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// Copyright 2017-2020 Parity Technologies (UK) Ltd.
// This file is part of Polkadot.
// Polkadot is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
// Polkadot is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
// You should have received a copy of the GNU General Public License
// along with Polkadot. If not, see <http://www.gnu.org/licenses/>.
//! Utility module for subsystems
//!
//! Many subsystems have common interests such as canceling a bunch of spawned jobs,
//! or determining what their validator ID is. These common interests are factored into
//! this module.
messages::{self, AllMessages, SchedulerRoster},
FromOverseer, SpawnedSubsystem, Subsystem, SubsystemContext, SubsystemResult,
};
use futures::{
channel::{mpsc, oneshot},
prelude::*,
stream::Stream,
task::{self, Spawn, SpawnError, SpawnExt},
};
use futures_timer::Delay;
use keystore::KeyStorePtr;
use parity_scale_codec::Encode;
use pin_project::{pin_project, pinned_drop};
use polkadot_node_primitives::ValidationResult;
use polkadot_primitives::v1::{
CandidateDescriptor, EncodeAs, Hash, PoV, Signed, SigningContext, ValidatorId, ValidatorIndex,
ValidatorPair,
};
use sp_core::Pair;
use std::{
collections::HashMap,
convert::{TryFrom, TryInto},
pin::Pin,
sync::Arc,
time::Duration,
};
use streamunordered::{StreamUnordered, StreamYield};
/// Duration a job will wait after sending a stop signal before hard-aborting.
pub const JOB_GRACEFUL_STOP_DURATION: Duration = Duration::from_secs(1);
/// Capacity of channels to and from individual jobs
pub const JOB_CHANNEL_CAPACITY: usize = 64;
#[derive(Debug, derive_more::From)]
pub enum Error {
/// Attempted to send or receive on a oneshot channel which had been canceled
#[from]
Oneshot(oneshot::Canceled),
/// Attempted to send on a MPSC channel which has been canceled
#[from]
Mpsc(mpsc::SendError),
/// Attempted to spawn a new task, and failed
#[from]
Spawn(SpawnError),
/// Failed to determine whether a candidate was valid or invalid
#[from]
ValidationFailed(messages::ValidationFailed),
/// Failed to determine whether a candidate was valid or invalid, in a different way
#[from]
ValidationResult(ValidationResult),
/// Attempted to convert from an AllMessages to a FromJob, and failed.
SenderConversion(String),
/// The local node is not a validator.
NotAValidator,
/// The desired job is not present in the jobs list.
JobNotFound(Hash),
}
/// From the given set of validators, find the first key we can sign with, if any.
pub fn signing_key(validators: &[ValidatorId], keystore: &KeyStorePtr) -> Option<ValidatorPair> {
let keystore = keystore.read();
validators
.iter()
.find_map(|v| keystore.key_pair::<ValidatorPair>(&v).ok())
}
/// Local validator information
///
/// It can be created if the local node is a validator in the context of a particular
/// relay chain block.
pub struct Validator {
signing_context: SigningContext,
key: ValidatorPair,
index: ValidatorIndex,
}
impl Validator {
/// Get a struct representing this node's validator if this node is in fact a validator in the context of the given block.
pub async fn new<Job: SubsystemRequests>(
job: Job,
keystore: KeyStorePtr,
) -> Result<Self, Error> {
let (validators, signing_context) = futures::try_join!(
job.request_validators().await?,
job.request_signing_context().await?,
Self::construct(&validators, signing_context, keystore)
}
/// Construct a validator instance
pub fn construct(
validators: &[ValidatorId],
signing_context: SigningContext,
keystore: KeyStorePtr,
) -> Result<Self, Error> {
let key = signing_key(validators, &keystore).ok_or(Error::NotAValidator)?;
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let index = validators
.iter()
.enumerate()
.find(|(_, k)| k == &&key.public())
.map(|(idx, _)| idx as ValidatorIndex)
.expect("signing_key would have already returned NotAValidator if the item we're searching for isn't in this list; qed");
Ok(Validator {
signing_context,
key,
index,
})
}
/// Get this validator's id.
