Allow CoreMeter implementations to use their own custom attribute reference

client/src/metrics.rs

@@ -18,6 +18,7 @@ use tower::Service;
 #[derive(Clone, derive_more::DebugCustom)]
 #[debug(fmt = "MetricsContext {{ attribs: {kvs:?}, poll_is_long: {poll_is_long} }}")]
 pub struct MetricsContext {
+    meter: Arc<dyn CoreMeter>,
     kvs: MetricAttributes,
     poll_is_long: bool,
 
@@ -66,19 +67,15 @@ impl MetricsContext {
                 unit: "ms".into(),
                 description: "Histogram of client long-poll request latencies".into(),
             }),
+            meter,
         }
     }
 
-    /// Extend an existing metrics context with new attributes, returning a new one
-    pub(crate) fn with_new_attrs(&self, new_kvs: impl IntoIterator<Item = MetricKeyValue>) -> Self {
-        let mut r = self.clone();
-        r.add_new_attrs(new_kvs);
-        r
-    }
-
-    /// Add new attributes to the context, mutating it
-    pub(crate) fn add_new_attrs(&mut self, new_kvs: impl IntoIterator<Item = MetricKeyValue>) {
-        self.kvs.add_new_attrs(new_kvs);
+    /// Mutate this metrics context with new attributes
+    pub(crate) fn with_new_attrs(&mut self, new_kvs: impl IntoIterator<Item = MetricKeyValue>) {
+        self.kvs = self
+            .meter
+            .extend_attributes(self.kvs.clone(), new_kvs.into());
     }
 
     pub(crate) fn set_is_long_poll(&mut self) {
@@ -152,19 +149,18 @@ impl Service<http::Request<BoxBody>> for GrpcMetricSvc {
         let metrics = self
             .metrics
             .clone()
-            .map(|m| {
+            .map(|mut m| {
                 // Attach labels from client wrapper
                 if let Some(other_labels) = req.extensions_mut().remove::<AttachMetricLabels>() {
                     m.with_new_attrs(other_labels.labels)
-                } else {
-                    m
                 }
+                m
             })
             .and_then(|mut metrics| {
                 // Attach method name label if possible
                 req.uri().to_string().rsplit_once('/').map(|split_tup| {
                     let method_name = split_tup.1;
-                    metrics.add_new_attrs([svc_operation(method_name.to_string())]);
+                    metrics.with_new_attrs([svc_operation(method_name.to_string())]);
                     if LONG_POLL_METHOD_NAMES.contains(&method_name) {
                         metrics.set_is_long_poll();
                     }

core-api/src/telemetry/metrics.rs

@@ -1,10 +1,26 @@
-use std::{borrow::Cow, collections::HashSet, fmt::Debug, sync::Arc};
+use std::{
+    any::Any,
+    borrow::Cow,
+    fmt::Debug,
+    sync::{Arc, OnceLock},
+};
 
 /// Implementors of this trait are expected to be defined in each language's bridge.
 /// The implementor is responsible for the allocation/instantiation of new metric meters which
 /// Core has requested.
 pub trait CoreMeter: Send + Sync + Debug {
-    fn new_attributes(&self, attribs: MetricsAttributesOptions) -> MetricAttributes;
+    /// Given some k/v pairs, create a return a new instantiated instance of metric attributes.
+    /// Only [MetricAttributes] created by this meter can be used when calling record on instruments
+    /// created by this meter.
+    fn new_attributes(&self, attribs: NewAttributes) -> MetricAttributes;
+    /// Extend some existing attributes with new values. Implementations should create new instances
+    /// when doing so, rather than mutating whatever is backing the passed in `existing` attributes.
+    /// Ideally that new instance retains a ref to the extended old attribute, promoting re-use.
+    fn extend_attributes(
+        &self,
+        existing: MetricAttributes,
+        attribs: NewAttributes,
+    ) -> MetricAttributes;
     fn counter(&self, params: MetricParameters) -> Arc<dyn Counter>;
     fn histogram(&self, params: MetricParameters) -> Arc<dyn Histogram>;
     fn gauge(&self, params: MetricParameters) -> Arc<dyn Gauge>;
@@ -36,48 +52,22 @@ impl From<&'static str> for MetricParameters {
 #[derive(derive_more::Constructor, Clone, Debug)]
 pub struct TemporalMeter {
     pub inner: Arc<dyn CoreMeter>,
-    pub default_attribs: MetricsAttributesOptions,
-}
-
-#[derive(Debug, Clone)]
-pub enum MetricEvent {
-    Create {
-        params: MetricParameters,
-        id: u64,
-        kind: MetricKind,
-    },
-    CreateAttributes {
-        id: u64,
-        attributes: Vec<MetricKeyValue>,
-    },
-    Update {
-        id: u64,
-        attributes: LangMetricAttributes,
-        update: MetricUpdateVal,
-    },
-}
-#[derive(Debug, Clone, Copy)]
-pub enum MetricKind {
-    Counter,
-    Gauge,
-    Histogram,
-}
-#[derive(Debug, Clone, Copy)]
-pub enum MetricUpdateVal {
-    // Currently all deltas are natural numbers
-    Delta(u64),
-    // Currently all values are natural numbers
-    Value(u64),
-}
-
-pub trait MetricCallBufferer: Send + Sync {
-    fn retrieve(&self) -> Vec<MetricEvent>;
+    pub default_attribs: NewAttributes,
 }
 
