internal/plot: use sync.Once for initIndices() to ensure init() order

Author: arl

internal/plot/plot_runnable_time.go

@@ -16,20 +16,18 @@ var _ = register(description{
 		counts := [maxBuckets]uint64{}
 
 		return func(_ time.Time, samples []metrics.Sample) any {
+			hist := samples[idx_sched_latencies_seconds].Value.Float64Histogram()
 			if histfactor == 0 {
-				schedlat := samples[idx_sched_latencies_seconds].Value.Float64Histogram()
-				histfactor = downsampleFactor(len(schedlat.Buckets), maxBuckets)
+				histfactor = downsampleFactor(len(hist.Buckets), maxBuckets)
 			}
 
-			schedlat := samples[idx_sched_latencies_seconds].Value.Float64Histogram()
-
-			return downsampleCounts(schedlat, histfactor, counts[:])
+			return downsampleCounts(hist, histfactor, counts[:])
 		}
 	},
 	layout: func(samples []metrics.Sample) Heatmap {
-		schedlat := samples[idx_sched_latencies_seconds].Value.Float64Histogram()
-		histfactor := downsampleFactor(len(schedlat.Buckets), maxBuckets)
-		buckets := downsampleBuckets(schedlat, histfactor)
+		hist := samples[idx_sched_latencies_seconds].Value.Float64Histogram()
+		histfactor := downsampleFactor(len(hist.Buckets), maxBuckets)
+		buckets := downsampleBuckets(hist, histfactor)
 
 		return Heatmap{
 			Name:       "TODO(set later)",

internal/plot/plot_stopping_pauses_gc.go

@@ -7,7 +7,7 @@ import (
 
 var _ = register(description{
 	name: "stopping-pauses-gc",
-	tags: []tag{tagScheduler},
+	tags: []tag{tagScheduler, tagGC},
 	metrics: []string{
 		"/sched/pauses/stopping/gc:seconds",
 	},

internal/plot/plot_total_pauses_gc.go

@@ -7,7 +7,7 @@ import (
 
 var _ = register(description{
 	name: "total-pauses-gc",
-	tags: []tag{tagScheduler},
+	tags: []tag{tagScheduler, tagGC},
 	metrics: []string{
 		"/sched/pauses/total/gc:seconds",
 	},

internal/plot/desc.go internal/plot/registry.gointernal/plot/desc.go renamed to internal/plot/registry.go

@@ -4,6 +4,7 @@ package plot
 import (
 	"runtime/debug"
 	"runtime/metrics"
+	"sync"
 	"time"
 )
 
@@ -32,7 +33,22 @@ var (
 	metricIdx map[string]int
 )
 
+var initIndices = sync.OnceValue(func() []metrics.Sample {
+	all := metrics.All()
+
+	metricIdx = make(map[string]int, len(all))
+
+	samples := make([]metrics.Sample, len(all))
+	for i := range samples {
+		samples[i].Name = all[i].Name
+		metricIdx[samples[i].Name] = i
+	}
+	metrics.Read(samples)
+	return samples
+})
+
 func mustidx(metric string) int {
+	_ = initIndices()
 	idx, ok := metricIdx[metric]
 	if !ok {
 		bnfo, ok := debug.ReadBuildInfo()
@@ -50,20 +66,9 @@ func register(desc description) struct{} {
 }
 
 func init() {
-	// We need a first set of sample in order to dimension and process the
-	// heatmaps buckets.
-	all := metrics.All()
-	samples := make([]metrics.Sample, len(all))
-	metricIdx = make(map[string]int)
-
-	for i := range samples {
-		samples[i].Name = all[i].Name
-		metricIdx[samples[i].Name] = i
-	}
-	metrics.Read(samples)
-
 	type heatmapLayoutFunc = func(samples []metrics.Sample) Heatmap
 
+	samples := initIndices()
 	for i := range registry {
 		desc := &registry[i]
 		if hm, ok := desc.layout.(heatmapLayoutFunc); ok {