pub fn id(&self) -> ValidatorId {
self.key.public()
}
/// Get this validator's local index.
pub fn index(&self) -> ValidatorIndex {
self.index
}
/// Get the current signing context.
pub fn signing_context(&self) -> &SigningContext {
&self.signing_context
}
/// Sign a payload with this validator
pub fn sign<Payload: EncodeAs<RealPayload>, RealPayload: Encode>(
&self,
payload: Payload,
) -> Signed<Payload, RealPayload> {
Signed::sign(payload, &self.signing_context, self.index, &self.key)
}
/// Validate the payload with this validator
///
/// Validation can only succeed if `signed.validator_index() == self.index()`.
/// Normally, this will always be the case for a properly operating program,
/// but it's double-checked here anyway.
pub fn check_payload<Payload: EncodeAs<RealPayload>, RealPayload: Encode>(
&self,
signed: Signed<Payload, RealPayload>,
) -> Result<(), ()> {
if signed.validator_index() != self.index {
return Err(());
}
signed.check_signature(&self.signing_context, &self.id())
}
}
/// ToJob is expected to be an enum declaring the set of messages of interest to a particular job.
///
/// Normally, this will be some subset of `Allmessages`, and a `Stop` variant.
pub trait ToJobTrait: TryFrom<AllMessages> {
/// The `Stop` variant of the ToJob enum.
const STOP: Self;
/// If the message variant contains its relay parent, return it here
fn relay_parent(&self) -> Option<Hash>;
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}
/// A JobHandle manages a particular job for a subsystem.
pub struct JobHandle<ToJob> {
abort_handle: future::AbortHandle,
to_job: mpsc::Sender<ToJob>,
finished: oneshot::Receiver<()>,
outgoing_msgs_handle: usize,
}
impl<ToJob> JobHandle<ToJob> {
/// Send a message to the job.
pub async fn send_msg(&mut self, msg: ToJob) -> Result<(), Error> {
self.to_job.send(msg).await.map_err(Into::into)
}
/// Abort the job without waiting for a graceful shutdown
pub fn abort(self) {
self.abort_handle.abort();
}
}
impl<ToJob: ToJobTrait> JobHandle<ToJob> {
/// Stop this job gracefully.
///
/// If it hasn't shut itself down after `JOB_GRACEFUL_STOP_DURATION`, abort it.
pub async fn stop(mut self) {
// we don't actually care if the message couldn't be sent
let _ = self.to_job.send(ToJob::STOP).await;
let stop_timer = Delay::new(JOB_GRACEFUL_STOP_DURATION);
match future::select(stop_timer, self.finished).await {
Either::Left((_, _)) => {}
Either::Right((_, _)) => {
self.abort_handle.abort();
}
}
}
}
/// This trait governs jobs.
///
/// Jobs are instantiated and killed automatically on appropriate overseer messages.
/// Other messages are passed along to and from the job via the overseer to other
/// subsystems.
pub trait JobTrait: Unpin {
/// Message type to the job. Typically a subset of AllMessages.
type ToJob: 'static + ToJobTrait + Send;
/// Message type from the job. Typically a subset of AllMessages.
type FromJob: 'static + Into<AllMessages> + Send;
/// Job runtime error.
type Error: std::fmt::Debug;
/// Extra arguments this job needs to run properly.
///
/// If no extra information is needed, it is perfectly acceptable to set it to `()`.
type RunArgs: 'static + Send;
/// Name of the job, i.e. `CandidateBackingJob`
const NAME: &'static str;
/// Run a job for the parent block indicated
fn run(
parent: Hash,
run_args: Self::RunArgs,
rx_to: mpsc::Receiver<Self::ToJob>,
tx_from: mpsc::Sender<Self::FromJob>,
) -> Pin<Box<dyn Future<Output = Result<(), Self::Error>> + Send>>;
/// Handle a message which has no relay parent, and therefore can't be dispatched to a particular job
///
/// By default, this is implemented with a NOP function. However, if
/// ToJob occasionally has messages which do not correspond to a particular
/// parent relay hash, then this function will be spawned as a one-off
/// task to handle those messages.
