refactor out validation hosts to pool struct (#972)

* refactor out validation hosts to pool struct

* make web-wasm compatible

* typo

* remove now-unused static hosts

polkadot/parachain/Cargo.toml

@@ -16,7 +16,6 @@ sp-wasm-interface = { git = "https://github.com/paritytech/substrate", branch =
 sp-externalities = { git = "https://github.com/paritytech/substrate", branch = "master", optional = true }
 sc-executor = { git = "https://github.com/paritytech/substrate", branch = "master", optional = true }
 sp-io = { git = "https://github.com/paritytech/substrate", branch = "master", optional = true }
-lazy_static = { version = "1.4.0", optional = true }
 parking_lot = { version = "0.10.0", optional = true }
 log = { version = "0.4.8", optional = true }
 
@@ -38,7 +37,6 @@ std = [
 	"sp-std/std",
 	"shared_memory",
 	"sp-core/std",
-	"lazy_static",
 	"parking_lot",
 	"log",
 	"sp-runtime-interface/std",

polkadot/parachain/src/wasm_executor/mod.rs

@@ -28,7 +28,7 @@ use sp_core::traits::CallInWasm;
 use sp_wasm_interface::HostFunctions as _;
 
 #[cfg(not(target_os = "unknown"))]
-pub use validation_host::{run_worker, EXECUTION_TIMEOUT_SEC};
+pub use validation_host::{run_worker, ValidationPool, EXECUTION_TIMEOUT_SEC};
 
 mod validation_host;
 
@@ -48,16 +48,31 @@ impl ParachainExt {
 	}
 }
 
+/// A stub validation-pool defined when compiling for WASM.
+#[cfg(target_os = "unknown")]
+#[derive(Clone)]
+pub struct ValidationPool {
+	_inner: (), // private field means not publicly-instantiable
+}
+
+#[cfg(target_os = "unknown")]
+impl ValidationPool {
+	/// Create a new `ValidationPool`.
+	pub fn new() -> Self {
+		ValidationPool { _inner: () }
+	}
+}
+
 /// WASM code execution mode.
 ///
 /// > Note: When compiling for WASM, the `Remote` variants are not available.
-pub enum ExecutionMode {
+pub enum ExecutionMode<'a> {
 	/// Execute in-process. The execution can not be interrupted or aborted.
 	Local,
 	/// Remote execution in a spawned process.
-	Remote,
+	Remote(&'a ValidationPool),
 	/// Remote execution in a spawned test runner.
-	RemoteTest,
+	RemoteTest(&'a ValidationPool),
 }
 
 /// Error type for the wasm executor
@@ -115,27 +130,27 @@ pub fn validate_candidate<E: Externalities + 'static>(
 	validation_code: &[u8],
 	params: ValidationParams,
 	ext: E,
-	options: ExecutionMode,
+	options: ExecutionMode<'_>,
 ) -> Result<ValidationResult, Error> {
 	match options {
 		ExecutionMode::Local => {
 			validate_candidate_internal(validation_code, &params.encode(), ext)
 		},
 		#[cfg(not(target_os = "unknown"))]
-		ExecutionMode::Remote => {
-			validation_host::validate_candidate(validation_code, params, ext, false)
+		ExecutionMode::Remote(pool) => {
+			pool.validate_candidate(validation_code, params, ext, false)
 		},
 		#[cfg(not(target_os = "unknown"))]
-		ExecutionMode::RemoteTest => {
-			validation_host::validate_candidate(validation_code, params, ext, true)
+		ExecutionMode::RemoteTest(pool) => {
+			pool.validate_candidate(validation_code, params, ext, true)
 		},
 		#[cfg(target_os = "unknown")]
-		ExecutionMode::Remote =>
+		ExecutionMode::Remote(pool) =>
 			Err(Error::System(Box::<dyn std::error::Error + Send + Sync>::from(
 				"Remote validator not available".to_string()
 			) as Box<_>)),
 		#[cfg(target_os = "unknown")]
-		ExecutionMode::RemoteTest =>
+		ExecutionMode::RemoteTest(pool) =>
 			Err(Error::System(Box::<dyn std::error::Error + Send + Sync>::from(
 				"Remote validator not available".to_string()
 			) as Box<_>)),

polkadot/parachain/src/wasm_executor/validation_host.rs

@@ -33,8 +33,6 @@ const WORKER_ARGS_TEST: &[&'static str] = &["--nocapture", "validation_worker"];
 const WORKER_ARG: &'static str = "validation-worker";
 const WORKER_ARGS: &[&'static str] = &[WORKER_ARG];
 
-const NUM_HOSTS: usize = 8;
-
 /// Execution timeout in seconds;
 #[cfg(debug_assertions)]
 pub const EXECUTION_TIMEOUT_SEC: u64 =  30;
@@ -69,8 +67,42 @@ enum Event {
 	WorkerReady = 2,
 }
 
-lazy_static::lazy_static! {
-	static ref HOSTS: [Mutex<ValidationHost>; NUM_HOSTS] = Default::default();
+/// A pool of hosts.
+#[derive(Clone)]
+pub struct ValidationPool {
+	hosts: Arc<Vec<Mutex<ValidationHost>>>,
+}
+
+const DEFAULT_NUM_HOSTS: usize = 8;
+
+impl ValidationPool {
+	/// Creates a validation pool with the default configuration.
+	pub fn new() -> ValidationPool {
+		ValidationPool {
+			hosts: Arc::new((0..DEFAULT_NUM_HOSTS).map(|_| Default::default()).collect()),
+		}
+	}
+
+	/// Validate a candidate under the given validation code using the next
+	/// free validation host.
+	///
+	/// This will fail if the validation code is not a proper parachain validation module.
+	pub fn validate_candidate<E: Externalities>(
+		&self,
+		validation_code: &[u8],
+		params: ValidationParams,
+		externalities: E,
+		test_mode: bool,
+	) -> Result<ValidationResult, Error> {
+		for host in self.hosts.iter() {
+			if let Some(mut host) = host.try_lock() {
+				return host.validate_candidate(validation_code, params, externalities, test_mode);
+			}
+		}
+
+		// all workers are busy, just wait for the first one
+		self.hosts[0].lock().validate_candidate(validation_code, params, externalities, test_mode)
+	}
 }
 
