rpc-http-threads cli arg (#8890)

* Add optional `rpc-http-threads` cli arg

* Update `http::ServerBuilder`threads

substrate/client/cli/src/commands/run_cmd.rs

@@ -122,6 +122,10 @@ pub struct RunCmd {
 	#[structopt(long = "ws-max-connections", value_name = "COUNT")]
 	pub ws_max_connections: Option<usize>,
 
+	/// Size of the RPC HTTP server thread pool.
+	#[structopt(long = "rpc-http-threads", value_name = "COUNT")]
+	pub rpc_http_threads: Option<usize>,
+
 	/// Specify browser Origins allowed to access the HTTP & WS RPC servers.
 	///
 	/// A comma-separated list of origins (protocol://domain or special `null`
@@ -376,6 +380,10 @@ impl CliConfiguration for RunCmd {
 		Ok(self.ws_max_connections)
 	}
 
+	fn rpc_http_threads(&self) -> Result<Option<usize>> {
+		Ok(self.rpc_http_threads)
+	}
+
 	fn rpc_cors(&self, is_dev: bool) -> Result<Option<Vec<String>>> {
 		Ok(self
 			.rpc_cors

substrate/client/cli/src/config.rs

@@ -358,6 +358,13 @@ pub trait CliConfiguration<DCV: DefaultConfigurationValues = ()>: Sized {
 		Ok(None)
 	}
 
+	/// Get the RPC HTTP thread pool size (`None` for a default 4-thread pool config).
+	///
+	/// By default this is `None`.
+	fn rpc_http_threads(&self) -> Result<Option<usize>> {
+		Ok(None)
+	}
+
 	/// Get the RPC cors (`None` if disabled)
 	///
 	/// By default this is `Some(Vec::new())`.
@@ -526,6 +533,7 @@ pub trait CliConfiguration<DCV: DefaultConfigurationValues = ()>: Sized {
 			rpc_ipc: self.rpc_ipc()?,
 			rpc_methods: self.rpc_methods()?,
 			rpc_ws_max_connections: self.rpc_ws_max_connections()?,
+			rpc_http_threads: self.rpc_http_threads()?,
 			rpc_cors: self.rpc_cors(is_dev)?,
 			prometheus_config: self.prometheus_config(DCV::prometheus_listen_port())?,
 			telemetry_endpoints,

substrate/client/rpc-servers/src/lib.rs

@@ -33,6 +33,9 @@ pub const MAX_PAYLOAD: usize = 15 * 1024 * 1024;
 /// Default maximum number of connections for WS RPC servers.
 const WS_MAX_CONNECTIONS: usize = 100;
 
+/// Default thread pool size for RPC HTTP servers.
+const HTTP_THREADS: usize = 4;
+
 /// The RPC IoHandler containing all requested APIs.
 pub type RpcHandler<T> = pubsub::PubSubHandler<T, RpcMiddleware>;
 
@@ -79,11 +82,12 @@ mod inner {
 	/// **Note**: Only available if `not(target_os = "unknown")`.
 	pub fn start_http<M: pubsub::PubSubMetadata + Default>(
 		addr: &std::net::SocketAddr,
+		thread_pool_size: Option<usize>,
 		cors: Option<&Vec<String>>,
 		io: RpcHandler<M>,
 	) -> io::Result<http::Server> {
 		http::ServerBuilder::new(io)
-			.threads(4)
+			.threads(thread_pool_size.unwrap_or(HTTP_THREADS))
 			.health_api(("/health", "system_health"))
 			.allowed_hosts(hosts_filtering(cors.is_some()))
 			.rest_api(if cors.is_some() {

substrate/client/service/src/config.rs

@@ -89,6 +89,8 @@ pub struct Configuration {
 	pub rpc_ipc: Option<String>,
 	/// Maximum number of connections for WebSockets RPC server. `None` if default.
 	pub rpc_ws_max_connections: Option<usize>,
+	/// Size of the RPC HTTP server thread pool. `None` if default.
+	pub rpc_http_threads: Option<usize>,
 	/// CORS settings for HTTP & WS servers. `None` if all origins are allowed.
 	pub rpc_cors: Option<Vec<String>>,
 	/// RPC methods to expose (by default only a safe subset or all of them).

substrate/client/service/src/lib.rs

@@ -381,6 +381,7 @@ fn start_rpc_servers<
 			config.rpc_http,
 			|address| sc_rpc_server::start_http(
 				address,
+				config.rpc_http_threads,
 				config.rpc_cors.as_ref(),
 				gen_handler(
 					deny_unsafe(&address, &config.rpc_methods),

substrate/client/service/test/src/lib.rs

@@ -262,6 +262,7 @@ fn node_config<G: RuntimeGenesis + 'static, E: ChainSpecExtension + Clone + 'sta
 		rpc_ipc: None,
 		rpc_ws: None,
 		rpc_ws_max_connections: None,
+		rpc_http_threads: None,
 		rpc_cors: None,
 		rpc_methods: Default::default(),
 		prometheus_config: None,

substrate/test-utils/test-runner/src/utils.rs

@@ -124,6 +124,7 @@ pub fn default_config(task_executor: TaskExecutor, mut chain_spec: Box<dyn Chain
 		rpc_ws: None,
 		rpc_ipc: None,
 		rpc_ws_max_connections: None,
+		rpc_http_threads: None,
 		rpc_cors: None,
 		rpc_methods: Default::default(),
 		prometheus_config: None,

substrate/utils/browser/src/lib.rs

@@ -101,6 +101,7 @@ where
 		rpc_ipc: Default::default(),
 		rpc_ws: Default::default(),
 		rpc_ws_max_connections: Default::default(),
+		rpc_http_threads: Default::default(),
 		rpc_methods: Default::default(),
 		state_cache_child_ratio: Default::default(),
 		state_cache_size: Default::default(),