fix(core/telemetry) do not produce allocator metrics if not enabled

CHANGELOG.md

@@ -21,6 +21,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 - telemetry: now `elfo_message_handling_time_seconds` doesn't include the time of task switching if an actor is preempted due to elfo's budget system.
+- telemetry: don't produce allocator metrics if not enabled.
 - telemeter: validate quantiles (0.0..=1.0) in the config.
 
 ## [0.2.0-alpha.14] - 2024-02-27

elfo-core/src/supervisor/measure_poll.rs

@@ -54,11 +54,7 @@ impl<F: Future> Future for MeasurePoll<F> {
             let res = this.inner.poll(cx);
             let elapsed = Instant::now().secs_f64_since(start_time);
             recorder.record_histogram(&BUSY_TIME_SECONDS, elapsed);
-            crate::scope::with(|scope| {
-                recorder.increment_counter(&ALLOCATED_BYTES, scope.take_allocated_bytes() as u64);
-                recorder
-                    .increment_counter(&DEALLOCATED_BYTES, scope.take_deallocated_bytes() as u64);
-            });
+            publish_alloc_metrics(recorder);
             res
         } else {
             crate::coop::reset(None);
@@ -72,3 +68,17 @@ impl<F: Future> Future for MeasurePoll<F> {
         result
     }
 }
+
+fn publish_alloc_metrics(recorder: &dyn metrics::Recorder) {
+    crate::scope::with(|scope| {
+        let allocated = scope.take_allocated_bytes();
+        let deallocated = scope.take_deallocated_bytes();
+
+        if allocated > 0 {
+            recorder.increment_counter(&ALLOCATED_BYTES, allocated as u64);
+        }
+        if deallocated > 0 {
+            recorder.increment_counter(&DEALLOCATED_BYTES, deallocated as u64);
+        }
+    });
+}

examples/Cargo.toml

@@ -9,8 +9,12 @@ license.workspace = true
 edition.workspace = true
 readme.workspace = true
 
+[features]
+unstable = ["elfo/unstable", "elfo-telemeter/unstable"]
+
 [dev-dependencies]
 elfo = { path = "../elfo", features = ["full", "network", "test-util"] }
+elfo-telemeter = { path = "../elfo-telemeter" } # for `AllocatorStats`
 
 anyhow = "1.0.40"
 futures = "0.3.12"

examples/examples/usage/main.rs

@@ -311,6 +311,12 @@ fn topology() -> elfo::Topology {
 //                setup
 //~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
+// Optionally, the allocation statistics can be also enabled.
+#[cfg(feature = "unstable")] // TODO: stabilize it
+#[global_allocator]
+static ALLOCATOR: elfo_telemeter::AllocatorStats<std::alloc::System> =
+    elfo_telemeter::AllocatorStats::new(std::alloc::System);
+
 #[tokio::main]
 async fn main() {
     elfo::init::start(topology()).await;