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// Copyright (c) Microsoft Corporation.
// Licensed under the MIT License.
//! Support for VM time.
//!
//! This is a VM-specific timeline, which monotonically increases when and only
//! when the VM is running. This module provides types used to access this time
//! and to wait for it to reach target times. This can be used in device
//! emulators to implement VM timers.
//!
//! This is related to the idea of the hypervisor reference time, but it is not
//! guaranteed to be the same value (and is likely not, except when the
//! hypervisor reference time is emulated using VM time).
//!
//! The root of VM time keeping is the [`VmTimeKeeper`]. It manages a clock that
//! can be shared via use of [`VmTimeAccess`] objects. Internally, this clock is
//! based on an offset from the OS's monotonic clock while the VM is running, and
//! a fixed time when the VM is not running.
//!
//! The infrastructure here supports access of VM time across multiple processes
//! in the same OS (but not across machines, virtual or physical). See the
//! comments on [`VmTimeSourceBuilder`] for more information.
#![warn(missing_docs)]
use futures::future::join_all;
use futures::StreamExt;
use futures_concurrency::future::Race;
use futures_concurrency::stream::Merge;
use inspect::adhoc;
use inspect::Inspect;
use inspect::InspectMut;
use mesh::payload::Protobuf;
use mesh::rpc::Rpc;
use mesh::rpc::RpcSend;
use mesh::MeshPayload;
use pal_async::driver::Driver;
use pal_async::driver::PollImpl;
use pal_async::driver::SpawnDriver;
use pal_async::task::Task;
use pal_async::timer::Instant;
use pal_async::timer::PollTimer;
use parking_lot::RwLock;
use save_restore_derive::SavedStateRoot;
use slab::Slab;
use std::future::poll_fn;
use std::sync::Arc;
use std::task::Context;
use std::task::Poll;
use std::task::Waker;
use std::time::Duration;
use thiserror::Error;
/// Roughly analogous to [`std::time::Instant`], but for VM time.
#[derive(Debug, Copy, Clone, PartialEq, Eq, Protobuf, Inspect)]
#[inspect(transparent)]
#[mesh(transparent)]
pub struct VmTime(#[inspect(hex)] u64);
impl VmTime {
/// Converts from a time in 100ns units.
pub fn from_100ns(n: u64) -> Self {
Self(n)
}
/// Gets the time from VM boot (or some other origin) in 100ns units.
pub const fn as_100ns(&self) -> u64 {
self.0
}
/// Adds `d` to the time.
pub fn wrapping_add(self, d: Duration) -> Self {
Self((self.0 as u128).wrapping_add(d.as_nanos() / 100) as u64)
}
/// Returns whether `self` is before `t`.
///
/// Note that this is a relative comparison in the 64-bit space and is not
/// transitive: if `a` is before `b`, and `b` is before `c`, `a` still may
/// be after `c`.
pub fn is_before(self, t: Self) -> bool {
let delta = self.0.wrapping_sub(t.0);
(delta as i64) < 0
}
/// Returns whether `self` is after `t`.
///
/// See the comment about transitivity in [`Self::is_before`].
pub fn is_after(self, t: Self) -> bool {
let delta = self.0.wrapping_sub(t.0);
(delta as i64) > 0
}
/// Returns the time between `self` and `t`, returning `None` if `self` is
/// before `t`.
pub fn checked_sub(self, t: Self) -> Option<Duration> {
let delta = self.0.wrapping_sub(t.0);
if (delta as i64) >= 0 {
Some(duration_from_100ns(delta))
} else {
None
}
}
/// Returns `self` or `t`, whichever is earlier.
pub fn min(self, t: Self) -> Self {
if self.is_before(t) {
self
} else {
t
}
}
/// Returns `self` or `t`, whichever is later.
