artifacts.rs

// Copyright (C) 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/>.

//! PVF artifacts (final compiled code blobs).
//!
//!	# Lifecycle of an artifact
//!
//! 1. During node start-up, the artifacts cache is cleaned up. This means that all local artifacts
//!    stored on-disk are cleared, and we start with an empty [`Artifacts`] table.
//!
//! 2. In order to be executed, a PVF should be prepared first. This means that artifacts should
//!    have an [`ArtifactState::Prepared`] entry for that artifact in the table. If not, the
//!    preparation process kicks in. The execution request is stashed until after the preparation is
//!    done, and the artifact state in the host is set to [`ArtifactState::Preparing`]. Preparation
//!    goes through the preparation queue and the pool.
//!
//!    1. If the artifact is already being processed, we add another execution request to the
//!       existing preparation job, without starting a new one.
//!
//!    2. Note that if the state is [`ArtifactState::FailedToProcess`], we usually do not retry
//!       preparation, though we may under certain conditions.
//!
//! 3. The pool gets an available worker and instructs it to work on the given PVF. The worker
//!    starts compilation. When the worker finishes successfully, it writes the serialized artifact
//!    into a temporary file and notifies the host that it's done. The host atomically moves
//!    (renames) the temporary file to the destination filename of the artifact.
//!
//! 4. If the worker concluded successfully or returned an error, then the pool notifies the queue.
//!    In both cases, the queue reports to the host that the result is ready.
//!
//! 5. The host will react by changing the artifact state to either [`ArtifactState::Prepared`] or
//!    [`ArtifactState::FailedToProcess`] for the PVF in question. On success, the
//!    `last_time_needed` will be set to the current time. It will also dispatch the pending
//!    execution requests.
//!
//! 6. On success, the execution request will come through the execution queue and ultimately be
//!    processed by an execution worker. When this worker receives the request, it will read the
//!    requested artifact. If it doesn't exist it reports an internal error. A request for execution
//!    will bump the `last_time_needed` to the current time.
//!
//! 7. There is a separate process for pruning the prepared artifacts whose `last_time_needed` is
//!    older by a predefined parameter. This process is run very rarely (say, once a day). Once the
//!    artifact is expired it is removed from disk eagerly atomically.

use crate::{error::PrepareError, host::PrepareResultSender, prepare::PrepareStats};
use always_assert::always;
use polkadot_parachain::primitives::ValidationCodeHash;
use polkadot_primitives::ExecutorParamsHash;
use std::{
	collections::HashMap,
	path::{Path, PathBuf},
	time::{Duration, SystemTime},
};

/// Contains the bytes for a successfully compiled artifact.
pub struct CompiledArtifact(Vec<u8>);

impl CompiledArtifact {
	/// Creates a `CompiledArtifact`.
	pub fn new(code: Vec<u8>) -> Self {
		Self(code)
	}
}

impl AsRef<[u8]> for CompiledArtifact {
	fn as_ref(&self) -> &[u8] {
		self.0.as_slice()
	}
}

/// Identifier of an artifact. Encodes a code hash of the PVF and a hash of executor parameter set.
#[derive(Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub struct ArtifactId {
	pub(crate) code_hash: ValidationCodeHash,
	pub(crate) executor_params_hash: ExecutorParamsHash,
}

impl ArtifactId {
	const PREFIX: &'static str = "wasmtime_";

	/// Creates a new artifact ID with the given hash.
	pub fn new(code_hash: ValidationCodeHash, executor_params_hash: ExecutorParamsHash) -> Self {
		Self { code_hash, executor_params_hash }
	}

	/// Tries to recover the artifact id from the given file name.
	#[cfg(test)]
	pub fn from_file_name(file_name: &str) -> Option<Self> {
		use polkadot_core_primitives::Hash;
		use std::str::FromStr as _;

		let file_name = file_name.strip_prefix(Self::PREFIX)?;
		let (code_hash_str, executor_params_hash_str) = file_name.split_once('_')?;
		let code_hash = Hash::from_str(code_hash_str).ok()?.into();
		let executor_params_hash =
			ExecutorParamsHash::from_hash(Hash::from_str(executor_params_hash_str).ok()?);

		Some(Self { code_hash, executor_params_hash })
	}

	/// Returns the expected path to this artifact given the root of the cache.
	pub fn path(&self, cache_path: &Path) -> PathBuf {
		let file_name =
			format!("{}{:#x}_{:#x}", Self::PREFIX, self.code_hash, self.executor_params_hash);
		cache_path.join(file_name)
	}
}

/// A bundle of the artifact ID and the path.
///
/// Rationale for having this is two-fold:
///
/// - While we can derive the artifact path from the artifact id, it makes sense to carry it around
/// sometimes to avoid extra work.
/// - At the same time, carrying only path limiting the ability for logging.
#[derive(Debug, Clone)]
pub struct ArtifactPathId {
	pub(crate) id: ArtifactId,
	pub(crate) path: PathBuf,
}

impl ArtifactPathId {
	pub(crate) fn new(artifact_id: ArtifactId, cache_path: &Path) -> Self {
		Self { path: artifact_id.path(cache_path), id: artifact_id }
	}
}

pub enum ArtifactState {
	/// The artifact is ready to be used by the executor.
	///
	/// That means that the artifact should be accessible through the path obtained by the artifact
	/// id (unless, it was removed externally).
	Prepared {
		/// The time when the artifact was last needed.
		///
		/// This is updated when we get the heads up for this artifact or when we just discover
		/// this file.
		last_time_needed: SystemTime,
		/// Stats produced by successful preparation.
		prepare_stats: PrepareStats,
	},
	/// A task to prepare this artifact is scheduled.
	Preparing {
		/// List of result senders that are waiting for a response.
		waiting_for_response: Vec<PrepareResultSender>,
		/// The number of times this artifact has failed to prepare.
		num_failures: u32,
	},
	/// The code couldn't be compiled due to an error. Such artifacts
	/// never reach the executor and stay in the host's memory.
	FailedToProcess {
		/// Keep track of the last time that processing this artifact failed.
		last_time_failed: SystemTime,
		/// The number of times this artifact has failed to prepare.
		num_failures: u32,
		/// The last error encountered for preparation.
		error: PrepareError,
	},
}

