slot: *mut E::Storage = slots.as_mut_ptr() as *mut _;
let slot = slot.add(i);
ptr::write(slot, E::Storage::default());
}
}
Self {
exfiltrator,
slots: unsafe { slots.assume_init() },
}
}
}
/// An internal trait to hide adding new signals into a Handle behind a dynamic dispatch.
trait AddSignal: Debug + Send + Sync {
fn add_signal(
self: Arc<Self>,
write: Arc<dyn SelfPipeWrite>,
signal: c_int,
) -> Result<SigId, Error>;
}
// Implemented manually because 1.36.0 doesn't yet support Debug for [X; BIG_NUMBER].
impl<E: Exfiltrator> Debug for PendingSignals<E> {
fn fmt(&self, fmt: &mut Formatter) -> FmtResult {
fmt.debug_struct("PendingSignals")
.field("exfiltrator", &self.exfiltrator)
// While the array does not, the slice does implement Debug
.field("slots", &&self.slots[..])
.finish()
}
}
impl<E: Exfiltrator> AddSignal for PendingSignals<E> {
fn add_signal(
self: Arc<Self>,
write: Arc<dyn SelfPipeWrite>,
signal: c_int,
) -> Result<SigId, Error> {
assert!(signal >= 0);
assert!(
(signal as usize) < MAX_SIGNUM,
"Signal number {} too large. If your OS really supports such signal, file a bug",
signal,
);
assert!(
self.exfiltrator.supports_signal(signal),
"Signal {} not supported by exfiltrator {:?}",
signal,
self.exfiltrator,
);
self.exfiltrator.init(&self.slots[signal as usize], signal);
let action = move |act: &_| {
let slot = &self.slots[signal as usize];
let ex = &self.exfiltrator;
ex.store(slot, signal, act);
write.wake_readers();
};
let id = unsafe { signal_hook_registry::register_sigaction(signal, action) }?;
Ok(id)
}
}
/// A struct to control an instance of an associated type
/// (like for example [`Signals`][super::Signals]).
///
/// It allows to register more signal handlers and to shutdown the signal
/// delivery. You can [`clone`][Handle::clone] this type which isn't a
/// very expensive operation. The cloned instances can be shared between
/// multiple threads.
#[derive(Debug, Clone)]
pub struct Handle {
pending: Arc<dyn AddSignal>,
write: Arc<dyn SelfPipeWrite>,
delivery_state: Arc<DeliveryState>,
}
impl Handle {
fn new<W>(write: W, pending: Arc<dyn AddSignal>) -> Self
where
W: 'static + SelfPipeWrite,
{
Self {
pending,
write: Arc::new(write),
delivery_state: Arc::new(DeliveryState::new()),
}
}
/// Registers another signal to the set watched by the associated instance.
///
/// # Notes
///
/// * This is safe to call concurrently from whatever thread.
/// * This is *not* safe to call from within a signal handler.
/// * If the signal number was already registered previously, this is a no-op.
/// * If this errors, the original set of signals is left intact.
///
/// # Panics
///
/// * If the given signal is [forbidden][crate::FORBIDDEN].
/// * If the signal number is negative or larger than internal limit. The limit should be
/// larger than any supported signal the OS supports.
/// * If the relevant [`Exfiltrator`] does not support this particular signal. The default
/// [`SignalOnly`] one supports all signals.
pub fn add_signal(&self, signal: c_int) -> Result<(), Error> {
let mut lock = self.delivery_state.registered_signal_ids.lock().unwrap();
// Already registered, ignoring
if lock[signal as usize].is_some() {
return Ok(());
}
let id = Arc::clone(&self.pending).add_signal(Arc::clone(&self.write), signal)?;
lock[signal as usize] = Some(id);
Ok(())
}
/// Closes the associated instance.
///
/// This is meant to signalize termination of the signal delivery process.
/// After calling close:
///
/// * [`is_closed`][Handle::is_closed] will return true.
/// * All currently blocking operations of associated instances
/// are interrupted and terminate.
/// * Any further operations will not block.
/// * Further signals may or may not be returned from the iterators. However, if any are
/// returned, these are real signals that happened.
///
/// The goal is to be able to shut down any background thread that handles only the signals.
pub fn close(&self) {
self.delivery_state.closed.store(true, Ordering::SeqCst);
self.write.wake_readers();
}
/// Is it closed?