pub fn max(self, t: Self) -> Self {
if self.is_before(t) {
t
} else {
self
}
}
}
fn duration_from_100ns(n: u64) -> Duration {
const NUM_100NS_IN_SEC: u64 = 10 * 1000 * 1000;
Duration::new(n / NUM_100NS_IN_SEC, (n % NUM_100NS_IN_SEC) as u32 * 100)
}
#[derive(Inspect)]
struct TimerState {
time: TimeState,
#[inspect(skip)]
timer: PollImpl<dyn PollTimer>,
#[inspect(with = "|x| inspect::iter_by_key(x.iter().map(|(_, w)| (&w.name, w)))")]
waiters: Slab<WaiterState>,
next: Option<VmTime>,
last: VmTime,
}
#[derive(Debug, Inspect)]
struct WaiterState {
#[inspect(skip)] // used as a key
name: Arc<str>,
next: Option<VmTime>,
#[inspect(rename = "waiting", with = "Option::is_some")]
waker: Option<Waker>,
}
impl WaiterState {
fn new(name: Arc<str>) -> Self {
Self {
name,
next: None,
waker: None,
}
}
}
#[derive(Copy, Clone, Debug, Protobuf)]
struct Timestamp {
vmtime: VmTime,
os_time: u64, // Instant::as_nanos()
}
impl Timestamp {
fn new(vmtime: VmTime, os_time: Instant) -> Self {
Self {
vmtime,
os_time: os_time.as_nanos(),
}
}
fn os_time(&self) -> Instant {
Instant::from_nanos(self.os_time)
}
}
impl TimerState {
fn new(driver: &impl Driver, uptime: VmTime) -> Self {
Self {
time: TimeState::Stopped(uptime),
timer: driver.new_dyn_timer(),
waiters: Slab::new(),
next: None,
last: uptime,
}
}
/// Starts the timer.
fn start(&mut self, now: Timestamp) {
let vmtime = self.time.stop_time().expect("should be stopped");
assert_eq!(now.vmtime, vmtime);
self.time = TimeState::Started(now);
tracing::trace!(?now, "vmtime start");
self.wake(now);
}
/// Stops the timer.
fn stop(&mut self, now_os: Instant) -> VmTime {
assert!(self.time.is_started());
let now = self.now(now_os);
self.time = TimeState::Stopped(now.vmtime);
tracing::debug!(?now, "vmtime stop");
now.vmtime
}
/// Resets the current time to `time`.
fn reset(&mut self, time: VmTime) {
assert!(!self.time.is_started());
self.time = TimeState::Stopped(time);
self.last = time;
self.next = None;
// Wake all the wakers to re-evaluate things.
for (_, waiter) in &mut self.waiters {
if let Some(waker) = waiter.waker.take() {
waker.wake();
}
}
}
/// Returns the timestamp corresponding to the given VM time.
///
/// If the VM time is before the last start time, then the timestamp is at
/// the host time when the VM last started.
fn timestamp(&self, time: VmTime) -> Option<Timestamp> {
let start_time = self.time.start_time()?;
let since = time
.checked_sub(start_time.vmtime)
.unwrap_or(Duration::ZERO);
Some(Timestamp::new(time, start_time.os_time() + since))
}
/// Returns the current guest time given a host time.
fn now(&self, now_os: Instant) -> Timestamp {
self.time.now(now_os)
}
fn set_next(&mut self, next: VmTime) {
if !self.time.is_started() {
return;
}
if self
.next
.map_or(true, |current_next| next.is_before(current_next))
{
let deadline = self.timestamp(next).unwrap().os_time();
tracing::trace!(?deadline, "updating deadline");
self.timer.set_deadline(deadline);
self.next = Some(next);
}
}
fn wake(&mut self, now: Timestamp) {
assert!(!now.vmtime.is_before(self.last));
self.last = now.vmtime;
let mut next = None;
for (_, state) in &mut self.waiters {
if let Some(this_next) = state.next {
if this_next.is_after(now.vmtime) {
if next.map_or(true, |next| this_next.is_before(next)) {
next = Some(this_next);
}
} else if let Some(waker) = state.waker.take() {
waker.wake();
}
}
}
if let Some(next) = next {
self.set_next(next);
}
}
fn cancel_timeout(&mut self, index: usize) {
self.waiters[index].next = None;
}
/// Updates the next timeout for an individual waiter.
