example_test.go

Documentation: runtime/metrics

		 1  // Copyright 2020 The Go Authors. All rights reserved.
		 2  // Use of this source code is governed by a BSD-style
		 3  // license that can be found in the LICENSE file.
		 4  
		 5  package metrics_test
		 6  
		 7  import (
		 8  	"fmt"
		 9  	"runtime/metrics"
		10  )
		11  
		12  func ExampleRead_readingOneMetric() {
		13  	// Name of the metric we want to read.
		14  	const myMetric = "/memory/classes/heap/free:bytes"
		15  
		16  	// Create a sample for the metric.
		17  	sample := make([]metrics.Sample, 1)
		18  	sample[0].Name = myMetric
		19  
		20  	// Sample the metric.
		21  	metrics.Read(sample)
		22  
		23  	// Check if the metric is actually supported.
		24  	// If it's not, the resulting value will always have
		25  	// kind KindBad.
		26  	if sample[0].Value.Kind() == metrics.KindBad {
		27  		panic(fmt.Sprintf("metric %q no longer supported", myMetric))
		28  	}
		29  
		30  	// Handle the result.
		31  	//
		32  	// It's OK to assume a particular Kind for a metric;
		33  	// they're guaranteed not to change.
		34  	freeBytes := sample[0].Value.Uint64()
		35  
		36  	fmt.Printf("free but not released memory: %d\n", freeBytes)
		37  }
		38  
		39  func ExampleRead_readingAllMetrics() {
		40  	// Get descriptions for all supported metrics.
		41  	descs := metrics.All()
		42  
		43  	// Create a sample for each metric.
		44  	samples := make([]metrics.Sample, len(descs))
		45  	for i := range samples {
		46  		samples[i].Name = descs[i].Name
		47  	}
		48  
		49  	// Sample the metrics. Re-use the samples slice if you can!
		50  	metrics.Read(samples)
		51  
		52  	// Iterate over all results.
		53  	for _, sample := range samples {
		54  		// Pull out the name and value.
		55  		name, value := sample.Name, sample.Value
		56  
		57  		// Handle each sample.
		58  		switch value.Kind() {
		59  		case metrics.KindUint64:
		60  			fmt.Printf("%s: %d\n", name, value.Uint64())
		61  		case metrics.KindFloat64:
		62  			fmt.Printf("%s: %f\n", name, value.Float64())
		63  		case metrics.KindFloat64Histogram:
		64  			// The histogram may be quite large, so let's just pull out
		65  			// a crude estimate for the median for the sake of this example.
		66  			fmt.Printf("%s: %f\n", name, medianBucket(value.Float64Histogram()))
		67  		case metrics.KindBad:
		68  			// This should never happen because all metrics are supported
		69  			// by construction.
		70  			panic("bug in runtime/metrics package!")
		71  		default:
		72  			// This may happen as new metrics get added.
		73  			//
		74  			// The safest thing to do here is to simply log it somewhere
		75  			// as something to look into, but ignore it for now.
		76  			// In the worst case, you might temporarily miss out on a new metric.
		77  			fmt.Printf("%s: unexpected metric Kind: %v\n", name, value.Kind())
		78  		}
		79  	}
		80  }
		81  
		82  func medianBucket(h *metrics.Float64Histogram) float64 {
		83  	total := uint64(0)
		84  	for _, count := range h.Counts {
		85  		total += count
		86  	}
		87  	thresh := total / 2
		88  	total = 0
		89  	for i, count := range h.Counts {
		90  		total += count
		91  		if total >= thresh {
		92  			return h.Buckets[i]
		93  		}
		94  	}
		95  	panic("should not happen")
		96  }
		97
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