// TODO: the API here is likely not precisely what we want; figure it out more
// once we're implementing a subsystem which actually needs this feature.
// In particular, we're quite likely to want this to return a future instead of
// interrupting the active thread for the duration of the handler.
fn handle_orphan_msg(_msg: Self::ToJob) -> Result<(), Self::Error> {
}
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/// This trait provides a helper abstraction for sending a message to another subsystem
/// and collecting their response.
pub trait JobTraitExt: JobTrait {
/// Get a clone of the sender to the overseer.
fn sender(&self) -> mpsc::Sender<Self::FromJob>;
/// Get the relay parent for this job.
fn relay_parent(&self) -> Hash;
/// Request some data from another subsystem via the Overseer.
///
/// The arguments to `request_builder` are `parent_hash, response_sender`.
fn request<RequestBuilder, Response>(
&self,
request_builder: RequestBuilder,
) -> Pin<Box<dyn Future<Output = Result<oneshot::Receiver<Response>, Error>> + Send>>
where
RequestBuilder: 'static + Send + FnOnce(Hash, oneshot::Sender<Response>) -> Self::FromJob,
Response: Send,
{
let mut sender = self.sender();
let parent = self.relay_parent();
async move {
let (tx, rx) = oneshot::channel();
sender.send(request_builder(parent, tx)).await?;
Ok(rx)
}
.boxed()
}
}
/// This trait enables a blanket impl of several useful getters.
///
/// The blanket impl takes effect for any job for which `Job: JobTraitExt` and
/// `Job::FromJob: TryFrom<AllMessages>`.
///
/// It's distinct from JobTraitExt because it may be useful to `impl JobTraitExt`
/// for some `Job` for which `Job::FromJob: !TryFrom<AllMessages>`, so we don't want
/// to tie this too tightly to that trait.
pub trait SubsystemRequests: JobTraitExt {
/// Request some data from another subsystem via the Overseer.
///
/// The arguments to `request_builder` are `parent_hash, response_sender`.
///
/// The difference between this methods and `self.request` is the return type of
/// `request_builder`: it returns an `AllMessages` instance instead of `Self::FromJob`.
fn request_allmessages<RequestBuilder, Response>(
&self,
request_builder: RequestBuilder,
) -> Pin<Box<dyn Future<Output = Result<oneshot::Receiver<Response>, Error>> + Send>>
where
RequestBuilder: 'static + Send + FnOnce(Hash, oneshot::Sender<Response>) -> AllMessages,
Response: Send;
/// Request that a particular candidate is validated by `CandidateValidation`.
fn request_candidate_validation(
&self,
candidate: CandidateDescriptor,
pov: Arc<PoV>,
) -> Pin<Box<dyn Future<Output = Result<oneshot::Receiver<ValidationResult>, Error>>>>;
/// Request a PoV from `PoVDistribution`
fn request_pov(
&self,
candidate: CandidateDescriptor,
) -> Pin<Box<dyn Future<Output = Result<oneshot::Receiver<Arc<PoV>>, Error>>>>;
/// Request the current scheduler roster from the `RuntimeApi`.
fn request_scheduler_roster(
&self,
) -> Pin<Box<dyn Future<Output = Result<oneshot::Receiver<SchedulerRoster>, Error>>>>;
/// Request the current signing context from the `RuntimeApi`.
fn request_signing_context(
&self,
) -> Pin<Box<dyn Future<Output = Result<oneshot::Receiver<SigningContext>, Error>>>>;
/// Request the current validator set from the `RuntimeApi`.
fn request_validators(
&self,
) -> Pin<Box<dyn Future<Output = Result<oneshot::Receiver<Vec<ValidatorId>>, Error>>>>;
}
// We do not and cannot know the exact type of Job::FromJob, and it would be tedious for extension in the future
// to write a `FromJobTrait` which produced all necessary variants. Instead, we bound `Job::FromJob: TryFrom<AllMessages>`
// so that we have a path to send the appropriate (limited) message through the job's outbound channel.