/// A container of all known artifact ids and their states.
pub struct Artifacts {
	artifacts: HashMap<ArtifactId, ArtifactState>,
}

impl Artifacts {
	/// Initialize a blank cache at the given path. This will clear everything present at the
	/// given path, to be populated over time.
	///
	/// The recognized artifacts will be filled in the table and unrecognized will be removed.
	pub async fn new(cache_path: &Path) -> Self {
		// Make sure that the cache path directory and all its parents are created.
		// First delete the entire cache. Nodes are long-running so this should populate shortly.
		let _ = tokio::fs::remove_dir_all(cache_path).await;
		let _ = tokio::fs::create_dir_all(cache_path).await;

		Self { artifacts: HashMap::new() }
	}

	#[cfg(test)]
	pub(crate) fn empty() -> Self {
		Self { artifacts: HashMap::new() }
	}

	/// Returns the state of the given artifact by its ID.
	pub fn artifact_state_mut(&mut self, artifact_id: &ArtifactId) -> Option<&mut ArtifactState> {
		self.artifacts.get_mut(artifact_id)
	}

	/// Inform the table about the artifact with the given ID. The state will be set to "preparing".
	///
	/// This function must be used only for brand-new artifacts and should never be used for
	/// replacing existing ones.
	pub fn insert_preparing(
		&mut self,
		artifact_id: ArtifactId,
		waiting_for_response: Vec<PrepareResultSender>,
	) {
		// See the precondition.
		always!(self
			.artifacts
			.insert(artifact_id, ArtifactState::Preparing { waiting_for_response, num_failures: 0 })
			.is_none());
	}

	/// Insert an artifact with the given ID as "prepared".
	///
	/// This function must be used only for brand-new artifacts and should never be used for
	/// replacing existing ones.
	#[cfg(test)]
	pub fn insert_prepared(
		&mut self,
		artifact_id: ArtifactId,
		last_time_needed: SystemTime,
		prepare_stats: PrepareStats,
	) {
		// See the precondition.
		always!(self
			.artifacts
			.insert(artifact_id, ArtifactState::Prepared { last_time_needed, prepare_stats })
			.is_none());
	}

	/// Remove and retrieve the artifacts from the table that are older than the supplied Time-To-Live.
	pub fn prune(&mut self, artifact_ttl: Duration) -> Vec<ArtifactId> {
		let now = SystemTime::now();

		let mut to_remove = vec![];
		for (k, v) in self.artifacts.iter() {
			if let ArtifactState::Prepared { last_time_needed, .. } = *v {
				if now
					.duration_since(last_time_needed)
					.map(|age| age > artifact_ttl)
					.unwrap_or(false)
				{
					to_remove.push(k.clone());
				}
			}
		}

		for artifact in &to_remove {
			self.artifacts.remove(artifact);
		}

		to_remove
	}
}

#[cfg(test)]
mod tests {
	use super::{ArtifactId, Artifacts};
	use polkadot_primitives::ExecutorParamsHash;
	use sp_core::H256;
	use std::{path::Path, str::FromStr};

	#[test]
	fn from_file_name() {
		assert!(ArtifactId::from_file_name("").is_none());
		assert!(ArtifactId::from_file_name("junk").is_none());

		assert_eq!(
			ArtifactId::from_file_name(
				"wasmtime_0x0022800000000000000000000000000000000000000000000000000000000000_0x0033900000000000000000000000000000000000000000000000000000000000"
			),
			Some(ArtifactId::new(
				hex_literal::hex![
					"0022800000000000000000000000000000000000000000000000000000000000"
				]
				.into(),
				ExecutorParamsHash::from_hash(sp_core::H256(hex_literal::hex![
					"0033900000000000000000000000000000000000000000000000000000000000"
				])),
			)),
		);
	}

	#[test]
	fn path() {
		let path = Path::new("/test");
		let hash =
			H256::from_str("1234567890123456789012345678901234567890123456789012345678901234")
				.unwrap();

		assert_eq!(
			ArtifactId::new(hash.into(), ExecutorParamsHash::from_hash(hash)).path(path).to_str(),
			Some(
				"/test/wasmtime_0x1234567890123456789012345678901234567890123456789012345678901234_0x1234567890123456789012345678901234567890123456789012345678901234"
			),
		);
	}

	#[tokio::test]
	async fn artifacts_removes_cache_on_startup() {
		let fake_cache_path = crate::worker_common::tmpfile("test-cache").await.unwrap();
		let fake_artifact_path = {
			let mut p = fake_cache_path.clone();
			p.push("wasmtime_0x1234567890123456789012345678901234567890123456789012345678901234");
			p
		};

		// create a tmp cache with 1 artifact.

		std::fs::create_dir_all(&fake_cache_path).unwrap();
		std::fs::File::create(fake_artifact_path).unwrap();

		// this should remove it and re-create.

		let p = &fake_cache_path;
		Artifacts::new(p).await;

		assert_eq!(std::fs::read_dir(&fake_cache_path).unwrap().count(), 0);

		std::fs::remove_dir_all(fake_cache_path).unwrap();
	}
}