1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
//! 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::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::pin::Pin;
use std::sync::atomic::{AtomicBool, Ordering};
use std::sync::Once;
use std::task::{Context, Poll};

pub(crate) mod driver;
use self::driver::Handle;

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,
    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.
    // See https://github.com/tokio-rs/tokio/issues/3767 for more.
    pub 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 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 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 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 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 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 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 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 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 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 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 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 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 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: Pin<&'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",
        ))
    }
}

/// A stream of events for receiving a particular type of OS signal.
///
/// 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 stream 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 stream = signal(SignalKind::hangup())?;
///
///     // Print whenever a HUP signal is received
///     loop {
///         stream.recv().await;
///         println!("got signal HUP");
///     }
/// }
/// ```
#[must_use = "streams do nothing unless polled"]
#[derive(Debug)]
pub struct Signal {
    inner: RxFuture,
}

/// Creates a new stream 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)
pub fn signal(kind: SignalKind) -> io::Result<Signal> {
    let rx = signal_with_handle(kind, &Handle::current())?;

    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 _);
    }
}