fn update_timeout(&mut self, index: usize, time: VmTime) {
let state = &mut self.waiters[index];
tracing::trace!(vmtime = ?time, user = state.name.as_ref(), "timeout update");
state.next = Some(time);
if time.is_before(self.last) {
// The wake time is even before the last timer wake, so just wake
// the waiter and skip updating the timer.
if let Some(waker) = state.waker.take() {
waker.wake();
}
return;
}
// Update the timer if needed.
if self.next.map_or(false, |next| next.is_before(time)) {
return;
}
self.set_next(time);
}
/// Polls a single waiter.
fn poll_timeout(
&mut self,
cx: &mut Context<'_>,
index: usize,
now_os: Instant,
next: Option<VmTime>,
) -> Poll<Timestamp> {
let now = self.now(now_os);
let state = &mut self.waiters[index];
if next.map_or(false, |next| next.is_before(now.vmtime)) {
state.waker = None;
state.next = None;
return Poll::Ready(now);
}
state.next = next;
state.waker = Some(cx.waker().clone());
if let Some(next) = next {
self.set_next(next);
}
Poll::Pending
}
/// Polls the timer, waking any waiters whose timeout has expired.
fn poll(&mut self, cx: &mut Context<'_>) {
while self.time.is_started() {
let next = match self.next {
Some(_) => {
// The timer's deadline is already set.
tracing::trace!("polling existing deadline");
None
}
None => {
// Set the timer far out in the future.
let deadline = Instant::now() + Duration::from_secs(86400);
tracing::trace!(?deadline, "polling with long timeout");
Some(deadline)
}
};
if let Poll::Ready(now) = self.timer.poll_timer(cx, next) {
self.next = None;
self.wake(self.now(now));
} else {
return;
}
}
}
}
/// A time keeper, which tracks the current time and all waiters.
#[derive(Debug)]
pub struct VmTimeKeeper {
_task: Task<()>,
req_send: mesh::Sender<KeeperRequest>,
builder: VmTimeSourceBuilder,
time: TimeState,
}
/// Saved state for [`VmTimeKeeper`].
#[derive(Protobuf, SavedStateRoot)]
#[mesh(package = "vmtime")]
pub struct SavedState {
#[mesh(1)]
vmtime: VmTime,
}
impl SavedState {
/// Create a new instance of `SavedState` from an existing `VmTime`.
pub fn from_vmtime(vmtime: VmTime) -> Self {
SavedState { vmtime }
}
}
#[derive(Debug, MeshPayload, Copy, Clone)]
enum TimeState {
Stopped(VmTime),
Started(Timestamp),
}
impl Inspect for TimeState {
fn inspect(&self, req: inspect::Request<'_>) {
let mut resp = req.respond();
let state = match *self {
TimeState::Stopped(_time) => "stopped",
TimeState::Started(time) => {
resp.field("start_time", time.vmtime);
"started"
}
};
resp.field("state", state)
.field("now", self.now(Instant::now()).vmtime);
}
}
impl TimeState {
fn is_started(&self) -> bool {
self.start_time().is_some()
}
fn stop_time(&self) -> Option<VmTime> {
match *self {
TimeState::Stopped(time) => Some(time),
TimeState::Started(_) => None,
}
}
fn start_time(&self) -> Option<Timestamp> {
match *self {
TimeState::Stopped(_) => None,
TimeState::Started(time) => Some(time),
}
}
fn now(&self, now_os: Instant) -> Timestamp {
match *self {
TimeState::Stopped(time) => Timestamp::new(time, now_os),
TimeState::Started(start_time) => {
if now_os >= start_time.os_time() {
Timestamp::new(
start_time
.vmtime
.wrapping_add(now_os - start_time.os_time()),
now_os,
)
} else {
// `now` can be before `running.start_host` if it was captured
// outside the lock and raced with the call to `start()`. Treat
// this as `now` being the same as `start_host`.