///
/// See [`close`][Handle::close].
pub fn is_closed(&self) -> bool {
self.delivery_state.closed.load(Ordering::SeqCst)
}
}
/// A struct for delivering received signals to the main program flow.
/// The self-pipe IO type is generic. See the
/// [`with_pipe`][SignalDelivery::with_pipe] method for requirements
/// for the IO type.
#[derive(Debug)]
pub struct SignalDelivery<R, E: Exfiltrator> {
read: R,
handle: Handle,
pending: Arc<PendingSignals<E>>,
}
impl<R, E: Exfiltrator> SignalDelivery<R, E>
where
R: 'static + AsRawFd + Send + Sync,
{
/// Creates the `SignalDelivery` structure.
///
/// The read and write arguments must be the ends of a suitable pipe type. These are used
/// for communication between the signal handler and main program flow.
///
/// Registers all the signals listed. The same restrictions (panics, errors) apply as with
/// [`add_signal`][Handle::add_signal].
///
/// # Requirements for the pipe type
///
/// * Must support [`send`](https://man7.org/linux/man-pages/man2/send.2.html) for
/// asynchronously writing bytes to the write end
/// * Must support [`recv`](https://man7.org/linux/man-pages/man2/recv.2.html) for
/// reading bytes from the read end
///
/// So UnixStream is a good choice for this.
pub fn with_pipe<I, S, W>(read: R, write: W, exfiltrator: E, signals: I) -> Result<Self, Error>
where
I: IntoIterator<Item = S>,
S: Borrow<c_int>,
W: 'static + AsRawFd + Debug + Send + Sync,
{
let pending = Arc::new(PendingSignals::new(exfiltrator));
let pending_add_signal = Arc::clone(&pending);
let handle = Handle::new(write, pending_add_signal);
let me = Self {
read,
handle,
pending,
};
for sig in signals {
me.handle.add_signal(*sig.borrow())?;
}
Ok(me)
}
/// Get a reference to the read end of the self pipe
///
/// You may use this method to register the underlying file descriptor
/// with an eventing system (e. g. epoll) to get notified if there are
/// bytes in the pipe. If the event system reports the file descriptor
/// ready for reading you can then call [`pending`][SignalDelivery::pending]
/// to get the arrived signals.
pub fn get_read(&self) -> &R {
&self.read
}
/// Get a mutable reference to the read end of the self pipe
///
/// See the [`get_read`][SignalDelivery::get_read] method for some additional
/// information.
pub fn get_read_mut(&mut self) -> &mut R {
&mut self.read
}
/// Drains all data from the internal self-pipe. This method will never block.
fn flush(&mut self) {
const SIZE: usize = 1024;
let mut buff = [0u8; SIZE];
unsafe {
// Draining the data in the self pipe. We ignore all errors on purpose. This
// should not be something like closed file descriptor. It could EAGAIN, but
// that's OK in case we say MSG_DONTWAIT. If it's EINTR, then it's OK too,
// it'll only create a spurious wakeup.
while libc::recv(
self.read.as_raw_fd(),
buff.as_mut_ptr() as *mut libc::c_void,
SIZE,
libc::MSG_DONTWAIT,
) > 0
{}
}
}
/// Returns an iterator of already received signals.
///
/// This returns an iterator over all the signal numbers of the signals received since last
/// time they were read (out of the set registered by this `SignalDelivery` instance). Note
/// that they are returned in arbitrary order and a signal number is returned only once even
/// if it was received multiple times.
///
/// This method returns immediately (does not block) and may produce an empty iterator if
/// there are no signals ready.
pub fn pending(&mut self) -> Pending<E> {
self.flush();
Pending::new(Arc::clone(&self.pending))
}
/// Checks the reading end of the self pipe for available signals.
///
/// If there are no signals available or this instance was already closed it returns
/// [`Option::None`]. If there are some signals it returns a [`Pending`]
/// instance wrapped inside a [`Option::Some`]. However, due to implementation details,
/// this still can produce an empty iterator.
///
/// This method doesn't check the reading end by itself but uses the passed in callback.
/// This method blocks if and only if the callback blocks trying to read some bytes.
pub fn poll_pending<F>(&mut self, has_signals: &mut F) -> Result<Option<Pending<E>>, Error>
where
F: FnMut(&mut R) -> Result<bool, Error>,
{
if self.handle.is_closed() {
return Ok(None);
}
match has_signals(self.get_read_mut()) {
Ok(false) => Ok(None),
Ok(true) => Ok(Some(self.pending())),
Err(err) => Err(err),
}
}
/// Get a [`Handle`] for this `SignalDelivery` instance.
