WIP: internal/traceprof: make endpoint call counting efficient

Switch to a data structure designed for efficient concurrent updates for
endpoint call counting. This is a prerequisite for enabling the feature
by default. TODO: say more about the choice of library

Benchmark results on my M1 Max Macbook Pro:

	goos: darwin
	goarch: arm64
	pkg: gopkg.in/DataDog/dd-trace-go.v1/internal/traceprof
	cpu: Apple M1 Max
					 │   before.txt   │               after.txt               │
					 │     sec/op     │    sec/op      vs base                │
	EndpointCounter/enabled=true-10    139.800n ± 11%    5.000n ± 18%  -96.42% (p=0.000 n=10)
	EndpointCounter/enabled=false-10    0.2716n ±  5%   0.2682n ±  1%        ~ (p=0.118 n=10)
	geomean                              6.162n          1.158n        -81.21%

					 │  before.txt  │              after.txt              │
					 │     B/op     │    B/op     vs base                 │
	EndpointCounter/enabled=true-10    0.000 ± 0%     0.000 ± 0%       ~ (p=1.000 n=10) ¹
	EndpointCounter/enabled=false-10   0.000 ± 0%     0.000 ± 0%       ~ (p=1.000 n=10) ¹
	geomean                                       ²               +0.00%                ²
	¹ all samples are equal
	² summaries must be >0 to compute geomean

					 │  before.txt  │              after.txt              │
					 │  allocs/op   │ allocs/op   vs base                 │
	EndpointCounter/enabled=true-10    0.000 ± 0%     0.000 ± 0%       ~ (p=1.000 n=10) ¹
	EndpointCounter/enabled=false-10   0.000 ± 0%     0.000 ± 0%       ~ (p=1.000 n=10) ¹
	geomean                                       ²               +0.00%                ²
	¹ all samples are equal
	² summaries must be >0 to compute geomean

go.mod

@@ -81,6 +81,7 @@ require (
 	github.com/miekg/dns v1.1.55
 	github.com/mitchellh/mapstructure v1.5.1-0.20231216201459-8508981c8b6c
 	github.com/opentracing/opentracing-go v1.2.0
+	github.com/puzpuzpuz/xsync/v3 v3.5.0
 	github.com/redis/go-redis/v9 v9.1.0
 	github.com/richardartoul/molecule v1.0.1-0.20240531184615-7ca0df43c0b3
 	github.com/segmentio/kafka-go v0.4.42

go.sum

@@ -855,6 +855,8 @@ github.com/prometheus/procfs v0.0.2/go.mod h1:TjEm7ze935MbeOT/UhFTIMYKhuLP4wbCsT
 github.com/prometheus/procfs v0.0.8/go.mod h1:7Qr8sr6344vo1JqZ6HhLceV9o3AJ1Ff+GxbHq6oeK9A=
 github.com/prometheus/procfs v0.15.0 h1:A82kmvXJq2jTu5YUhSGNlYoxh85zLnKgPz4bMZgI5Ek=
 github.com/prometheus/procfs v0.15.0/go.mod h1:Y0RJ/Y5g5wJpkTisOtqwDSo4HwhGmLB4VQSw2sQJLHk=
+github.com/puzpuzpuz/xsync/v3 v3.5.0 h1:i+cMcpEDY1BkNm7lPDkCtE4oElsYLn+EKF8kAu2vXT4=
+github.com/puzpuzpuz/xsync/v3 v3.5.0/go.mod h1:VjzYrABPabuM4KyBh1Ftq6u8nhwY5tBPKP9jpmh0nnA=
 github.com/rcrowley/go-metrics v0.0.0-20201227073835-cf1acfcdf475 h1:N/ElC8H3+5XpJzTSTfLsJV/mx9Q9g7kxmchpfZyxgzM=
 github.com/rcrowley/go-metrics v0.0.0-20201227073835-cf1acfcdf475/go.mod h1:bCqnVzQkZxMG4s8nGwiZ5l3QUCyqpo9Y+/ZMZ9VjZe4=
 github.com/redis/go-redis/v9 v9.1.0 h1:137FnGdk+EQdCbye1FW+qOEcY5S+SpY9T0NiuqvtfMY=