//
// But if `now` is too much before `running.start_host`, then
// there is probably some serious OS timekeeping bug, or maybe
// the debugger broke in at just the wrong time.
let delta = start_time.os_time() - now_os;
if delta > Duration::from_secs(1) {
tracing::error!(
now = now_os.as_nanos(),
start_host = start_time.os_time().as_nanos(),
?delta,
"time went backward"
);
}
start_time
}
}
}
}
}
impl InspectMut for VmTimeKeeper {
fn inspect_mut(&mut self, req: inspect::Request<'_>) {
self.req_send.send(KeeperRequest::Inspect(req.defer()));
}
}
impl VmTimeKeeper {
/// Creates a new time keeper with the specified current guest time.
pub fn new(driver: &impl SpawnDriver, uptime: VmTime) -> Self {
let (new_send, new_recv) = mesh::mpsc_channel();
let (req_send, req_recv) = mesh::channel();
let time = TimeState::Stopped(uptime);
let task = driver.spawn("vm-time-keeper", async move {
let mut primary = PrimaryKeeper {
req_recv,
new_recv,
keepers: Vec::new(),
next_id: 0,
time,
};
primary.run().await;
});
Self {
time,
req_send,
builder: VmTimeSourceBuilder { new_send },
_task: task,
}
}
/// Saves the time state.
pub fn save(&self) -> SavedState {
SavedState {
vmtime: self.time.stop_time().expect("should be stopped"),
}
}
/// Restores the time state.
pub async fn restore(&mut self, state: SavedState) {
let SavedState { vmtime } = state;
self.reset_to(vmtime).await
}
async fn reset_to(&mut self, vmtime: VmTime) {
assert!(!self.time.is_started(), "should be stopped");
self.time = TimeState::Stopped(vmtime);
self.req_send
.call(KeeperRequest::Reset, vmtime)
.await
.unwrap();
}
/// Reset the VM time to 0.
pub async fn reset(&mut self) {
self.reset_to(VmTime::from_100ns(0)).await
}
/// Starts the timer, so that the current time will increase.
pub async fn start(&mut self) {
let vmtime = self.time.stop_time().expect("should be stopped");
let timestamp = Timestamp::new(vmtime, Instant::now());
self.time = TimeState::Started(timestamp);
self.req_send
.call(KeeperRequest::Start, timestamp)
.await
.unwrap();
}
/// Stops the timer, so that the current time will stop increasing.
pub async fn stop(&mut self) {
assert!(self.time.is_started(), "should be running");
let stop_time = self.req_send.call(KeeperRequest::Stop, ()).await.unwrap();
self.time = TimeState::Stopped(stop_time);
}
/// Returns a time source builder, which can be used to spawn tasks that
/// back [`VmTimeSource`] instances, all backed by this time keeper's clock.
pub fn builder(&self) -> &VmTimeSourceBuilder {
&self.builder
}
}
/// A time source builder, used to spawn tasks that back [`VmTimeSource`]
/// instances.
///
/// Note that this can be sent across processes via `mesh`.
///
/// However, the time keeping infrastructure assumes that all time keeping tasks
/// share a single global monotonic OS clock. This means that if you send this
/// across a VM/kernel/network boundary, the resulting time sources will not be
/// in sync with each other.
#[derive(MeshPayload, Clone, Debug)]
pub struct VmTimeSourceBuilder {
new_send: mesh::MpscSender<NewKeeperRequest>,
}
/// Error returned by [`VmTimeSourceBuilder::build`] when the time keeper has
/// been torn down.
