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tor-rtmock: Provide MockExecutor

This commit is contained in:
Ian Jackson 2023-07-03 13:11:18 +01:00
parent 70fdd92030
commit d82ed8d793
4 changed files with 588 additions and 0 deletions
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3
Cargo.lock generated
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@ -4820,11 +4820,14 @@ name = "tor-rtmock"
version = "0.8.2"
dependencies = [
"async-trait",
"educe",
"futures",
"futures-await-test",
"humantime 2.1.0",
"itertools 0.11.0",
"pin-project",
"rand 0.8.5",
"slotmap",
"thiserror",
"tor-basic-utils",
"tor-rtcompat",

3
crates/tor-rtmock/Cargo.toml
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@ -13,9 +13,12 @@ repository = "https://gitlab.torproject.org/tpo/core/arti.git/"
[dependencies]
async-trait = "0.1.54"
educe = "0.4.6"
futures = "0.3.14"
humantime = "2"
itertools = "0.11.0"
pin-project = "1"
slotmap = "1.0.6"
thiserror = "1"
tor-rtcompat = { version = "0.9.1", path = "../tor-rtcompat" }
tracing = "0.1.36"

1
crates/tor-rtmock/src/lib.rs
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@ -47,6 +47,7 @@ mod util;
pub mod io;
pub mod net;
pub mod task;
pub mod time;
mod net_runtime;

581
crates/tor-rtmock/src/task.rs Normal file
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@ -0,0 +1,581 @@
//! Executor for running tests with mocked environment
//!
//! See [`MockExecutor`]
use std::fmt::{self, Debug, Display};
use std::future::Future;
use std::iter;
use std::pin::Pin;
use std::sync::{Arc, Mutex, MutexGuard};
use std::task::{Context, Poll, Wake, Waker};
use futures::pin_mut;
use futures::task::{FutureObj, Spawn, SpawnError};
use futures::FutureExt as _;
use educe::Educe;
use itertools::{chain, izip};
use slotmap::DenseSlotMap;
use tracing::trace;
use tor_rtcompat::BlockOn;
use Poll::*;
use TaskState::*;
/// Type-erased future, one for each of our (normal) tasks
type TaskFuture = FutureObj<'static, ()>;
/// Future for the argument to `block_on`, which is handled specially
type MainFuture<'m> = Pin<&'m mut dyn Future<Output = ()>>;
//---------- principal data structures ----------
/// Executor for running tests with mocked environment
///
/// For test cases which don't actually wait for anything in the real world.
///
/// This is the executor.
/// It implements [`Spawn`] and [`BlockOn`]
///
/// It will usually be used as part of a `MockRuntime`.
///
/// # Restricted environment
///
/// Tests run with this executor must not attempt to block
/// on anything "outside":
/// every future that anything awaits must (eventually) be woken directly
/// *by some other task* in the same test case.
///
/// (By directly we mean that the [`Waker::wake`] call is made
/// by that waking future, before that future itself awaits anything.)
///
/// # Panics
///
/// This executor will malfunction or panic if reentered.
#[derive(Clone, Default, Educe)]
#[educe(Debug)]
pub struct MockExecutor {
/// Mutable state
#[educe(Debug(ignore))]
data: ArcMutexData,
}
/// Mutable state, wrapper type mostly so we can provide `.lock()`
#[derive(Clone, Default)]
struct ArcMutexData(Arc<Mutex<Data>>);
/// Task id, module to hide `Ti` alias
mod task_id {
slotmap::new_key_type! {
/// Task ID, usually called `TaskId`
///
/// Short name in special `task_id` module so that [`Debug`] is nice
pub(super) struct Ti;
}
}
use task_id::Ti as TaskId;
/// Executor's state
///
/// ### Task state machine
///
/// A task is created in `tasks`, `Awake`, so also in `awake`.
///
/// When we poll it, we take it out of `awake` and set it to `Asleep`,
/// and then call `poll()`.
/// Any time after that, it can be made `Awake` again (and put back onto `awake`)
/// by the waker ([`ActualWaker`], wrapped in [`Waker`]).
///
/// The task's future is of course also present here in this data structure.
/// However, during poll we must release the lock,
/// so we cannot borrow the future from `Data`.
/// Instead, we move it out. So `Task.fut` is an `Option`.
///
/// ### "Main" task - the argument to `block_on`
///
/// The signature of `BlockOn::block_on` accepts a non-`'static` future
/// (and a non-`Send`/`Sync` one).
///
/// So we cannot store that future in `Data` because `Data` is `'static`.
/// Instead, this main task future is passed as an argument down the call stack.
/// In the data structure we simply store a placeholder, `TaskFutureInfo::Main`.