//
// This isn't an ideal API, as invalid requests become runtime errors instead of compile-time errors,
// but there isn't a better API apparent as of right now.
impl<Job> SubsystemRequests for Job
where
Job: JobTraitExt,
Job::FromJob: TryFrom<AllMessages>,
<Job::FromJob as TryFrom<AllMessages>>::Error: std::fmt::Debug,
{
fn request_allmessages<RequestBuilder, Response>(
&self,
request_builder: RequestBuilder,
) -> Pin<Box<dyn Future<Output = Result<oneshot::Receiver<Response>, Error>> + Send>>
where
RequestBuilder: 'static + Send + FnOnce(Hash, oneshot::Sender<Response>) -> AllMessages,
Response: Send,
{
// although it would be cleaner to delegate to self.request(), doing so doesn't give us any good way
// to return an error in the event of conversion failure, so we just have to copy the implementation
// instead.
let mut sender = self.sender();
let parent = self.relay_parent();
async move {
let (tx, rx) = oneshot::channel();
let msg = request_builder(parent, tx).try_into().map_err(|err| {
Error::SenderConversion(format!("could not construct AllMessages: {:?}", err))
})?;
sender.send(msg).await?;
Ok(rx)
}
.boxed()
}
fn request_candidate_validation(
&self,
candidate: CandidateDescriptor,
pov: Arc<PoV>,
) -> Pin<Box<dyn Future<Output = Result<oneshot::Receiver<ValidationResult>, Error>>>> {
use messages::CandidateValidationMessage::ValidateFromChainState;
use AllMessages::CandidateValidation;
let (tx, rx) = oneshot::channel();
let ram = self.request_allmessages(move |_parent, tx| {
CandidateValidation(ValidateFromChainState(candidate, pov, tx))
});
async move {
let result = ram.await?.await??;
tx.send(result)?;
Ok(rx)
}.boxed()
}
fn request_pov(
&self,
descriptor: CandidateDescriptor,
) -> Pin<Box<dyn Future<Output = Result<oneshot::Receiver<Arc<PoV>>, Error>>>> {
use messages::PoVDistributionMessage::FetchPoV;
use AllMessages::PoVDistribution;
self.request_allmessages(move |parent, tx| {
PoVDistribution(FetchPoV(parent, descriptor, tx))
})
}
fn request_scheduler_roster(
&self,
) -> Pin<Box<dyn Future<Output = Result<oneshot::Receiver<SchedulerRoster>, Error>>>> {
unimplemented!()
}
fn request_signing_context(
&self,
) -> Pin<Box<dyn Future<Output = Result<oneshot::Receiver<SigningContext>, Error>>>> {
use messages::RuntimeApiMessage::Request;
use messages::RuntimeApiRequest::SigningContext;
use AllMessages::RuntimeApi;
self
.request_allmessages(move |parent, tx| RuntimeApi(Request(parent, SigningContext(tx))))
}
fn request_validators(
&self,
) -> Pin<Box<dyn Future<Output = Result<oneshot::Receiver<Vec<ValidatorId>>, Error>>>> {
unimplemented!()
}
}
/// Jobs manager for a subsystem
///
/// - Spawns new jobs for a given relay-parent on demand.
/// - Closes old jobs for a given relay-parent on demand.
/// - Dispatches messages to the appropriate job for a given relay-parent.
/// - When dropped, aborts all remaining jobs.
/// - implements `Stream<Item=Job::FromJob>`, collecting all messages from subordinate jobs.
