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//! Timer API via signals.
//!
//! Timer is a POSIX API to create timers and get expiration notifications
//! through queued Unix signals, for the current process. This is similar to
//! Linux's timerfd mechanism, except that API is specific to Linux and makes
//! use of file polling.
//!
//! For more documentation, please read [timer_create](https://pubs.opengroup.org/onlinepubs/9699919799/functions/timer_create.html).
//!
//! # Examples
//!
//! Create an interval timer that signals SIGALARM every 250 milliseconds.
//!
//! ```no_run
//! use nix::sys::signal::{self, SigEvent, SigHandler, SigevNotify, Signal};
//! use nix::sys::timer::{Expiration, Timer, TimerSetTimeFlags};
//! use nix::time::ClockId;
//! use std::convert::TryFrom;
//! use std::sync::atomic::{AtomicU64, Ordering};
//! use std::thread::yield_now;
//! use std::time::Duration;
//!
//! const SIG: Signal = Signal::SIGALRM;
//! static ALARMS: AtomicU64 = AtomicU64::new(0);
//!
//! extern "C" fn handle_alarm(signal: libc::c_int) {
//! let signal = Signal::try_from(signal).unwrap();
//! if signal == SIG {
//! ALARMS.fetch_add(1, Ordering::Relaxed);
//! }
//! }
//!
//! fn main() {
//! let clockid = ClockId::CLOCK_MONOTONIC;
//! let sigevent = SigEvent::new(SigevNotify::SigevSignal {
//! signal: SIG,
//! si_value: 0,
//! });
//!
//! let mut timer = Timer::new(clockid, sigevent).unwrap();
//! let expiration = Expiration::Interval(Duration::from_millis(250).into());
//! let flags = TimerSetTimeFlags::empty();
//! timer.set(expiration, flags).expect("could not set timer");
//!
//! let handler = SigHandler::Handler(handle_alarm);
//! unsafe { signal::signal(SIG, handler) }.unwrap();
//!
//! loop {
//! let alarms = ALARMS.load(Ordering::Relaxed);
//! if alarms >= 10 {
//! println!("total alarms handled: {}", alarms);
//! break;
//! }
//! yield_now()
//! }
//! }
//! ```
use crate::sys::signal::SigEvent;
use crate::sys::time::timer::TimerSpec;
pub use crate::sys::time::timer::{Expiration, TimerSetTimeFlags};
use crate::time::ClockId;
use crate::{errno::Errno, Result};
use core::mem;
/// A Unix signal per-process timer.
#[derive(Debug)]
#[repr(transparent)]
pub struct Timer(libc::timer_t);
impl Timer {
/// Creates a new timer based on the clock defined by `clockid`. The details
/// of the signal and its handler are defined by the passed `sigevent`.
pub fn new(clockid: ClockId, mut sigevent: SigEvent) -> Result<Self> {
let mut timer_id: mem::MaybeUninit<libc::timer_t> = mem::MaybeUninit::uninit();
Errno::result(unsafe {
libc::timer_create(
clockid.as_raw(),
sigevent.as_mut_ptr(),
timer_id.as_mut_ptr(),
)
})
.map(|_| {
// SAFETY: libc::timer_create is responsible for initializing
// timer_id.
unsafe { Self(timer_id.assume_init()) }
})
}
/// Set a new alarm on the timer.
///
/// # Types of alarm
///
/// There are 3 types of alarms you can set:
///
/// - one shot: the alarm will trigger once after the specified amount of
/// time.
/// Example: I want an alarm to go off in 60s and then disable itself.
///
/// - interval: the alarm will trigger every specified interval of time.
/// Example: I want an alarm to go off every 60s. The alarm will first
/// go off 60s after I set it and every 60s after that. The alarm will
/// not disable itself.
///
/// - interval delayed: the alarm will trigger after a certain amount of
/// time and then trigger at a specified interval.
/// Example: I want an alarm to go off every 60s but only start in 1h.
/// The alarm will first trigger 1h after I set it and then every 60s
/// after that. The alarm will not disable itself.
///
/// # Relative vs absolute alarm
///
/// If you do not set any `TimerSetTimeFlags`, then the `TimeSpec` you pass
/// to the `Expiration` you want is relative. If however you want an alarm
/// to go off at a certain point in time, you can set `TFD_TIMER_ABSTIME`.
/// Then the one shot TimeSpec and the delay TimeSpec of the delayed
/// interval are going to be interpreted as absolute.
///
/// # Disabling alarms
///
/// Note: Only one alarm can be set for any given timer. Setting a new alarm
/// actually removes the previous one.
///
/// Note: Setting a one shot alarm with a 0s TimeSpec disable the alarm
/// altogether.
pub fn set(&mut self, expiration: Expiration, flags: TimerSetTimeFlags) -> Result<()> {
let timerspec: TimerSpec = expiration.into();
Errno::result(unsafe {
libc::timer_settime(
self.0,
flags.bits(),
timerspec.as_ref(),
core::ptr::null_mut(),
)
})
.map(drop)
}
/// Get the parameters for the alarm currently set, if any.
pub fn get(&self) -> Result<Option<Expiration>> {
let mut timerspec = TimerSpec::none();
Errno::result(unsafe { libc::timer_gettime(self.0, timerspec.as_mut()) }).map(|_| {
if timerspec.as_ref().it_interval.tv_sec == 0
&& timerspec.as_ref().it_interval.tv_nsec == 0
&& timerspec.as_ref().it_value.tv_sec == 0
&& timerspec.as_ref().it_value.tv_nsec == 0
{
None
} else {
Some(timerspec.into())
}
})
}
/// Return the number of timers that have overrun
///
/// Each timer is able to queue one signal to the process at a time, meaning
/// if the signal is not handled before the next expiration the timer has
/// 'overrun'. This function returns how many times that has happened to
/// this timer, up to `libc::DELAYTIMER_MAX`. If more than the maximum
/// number of overruns have happened the return is capped to the maximum.
pub fn overruns(&self) -> i32 {
unsafe { libc::timer_getoverrun(self.0) }
}
}
impl Drop for Timer {
fn drop(&mut self) {
if !std::thread::panicking() {
let result = Errno::result(unsafe { libc::timer_delete(self.0) });
if let Err(Errno::EINVAL) = result {
panic!("close of Timer encountered EINVAL");
}
}
}
}
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