96 lines
2.6 KiB
Go
96 lines
2.6 KiB
Go
// Copyright 2020 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package metrics_test
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import (
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"fmt"
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"runtime/metrics"
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)
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func ExampleRead_readingOneMetric() {
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// Name of the metric we want to read.
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const myMetric = "/memory/classes/heap/free:bytes"
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// Create a sample for the metric.
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sample := make([]metrics.Sample, 1)
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sample[0].Name = myMetric
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// Sample the metric.
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metrics.Read(sample)
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// Check if the metric is actually supported.
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// If it's not, the resulting value will always have
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// kind KindBad.
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if sample[0].Value.Kind() == metrics.KindBad {
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panic(fmt.Sprintf("metric %q no longer supported", myMetric))
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}
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// Handle the result.
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//
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// It's OK to assume a particular Kind for a metric;
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// they're guaranteed not to change.
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freeBytes := sample[0].Value.Uint64()
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fmt.Printf("free but not released memory: %d\n", freeBytes)
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}
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func ExampleRead_readingAllMetrics() {
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// Get descriptions for all supported metrics.
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descs := metrics.All()
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// Create a sample for each metric.
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samples := make([]metrics.Sample, len(descs))
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for i := range samples {
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samples[i].Name = descs[i].Name
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}
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// Sample the metrics. Re-use the samples slice if you can!
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metrics.Read(samples)
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// Iterate over all results.
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for _, sample := range samples {
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// Pull out the name and value.
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name, value := sample.Name, sample.Value
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// Handle each sample.
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switch value.Kind() {
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case metrics.KindUint64:
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fmt.Printf("%s: %d\n", name, value.Uint64())
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case metrics.KindFloat64:
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fmt.Printf("%s: %f\n", name, value.Float64())
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case metrics.KindFloat64Histogram:
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// The histogram may be quite large, so let's just pull out
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// a crude estimate for the median for the sake of this example.
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fmt.Printf("%s: %f\n", name, medianBucket(value.Float64Histogram()))
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case metrics.KindBad:
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// This should never happen because all metrics are supported
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// by construction.
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panic("bug in runtime/metrics package!")
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default:
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// This may happen as new metrics get added.
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//
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// The safest thing to do here is to simply log it somewhere
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// as something to look into, but ignore it for now.
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// In the worst case, you might temporarily miss out on a new metric.
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fmt.Printf("%s: unexpected metric Kind: %v\n", name, value.Kind())
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}
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}
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}
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func medianBucket(h *metrics.Float64Histogram) float64 {
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total := uint64(0)
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for _, count := range h.Counts {
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total += count
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}
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thresh := total / 2
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total = 0
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for i, count := range h.Counts {
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total += count
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if total >= thresh {
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return h.Buckets[i]
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}
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}
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panic("should not happen")
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}
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