use RWMutex for map access in the metrics SDK

Author: dashpole

CHANGELOG.md

@@ -31,6 +31,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 - `WithInstrumentationAttributes` in `go.opentelemetry.io/otel/meter` synchronously de-duplicates the passed attributes instead of delegating it to the returned `MeterOption`. (#7266)
 - `WithInstrumentationAttributes` in `go.opentelemetry.io/otel/log` synchronously de-duplicates the passed attributes instead of delegating it to the returned `LoggerOption`. (#7266)
 - `Distinct` in `go.opentelemetry.io/otel/attribute` is no longer guaranteed to uniquely identify an attribute set. Collisions between `Distinct` values for different Sets are possible with extremely high cardinality (billions of series per instrument), but are highly unlikely. (#7175)
+- Improve performance of concurrent measurements in `go.opentelemetry.io/otel/sdk/metric`. (#7189)
 
 <!-- Released section -->
 <!-- Don't change this section unless doing release -->

sdk/metric/internal/aggregate/atomic.go

@@ -0,0 +1,108 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package aggregate // import "go.opentelemetry.io/otel/sdk/metric/internal/aggregate"
+
+import (
+	"math"
+	"sync/atomic"
+)
+
+// atomicSum is an efficient way of adding to a number which is either an
+// int64 or float64.
+type atomicSum[N int64 | float64] struct {
+	// nFloatBits contains only the non-integer portion of the counter.
+	nFloatBits atomic.Uint64
+	// nInt contains only the integer portion of the counter.
+	nInt atomic.Int64
+}
+
+// load returns the float or integer value.
+func (n *atomicSum[N]) load() N {
+	fval := math.Float64frombits(n.nFloatBits.Load())
+	ival := n.nInt.Load()
+	return N(fval + float64(ival))
+}
+
+func (n *atomicSum[N]) add(value N) {
+	ival := int64(value)
+	// This case is where the value is an int, or if it is a whole-numbered float.
+	if float64(ival) == float64(value) {
+		n.nInt.Add(ival)
+		return
+	}
+
+	// Value must be a float below.
+	for {
+		oldBits := n.nFloatBits.Load()
+		newBits := math.Float64bits(math.Float64frombits(oldBits) + float64(value))
+		if n.nFloatBits.CompareAndSwap(oldBits, newBits) {
+			return
+		}
+	}
+}
+
+type atomicIntOrFloat[N int64 | float64] struct {
+	// nFloatBits contains the float bits if N is float64.
+	nFloatBits atomic.Uint64
+	// nInt contains the int64 if N is int64
+	nInt atomic.Int64
+}
+
+func (n *atomicIntOrFloat[N]) store(value N) {
+	switch v := any(value).(type) {
+	case int64:
+		n.nInt.Store(v)
+	case float64:
+		n.nFloatBits.Store(math.Float64bits(v))
+	}
+}
+
+func (n *atomicIntOrFloat[N]) load() (value N) {
+	switch any(value).(type) {
+	case int64:
+		value = N(n.nInt.Load())
+	case float64:
+		value = N(math.Float64frombits(n.nFloatBits.Load()))
+	}
+	return
+}
+
+func (n *atomicIntOrFloat[N]) compareAndSwap(old, new N) bool {
+	switch any(old).(type) {
+	case float64:
+		return n.nFloatBits.CompareAndSwap(math.Float64bits(float64(old)), math.Float64bits(float64(new)))
+	}
+	return n.nInt.CompareAndSwap(int64(old), int64(new))
+}
+
+type atomicMinMax[N int64 | float64] struct {
+	min   atomicIntOrFloat[N]
+	max   atomicIntOrFloat[N]
+	isSet atomic.Bool
+}
+
+func (n *atomicMinMax[N]) observe(value N) {
+	for {
+		minLoaded := n.min.load()
+		if (!n.isSet.Load() || value < minLoaded) && !n.min.compareAndSwap(minLoaded, value) {
+			// We got a new min value, but lost the race. Try again.
+			continue
+		}
+		maxLoaded := n.max.load()
+		if (!n.isSet.Load() || value > maxLoaded) && !n.max.compareAndSwap(maxLoaded, value) {
+			// We got a new max value, but lost the race. Try again.
+			continue
+		}
+		break
+	}
+	n.isSet.Store(true)
+}
+
+func (n *atomicMinMax[N]) loadMin() (value N) {
+	return n.min.load()
+}
+
+func (n *atomicMinMax[N]) loadMax() (value N) {
+	return n.max.load()
+}