#[derive(Default)]
struct Data {
/// Tasks
///
/// Includes tasks spawned with `spawn`,
/// and also the future passed to `block_on`.
tasks: DenseSlotMap<TaskId, Task>,
/// `awake` lists precisely: tasks that are `Awake`, plus maybe stale `TaskId`s
awake: Vec<TaskId>,
/// If a future from `progress_until_stalled` exists
progressing_until_stalled: Option<ProgressingUntilStalled>,
}
/// Record of a single task
///
/// Tracks a spawned task, or the main task (the argument to `block_on`).
///
/// Stored in [`Data`]`.tasks`.
struct Task {
/// For debugging output
desc: String,
/// Has this been woken via a waker? (And is it in `Data.awake`?)
state: TaskState,
/// The actual future (or a placeholder for it)
///
/// May be `None` because we've temporarily moved it out so we can poll it
fut: Option<TaskFutureInfo>,
}
/// A future as stored in our record of a [`Task`]
enum TaskFutureInfo {
/// The [`Future`]. All is normal.
Normal(TaskFuture),
/// The future isn't here because this task is the main future for `block_on`
Main,
}
use TaskFutureInfo as TFI;
/// State of a task - do we think it needs to be polled?
///
/// Stored in [`Task`]`.state`.
#[derive(Debug)]
enum TaskState {
/// Awake - needs to be polled
///
/// Established by [`waker.wake()`](Waker::wake)
Awake,
/// Asleep - does *not* need to be polled
///
/// Established each time just before we call the future's [`poll`](Future::poll)
Asleep,
}
/// Actual implementor of `Wake` for use in a `Waker`
///
/// Futures (eg, channels from [`futures`]) will use this to wake a task
/// when it should be polled.
struct ActualWaker {
/// Executor state
data: ArcMutexData,
/// Which task this is
id: TaskId,
}
/// State used for an in-progress call to
/// [`progress_until_stalled`][`MockExecutor::progress_until_stalled`]
///
/// If present in [`Data`], an (async) call to `progress_until_stalled`
/// is in progress.
///
/// The future from `progress_until_stalled`, [`ProgressUntilStalledFuture`]
/// is a normal-ish future.
/// It can be polled in the normal way.
/// When it is polled, it looks here, in `finished`, to see if it's `Ready`.
///
/// The future is made ready, and woken (via `waker`),
/// by bespoke code in the task executor loop.
///
/// When `ProgressUntilStalledFuture` (maybe completes and) is dropped,
/// its `Drop` impl is used to remove this from `Data.progressing_until_stalled`.
#[derive(Debug)]
struct ProgressingUntilStalled {
/// Have we, in fact, stalled?
///
/// Made `Ready` by special code in the executor loop
finished: Poll<()>,
/// Waker
///
/// Signalled by special code in the executor loop
waker: Option<Waker>,
}
/// Future from
/// [`progress_until_stalled`][`MockExecutor::progress_until_stalled`]
///
/// See [`ProgressingUntilStalled`] for an overview of this aspect of the contraption.
///
/// Existence of this struct implies `Data.progressing_until_stalled` is `Some`.
/// There can only be one at a time.
#[derive(Educe)]
#[educe(Debug)]
struct ProgressUntilStalledFuture {
/// Executor's state; this future's state is in `.progressing_until_stalled`
#[educe(Debug(ignore))]
data: ArcMutexData,
}
//---------- creation ----------
impl MockExecutor {
/// Make a `MockExecutor` with default parameters
pub fn new() -> Self {
Self::default()
}
}
//---------- spawning ----------
impl MockExecutor {
/// Spawn a task and return something to identify it
///
/// `desc` should `Display` as some kind of short string (ideally without spaces)
/// and will be used in the `Debug` impl and trace log messages from `MockExecutor`.
///
/// The returned value is an opaque task identifier which is very cheap to clone
/// and which can be used by the caller in debug logging,
/// if it's desired to correlate with the debug output from `MockExecutor`.
/// Most callers will want to ignore it.
///
/// This method is infalliable. (The `MockExecutor` cannot be shut down.)
pub fn spawn_identified(
&self,
desc: impl Display,
fut: impl Future<Output = ()> + Send + Sync + 'static,
) -> impl Debug + Clone + Send + Sync + 'static {
self.spawn_internal(desc.to_string(), FutureObj::from(Box::new(fut)))
}
/// Spawn a task and return its `TaskId`
///
/// Convenience method for use by `spawn_identified` and `spawn_obj`.