internal/apps/go.mod

@@ -35,6 +35,7 @@ require (
 	github.com/outcaste-io/ristretto v0.2.3 // indirect
 	github.com/pmezard/go-difflib v1.0.1-0.20181226105442-5d4384ee4fb2 // indirect
 	github.com/power-devops/perfstat v0.0.0-20220216144756-c35f1ee13d7c // indirect
+	github.com/puzpuzpuz/xsync/v3 v3.5.0 // indirect
 	github.com/ryanuber/go-glob v1.0.0 // indirect
 	github.com/shirou/gopsutil/v3 v3.24.4 // indirect
 	github.com/shoenig/go-m1cpu v0.1.6 // indirect

internal/apps/go.sum

@@ -139,6 +139,8 @@ github.com/prometheus/common v0.54.0 h1:ZlZy0BgJhTwVZUn7dLOkwCZHUkrAqd3WYtcFCWnM
 github.com/prometheus/common v0.54.0/go.mod h1:/TQgMJP5CuVYveyT7n/0Ix8yLNNXy9yRSkhnLTHPDIQ=
 github.com/prometheus/procfs v0.15.0 h1:A82kmvXJq2jTu5YUhSGNlYoxh85zLnKgPz4bMZgI5Ek=
 github.com/prometheus/procfs v0.15.0/go.mod h1:Y0RJ/Y5g5wJpkTisOtqwDSo4HwhGmLB4VQSw2sQJLHk=
+github.com/puzpuzpuz/xsync/v3 v3.5.0 h1:i+cMcpEDY1BkNm7lPDkCtE4oElsYLn+EKF8kAu2vXT4=
+github.com/puzpuzpuz/xsync/v3 v3.5.0/go.mod h1:VjzYrABPabuM4KyBh1Ftq6u8nhwY5tBPKP9jpmh0nnA=
 github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec h1:W09IVJc94icq4NjY3clb7Lk8O1qJ8BdBEF8z0ibU0rE=
 github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec/go.mod h1:qqbHyh8v60DhA7CoWK5oRCqLrMHRGoxYCSS9EjAz6Eo=
 github.com/richardartoul/molecule v1.0.1-0.20240531184615-7ca0df43c0b3 h1:4+LEVOB87y175cLJC/mbsgKmoDOjrBldtXvioEy96WY=

internal/exectracetest/go.mod

@@ -46,6 +46,7 @@ require (
 	github.com/philhofer/fwd v1.1.3-0.20240612014219-fbbf4953d986 // indirect
 	github.com/pkg/errors v0.9.1 // indirect
 	github.com/power-devops/perfstat v0.0.0-20220216144756-c35f1ee13d7c // indirect
+	github.com/puzpuzpuz/xsync/v3 v3.5.0 // indirect
 	github.com/ryanuber/go-glob v1.0.0 // indirect
 	github.com/secure-systems-lab/go-securesystemslib v0.7.0 // indirect
 	github.com/shirou/gopsutil/v3 v3.24.4 // indirect

internal/exectracetest/go.sum

@@ -146,6 +146,8 @@ github.com/prometheus/common v0.54.0 h1:ZlZy0BgJhTwVZUn7dLOkwCZHUkrAqd3WYtcFCWnM
 github.com/prometheus/common v0.54.0/go.mod h1:/TQgMJP5CuVYveyT7n/0Ix8yLNNXy9yRSkhnLTHPDIQ=
 github.com/prometheus/procfs v0.15.0 h1:A82kmvXJq2jTu5YUhSGNlYoxh85zLnKgPz4bMZgI5Ek=
 github.com/prometheus/procfs v0.15.0/go.mod h1:Y0RJ/Y5g5wJpkTisOtqwDSo4HwhGmLB4VQSw2sQJLHk=
+github.com/puzpuzpuz/xsync/v3 v3.5.0 h1:i+cMcpEDY1BkNm7lPDkCtE4oElsYLn+EKF8kAu2vXT4=
+github.com/puzpuzpuz/xsync/v3 v3.5.0/go.mod h1:VjzYrABPabuM4KyBh1Ftq6u8nhwY5tBPKP9jpmh0nnA=
 github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec h1:W09IVJc94icq4NjY3clb7Lk8O1qJ8BdBEF8z0ibU0rE=
 github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec/go.mod h1:qqbHyh8v60DhA7CoWK5oRCqLrMHRGoxYCSS9EjAz6Eo=
 github.com/richardartoul/molecule v1.0.1-0.20240531184615-7ca0df43c0b3 h1:4+LEVOB87y175cLJC/mbsgKmoDOjrBldtXvioEy96WY=