#[derive(Debug, Error)]
#[error("the time keeper has been torn down")]
pub struct TimeKeeperIsGone;
impl VmTimeSourceBuilder {
/// Builds and spawns a backing task for [`VmTimeSource`]s. All
/// [`VmTimeSource`] instances cloned from the first one will share a
/// backing task.
pub async fn build(&self, driver: &impl SpawnDriver) -> Result<VmTimeSource, TimeKeeperIsGone> {
let (send, recv) = mesh::channel();
let time = self
.new_send
.call(NewKeeperRequest::New, send)
.await
.map_err(|_| TimeKeeperIsGone)?;
let mut state = Arc::new(RwLock::new(TimerState::new(driver, VmTime::from_100ns(0))));
// Synchronize the time.
{
let state = Arc::get_mut(&mut state).unwrap().get_mut();
match time {
TimeState::Stopped(vmtime) => state.reset(vmtime),
TimeState::Started(timestamp) => state.start(timestamp),
}
}
let mut keeper = SecondaryKeeper {
state: state.clone(),
recv,
};
driver
.spawn("vm-time", async move { keeper.run().await })
.detach();
Ok(VmTimeSource {
state,
remote: self.clone(),
})
}
}
/// Task that stores the current time state and manages the list of secondary
/// keepers.
///
/// There is one of these per VM time clock (i.e. one per VM).
#[derive(Inspect)]
#[inspect(extra = "Self::inspect_extra")]
struct PrimaryKeeper {
#[inspect(skip)]
req_recv: mesh::Receiver<KeeperRequest>,
#[inspect(skip)]
new_recv: mesh::MpscReceiver<NewKeeperRequest>,
#[inspect(skip)]
keepers: Vec<(u64, mesh::Sender<KeeperRequest>)>,
#[inspect(skip)]
next_id: u64,
time: TimeState,
}
#[derive(MeshPayload)]
enum KeeperRequest {
Start(Rpc<Timestamp, ()>),
Stop(Rpc<(), VmTime>),
Reset(Rpc<VmTime, ()>),
Inspect(inspect::Deferred),
}
#[derive(MeshPayload)]
enum NewKeeperRequest {
New(Rpc<mesh::Sender<KeeperRequest>, TimeState>),
}
impl PrimaryKeeper {
fn inspect_extra(&self, resp: &mut inspect::Response<'_>) {
resp.fields(
"keepers",
self.keepers
.iter()
.map(|&(id, ref s)| (id, adhoc(|req| s.send(KeeperRequest::Inspect(req.defer()))))),
);
}
async fn run(&mut self) {
enum Event {
New(NewKeeperRequest),
Request(KeeperRequest),
}
while let Some(event) = (
(&mut self.new_recv).map(Event::New),
(&mut self.req_recv).map(Event::Request),
)
.merge()
.next()
.await
{
// Garbage collect the existing keepers.
self.keepers.retain(|(_, s)| !s.is_closed());
match event {
Event::New(req) => match req {
NewKeeperRequest::New(rpc) => rpc.handle_sync(|sender| {
self.keepers.push((self.next_id, sender));
self.next_id += 1;
self.time
}),
},
Event::Request(req) => {
match req {
KeeperRequest::Start(rpc) => {
rpc.handle(|start_time| {
let this = &mut *self;
async move {
assert!(!this.time.is_started());
this.time = TimeState::Started(start_time);
join_all(this.keepers.iter().map(|(_, sender)| {
sender.call(KeeperRequest::Start, start_time)
}))
.await;
}
})
.await
}
KeeperRequest::Stop(rpc) => {
rpc.handle(|()| async {
let results = join_all(
self.keepers
.iter()
.map(|(_, sender)| sender.call(KeeperRequest::Stop, ())),
)
.await;
let start_time = self.time.start_time().expect("should be running");
let now = start_time
.vmtime
.wrapping_add(Instant::now() - start_time.os_time());
// Compute the stop time as the max of all stop
// times so that no keeper goes backwards next
// start.