/// The future passed to `block_on` is not handled here.
fn spawn_internal(&self, desc: String, fut: TaskFuture) -> TaskId {
let mut data = self.data.lock();
data.insert_task(desc, TFI::Normal(fut))
}
}
impl Data {
/// Insert a task given its `TaskFutureInfo` and return its `TaskId`.
fn insert_task(&mut self, desc: String, fut: TaskFutureInfo) -> TaskId {
let state = Awake;
let id = self.tasks.insert(Task {
state,
desc,
fut: Some(fut),
});
self.awake.push(id);
trace!("MockExecutor spawned {:?}={:?}", id, self.tasks[id]);
id
}
}
impl Spawn for MockExecutor {
fn spawn_obj(&self, future: TaskFuture) -> Result<(), SpawnError> {
self.spawn_internal("".into(), future);
Ok(())
}
}
//---------- block_on ----------
impl BlockOn for MockExecutor {
/// Run `fut` to completion, synchronously
///
/// # Panics
///
/// Might malfunction or panic if:
///
/// * The provided future doesn't complete (without externally blocking),
/// but instead waits for something.
///
/// * The `MockExecutor` is reentered. (Eg, `block_on` is reentered.)
fn block_on<F>(&self, fut: F) -> F::Output
where
F: Future,
{
let mut value: Option<F::Output> = None;
let fut = {
let value = &mut value;
async move {
trace!("MockExecutor block_on future...");
let t = fut.await;
trace!("MockExecutor block_on future returned...");
*value = Some(t);
trace!("MockExecutor block_on future exiting.");
}
};
{
pin_mut!(fut);
self.data.lock().insert_task("main".into(), TFI::Main);
self.execute_to_completion(fut);
}
#[allow(clippy::let_and_return)] // clarity
let value = value.take().unwrap_or_else(|| {
let data = self.data.lock();
panic!(
r"
all futures blocked. waiting for the real world? or deadlocked (waiting for each other) ?
{data:#?}
"
);
});
value
}
}
//---------- execution - core implementation ----------
impl MockExecutor {
/// Keep polling tasks until nothing more can be done
///
/// Ie, stop when `awake` is empty and `progressing_until_stalled` is `None`.
fn execute_to_completion(&self, mut main_fut: MainFuture) {
trace!("MockExecutor execute_to_completion...");
loop {
self.execute_until_first_stall(main_fut.as_mut());
// Handle `progressing_until_stalled`
let pus_waker = {
let mut data = self.data.lock();
let pus = &mut data.progressing_until_stalled;
trace!("MockExecutor execute_to_completion PUS={:?}", &pus);
let Some(pus) = pus else {
// No progressing_until_stalled, we're actually done.
break;
};
assert_eq!(
pus.finished, Pending,
"ProgressingUntilStalled finished twice?!"
);
pus.finished = Ready(());
pus.waker
.clone()
.expect("ProgressUntilStalledFuture not ever polled!")
};
pus_waker.wake();
}
trace!("MockExecutor execute_to_completion done");
}
/// Keep polling tasks until `awake` is empty
///
/// (Ignores `progressing_until_stalled` - so if one is active,
/// will return when all other tasks have blocked.)
///
/// # Panics
///
/// Might malfunction or panic if called reentrantly
fn execute_until_first_stall(&self, mut main_fut: MainFuture) {
trace!("MockExecutor execute_until_first_stall ...");
'outer: loop {
// Take a `Awake` task off `awake` and make it `Polling`
let (id, mut fut) = 'inner: loop {
let mut data = self.data.lock();
let Some(id) = data.awake.pop() else { break 'outer };
let Some(task) = data.tasks.get_mut(id) else {
trace!("MockExecutor {id:?} vanished");
continue;
};
task.state = Asleep;
let fut = task.fut.take().expect("future missing from task!");
break 'inner (id, fut);
};
// Poll the selected task
let waker = Waker::from(Arc::new(ActualWaker {
data: self.data.clone(),
id,
}));
trace!("MockExecutor {id:?} polling...");
let mut cx = Context::from_waker(&waker);
let r = match &mut fut {
TFI::Normal(fut) => fut.poll_unpin(&mut cx),
TFI::Main => main_fut.as_mut().poll(&mut cx),
};
// Deal with the returned `Poll`
{
let mut data = self.data.lock();
let task = data
.tasks
.get_mut(id)
.expect("task vanished while we were polling it");
match r {
Pending => {
trace!("MockExecutor {id:?} -> Pending");
if task.fut.is_some() {
panic!("task reinserted while we polled it?!");
}
// The task might have been woking *by its own poll method*.
// That's why we set it to `Asleep` *earlier* rather than here.
// All we need to do is put the future back.
task.fut = Some(fut);
}
Ready(()) => {
trace!("MockExecutor {id:?} -> Ready");
// Oh, it finished!
