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//! Unix-specific types for signal handling.
//!
//! This module is only defined on Unix platforms and contains the primary
//! `Signal` type for receiving notifications of signals.
#![cfg(unix)]
#![cfg_attr(docsrs, doc(cfg(all(unix, feature = "signal"))))]
use crate::runtime::scheduler;
use crate::runtime::signal::Handle;
use crate::signal::registry::{globals, EventId, EventInfo, Globals, Init, Storage};
use crate::signal::RxFuture;
use crate::sync::watch;
use mio::net::UnixStream;
use std::io::{self, Error, ErrorKind, Write};
use std::sync::atomic::{AtomicBool, Ordering};
use std::sync::Once;
use std::task::{Context, Poll};
pub(crate) type OsStorage = Vec<SignalInfo>;
impl Init for OsStorage {
fn init() -> Self {
// There are reliable signals ranging from 1 to 33 available on every Unix platform.
#[cfg(not(target_os = "linux"))]
let possible = 0..=33;
// On Linux, there are additional real-time signals available.
#[cfg(target_os = "linux")]
let possible = 0..=libc::SIGRTMAX();
possible.map(|_| SignalInfo::default()).collect()
}
}
impl Storage for OsStorage {
fn event_info(&self, id: EventId) -> Option<&EventInfo> {
self.get(id).map(|si| &si.event_info)
}
fn for_each<'a, F>(&'a self, f: F)
where
F: FnMut(&'a EventInfo),
{
self.iter().map(|si| &si.event_info).for_each(f)
}
}
#[derive(Debug)]
pub(crate) struct OsExtraData {
sender: UnixStream,
pub(crate) receiver: UnixStream,
}
impl Init for OsExtraData {
fn init() -> Self {
let (receiver, sender) = UnixStream::pair().expect("failed to create UnixStream");
Self { sender, receiver }
}
}
/// Represents the specific kind of signal to listen for.
#[derive(Debug, Clone, Copy, Hash, PartialEq, Eq)]
pub struct SignalKind(libc::c_int);
impl SignalKind {
/// Allows for listening to any valid OS signal.
///
/// For example, this can be used for listening for platform-specific
/// signals.
/// ```rust,no_run
/// # use tokio::signal::unix::SignalKind;
/// # let signum = -1;
/// // let signum = libc::OS_SPECIFIC_SIGNAL;
/// let kind = SignalKind::from_raw(signum);
/// ```
// Use `std::os::raw::c_int` on public API to prevent leaking a non-stable
// type alias from libc.
// `libc::c_int` and `std::os::raw::c_int` are currently the same type, and are
// unlikely to change to other types, but technically libc can change this
// in the future minor version.
pub const fn from_raw(signum: std::os::raw::c_int) -> Self {
Self(signum as libc::c_int)
}
/// Get the signal's numeric value.
///
/// ```rust
/// # use tokio::signal::unix::SignalKind;
/// let kind = SignalKind::interrupt();
/// assert_eq!(kind.as_raw_value(), libc::SIGINT);
/// ```
pub const fn as_raw_value(&self) -> std::os::raw::c_int {
self.0
}
/// Represents the SIGALRM signal.
///
/// On Unix systems this signal is sent when a real-time timer has expired.
/// By default, the process is terminated by this signal.
pub const fn alarm() -> Self {
Self(libc::SIGALRM)
}
/// Represents the SIGCHLD signal.
///
/// On Unix systems this signal is sent when the status of a child process
/// has changed. By default, this signal is ignored.
pub const fn child() -> Self {
Self(libc::SIGCHLD)
}
/// Represents the SIGHUP signal.
///
/// On Unix systems this signal is sent when the terminal is disconnected.
/// By default, the process is terminated by this signal.
pub const fn hangup() -> Self {
Self(libc::SIGHUP)
}
/// Represents the SIGINFO signal.
///
/// On Unix systems this signal is sent to request a status update from the
/// process. By default, this signal is ignored.