let stop_time = results
.into_iter()
.filter_map(|r| r.ok())
.fold(now, |a, b| a.max(b));
self.time = TimeState::Stopped(stop_time);
// Update all the keepers with the stop time so that
// it's consistent.
join_all(self.keepers.iter().map(|(_, sender)| {
sender.call(KeeperRequest::Reset, stop_time)
}))
.await;
stop_time
})
.await
}
KeeperRequest::Reset(rpc) => {
rpc.handle(|time| {
let this = &mut *self;
async move {
assert!(!this.time.is_started(), "should not be running");
this.time = TimeState::Stopped(time);
join_all(this.keepers.iter().map(|(_, sender)| {
sender.call(KeeperRequest::Reset, time)
}))
.await;
}
})
.await
}
KeeperRequest::Inspect(deferred) => deferred.inspect(&self),
}
}
}
}
}
}
/// Task that provides access to the current VM time.
///
/// There can be multiple of these per VM, across multiple processes. They are
/// all backed by the same clock and report the same time.
#[derive(InspectMut)]
struct SecondaryKeeper {
#[inspect(flatten)]
state: Arc<RwLock<TimerState>>,
#[inspect(skip)]
recv: mesh::Receiver<KeeperRequest>,
}
impl SecondaryKeeper {
async fn run(&mut self) {
loop {
let r = {
let state = &self.state;
(
self.recv.next(),
poll_fn(|cx| {
state.write().poll(cx);
Poll::Pending
}),
)
.race()
.await
};
match r {
Some(req) => match req {
KeeperRequest::Start(rpc) => rpc.handle_sync(|start_time| {
let mut state = self.state.write();
state.start(start_time);
}),
KeeperRequest::Reset(rpc) => rpc.handle_sync(|vmtime| {
let mut state = self.state.write();
state.reset(vmtime);
}),
KeeperRequest::Stop(rpc) => rpc.handle_sync(|()| {
let mut state = self.state.write();
state.stop(Instant::now())
}),
KeeperRequest::Inspect(deferred) => deferred.inspect(&mut *self),
},
None => break,
}
}
}
}
/// A time source, used to instantiate [`VmTimeAccess`].
#[derive(Clone)]
pub struct VmTimeSource {
state: Arc<RwLock<TimerState>>,
remote: VmTimeSourceBuilder,
}
impl VmTimeSource {
/// Gets a time accessor.
///
/// `name` is used for diagnostics via `inspect`.
pub fn access(&self, name: impl Into<Arc<str>>) -> VmTimeAccess {
let name = name.into();
VmTimeAccess {
timeout: None,
waiting: false,
index: self
.state
.write()
.waiters
.insert(WaiterState::new(name.clone())),
state: self.state.clone(),
name,
}
}
/// Gets the builder for creating additional time sources backing tasks
/// whose times are in sync with this one.
pub fn builder(&self) -> &VmTimeSourceBuilder {
&self.remote
}
}
/// An individual time accessor, used to query and wait for time.
#[derive(Inspect)]
pub struct VmTimeAccess {
timeout: Option<VmTime>,
waiting: bool,
#[inspect(skip)]
index: usize,
#[inspect(skip)]
state: Arc<RwLock<TimerState>>,
name: Arc<str>,
}
impl Drop for VmTimeAccess {
fn drop(&mut self) {
self.state.write().waiters.remove(self.index);
}
}
impl VmTimeAccess {
/// Gets the current time.
pub fn now(&self) -> VmTime {
let now = Instant::now();
self.state.read().now(now).vmtime
}
/// Returns the host time corresponding to a guest time.
///
/// If the guest time is before the VM last resumed, then returns the time
/// the VM last resumed.
