[otel] Fix memory leak caused by OTEL callbacks (#2771)

src/telemetry/metrics/http/mod.rs

@@ -1,7 +1,7 @@
 pub(super) mod tower_layer;
 
 use once_cell::sync::Lazy;
-use opentelemetry::metrics::{Histogram, MetricsError, ObservableUpDownCounter, Unit};
+use opentelemetry::metrics::{Histogram, MetricsError, Unit, UpDownCounter};
 use opentelemetry::Context as TelemetryContext;
 
 use self::tower_layer::HttpCallMetricTracker;
@@ -16,9 +16,9 @@ pub static HTTP_SERVER_DURATION: Lazy<Histogram<u64>> = Lazy::new(|| {
 		.init()
 });
 
-pub static HTTP_SERVER_ACTIVE_REQUESTS: Lazy<ObservableUpDownCounter<i64>> = Lazy::new(|| {
+pub static HTTP_SERVER_ACTIVE_REQUESTS: Lazy<UpDownCounter<i64>> = Lazy::new(|| {
 	METER_DURATION
-		.i64_observable_up_down_counter("http.server.active_requests")
+		.i64_up_down_counter("http.server.active_requests")
 		.with_description("The number of active HTTP requests.")
 		.init()
 });
@@ -39,19 +39,11 @@ pub static HTTP_SERVER_RESPONSE_SIZE: Lazy<Histogram<u64>> = Lazy::new(|| {
 		.init()
 });
 
-fn observe_request_start(tracker: &HttpCallMetricTracker) -> Result<(), MetricsError> {
-	observe_active_request(1, tracker)
-}
-
-fn observe_request_finish(tracker: &HttpCallMetricTracker) -> Result<(), MetricsError> {
-	observe_active_request(-1, tracker)
-}
-
 fn observe_active_request(value: i64, tracker: &HttpCallMetricTracker) -> Result<(), MetricsError> {
 	let attrs = tracker.active_req_attrs();
 
-	METER_DURATION
-		.register_callback(move |ctx| HTTP_SERVER_ACTIVE_REQUESTS.observe(ctx, value, &attrs))
+	HTTP_SERVER_ACTIVE_REQUESTS.add(&TelemetryContext::current(), value, &attrs);
+	Ok(())
 }
 
 fn record_request_duration(tracker: &HttpCallMetricTracker) {

src/telemetry/metrics/http/tower_layer.rs

@@ -81,6 +81,8 @@ where
 	fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
 		let this = self.project();
 
+		// Initialize the metrics if not already done.
+		if this.tracker.state.get_mut() == &ResultState::None {
 			this.tracker.set_state(ResultState::Started);
 
 			if let Err(err) = on_request_start(this.tracker) {
@@ -88,6 +90,7 @@ where
 				// Consider this request not tracked: reset the state to None, so that the drop handler does not decrease the counter.
 				this.tracker.set_state(ResultState::None);
 			};
+		}
 
 		let response = futures_util::ready!(this.inner.poll(cx));
 
@@ -123,6 +126,7 @@ pub struct HttpCallMetricTracker {
 	finish: Option<Instant>,
 }
 
+#[derive(PartialEq, Eq)]
 pub enum ResultState {
 	/// The result was already processed.
 	None,
@@ -241,13 +245,13 @@ impl Drop for HttpCallMetricTracker {
 }
 
 pub fn on_request_start(tracker: &HttpCallMetricTracker) -> Result<(), MetricsError> {
-	// Setup the active_requests observer
-	super::observe_request_start(tracker)
+	// Increase the number of active requests.
+	super::observe_active_request(1, tracker)
 }
 
 pub fn on_request_finish(tracker: &HttpCallMetricTracker) -> Result<(), MetricsError> {
-	// Setup the active_requests observer
-	super::observe_request_finish(tracker)?;
+	// Decrease the number of active requests.
+	super::observe_active_request(-1, tracker)?;
 
 	// Record the duration of the request.
 	super::record_request_duration(tracker);

src/telemetry/metrics/ws/mod.rs

@@ -3,7 +3,7 @@ use std::time::Instant;
 use once_cell::sync::Lazy;
 use opentelemetry::KeyValue;
 use opentelemetry::{
-	metrics::{Histogram, MetricsError, ObservableUpDownCounter, Unit},
+	metrics::{Histogram, MetricsError, Unit, UpDownCounter},
 	Context as TelemetryContext,
 };
 
@@ -17,9 +17,9 @@ pub static RPC_SERVER_DURATION: Lazy<Histogram<u64>> = Lazy::new(|| {
 		.init()
 });
 
-pub static RPC_SERVER_ACTIVE_CONNECTIONS: Lazy<ObservableUpDownCounter<i64>> = Lazy::new(|| {
+pub static RPC_SERVER_ACTIVE_CONNECTIONS: Lazy<UpDownCounter<i64>> = Lazy::new(|| {
 	METER_DURATION
-		.i64_observable_up_down_counter("rpc.server.active_connections")
+		.i64_up_down_counter("rpc.server.active_connections")
 		.with_description("The number of active WebSocket connections.")
 		.init()
 });
@@ -57,8 +57,8 @@ pub fn on_disconnect() -> Result<(), MetricsError> {
 pub(super) fn observe_active_connection(value: i64) -> Result<(), MetricsError> {
 	let attrs = otel_common_attrs();
 
-	METER_DURATION
-		.register_callback(move |cx| RPC_SERVER_ACTIVE_CONNECTIONS.observe(cx, value, &attrs))
+	RPC_SERVER_ACTIVE_CONNECTIONS.add(&TelemetryContext::current(), value, &attrs);
+	Ok(())
 }
 
 //