internal/orchestrion/_integration/go.mod

@@ -243,6 +243,7 @@ require (
 	github.com/pkg/errors v0.9.1 // indirect
 	github.com/pmezard/go-difflib v1.0.1-0.20181226105442-5d4384ee4fb2 // indirect
 	github.com/power-devops/perfstat v0.0.0-20240221224432-82ca36839d55 // indirect
+	github.com/puzpuzpuz/xsync/v3 v3.5.0 // indirect
 	github.com/rcrowley/go-metrics v0.0.0-20201227073835-cf1acfcdf475 // indirect
 	github.com/richardartoul/molecule v1.0.1-0.20240531184615-7ca0df43c0b3 // indirect
 	github.com/rivo/uniseg v0.4.7 // indirect

internal/orchestrion/_integration/go.sum

@@ -1489,6 +1489,8 @@ github.com/prometheus/common v0.60.0 h1:+V9PAREWNvJMAuJ1x1BaWl9dewMW4YrHZQbx0sJN
 github.com/prometheus/common v0.60.0/go.mod h1:h0LYf1R1deLSKtD4Vdg8gy4RuOvENW2J/h19V5NADQw=
 github.com/prometheus/procfs v0.15.1 h1:YagwOFzUgYfKKHX6Dr+sHT7km/hxC76UB0learggepc=
 github.com/prometheus/procfs v0.15.1/go.mod h1:fB45yRUv8NstnjriLhBQLuOUt+WW4BsoGhij/e3PBqk=
+github.com/puzpuzpuz/xsync/v3 v3.5.0 h1:i+cMcpEDY1BkNm7lPDkCtE4oElsYLn+EKF8kAu2vXT4=
+github.com/puzpuzpuz/xsync/v3 v3.5.0/go.mod h1:VjzYrABPabuM4KyBh1Ftq6u8nhwY5tBPKP9jpmh0nnA=
 github.com/rcrowley/go-metrics v0.0.0-20201227073835-cf1acfcdf475 h1:N/ElC8H3+5XpJzTSTfLsJV/mx9Q9g7kxmchpfZyxgzM=
 github.com/rcrowley/go-metrics v0.0.0-20201227073835-cf1acfcdf475/go.mod h1:bCqnVzQkZxMG4s8nGwiZ5l3QUCyqpo9Y+/ZMZ9VjZe4=
 github.com/redis/go-redis/v9 v9.7.0 h1:HhLSs+B6O021gwzl+locl0zEDnyNkxMtf/Z3NNBMa9E=

internal/traceprof/endpoint_counter.go

@@ -8,6 +8,8 @@ package traceprof
 import (
 	"sync"
 	"sync/atomic"
+
+	"github.com/puzpuzpuz/xsync/v3"
 )
 
 // globalEndpointCounter is shared between the profiler and the tracer.
@@ -38,7 +40,11 @@ func GlobalEndpointCounter() *EndpointCounter {
 // NewEndpointCounter returns a new NewEndpointCounter that will track hit
 // counts for up to limit endpoints. A limit of <= 0 indicates no limit.
 func NewEndpointCounter(limit int) *EndpointCounter {
-	return &EndpointCounter{enabled: 1, limit: limit, counts: map[string]uint64{}}
+	return &EndpointCounter{
+		enabled: 1,
+		limit:   limit,
+		counts:  xsync.NewMapOf[string, *xsync.Counter](),
+	}
 }
 
 // EndpointCounter counts hits per endpoint.
@@ -50,7 +56,7 @@ func NewEndpointCounter(limit int) *EndpointCounter {
 type EndpointCounter struct {
 	enabled uint64
 	mu      sync.Mutex
-	counts  map[string]uint64
+	counts  *xsync.MapOf[string, *xsync.Counter]
 	limit   int
 }
 
