src/internal/runtime/atomic/xchg8_test.go

// Copyright 2024 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 atomic_test

import (
	"internal/runtime/atomic"
	"testing"
)

func TestXchg8(t *testing.T) {
	var a [16]uint8
	for i := range a {
		next := uint8(i + 50)
		a[i] = next
	}
	b := a

	// Compare behavior against non-atomic implementation. Expect the operation
	// to work at any byte offset and to not clobber neighboring values.
	for i := range a {
		next := uint8(i + 100)
		pa := atomic.Xchg8(&a[i], next)
		pb := b[i]
		b[i] = next
		if pa != pb {
			t.Errorf("atomic.Xchg8(a[%d]); %d != %d", i, pa, pb)
		}
		if a != b {
			t.Errorf("after atomic.Xchg8(a[%d]); %d != %d", i, a, b)
		}
		if t.Failed() {
			break
		}
	}
}

func BenchmarkXchg8(b *testing.B) {
	var x [512]uint8 // give byte its own cache line
	sink = &x
	for i := 0; i < b.N; i++ {
		atomic.Xchg8(&x[255], uint8(i))
	}
}

func BenchmarkXchg8Parallel(b *testing.B) {
	var x [512]uint8 // give byte its own cache line
	sink = &x
	b.RunParallel(func(pb *testing.PB) {
		i := uint8(0)
		for pb.Next() {
			atomic.Xchg8(&x[255], i)
			i++
		}
	})
}