#[cfg(any(
target_os = "dragonfly",
target_os = "freebsd",
target_os = "macos",
target_os = "netbsd",
target_os = "openbsd"
))]
pub const fn info() -> Self {
Self(libc::SIGINFO)
}
/// Represents the SIGINT signal.
///
/// On Unix systems this signal is sent to interrupt a program.
/// By default, the process is terminated by this signal.
pub const fn interrupt() -> Self {
Self(libc::SIGINT)
}
/// Represents the SIGIO signal.
///
/// On Unix systems this signal is sent when I/O operations are possible
/// on some file descriptor. By default, this signal is ignored.
pub const fn io() -> Self {
Self(libc::SIGIO)
}
/// Represents the SIGPIPE signal.
///
/// On Unix systems this signal is sent when the process attempts to write
/// to a pipe which has no reader. By default, the process is terminated by
/// this signal.
pub const fn pipe() -> Self {
Self(libc::SIGPIPE)
}
/// Represents the SIGQUIT signal.
///
/// On Unix systems this signal is sent to issue a shutdown of the
/// process, after which the OS will dump the process core.
/// By default, the process is terminated by this signal.
pub const fn quit() -> Self {
Self(libc::SIGQUIT)
}
/// Represents the SIGTERM signal.
///
/// On Unix systems this signal is sent to issue a shutdown of the
/// process. By default, the process is terminated by this signal.
pub const fn terminate() -> Self {
Self(libc::SIGTERM)
}
/// Represents the SIGUSR1 signal.
///
/// On Unix systems this is a user defined signal.
/// By default, the process is terminated by this signal.
pub const fn user_defined1() -> Self {
Self(libc::SIGUSR1)
}
/// Represents the SIGUSR2 signal.
///
/// On Unix systems this is a user defined signal.
/// By default, the process is terminated by this signal.
pub const fn user_defined2() -> Self {
Self(libc::SIGUSR2)
}
/// Represents the SIGWINCH signal.
///
/// On Unix systems this signal is sent when the terminal window is resized.
/// By default, this signal is ignored.
pub const fn window_change() -> Self {
Self(libc::SIGWINCH)
}
}
impl From<std::os::raw::c_int> for SignalKind {
fn from(signum: std::os::raw::c_int) -> Self {
Self::from_raw(signum as libc::c_int)
}
}
impl From<SignalKind> for std::os::raw::c_int {
fn from(kind: SignalKind) -> Self {
kind.as_raw_value()
}
}
pub(crate) struct SignalInfo {
event_info: EventInfo,
init: Once,
initialized: AtomicBool,
}
impl Default for SignalInfo {
fn default() -> SignalInfo {
SignalInfo {
event_info: Default::default(),
init: Once::new(),
initialized: AtomicBool::new(false),
}
}
}
/// Our global signal handler for all signals registered by this module.
///
/// The purpose of this signal handler is to primarily:
///
/// 1. Flag that our specific signal was received (e.g. store an atomic flag)
/// 2. Wake up the driver by writing a byte to a pipe
///
/// Those two operations should both be async-signal safe.
fn action(globals: &'static Globals, signal: libc::c_int) {
globals.record_event(signal as EventId);
// Send a wakeup, ignore any errors (anything reasonably possible is
// full pipe and then it will wake up anyway).
let mut sender = &globals.sender;
drop(sender.write(&[1]));
}
/// Enables this module to receive signal notifications for the `signal`
/// provided.
///
/// This will register the signal handler if it hasn't already been registered,
/// returning any error along the way if that fails.
fn signal_enable(signal: SignalKind, handle: &Handle) -> io::Result<()> {
let signal = signal.0;
if signal < 0 || signal_hook_registry::FORBIDDEN.contains(&signal) {
return Err(Error::new(
ErrorKind::Other,
format!("Refusing to register signal {}", signal),
));
}
// Check that we have a signal driver running
handle.check_inner()?;
let globals = globals();
let siginfo = match globals.storage().get(signal as EventId) {
Some(slot) => slot,
None => return Err(io::Error::new(io::ErrorKind::Other, "signal too large")),
};
let mut registered = Ok(());
siginfo.init.call_once(|| {
registered = unsafe {
signal_hook_registry::register(signal, move || action(globals, signal)).map(|_| ())
};
if registered.is_ok() {
siginfo.initialized.store(true, Ordering::Relaxed);
}
});
registered?;
// If the call_once failed, it won't be retried on the next attempt to register the signal. In
// such case it is not run, registered is still `Ok(())`, initialized is still `false`.