#[pin_project(PinnedDrop)]
pub struct Jobs<Spawner, Job: JobTrait> {
spawner: Spawner,
running: HashMap<Hash, JobHandle<Job::ToJob>>,
#[pin]
outgoing_msgs: StreamUnordered<mpsc::Receiver<Job::FromJob>>,
job: std::marker::PhantomData<Job>,
}
impl<Spawner: Spawn, Job: JobTrait> Jobs<Spawner, Job> {
/// Create a new Jobs manager which handles spawning appropriate jobs.
pub fn new(spawner: Spawner) -> Self {
Self {
spawner,
running: HashMap::new(),
outgoing_msgs: StreamUnordered::new(),
job: std::marker::PhantomData,
}
}
/// Spawn a new job for this `parent_hash`, with whatever args are appropriate.
fn spawn_job(&mut self, parent_hash: Hash, run_args: Job::RunArgs) -> Result<(), Error> {
let (to_job_tx, to_job_rx) = mpsc::channel(JOB_CHANNEL_CAPACITY);
let (from_job_tx, from_job_rx) = mpsc::channel(JOB_CHANNEL_CAPACITY);
let (finished_tx, finished) = oneshot::channel();
let (future, abort_handle) = future::abortable(async move {
if let Err(e) = Job::run(parent_hash, run_args, to_job_rx, from_job_tx).await {
log::error!(
"{}({}) finished with an error {:?}",
Job::NAME,
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parent_hash,
e,
);
}
});
// discard output
let future = async move {
let _ = future.await;
let _ = finished_tx.send(());
};
self.spawner.spawn(future)?;
// this handle lets us remove the appropriate receiver from self.outgoing_msgs
// when it's time to stop the job.
let outgoing_msgs_handle = self.outgoing_msgs.push(from_job_rx);
let handle = JobHandle {
abort_handle,
to_job: to_job_tx,
finished,
outgoing_msgs_handle,
};
self.running.insert(parent_hash, handle);
Ok(())
}
/// Stop the job associated with this `parent_hash`.
pub async fn stop_job(&mut self, parent_hash: Hash) -> Result<(), Error> {
match self.running.remove(&parent_hash) {
Some(handle) => {
Pin::new(&mut self.outgoing_msgs).remove(handle.outgoing_msgs_handle);
handle.stop().await;
Ok(())
}
None => Err(Error::JobNotFound(parent_hash)),
}
}
/// Send a message to the appropriate job for this `parent_hash`.
async fn send_msg(&mut self, parent_hash: Hash, msg: Job::ToJob) -> Result<(), Error> {
match self.running.get_mut(&parent_hash) {
Some(job) => job.send_msg(msg).await?,
None => return Err(Error::JobNotFound(parent_hash)),
}
Ok(())
}
}
// Note that on drop, we don't have the chance to gracefully spin down each of the remaining handles;
// we just abort them all. Still better than letting them dangle.
#[pinned_drop]
impl<Spawner, Job: JobTrait> PinnedDrop for Jobs<Spawner, Job> {
fn drop(self: Pin<&mut Self>) {
for job_handle in self.running.values() {
job_handle.abort_handle.abort();
}
}
}
impl<Spawner, Job> Stream for Jobs<Spawner, Job>
where
Spawner: Spawn,
Job: JobTrait,
{
type Item = Job::FromJob;
fn poll_next(self: Pin<&mut Self>, cx: &mut task::Context) -> task::Poll<Option<Self::Item>> {
// pin-project the outgoing messages
self.project().outgoing_msgs.poll_next(cx).map(|opt| {
opt.and_then(|(stream_yield, _)| match stream_yield {
StreamYield::Item(msg) => Some(msg),
StreamYield::Finished(_) => None,
})
})
/// A basic implementation of a subsystem.
///
/// This struct is responsible for handling message traffic between
/// this subsystem and the overseer. It spawns and kills jobs on the
/// appropriate Overseer messages, and dispatches standard traffic to
/// the appropriate job the rest of the time.
pub struct JobManager<Spawner, Context, Job: JobTrait> {
spawner: Spawner,
run_args: Job::RunArgs,
context: std::marker::PhantomData<Context>,
job: std::marker::PhantomData<Job>,
}
impl<Spawner, Context, Job> JobManager<Spawner, Context, Job>
where
Spawner: Spawn + Clone + Send + Unpin,
Context: SubsystemContext,
Job: JobTrait,
Job::RunArgs: Clone,
Job::ToJob: TryFrom<AllMessages> + TryFrom<<Context as SubsystemContext>::Message> + Sync,
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{
/// Creates a new `Subsystem`.
pub fn new(spawner: Spawner, run_args: Job::RunArgs) -> Self {
Self {
spawner,
run_args,
context: std::marker::PhantomData,
job: std::marker::PhantomData,
}
}
/// Run this subsystem
///
/// Conceptually, this is very simple: it just loops forever.