///
/// If the VM is not running, returns `None`.
pub fn host_time(&self, time: VmTime) -> Option<Instant> {
Some(self.state.read().timestamp(time)?.os_time())
}
/// Get the currently set timeout.
pub fn get_timeout(&self) -> Option<VmTime> {
self.timeout
}
/// Sets the timeout [`poll_timeout`](Self::poll_timeout) will return ready.
pub fn set_timeout(&mut self, time: VmTime) {
self.timeout = Some(time);
if self.waiting {
self.state.write().update_timeout(self.index, time);
}
}
/// Sets the timeout for [`poll_timeout`](Self::poll_timeout) will return ready,
/// but only if `time` is earlier than the current timeout.
pub fn set_timeout_if_before(&mut self, time: VmTime) {
if self.timeout.map_or(true, |timeout| time.is_before(timeout)) {
self.set_timeout(time);
}
}
/// Clears the current timeout for [`poll_timeout`](Self::poll_timeout).
pub fn cancel_timeout(&mut self) {
if self.waiting && self.timeout.is_some() {
self.state.write().cancel_timeout(self.index);
}
self.timeout = None;
}
/// Polls the current time against the current timeout.
///
/// Returns `Poll::Ready(self.now())` if the current timeout is before now.
/// Returns `Poll::Pending` if there is no current timeout, or if the
/// current timeout is after now.
///
/// Although this takes `&self`, note that it only stores a single waker,
/// meaning that if you poll this from multiple tasks concurrently, only one
/// task will be woken when the time elapses. Create another instance of
/// this type with [`VmTimeSource`] if you need to poll this from multiple
/// tasks.
pub fn poll_timeout(&mut self, cx: &mut Context<'_>) -> Poll<VmTime> {
let now = Instant::now();
match self
.state
.write()
.poll_timeout(cx, self.index, now, self.timeout)
{
Poll::Ready(now) => {
self.waiting = false;
self.timeout = None;
Poll::Ready(now.vmtime)
}
Poll::Pending => {
self.waiting = true;
Poll::Pending
}
}
}
}
#[derive(Debug, Inspect)]
#[inspect(tag = "state")]
enum VmTimerPeriodicInner {
Stopped,
Running {
last_timeout: VmTime,
#[inspect(debug)]
period: Duration,
},
}
/// An abstraction over [`VmTimeAccess`] that streamlines the process of setting
/// up a periodic timer.
#[derive(Inspect)]
pub struct VmTimerPeriodic {
vmtime: VmTimeAccess,
inner: VmTimerPeriodicInner,
}
impl VmTimerPeriodic {
/// Create a new periodic timer, backed by the given [`VmTimeAccess`].
pub fn new(vmtime_access: VmTimeAccess) -> Self {
Self {
vmtime: vmtime_access,
inner: VmTimerPeriodicInner::Stopped,
}
}
/// Cancel the timer.
///
/// If the timer isn't running, this method is a no-op.
pub fn cancel(&mut self) {
self.vmtime.cancel_timeout();
self.inner = VmTimerPeriodicInner::Stopped;
}
/// Start the timer, configuring it to fire at the specified period.
///
/// If the timer is currently running, the timer will be cancelled +
/// restarted.
pub fn start(&mut self, period: Duration) {
self.cancel();
let time = self.vmtime.now().wrapping_add(period);
self.vmtime.set_timeout(time);
self.inner = VmTimerPeriodicInner::Running {
last_timeout: time,
period,
}
}
/// Check if the timer is currently running.
pub fn is_running(&self) -> bool {
matches!(self.inner, VmTimerPeriodicInner::Running { .. })
}
/// Polls the timer.