if siginfo.initialized.load(Ordering::Relaxed) {
Ok(())
} else {
Err(Error::new(
ErrorKind::Other,
"Failed to register signal handler",
))
}
}
/// An listener for receiving a particular type of OS signal.
///
/// The listener can be turned into a `Stream` using [`SignalStream`].
///
/// [`SignalStream`]: https://docs.rs/tokio-stream/latest/tokio_stream/wrappers/struct.SignalStream.html
///
/// In general signal handling on Unix is a pretty tricky topic, and this
/// structure is no exception! There are some important limitations to keep in
/// mind when using `Signal` streams:
///
/// * Signals handling in Unix already necessitates coalescing signals
/// together sometimes. This `Signal` stream is also no exception here in
/// that it will also coalesce signals. That is, even if the signal handler
/// for this process runs multiple times, the `Signal` stream may only return
/// one signal notification. Specifically, before `poll` is called, all
/// signal notifications are coalesced into one item returned from `poll`.
/// Once `poll` has been called, however, a further signal is guaranteed to
/// be yielded as an item.
///
/// Put another way, any element pulled off the returned listener corresponds to
/// *at least one* signal, but possibly more.
///
/// * Signal handling in general is relatively inefficient. Although some
/// improvements are possible in this crate, it's recommended to not plan on
/// having millions of signal channels open.
///
/// If you've got any questions about this feel free to open an issue on the
/// repo! New approaches to alleviate some of these limitations are always
/// appreciated!
///
/// # Caveats
///
/// The first time that a `Signal` instance is registered for a particular
/// signal kind, an OS signal-handler is installed which replaces the default
/// platform behavior when that signal is received, **for the duration of the
/// entire process**.
///
/// For example, Unix systems will terminate a process by default when it
/// receives SIGINT. But, when a `Signal` instance is created to listen for
/// this signal, the next SIGINT that arrives will be translated to a stream
/// event, and the process will continue to execute. **Even if this `Signal`
/// instance is dropped, subsequent SIGINT deliveries will end up captured by
/// Tokio, and the default platform behavior will NOT be reset**.
///
/// Thus, applications should take care to ensure the expected signal behavior
/// occurs as expected after listening for specific signals.
///
/// # Examples
///
/// Wait for SIGHUP
///
/// ```rust,no_run
/// use tokio::signal::unix::{signal, SignalKind};
///
/// #[tokio::main]
/// async fn main() -> Result<(), Box<dyn std::error::Error>> {
/// // An infinite stream of hangup signals.
/// let mut sig = signal(SignalKind::hangup())?;
///
/// // Print whenever a HUP signal is received
/// loop {
/// sig.recv().await;
/// println!("got signal HUP");
/// }
/// }
/// ```
#[must_use = "streams do nothing unless polled"]
#[derive(Debug)]
pub struct Signal {
inner: RxFuture,
}
/// Creates a new listener which will receive notifications when the current
/// process receives the specified signal `kind`.
///
/// This function will create a new stream which binds to the default reactor.
/// The `Signal` stream is an infinite stream which will receive
/// notifications whenever a signal is received. More documentation can be
/// found on `Signal` itself, but to reiterate:
///
/// * Signals may be coalesced beyond what the kernel already does.
/// * Once a signal handler is registered with the process the underlying
/// libc signal handler is never unregistered.
///
/// A `Signal` stream can be created for a particular signal number
/// multiple times. When a signal is received then all the associated
/// channels will receive the signal notification.
///
/// # Errors
///
/// * If the lower-level C functions fail for some reason.