///
/// - On incoming overseer messages, it starts or stops jobs as appropriate.
/// - On other incoming messages, if they can be converted into Job::ToJob and
/// include a hash, then they're forwarded to the appropriate individual job.
/// - On outgoing messages from the jobs, it forwards them to the overseer.
pub async fn run(mut ctx: Context, run_args: Job::RunArgs, spawner: Spawner) {
let mut jobs = Jobs::new(spawner.clone());
loop {
select! {
incoming = ctx.recv().fuse() => if Self::handle_incoming(incoming, &mut jobs, &run_args).await { break },
outgoing = jobs.next().fuse() => if Self::handle_outgoing(outgoing, &mut ctx).await { break },
complete => break,
}
}
}
// handle an incoming message. return true if we should break afterwards.
async fn handle_incoming(
incoming: SubsystemResult<FromOverseer<Context::Message>>,
jobs: &mut Jobs<Spawner, Job>,
run_args: &Job::RunArgs,
) -> bool {
use crate::FromOverseer::{Communication, Signal};
use crate::OverseerSignal::{Conclude, StartWork, StopWork};
match incoming {
Ok(Signal(StartWork(hash))) => {
if let Err(e) = jobs.spawn_job(hash, run_args.clone()) {
log::error!("Failed to spawn a job: {:?}", e);
return true;
}
}
Ok(Signal(StopWork(hash))) => {
if let Err(e) = jobs.stop_job(hash).await {
log::error!("Failed to stop a job: {:?}", e);
return true;
}
}
Ok(Signal(Conclude)) => {
// Breaking the loop ends fn run, which drops `jobs`, which immediately drops all ongoing work.
// We can afford to wait a little while to shut them all down properly before doing that.
future::join_all(jobs.running.drain().map(|(_, handle)| handle.stop())).await;
return true;
}
Ok(Communication { msg }) => {
if let Ok(to_job) = <Job::ToJob>::try_from(msg) {
match to_job.relay_parent() {
Some(hash) => {
if let Err(err) = jobs.send_msg(hash, to_job).await {
log::error!("Failed to send a message to a job: {:?}", err);
return true;
}
}
if let Err(err) = Job::handle_orphan_msg(to_job) {
log::error!("Failed to handle unhashed message: {:?}", err);
return true;
}
}
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}
}
}
Err(err) => {
log::error!("error receiving message from subsystem context: {:?}", err);
return true;
}
}
false
}
// handle an outgoing message. return true if we should break afterwards.
async fn handle_outgoing(outgoing: Option<Job::FromJob>, ctx: &mut Context) -> bool {
match outgoing {
Some(msg) => {
// discard errors when sending the message upstream
let _ = ctx.send_message(msg.into()).await;
}
None => return true,
}
false
}
}
impl<Spawner, Context, Job> Subsystem<Context> for JobManager<Spawner, Context, Job>
where
Spawner: Spawn + Send + Clone + Unpin + 'static,
Context: SubsystemContext,
<Context as SubsystemContext>::Message: Into<Job::ToJob>,
Job: JobTrait + Send,
Job::RunArgs: Clone + Sync,
Job::ToJob: TryFrom<AllMessages> + Sync,
{
fn start(self, ctx: Context) -> SpawnedSubsystem {
let spawner = self.spawner.clone();
let run_args = self.run_args.clone();
SpawnedSubsystem(Box::pin(async move {
Self::run(ctx, run_args, spawner).await;
}))
}
}