///
/// This can be used to add further signals or close the whole
/// signal delivery mechanism.
pub fn handle(&self) -> Handle {
self.handle.clone()
}
}
/// The iterator of one batch of signals.
///
/// This is returned by the [`pending`][SignalDelivery::pending] method.
#[derive(Debug)]
pub struct Pending<E: Exfiltrator> {
pending: Arc<PendingSignals<E>>,
position: usize,
}
impl<E: Exfiltrator> Pending<E> {
fn new(pending: Arc<PendingSignals<E>>) -> Self {
Self {
pending,
position: 0,
}
}
}
impl<E: Exfiltrator> Iterator for Pending<E> {
type Item = E::Output;
fn next(&mut self) -> Option<E::Output> {
while self.position < self.pending.slots.len() {
let sig = self.position;
let slot = &self.pending.slots[sig];
let result = self.pending.exfiltrator.load(slot, sig as c_int);
if result.is_some() {
return result;
} else {
self.position += 1;
}
}
None
}
}
/// Possible results of the [`poll_signal`][SignalIterator::poll_signal] function.
pub enum PollResult<O> {
/// A signal arrived
Signal(O),
/// There are no signals yet but there may arrive some in the future
Pending,
/// The iterator was closed. There won't be any signals reported from now on.
Closed,
/// An error happened during polling for arrived signals.
Err(Error),
}
/// An infinite iterator of received signals.
pub struct SignalIterator<SD, E: Exfiltrator> {
signals: SD,
iter: Pending<E>,
}
impl<SD, E: Exfiltrator> SignalIterator<SD, E> {
/// Create a new infinite iterator for signals registered with the passed
/// in [`SignalDelivery`] instance.
pub fn new<R>(mut signals: SD) -> Self
where
SD: BorrowMut<SignalDelivery<R, E>>,
R: 'static + AsRawFd + Send + Sync,
{
let iter = signals.borrow_mut().pending();
Self { signals, iter }
}
/// Return a signal if there is one or tell the caller that there is none at the moment.
///
/// You have to pass in a callback which checks the underlying reading end of the pipe if
/// there may be any pending signals. This callback may or may not block. If the callback
/// returns [`true`] this method will try to fetch the next signal and return it as a
/// [`PollResult::Signal`]. If the callback returns [`false`] the method will return
/// [`PollResult::Pending`] and assume it will be called again at a later point in time.
/// The callback may be called any number of times by this function.
///
/// If the iterator was closed by the [`close`][Handle::close] method of the associtated
/// [`Handle`] this method will return [`PollResult::Closed`].
pub fn poll_signal<R, F>(&mut self, has_signals: &mut F) -> PollResult<E::Output>
where
SD: BorrowMut<SignalDelivery<R, E>>,
R: 'static + AsRawFd + Send + Sync,
F: FnMut(&mut R) -> Result<bool, Error>,
{
// The loop is necessary because it is possible that a signal was already consumed
// by a previous pending iterator due to the asynchronous nature of signals and
// always moving to the end of the iterator before calling has_more.
while !self.signals.borrow_mut().handle.is_closed() {
if let Some(result) = self.iter.next() {
return PollResult::Signal(result);
}
match self.signals.borrow_mut().poll_pending(has_signals) {
Ok(Some(pending)) => self.iter = pending,
Ok(None) => return PollResult::Pending,
Err(err) => return PollResult::Err(err),
}
}
PollResult::Closed
}
/// Get a shareable [`Handle`] for this instance.
///
/// This can be used to add further signals or terminate the whole
/// signal iteration using the [`close`][Handle::close] method.
pub fn handle<R>(&self) -> Handle
where
SD: Borrow<SignalDelivery<R, E>>,
R: 'static + AsRawFd + Send + Sync,
{
self.signals.borrow().handle()
}
}
/// A signal iterator which consumes a [`SignalDelivery`] instance and takes
/// ownership of it.
pub type OwningSignalIterator<R, E> = SignalIterator<SignalDelivery<R, E>, E>;
/// A signal iterator which takes a mutable reference to a [`SignalDelivery`]
/// instance.
pub type RefSignalIterator<'a, R, E> = SignalIterator<&'a mut SignalDelivery<R, E>, E>;