 impl CoreMeter for Arc<dyn CoreMeter> {
-    fn new_attributes(&self, attribs: MetricsAttributesOptions) -> MetricAttributes {
+    fn new_attributes(&self, attribs: NewAttributes) -> MetricAttributes {
         self.as_ref().new_attributes(attribs)
     }
+
+    fn extend_attributes(
+        &self,
+        existing: MetricAttributes,
+        attribs: NewAttributes,
+    ) -> MetricAttributes {
+        self.as_ref().extend_attributes(existing, attribs)
+    }
+
     fn counter(&self, params: MetricParameters) -> Arc<dyn Counter> {
         self.as_ref().counter(params)
     }
@@ -98,60 +88,37 @@ pub enum MetricAttributes {
     OTel {
         kvs: Arc<Vec<opentelemetry::KeyValue>>,
     },
-    Lang(LangMetricAttributes),
-}
-#[derive(Clone, Debug)]
-pub struct LangMetricAttributes {
-    /// A set of references to attributes stored in lang memory. All referenced attributes should
-    /// be attached to the metric when recording.
-    pub ids: HashSet<u64>,
-    /// If populated, these key values should also be used in addition to the referred-to
-    /// existing attributes when recording
-    pub new_attributes: Vec<MetricKeyValue>,
+    Buffer(BufferAttributes),
+    Dynamic(Arc<dyn CustomMetricAttributes>),
 }
 
-impl MetricAttributes {
-    /// Extend existing metrics attributes with others, returning a new instance
-    pub fn merge(&self, other: MetricAttributes) -> Self {
-        let mut me = self.clone();
-        match (&mut me, other) {
-            #[cfg(feature = "otel_impls")]
-            (MetricAttributes::OTel { ref mut kvs }, MetricAttributes::OTel { kvs: other_kvs }) => {
-                Arc::make_mut(kvs).extend((*other_kvs).clone());
-            }
-            (MetricAttributes::Lang(ref mut l), MetricAttributes::Lang(ol)) => {
-                l.ids.extend(ol.ids);
-                l.new_attributes.extend(ol.new_attributes);
-            }
-            _ => panic!("Cannot merge metric attributes of different kinds"),
-        }
-        me
-    }
-
-    /// Mutate self to add new kvs
-    pub fn add_new_attrs(&mut self, new_kvs: impl IntoIterator<Item = MetricKeyValue>) {
-        match self {
-            #[cfg(feature = "otel_impls")]
-            MetricAttributes::OTel { ref mut kvs, .. } => {
-                Arc::make_mut(kvs).extend(new_kvs.into_iter().map(Into::into));
-            }
-            MetricAttributes::Lang(ref mut attrs, ..) => {
-                attrs.new_attributes.extend(new_kvs);
-            }
-        }
-    }
+/// A reference to some attributes created lang side.
+pub trait CustomMetricAttributes: Debug + Send + Sync {
+    /// Must be implemented to work around existing type system restrictions, see
+    /// [here](https://internals.rust-lang.org/t/downcast-not-from-any-but-from-any-trait/16736/12)
+    fn as_any(self: Arc<Self>) -> Arc<dyn Any + Send + Sync>;
 }
 
 /// Options that are attached to metrics on a per-call basis
 #[derive(Clone, Debug, Default, derive_more::Constructor)]
-pub struct MetricsAttributesOptions {
+pub struct NewAttributes {
     pub attributes: Vec<MetricKeyValue>,
 }
-impl MetricsAttributesOptions {
+impl NewAttributes {
     pub fn extend(&mut self, new_kvs: impl IntoIterator<Item = MetricKeyValue>) {
         self.attributes.extend(new_kvs)
     }
 }
+impl<I> From<I> for NewAttributes
+where
+    I: IntoIterator<Item = MetricKeyValue>,
+{
+    fn from(value: I) -> Self {
+        Self {
+            attributes: value.into_iter().collect(),
+        }
+    }
+}
 
