1 files changed, 112 insertions, 0 deletions
diff --git a/src/runtime/histogram_test.go b/src/runtime/histogram_test.go
new file mode 100644
index 0000000..5246e86
--- /dev/null
+++ b/src/runtime/histogram_test.go
@@ -0,0 +1,112 @@
+// 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 j := 0; j < TimeHistNumSubBuckets; j++ {
+		v := int64(j) << (TimeHistMinBucketBits - 1 - TimeHistSubBucketBits)
+		for k := 0; k < j; k++ {
+			// Record a number of times equal to the bucket index.
+			h.Record(v)
+		}
+	}
+	for i := TimeHistMinBucketBits; i < TimeHistMaxBucketBits; i++ {
+		base := int64(1) << (i - 1)
+		for j := 0; j < TimeHistNumSubBuckets; j++ {
+			v := int64(j) << (i - 1 - TimeHistSubBucketBits)
+			for k := 0; k < (i+1-TimeHistMinBucketBits)*TimeHistNumSubBuckets+j; k++ {
+				// Record a number of times equal to the bucket index.
+				h.Record(base + v)
+			}
+		}
+	}
+	// Hit the underflow and overflow buckets.
+	h.Record(int64(-1))
+	h.Record(math.MaxInt64)
+	h.Record(math.MaxInt64)
+
+	// Check to make sure there's exactly one count in each
+	// bucket.
+	for i := 0; i < TimeHistNumBuckets; i++ {
+		for j := 0; j < TimeHistNumSubBuckets; j++ {
+			c, ok := h.Count(i, j)
+			if !ok {
+				t.Errorf("unexpected invalid bucket: (%d, %d)", i, j)
+			} else if idx := uint64(i*TimeHistNumSubBuckets + j); c != idx {
+				t.Errorf("bucket (%d, %d) has count that is not %d: %d", i, j, idx, c)
+			}
+		}
+	}
+	c, ok := h.Count(-1, 0)
+	if ok {
+		t.Errorf("expected to hit underflow bucket: (%d, %d)", -1, 0)
+	}
+	if c != 1 {
+		t.Errorf("overflow bucket has count that is not 1: %d", c)
+	}
+
+	c, ok = h.Count(TimeHistNumBuckets+1, 0)
+	if ok {
+		t.Errorf("expected to hit overflow bucket: (%d, %d)", TimeHistNumBuckets+1, 0)
+	}
+	if c != 2 {
+		t.Errorf("overflow bucket has count that is not 2: %d", c)
+	}
+
+	dummyTimeHistogram = TimeHistogram{}
+}
+
+func TestTimeHistogramMetricsBuckets(t *testing.T) {
+	buckets := TimeHistogramMetricsBuckets()
+
+	nonInfBucketsLen := TimeHistNumSubBuckets * TimeHistNumBuckets
+	expBucketsLen := nonInfBucketsLen + 3 // Count -Inf, the edge for the overflow bucket, and +Inf.
+	if len(buckets) != expBucketsLen {
+		t.Fatalf("unexpected length of buckets: got %d, want %d", len(buckets), expBucketsLen)
+	}
+	// Check some values.
+	idxToBucket := map[int]float64{
+		0:                 math.Inf(-1),
+		1:                 0.0,
+		2:                 float64(0x040) / 1e9,
+		3:                 float64(0x080) / 1e9,
+		4:                 float64(0x0c0) / 1e9,
+		5:                 float64(0x100) / 1e9,
+		6:                 float64(0x140) / 1e9,
+		7:                 float64(0x180) / 1e9,
+		8:                 float64(0x1c0) / 1e9,
+		9:                 float64(0x200) / 1e9,
+		10:                float64(0x280) / 1e9,
+		11:                float64(0x300) / 1e9,
+		12:                float64(0x380) / 1e9,
+		13:                float64(0x400) / 1e9,
+		15:                float64(0x600) / 1e9,
+		81:                float64(0x8000000) / 1e9,
+		82:                float64(0xa000000) / 1e9,
+		108:               float64(0x380000000) / 1e9,
+		expBucketsLen - 2: float64(0x1<<47) / 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)
+		}
+	}
+}