/// * If the previous initialization of this specific signal failed.
/// * If the signal is one of
/// [`signal_hook::FORBIDDEN`](fn@signal_hook_registry::register#panics)
///
/// # Panics
///
/// This function panics if there is no current reactor set, or if the `rt`
/// feature flag is not enabled.
#[track_caller]
pub fn signal(kind: SignalKind) -> io::Result<Signal> {
let handle = scheduler::Handle::current();
let rx = signal_with_handle(kind, handle.driver().signal())?;
Ok(Signal {
inner: RxFuture::new(rx),
})
}
pub(crate) fn signal_with_handle(
kind: SignalKind,
handle: &Handle,
) -> io::Result<watch::Receiver<()>> {
// Turn the signal delivery on once we are ready for it
signal_enable(kind, handle)?;
Ok(globals().register_listener(kind.0 as EventId))
}
impl Signal {
/// Receives the next signal notification event.
///
/// `None` is returned if no more events can be received by this stream.
///
/// # Cancel safety
///
/// This method is cancel safe. If you use it as the event in a
/// [`tokio::select!`](crate::select) statement and some other branch
/// completes first, then it is guaranteed that no signal is lost.
///
/// # Examples
///
/// Wait for SIGHUP
///
/// ```rust,no_run
/// use tokio::signal::unix::{signal, SignalKind};
///
/// #[tokio::main]
/// async fn main() -> Result<(), Box<dyn std::error::Error>> {
/// // An infinite stream of hangup signals.
/// let mut stream = signal(SignalKind::hangup())?;
///
/// // Print whenever a HUP signal is received
/// loop {
/// stream.recv().await;
/// println!("got signal HUP");
/// }
/// }
/// ```
pub async fn recv(&mut self) -> Option<()> {
self.inner.recv().await
}
/// Polls to receive the next signal notification event, outside of an
/// `async` context.
///
/// This method returns:
///
/// * `Poll::Pending` if no signals are available but the channel is not
/// closed.
/// * `Poll::Ready(Some(()))` if a signal is available.
/// * `Poll::Ready(None)` if the channel has been closed and all signals
/// sent before it was closed have been received.
///
/// # Examples
///
/// Polling from a manually implemented future
///
/// ```rust,no_run
/// use std::pin::Pin;
/// use std::future::Future;
/// use std::task::{Context, Poll};
/// use tokio::signal::unix::Signal;
///
/// struct MyFuture {
/// signal: Signal,
/// }
///
/// impl Future for MyFuture {
/// type Output = Option<()>;
///
/// fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
/// println!("polling MyFuture");
/// self.signal.poll_recv(cx)
/// }
/// }
/// ```
pub fn poll_recv(&mut self, cx: &mut Context<'_>) -> Poll<Option<()>> {
self.inner.poll_recv(cx)
}
}
// Work around for abstracting streams internally
pub(crate) trait InternalStream {
fn poll_recv(&mut self, cx: &mut Context<'_>) -> Poll<Option<()>>;
}
impl InternalStream for Signal {
fn poll_recv(&mut self, cx: &mut Context<'_>) -> Poll<Option<()>> {
self.poll_recv(cx)
}
}
pub(crate) fn ctrl_c() -> io::Result<Signal> {
signal(SignalKind::interrupt())
}
#[cfg(all(test, not(loom)))]
mod tests {
use super::*;
#[test]
fn signal_enable_error_on_invalid_input() {
signal_enable(SignalKind::from_raw(-1), &Handle::default()).unwrap_err();
}
#[test]
fn signal_enable_error_on_forbidden_input() {
signal_enable(
SignalKind::from_raw(signal_hook_registry::FORBIDDEN[0]),
&Handle::default(),
)
.unwrap_err();
}
#[test]
fn from_c_int() {
assert_eq!(SignalKind::from(2), SignalKind::interrupt());
}
#[test]
fn into_c_int() {
let value: std::os::raw::c_int = SignalKind::interrupt().into();
assert_eq!(value, libc::SIGINT as _);
}
}