@@ -69,30 +75,59 @@ func (e *EndpointCounter) Inc(endpoint string) {
 		return
 	}
 
-	// Acquire lock until func returns
-	e.mu.Lock()
-	defer e.mu.Unlock()
-
-	// Don't add another endpoint to the map if the limit is reached. See
-	// globalEndpointCounter comment.
-	count, ok := e.counts[endpoint]
-	if !ok && e.limit > 0 && len(e.counts) >= e.limit {
+	count, ok := e.counts.Load(endpoint)
+	if !ok {
+		// If we haven't seen this endpoint yet, add it. Another
+		// goroutine might be racing to add it, so use
+		// LoadOrStore: we'll only store if this goroutine
+		// "wins" the race to add it, and we'll have a small
+		// wasted allocation if the goroutine "loses" the race.
+		// In microbenchmarks this seems to be faster than a
+		// single LoadOrCompute
+		// TODO: our tests pass whether or not we re-set ok
+		// here. re-setting seems right because we need to check
+		// whether we hit the limit _if_ we added
+		// Can we test more thoroughly?
+		count, ok = e.counts.LoadOrStore(endpoint, xsync.NewCounter())
+	}
+	if !ok && e.limit > 0 && e.counts.Size() > e.limit {
+		// If we went over the limit when we added the counter,
+		// delete it.
+		// TODO: this is racy: another goroutine might also add
+		// a different endpoint and exceed the limit _after_
+		// this one, yet we check the size first end delete our
+		// endpoint _before_ the other goroutine.
+		// Does it matter in practice?
+		e.counts.Delete(endpoint)
 		return
 	}
 	// Increment the endpoint count
-	e.counts[endpoint] = count + 1
+	count.Inc()
+	return
 }
 
 // GetAndReset returns the hit counts for all endpoints and resets their counts
 // back to 0.
 func (e *EndpointCounter) GetAndReset() map[string]uint64 {
-	// Acquire lock until func returns
-	e.mu.Lock()
-	defer e.mu.Unlock()
-
-	// Return current counts and reset internal map.
-	counts := e.counts
-	e.counts = make(map[string]uint64)
+	// Try to right-size the allocation
+	counts := make(map[string]uint64, e.counts.Size())
+	e.counts.Range(func(key string, _ *xsync.Counter) bool {
+		// TODO: in https://github.com/felixge/countermap/blob/main/xsync_map_counter_map.go,
+		// Felix reads the input value and then deletes the key.
+		// A LoadAndDelete ensures we don't miss updates to the
+		// count for the endpoint: either we get them here or in
+		// the next cycle. We could also consider not deleting
+		// the value, but instead reset it, if we aren't at the
+		// size limit? Would be nice if xsync.Counter had a
+		// Swap operation for that.
+		v, ok := e.counts.LoadAndDelete(key)
+		if ok {
+			// ok should always be true unless we're calling
+			// GetAndReset concurrently somewhere else...
+			counts[key] = uint64(v.Value())
+		}
+		return true
+	})
 	return counts
 }
 

internal/traceprof/endpoint_counter_test.go

@@ -7,6 +7,7 @@ package traceprof
 
 import (
 	"fmt"
+	"sync"
 	"testing"
 
 	"github.com/stretchr/testify/require"
@@ -27,6 +28,24 @@ func TestEndpointCounter(t *testing.T) {
 		require.Equal(t, map[string]uint64{}, ec.GetAndReset())
 	})
 
+	t.Run("fixed limit parallel", func(t *testing.T) {
+		ec := NewEndpointCounter(10)
+		var wg sync.WaitGroup
+		for i := range 10 {
+			wg.Add(1)
+			go func() {
+				defer wg.Done()
+				for j := range 10 {
+					// Non-overlapping keys
+					// TODO: explain why (if?) this is a good thing to check
+					ec.Inc(fmt.Sprintf("%d", i*10+j))
+				}
+			}()
+		}
+		wg.Wait()
+		require.Len(t, ec.GetAndReset(), 10)
+	})
+
 	t.Run("no limit", func(t *testing.T) {
 		ec := NewEndpointCounter(-1)
 		for i := 0; i < 100; i++ {