Add prometheus registry to transaction pool, with couple of initial metrics (#5657)

* make new contructor

* add metrics to txpool

* fix review

* fix doc comment

* change to counters

* Update client/transaction-pool/src/metrics.rs

Co-Authored-By: Max Inden <mail@max-inden.de>

* Update client/transaction-pool/src/metrics.rs

Co-Authored-By: Max Inden <mail@max-inden.de>

* Update client/transaction-pool/src/metrics.rs

Co-Authored-By: Max Inden <mail@max-inden.de>

* Update client/transaction-pool/src/lib.rs

Co-Authored-By: Max Inden <mail@max-inden.de>

* Update client/transaction-pool/src/lib.rs

Co-Authored-By: Max Inden <mail@max-inden.de>

* use dedicated wrapper

Co-authored-by: Max Inden <mail@max-inden.de>

substrate/client/transaction-pool/src/metrics.rs

@@ -0,0 +1,69 @@
+// Copyright 2020 Parity Technologies (UK) Ltd.
+// This file is part of Substrate.
+
+// Substrate 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.
+
+// Substrate 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 Substrate.  If not, see <http://www.gnu.org/licenses/>.
+
+//! Transaction pool Prometheus metrics.
+
+use std::sync::Arc;
+
+use prometheus_endpoint::{register, Counter, PrometheusError, Registry, U64};
+
+#[derive(Clone, Default)]
+pub struct MetricsLink(Arc<Option<Metrics>>);
+
+impl MetricsLink {
+	pub fn new(registry: Option<&Registry>) -> Self {
+		Self(Arc::new(
+			registry.and_then(|registry|
+				Metrics::register(registry)
+					.map_err(|err| { log::warn!("Failed to register prometheus metrics: {}", err); })
+					.ok()
+			)
+		))
+	}
+
+	pub fn report(&self, do_this: impl FnOnce(&Metrics)) {
+		if let Some(metrics) = self.0.as_ref() {
+			do_this(metrics);
+		}
+	}
+}
+
+/// Transaction pool Prometheus metrics.
+pub struct Metrics {
+	pub validations_scheduled: Counter<U64>,
+	pub validations_finished: Counter<U64>,
+}
+
+impl Metrics {
+	pub fn register(registry: &Registry) -> Result<Self, PrometheusError> {
+		Ok(Self {
+			validations_scheduled: register(
+				Counter::new(
+					"sub_txpool_validations_scheduled",
+					"Total number of transactions scheduled for validation",
+				)?,
+				registry,
+			)?,
+			validations_finished: register(
+				Counter::new(
+					"sub_txpool_validations_finished",
+					"Total number of transactions that finished validation",
+				)?,
+				registry,
+			)?,
+		})
+	}
+}