mem_leak_test.go

package simple

import (
	"reflect"
	"runtime"
	"testing"
)

func AssertDeepEqual(x, y interface{}, t *testing.T) {
	if !reflect.DeepEqual(x, y) {
		t.Errorf("\ngot %s\nexp %s", x, y)
	}
}

type Widget struct {
	data []byte
}

func BuildWidgets(builder func(d []byte) Widget) []Widget {
	widgets := []Widget{}
	for i := 1; i <= 10; i++ {
		data := make([]byte, 100*1024*1024)
		widget := builder(data)
		widgets = append(widgets, widget)

		// Force GC to attempt clean up of each widget
		runtime.GC()
	}
	return widgets
}

func TestDirectSliceHoldsMemory(t *testing.T) {
	rtm := runtime.MemStats{}
	builder := func(data []byte) Widget {
		return Widget{data: data[0:1]}
	}
	widgets := BuildWidgets(builder)
	AssertDeepEqual(len(widgets), 10, t)

	// Memory is still on heap
	runtime.ReadMemStats(&rtm)
	AssertDeepEqual(int(rtm.HeapInuse/1024/1024), 1000, t)

	// Running GC at this point collects the memory
	runtime.GC()
	runtime.ReadMemStats(&rtm)
	AssertDeepEqual(int(rtm.HeapInuse/1024/1024), 0, t)
}

func TestCopyReleasesMemory(t *testing.T) {
	rtm := runtime.MemStats{}
	builder := func(data []byte) Widget {
		copiedData := make([]byte, 2)
		copy(copiedData, data[0:1])
		return Widget{data: copiedData}
	}
	widgets := BuildWidgets(builder)
	AssertDeepEqual(len(widgets), 10, t)

	// Memory has already been collected
	runtime.ReadMemStats(&rtm)
	AssertDeepEqual(int(rtm.HeapInuse/1024/1024), 0, t)
}

func TestAppendReleasesMemory(t *testing.T) {
	rtm := runtime.MemStats{}
	builder := func(data []byte) Widget {
		return Widget{data: append([]byte{}, data[0:1]...)}
	}
	widgets := BuildWidgets(builder)
	AssertDeepEqual(len(widgets), 10, t)

	// Memory has already been collected
	runtime.ReadMemStats(&rtm)
	AssertDeepEqual(int(rtm.HeapInuse/1024/1024), 0, t)
}