 /// A K/V pair that can be used to label a specific recording of a metric
 #[derive(Clone, Debug)]
@@ -197,14 +164,92 @@ pub trait Gauge: Send + Sync {
     fn record(&self, value: u64, attributes: &MetricAttributes);
 }
 
+#[derive(Debug, Clone)]
+pub enum MetricEvent<I: BufferInstrumentRef> {
+    Create {
+        params: MetricParameters,
+        /// One you receive this event, call `set` on this with the initialized instrument reference
+        populate_into: LazyBufferInstrument<I>,
+        kind: MetricKind,
+    },
+    CreateAttributes {
+        /// One you receive this event, call `set` on this with the initialized attributes
+        populate_into: BufferAttributes,
+        /// If not `None`, use these already-initialized attributes as the base (extended with
+        /// `attributes`) for the ones you are about to initialize.
+        append_from: Option<BufferAttributes>,
+        attributes: Vec<MetricKeyValue>,
+    },
+    Update {
+        instrument: LazyBufferInstrument<I>,
+        attributes: BufferAttributes,
+        update: MetricUpdateVal,
+    },
+}
+#[derive(Debug, Clone, Copy)]
+pub enum MetricKind {
+    Counter,
+    Gauge,
+    Histogram,
+}
+#[derive(Debug, Clone, Copy)]
+pub enum MetricUpdateVal {
+    // Currently all deltas are natural numbers
+    Delta(u64),
+    // Currently all values are natural numbers
+    Value(u64),
+}
+
+pub trait MetricCallBufferer<I: BufferInstrumentRef>: Send + Sync {
+    fn retrieve(&self) -> Vec<MetricEvent<I>>;
+}
+
+/// A lazy reference to some metrics buffer attributes
+pub type BufferAttributes = LazyRef<Arc<dyn CustomMetricAttributes + 'static>>;
+
+/// Types lang uses to contain references to its lang-side defined instrument references must
+/// implement this marker trait
+pub trait BufferInstrumentRef {}
+/// A lazy reference to a metrics buffer instrument
+pub type LazyBufferInstrument<T> = LazyRef<Arc<T>>;
+
+#[derive(Debug, Clone)]
+pub struct LazyRef<T> {
+    to_be_initted: Arc<OnceLock<T>>,
+}
+impl<T> LazyRef<T> {
+    pub fn hole() -> Self {
+        Self {
+            to_be_initted: Arc::new(OnceLock::new()),
+        }
+    }
+
+    /// Get the reference you previously initialized
+    ///
+    /// # Panics
+    /// If `set` has not already been called. You must set the reference before using it.
+    pub fn get(&self) -> &T {
+        self.to_be_initted
+            .get()
+            .expect("You must initialize the reference before using it")
+    }
+
+    /// Assigns a value to fill this reference.
+    /// Returns according to semantics of [OnceLock].
+    pub fn set(&self, val: T) -> Result<(), T> {
+        self.to_be_initted.set(val)
+    }
+}
+
 #[derive(Debug)]
 pub struct NoOpCoreMeter;
 impl CoreMeter for NoOpCoreMeter {
-    fn new_attributes(&self, _: MetricsAttributesOptions) -> MetricAttributes {
-        MetricAttributes::Lang(LangMetricAttributes {
-            ids: HashSet::new(),
-            new_attributes: vec![],
-        })
+    fn new_attributes(&self, _: NewAttributes) -> MetricAttributes {
+        MetricAttributes::Dynamic(Arc::new(NoOpAttributes))
+    }
+
+    fn extend_attributes(&self, existing: MetricAttributes, _: NewAttributes) -> MetricAttributes {
+        existing
     }
 
     fn counter(&self, _: MetricParameters) -> Arc<dyn Counter> {
@@ -231,6 +276,14 @@ impl Gauge for NoOpInstrument {
     fn record(&self, _: u64, _: &MetricAttributes) {}
 }
 
+#[derive(Debug, Clone)]
+pub struct NoOpAttributes;
+impl CustomMetricAttributes for NoOpAttributes {
+    fn as_any(self: Arc<Self>) -> Arc<dyn Any + Send + Sync> {
+        self as Arc<dyn Any + Send + Sync>
+    }
+}
+
 #[cfg(feature = "otel_impls")]
 mod otel_impls {
     use super::*;