src/runtime/histogram_test.go

// Copyright 2020 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package runtime_test

import (
	"math"
	. "runtime"
	"testing"
)

var dummyTimeHistogram TimeHistogram

func TestTimeHistogram(t *testing.T) {
	// We need to use a global dummy because this
	// could get stack-allocated with a non-8-byte alignment.
	// The result of this bad alignment is a segfault on
	// 32-bit platforms when calling Record.
	h := &dummyTimeHistogram

	// Record exactly one sample in each bucket.
	for i := 0; i < TimeHistNumSuperBuckets; i++ {
		var base int64
		if i > 0 {
			base = int64(1) << (i + TimeHistSubBucketBits - 1)
		}
		for j := 0; j < TimeHistNumSubBuckets; j++ {
			v := int64(j)
			if i > 0 {
				v <<= i - 1
			}
			h.Record(base + v)
		}
	}
	// Hit the underflow bucket.
	h.Record(int64(-1))

	// Check to make sure there's exactly one count in each
	// bucket.
	for i := uint(0); i < TimeHistNumSuperBuckets; i++ {
		for j := uint(0); j < TimeHistNumSubBuckets; j++ {
			c, ok := h.Count(i, j)
			if !ok {
				t.Errorf("hit underflow bucket unexpectedly: (%d, %d)", i, j)
			} else if c != 1 {
				t.Errorf("bucket (%d, %d) has count that is not 1: %d", i, j, c)
			}
		}
	}
	c, ok := h.Count(TimeHistNumSuperBuckets, 0)
	if ok {
		t.Errorf("expected to hit underflow bucket: (%d, %d)", TimeHistNumSuperBuckets, 0)
	}
	if c != 1 {
		t.Errorf("underflow bucket has count that is not 1: %d", c)
	}

	// Check overflow behavior.
	// By hitting a high value, we should just be adding into the highest bucket.
	h.Record(math.MaxInt64)
	c, ok = h.Count(TimeHistNumSuperBuckets-1, TimeHistNumSubBuckets-1)
	if !ok {
		t.Error("hit underflow bucket in highest bucket unexpectedly")
	} else if c != 2 {
		t.Errorf("highest has count that is not 2: %d", c)
	}

	dummyTimeHistogram = TimeHistogram{}
}

func TestTimeHistogramMetricsBuckets(t *testing.T) {
	buckets := TimeHistogramMetricsBuckets()

	nonInfBucketsLen := TimeHistNumSubBuckets * TimeHistNumSuperBuckets
	expBucketsLen := nonInfBucketsLen + 2 // Count -Inf and +Inf.
	if len(buckets) != expBucketsLen {
		t.Fatalf("unexpected length of buckets: got %d, want %d", len(buckets), expBucketsLen)
	}
	// Check the first non-Inf 2*TimeHistNumSubBuckets buckets in order, skipping the
	// first bucket which should be -Inf (checked later).
	//
	// Because of the way this scheme works, the bottom TimeHistNumSubBuckets
	// buckets are fully populated, and then the next TimeHistNumSubBuckets
	// have the TimeHistSubBucketBits'th bit set, while the bottom are once
	// again fully populated.
	for i := 1; i <= 2*TimeHistNumSubBuckets+1; i++ {
		if got, want := buckets[i], float64(i-1)/1e9; got != want {
			t.Errorf("expected bucket %d to have value %e, got %e", i, want, got)
		}
	}
	// Check some values.
	idxToBucket := map[int]float64{
		0:                 math.Inf(-1),
		33:                float64(0x10<<1) / 1e9,
		34:                float64(0x11<<1) / 1e9,
		49:                float64(0x10<<2) / 1e9,
		58:                float64(0x19<<2) / 1e9,
		65:                float64(0x10<<3) / 1e9,
		513:               float64(0x10<<31) / 1e9,
		519:               float64(0x16<<31) / 1e9,
		expBucketsLen - 2: float64(0x1f<<43) / 1e9,
		expBucketsLen - 1: math.Inf(1),
	}
	for idx, bucket := range idxToBucket {
		if got, want := buckets[idx], bucket; got != want {
			t.Errorf("expected bucket %d to have value %e, got %e", idx, want, got)
		}
	}
}