Reduce cost of no attribute counters

opentelemetry-sdk/CHANGELOG.md

@@ -46,6 +46,10 @@
   - `LoggerProviderInner` is no longer `pub (crate)`
   - `Logger.provider()` now returns `&LoggerProvider` instead of an `Option<LoggerProvider>`
 
+- [1519](https://github.com/open-telemetry/opentelemetry-rust/pull/1519) Performance improvements 
+    when calling `Counter::add()` and `UpDownCounter::add()` with an empty set of attributes
+    (e.g. `counter.Add(5, &[])`)
+
 ### Fixed
 
 - [#1481](https://github.com/open-telemetry/opentelemetry-rust/pull/1481) Fix error message caused by race condition when using PeriodicReader

opentelemetry-sdk/src/metrics/internal/mod.rs

@@ -6,10 +6,26 @@ mod sum;
 
 use core::fmt;
 use std::ops::{Add, AddAssign, Sub};
+use std::sync::atomic::{AtomicI64, AtomicU64, Ordering};
+use std::sync::Mutex;
 
 pub(crate) use aggregate::{AggregateBuilder, ComputeAggregation, Measure};
 pub(crate) use exponential_histogram::{EXPO_MAX_SCALE, EXPO_MIN_SCALE};
 
+/// Marks a type that can have a value added and retrieved atomically. Required since
+/// different types have different backing atomic mechanisms
+pub(crate) trait AtomicTracker<T>: Sync + Send + 'static {
+    fn add(&self, value: T);
+    fn get_value(&self) -> T;
+    fn get_and_reset_value(&self) -> T;
+}
+
+/// Marks a type that can have an atomic tracker generated for it
+pub(crate) trait AtomicallyUpdate<T> {
+    type AtomicTracker: AtomicTracker<T>;
+    fn new_atomic_tracker() -> Self::AtomicTracker;
+}
+
 pub(crate) trait Number<T>:
     Add<Output = T>
     + AddAssign
@@ -23,6 +39,7 @@ pub(crate) trait Number<T>:
     + Send
     + Sync
     + 'static
+    + AtomicallyUpdate<T>
 {
     fn min() -> Self;
     fn max() -> Self;
@@ -71,3 +88,159 @@ impl Number<f64> for f64 {
         self
     }
 }
+
+impl AtomicTracker<u64> for AtomicU64 {
+    fn add(&self, value: u64) {
+        self.fetch_add(value, Ordering::Relaxed);
+    }
+
+    fn get_value(&self) -> u64 {
+        self.load(Ordering::Relaxed)
+    }
+
+    fn get_and_reset_value(&self) -> u64 {
+        self.swap(0, Ordering::Relaxed)
+    }
+}
+
+impl AtomicallyUpdate<u64> for u64 {
+    type AtomicTracker = AtomicU64;
+
+    fn new_atomic_tracker() -> Self::AtomicTracker {
+        AtomicU64::new(0)
+    }
+}
+
+impl AtomicTracker<i64> for AtomicI64 {
+    fn add(&self, value: i64) {
+        self.fetch_add(value, Ordering::Relaxed);
+    }
+
+    fn get_value(&self) -> i64 {
+        self.load(Ordering::Relaxed)
+    }
+
+    fn get_and_reset_value(&self) -> i64 {
+        self.swap(0, Ordering::Relaxed)
+    }
+}
+
+impl AtomicallyUpdate<i64> for i64 {
+    type AtomicTracker = AtomicI64;
+
+    fn new_atomic_tracker() -> Self::AtomicTracker {
+        AtomicI64::new(0)
+    }
+}
+
+pub(crate) struct F64AtomicTracker {
+    inner: Mutex<f64>, // Floating points don't have true atomics, so we need to use mutex for them
+}
+
+impl F64AtomicTracker {
+    fn new() -> Self {
+        F64AtomicTracker {
+            inner: Mutex::new(0.0),
+        }
+    }
+}
+
+impl AtomicTracker<f64> for F64AtomicTracker {
+    fn add(&self, value: f64) {
+        let mut guard = self.inner.lock().expect("F64 mutex was poisoned");
+        *guard += value;
+    }
+
+    fn get_value(&self) -> f64 {
+        let guard = self.inner.lock().expect("F64 mutex was poisoned");
+        *guard
+    }
+
+    fn get_and_reset_value(&self) -> f64 {
+        let mut guard = self.inner.lock().expect("F64 mutex was poisoned");
+        let value = *guard;
+        *guard = 0.0;
+
+        value
+    }
+}
+
+impl AtomicallyUpdate<f64> for f64 {
+    type AtomicTracker = F64AtomicTracker;
+
+    fn new_atomic_tracker() -> Self::AtomicTracker {
+        F64AtomicTracker::new()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn can_add_and_get_u64_atomic_value() {
+        let atomic = u64::new_atomic_tracker();
+        atomic.add(15);
+        atomic.add(10);
+
+        let value = atomic.get_value();
+        assert_eq!(value, 25);
+    }
+
+    #[test]
+    fn can_reset_u64_atomic_value() {
+        let atomic = u64::new_atomic_tracker();
+        atomic.add(15);
+
+        let value = atomic.get_and_reset_value();
+        let value2 = atomic.get_value();
+
+        assert_eq!(value, 15, "Incorrect first value");
+        assert_eq!(value2, 0, "Incorrect second value");
+    }
+
+    #[test]
+    fn can_add_and_get_i64_atomic_value() {
+        let atomic = i64::new_atomic_tracker();
+        atomic.add(15);
+        atomic.add(-10);
+
+        let value = atomic.get_value();
+        assert_eq!(value, 5);
+    }
+
+    #[test]
+    fn can_reset_i64_atomic_value() {
+        let atomic = i64::new_atomic_tracker();
+        atomic.add(15);
+
+        let value = atomic.get_and_reset_value();
+        let value2 = atomic.get_value();
+
+        assert_eq!(value, 15, "Incorrect first value");
+        assert_eq!(value2, 0, "Incorrect second value");
+    }
+
+    #[test]
+    fn can_add_and_get_f64_atomic_value() {
+        let atomic = f64::new_atomic_tracker();
+        atomic.add(15.3);
+        atomic.add(10.4);
+
+        let value = atomic.get_value();
+
+        assert!(f64::abs(25.7 - value) < 0.0001);
+    }
+
+    #[test]
+    fn can_reset_f64_atomic_value() {
+        let atomic = f64::new_atomic_tracker();
+        atomic.add(15.5);
+
+        let value = atomic.get_and_reset_value();
+        let value2 = atomic.get_value();
+
+        assert!(f64::abs(15.5 - value) < 0.0001, "Incorrect first value");
+        assert!(f64::abs(0.0 - value2) < 0.0001, "Incorrect second value");
+    }
+}