 /// Validation worker process entry point. Runs a loop waiting for candidates to validate
@@ -184,25 +216,6 @@ struct ValidationHost {
 	id: u32,
 }
 
-/// Validate a candidate under the given validation code.
-///
-/// This will fail if the validation code is not a proper parachain validation module.
-pub fn validate_candidate<E: Externalities>(
-	validation_code: &[u8],
-	params: ValidationParams,
-	externalities: E,
-	test_mode: bool,
-) -> Result<ValidationResult, Error> {
-	for host in HOSTS.iter() {
-		if let Some(mut host) = host.try_lock() {
-			return host.validate_candidate(validation_code, params, externalities, test_mode);
-		}
-	}
-
-	// all workers are busy, just wait for the first one
-	HOSTS[0].lock().validate_candidate(validation_code, params, externalities, test_mode)
-}
-
 impl Drop for ValidationHost {
 	fn drop(&mut self) {
 		if let Some(ref mut worker) = &mut self.worker {

polkadot/parachain/tests/adder/mod.rs

@@ -70,6 +70,8 @@ pub fn execute_good_on_parent() {
 		add: 512,
 	};
 
+	let pool = parachain::wasm_executor::ValidationPool::new();
+
 	let ret = parachain::wasm_executor::validate_candidate(
 		TEST_CODE,
 		ValidationParams {
@@ -77,7 +79,7 @@ pub fn execute_good_on_parent() {
 			block_data: block_data.encode(),
 		},
 		DummyExt,
-		parachain::wasm_executor::ExecutionMode::RemoteTest,
+		parachain::wasm_executor::ExecutionMode::RemoteTest(&pool),
 	).unwrap();
 
 	let new_head = HeadData::decode(&mut &ret.head_data[..]).unwrap();
@@ -92,6 +94,7 @@ fn execute_good_chain_on_parent() {
 	let mut number = 0;
 	let mut parent_hash = [0; 32];
 	let mut last_state = 0;
+	let pool = parachain::wasm_executor::ValidationPool::new();
 
 	for add in 0..10 {
 		let parent_head = HeadData {
@@ -112,7 +115,7 @@ fn execute_good_chain_on_parent() {
 				block_data: block_data.encode(),
 			},
 			DummyExt,
-			parachain::wasm_executor::ExecutionMode::RemoteTest,
+			parachain::wasm_executor::ExecutionMode::RemoteTest(&pool),
 		).unwrap();
 
 		let new_head = HeadData::decode(&mut &ret.head_data[..]).unwrap();
@@ -129,6 +132,8 @@ fn execute_good_chain_on_parent() {
 
 #[test]
 fn execute_bad_on_parent() {
+	let pool = parachain::wasm_executor::ValidationPool::new();
+
 	let parent_head = HeadData {
 		number: 0,
 		parent_hash: [0; 32],
@@ -147,6 +152,6 @@ fn execute_bad_on_parent() {
 			block_data: block_data.encode(),
 		},
 		DummyExt,
-		parachain::wasm_executor::ExecutionMode::RemoteTest,
+		parachain::wasm_executor::ExecutionMode::RemoteTest(&pool),
 	).unwrap_err();
 }

polkadot/parachain/tests/wasm_executor/mod.rs

@@ -25,6 +25,8 @@ const INFINITE_LOOP_CODE: &[u8] = halt::WASM_BINARY;
 
 #[test]
 fn terminates_on_timeout() {
+	let pool = parachain::wasm_executor::ValidationPool::new();
+
 	let result = parachain::wasm_executor::validate_candidate(
 		INFINITE_LOOP_CODE,
 		ValidationParams {
@@ -32,7 +34,7 @@ fn terminates_on_timeout() {
 			block_data: Vec::new(),
 		},
 		DummyExt,
-		parachain::wasm_executor::ExecutionMode::RemoteTest,
+		parachain::wasm_executor::ExecutionMode::RemoteTest(&pool),
 	);
 	match result {
 		Err(parachain::wasm_executor::Error::Timeout) => {},
@@ -45,7 +47,11 @@ fn terminates_on_timeout() {
 
 #[test]
 fn parallel_execution() {
+	let pool = parachain::wasm_executor::ValidationPool::new();
+
 	let start = std::time::Instant::now();
+
+	let pool2 = pool.clone();
 	let thread = std::thread::spawn(move ||
 		parachain::wasm_executor::validate_candidate(
 		INFINITE_LOOP_CODE,
@@ -54,7 +60,7 @@ fn parallel_execution() {
 			block_data: Vec::new(),
 		},
 		DummyExt,
-		parachain::wasm_executor::ExecutionMode::RemoteTest,
+		parachain::wasm_executor::ExecutionMode::RemoteTest(&pool2),
 	).ok());
 	let _ = parachain::wasm_executor::validate_candidate(
 		INFINITE_LOOP_CODE,
@@ -63,7 +69,7 @@ fn parallel_execution() {
 			block_data: Vec::new(),
 		},
 		DummyExt,
-		parachain::wasm_executor::ExecutionMode::RemoteTest,
+		parachain::wasm_executor::ExecutionMode::RemoteTest(&pool),
 	);
 	thread.join().unwrap();
 	// total time should be < 2 x EXECUTION_TIMEOUT_SEC