PVF host prechecking support v2

node/core/pvf/src/artifacts.rs

@@ -14,6 +14,7 @@
 // You should have received a copy of the GNU General Public License
 // along with Polkadot.  If not, see <http://www.gnu.org/licenses/>.
 
+use crate::{error::PrepareError, host::PrepareResultSender};
 use always_assert::always;
 use async_std::path::{Path, PathBuf};
 use parity_scale_codec::{Decode, Encode};
@@ -23,30 +24,19 @@ use std::{
 	time::{Duration, SystemTime},
 };
 
-/// A final product of preparation process. Contains either a ready to run compiled artifact or
-/// a description what went wrong.
+/// A wrapper for the compiled PVF code.
 #[derive(Encode, Decode)]
-pub enum Artifact {
-	/// During the prevalidation stage of preparation an issue was found with the PVF.
-	PrevalidationErr(String),
-	/// Compilation failed for the given PVF.
-	PreparationErr(String),
-	/// This state indicates that the process assigned to prepare the artifact wasn't responsible
-	/// or were killed. This state is reported by the validation host (not by the worker).
-	DidntMakeIt,
-	/// The PVF passed all the checks and is ready for execution.
-	Compiled { compiled_artifact: Vec<u8> },
-}
+pub struct CompiledArtifact(Vec<u8>);
 
-impl Artifact {
-	/// Serializes this struct into a byte buffer.
-	pub fn serialize(&self) -> Vec<u8> {
-		self.encode()
+impl CompiledArtifact {
+	pub fn new(code: Vec<u8>) -> Self {
+		Self(code)
 	}
+}
 
-	/// Deserialize the given byte buffer to an artifact.
-	pub fn deserialize(mut bytes: &[u8]) -> Result<Self, String> {
-		Artifact::decode(&mut bytes).map_err(|e| format!("{:?}", e))
+impl AsRef<[u8]> for CompiledArtifact {
+	fn as_ref(&self) -> &[u8] {
+		self.0.as_slice()
 	}
 }
 
@@ -116,7 +106,10 @@ pub enum ArtifactState {
 		last_time_needed: SystemTime,
 	},
 	/// A task to prepare this artifact is scheduled.
-	Preparing,
+	Preparing { waiting_for_response: Vec<PrepareResultSender> },
+	/// The code couldn't be compiled due to an error. Such artifacts
+	/// never reach the executor and stay in the host's memory.
+	FailedToProcess(PrepareError),
 }
 
 /// A container of all known artifact ids and their states.
@@ -152,9 +145,16 @@ impl Artifacts {
 	///
 	/// 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) {
+	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).is_none());
+		always!(self
+			.artifacts
+			.insert(artifact_id, ArtifactState::Preparing { waiting_for_response })
+			.is_none());
 	}
 
 	/// Insert an artifact with the given ID as "prepared".

node/core/pvf/src/error.rs

@@ -14,6 +14,22 @@
 // You should have received a copy of the GNU General Public License
 // along with Polkadot.  If not, see <http://www.gnu.org/licenses/>.
 
+use parity_scale_codec::{Decode, Encode};
+
+/// An error that occurred during the prepare part of the PVF pipeline.
+#[derive(Debug, Clone, Encode, Decode)]
+pub enum PrepareError {
+	/// During the prevalidation stage of preparation an issue was found with the PVF.
+	Prevalidation(String),
+	/// Compilation failed for the given PVF.
+	Preparation(String),
+	/// Failed to prepare the PVF due to the time limit.
+	TimedOut,
+	/// This state indicates that the process assigned to prepare the artifact wasn't responsible
+	/// or were killed. This state is reported by the validation host (not by the worker).
+	DidNotMakeIt,
+}
+
 /// A error raised during validation of the candidate.
 #[derive(Debug, Clone)]
 pub enum ValidationError {
@@ -54,3 +70,15 @@ pub enum InvalidCandidate {
 	/// PVF execution (compilation is not included) took more time than was allotted.
 	HardTimeout,
 }
+
+impl From<PrepareError> for ValidationError {
+	fn from(error: PrepareError) -> Self {
+		let error_str = match error {
+			PrepareError::Prevalidation(err) => err,
+			PrepareError::Preparation(err) => err,
+			PrepareError::TimedOut => "preparation timeout".to_owned(),
+			PrepareError::DidNotMakeIt => "communication error".to_owned(),
+		};
+		ValidationError::InvalidCandidate(InvalidCandidate::WorkerReportedError(error_str))
+	}
+}

node/core/pvf/src/execute/worker.rs

@@ -15,7 +15,7 @@
 // along with Polkadot.  If not, see <http://www.gnu.org/licenses/>.
 
 use crate::{
-	artifacts::{Artifact, ArtifactPathId},
+	artifacts::{ArtifactPathId, CompiledArtifact},
 	executor_intf::TaskExecutor,
 	worker_common::{
 		bytes_to_path, framed_recv, framed_send, path_to_bytes, spawn_with_program_path,
@@ -49,8 +49,8 @@ pub enum Outcome {
 	/// PVF execution completed successfully and the result is returned. The worker is ready for
 	/// another job.
 	Ok { result_descriptor: ValidationResult, duration_ms: u64, idle_worker: IdleWorker },
-	/// The candidate validation failed. It may be for example because the preparation process
-	/// produced an error or the wasm execution triggered a trap.
+	/// The candidate validation failed. It may be for example because the wasm execution triggered a trap.
+	/// Errors related to the preparation process are not expected to be encountered by the execution workers.
 	InvalidCandidate { err: String, idle_worker: IdleWorker },
 	/// An internal error happened during the validation. Such an error is most likely related to
 	/// some transient glitch.
@@ -216,18 +216,12 @@ async fn validate_using_artifact(
 		Ok(b) => b,
 	};
 
-	let artifact = match Artifact::deserialize(&artifact_bytes) {
+	let artifact = match CompiledArtifact::decode(&mut artifact_bytes.as_slice()) {
 		Err(e) => return Response::InternalError(format!("artifact deserialization: {:?}", e)),
 		Ok(a) => a,
 	};
 
-	let compiled_artifact = match &artifact {
-		Artifact::PrevalidationErr(msg) => return Response::format_invalid("prevalidation", msg),
-		Artifact::PreparationErr(msg) => return Response::format_invalid("preparation", msg),
-		Artifact::DidntMakeIt => return Response::format_invalid("preparation timeout", ""),
-
-		Artifact::Compiled { compiled_artifact } => compiled_artifact,
-	};
+	let compiled_artifact = artifact.as_ref();
 
 	let validation_started_at = Instant::now();
 	let descriptor_bytes = match unsafe {

node/core/pvf/src/executor_intf.rs

@@ -68,7 +68,7 @@ const CONFIG: Config = Config {
 			native_stack_max: 256 * 1024 * 1024,
 		}),
 		canonicalize_nans: true,
-		parallel_compilation: true,
+		parallel_compilation: false,
 	},
 };