///
/// Returns `Poll::Ready(now)` when the timer is past-due, returning
/// `Poll::Pending` otherwise.
pub fn poll_timeout(&mut self, cx: &mut Context<'_>) -> Poll<VmTime> {
match self.inner {
VmTimerPeriodicInner::Stopped => {
assert_eq!(self.vmtime.get_timeout(), None);
// Make sure the waker is still managed properly
// This is guaranteed to return Pending according to its documentation thanks to the above assert.
self.vmtime.poll_timeout(cx)
}
VmTimerPeriodicInner::Running {
ref mut last_timeout,
period,
} => {
let mut res = Poll::Pending;
while let Poll::Ready(now) = self.vmtime.poll_timeout(cx) {
res = Poll::Ready(now);
let time = last_timeout.wrapping_add(period);
self.vmtime.set_timeout(time);
*last_timeout = time;
}
res
}
}
}
}
#[cfg(test)]
mod tests {
use super::VmTime;
use super::VmTimeKeeper;
use futures::FutureExt;
use pal_async::async_test;
use pal_async::timer::PolledTimer;
use pal_async::DefaultDriver;
use std::future::poll_fn;
use std::time::Duration;
#[async_test]
async fn test_vmtime(driver: DefaultDriver) {
let mut keeper = VmTimeKeeper::new(&driver, VmTime::from_100ns(0));
let mut access = keeper
.builder()
.build(&driver)
.await
.unwrap()
.access("test");
keeper.start().await;
// Test long timeout.
access.set_timeout(access.now().wrapping_add(Duration::from_secs(1000)));
let mut timer = PolledTimer::new(&driver);
futures::select! {
_ = timer.sleep(Duration::from_millis(50)).fuse() => {}
_ = poll_fn(|cx| access.poll_timeout(cx)).fuse() => panic!("unexpected wait completion"),
}
// Test short timeout.
let deadline = access.now().wrapping_add(Duration::from_millis(10));
access.set_timeout(deadline);
futures::select! {
_ = timer.sleep(Duration::from_millis(1000)).fuse() => panic!("unexpected timeout"),
now = poll_fn(|cx| access.poll_timeout(cx)).fuse() => {
assert!(now.is_after(deadline));
}
}
// Timeout should be cleared by the successful poll.
assert!(poll_fn(|cx| access.poll_timeout(cx))
.now_or_never()
.is_none());
// Test changing timeout.
let now = access.now();
let deadline = now.wrapping_add(Duration::from_millis(2000));
access.set_timeout(deadline);
futures::select! {
_ = timer.sleep(Duration::from_millis(30)).fuse() => {
let deadline = now.wrapping_add(Duration::from_millis(50));
access.set_timeout(deadline);
futures::select! {
_ = timer.sleep(Duration::from_millis(1000)).fuse() => panic!("unexpected timeout"),
now = poll_fn(|cx| access.poll_timeout(cx)).fuse() => {
assert!(now.is_after(deadline));
}
}
}
_ = poll_fn(|cx| access.poll_timeout(cx)).fuse() => panic!("unexpected wait completion"),
}
keeper.stop().await;
}
#[async_test]
async fn test_multi_vmtime(driver: DefaultDriver) {
let mut keeper = VmTimeKeeper::new(&driver, VmTime::from_100ns(0));
let src1 = keeper.builder().build(&driver).await.unwrap();
keeper.start().await;
let src2 = src1.builder().build(&driver).await.unwrap();
let acc1 = src1.access("test");
let acc2 = src2.access("test");
{
let t1 = acc1.now();
let t2 = acc2.now();
let t3 = acc1.now();
assert!(!t2.is_before(t1), "{t1:?} {t2:?}");
assert!(!t3.is_before(t2), "{t2:?} {t3:?}");
}
let now = acc1.now();
keeper.stop().await;
let t1 = acc1.now();
let t2 = acc2.now();
assert!(!t1.is_before(now));
assert_eq!(t1, t2);
let zero = VmTime::from_100ns(0);
// Even on very fast machines, at least _some_ time will have advanced.
assert_ne!(t1, zero);
keeper.reset().await;
assert_eq!(acc1.now(), zero);
assert_eq!(acc2.now(), zero);
}
}