// It might be in `awake`, but that's allowed to contain stale tasks,
// so we *don't* need to scan that list and remove it.
data.tasks.remove(id);
}
}
}
}
trace!("MockExecutor execute_until_first_stall done.");
}
}
impl Wake for ActualWaker {
fn wake(self: Arc<Self>) {
let mut data = self.data.lock();
trace!("MockExecutor {:?} wake", &self.id);
let Some(task) = data.tasks.get_mut(self.id) else { return };
match task.state {
Awake => {}
Asleep => {
task.state = Awake;
data.awake.push(self.id);
}
}
}
}
//---------- "progress until stalled" functionality ----------
impl MockExecutor {
/// Run tasks in the current executor until every task is waiting
///
/// # Panics
///
/// Might malfunction or panic if more than one such call is running at once.
///
/// (Ie, you must `.await` or drop the returned `Future`
/// before calling this method again.)
pub fn progress_until_stalled(&self) -> impl Future<Output = ()> {
let mut data = self.data.lock();
assert!(
data.progressing_until_stalled.is_none(),
"progress_until_stalled called more than once"
);
trace!("MockExecutor progress_until_stalled...");
data.progressing_until_stalled = Some(ProgressingUntilStalled {
finished: Pending,
waker: None,
});
ProgressUntilStalledFuture {
data: self.data.clone(),
}
}
}
impl Future for ProgressUntilStalledFuture {
type Output = ();
fn poll(self: Pin<&mut Self>, cx: &mut Context) -> Poll<()> {
let mut data = self.data.lock();
let pus = data.progressing_until_stalled.as_mut();
trace!("MockExecutor progress_until_stalled polling... {:?}", &pus);
let pus = pus.expect("ProgressingUntilStalled missing");
pus.waker = Some(cx.waker().clone());
pus.finished
}
}
impl Drop for ProgressUntilStalledFuture {
fn drop(&mut self) {
self.data.lock().progressing_until_stalled = None;
}
}
//---------- ancillary and convenience functions ----------
/// Trait to let us assert at compile time that something is nicely `Sync` etc.
trait EnsureSyncSend: Sync + Send + 'static {}
impl EnsureSyncSend for ActualWaker {}
impl EnsureSyncSend for MockExecutor {}
impl ArcMutexData {
/// Lock and obtain the guard
///
/// Convenience method which panics on poison
fn lock(&self) -> MutexGuard<Data> {
self.0.lock().expect("data lock poisoned")
}
}
//---------- bespoke Debug impls ----------
// See `impl Debug for Data` for notes on the output
impl Debug for Task {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
let Task { desc, state, fut } = self;
write!(f, "{:?}", desc)?;
write!(f, "=")?;
match fut {
None => write!(f, "P")?,
Some(TFI::Normal(_)) => write!(f, "f")?,
Some(TFI::Main) => write!(f, "m")?,
}
match state {
Awake => write!(f, "W")?,
Asleep => write!(f, "s")?,
};
Ok(())
}
}
/// Helper: `Debug`s as a list of tasks, given the `Data` for lookups and a list of the ids
struct DebugTasks<'d, F>(&'d Data, F);
// See `impl Debug for Data` for notes on the output
impl<F, I> Debug for DebugTasks<'_, F>
where
F: Fn() -> I,
I: Iterator<Item = TaskId>,
{
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
let DebugTasks(data, ids) = self;
for (id, delim) in izip!(ids(), chain!(iter::once(""), iter::repeat(" ")),) {
write!(f, "{delim}{id:?}")?;
match data.tasks.get(id) {
None => write!(f, "-")?,
Some(task) => write!(f, "={task:?}")?,
}
}
Ok(())
}
}
/// `Task`s in `Data` are printed as `Ti(ID)"SPEC"=FLAGS"`.
///
/// `FLAGS` are:
///
/// * `P`: this task is being polled (its `TaskFutureInfo` is absent)
/// * `f`: this is a normal task with a future and its future is present in `Data`
/// * `m`: this is the main task from `block_on`
///
/// * `W`: the task is awake
/// * `s`: the task is asleep
//
// We do it this way because the naive dump from derive is very expansive
// and makes it impossible to see the wood for the trees.
// This very compact representation it easier to find a task of interest in the output.
//
// This is implemented in `impl Debug for Task`.
impl Debug for Data {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
let Data {
tasks,
awake,
progressing_until_stalled: pus,
} = self;
let mut s = f.debug_struct("Data");
s.field("tasks", &DebugTasks(self, || tasks.keys()));
s.field("awake", &DebugTasks(self, || awake.iter().cloned()));
s.field("p.u.s", pus);
s.finish()
}
}