src/runtime/gc_test.go

// Copyright 2011 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 (
	"os"
	"runtime"
	"runtime/debug"
	"testing"
	"time"
	"unsafe"
)

func TestGcSys(t *testing.T) {
	if os.Getenv("GOGC") == "off" {
		t.Skip("skipping test; GOGC=off in environment")
	}
	data := struct{ Short bool }{testing.Short()}
	got := executeTest(t, testGCSysSource, &data)
	want := "OK\n"
	if got != want {
		t.Fatalf("expected %q, but got %q", want, got)
	}
}

const testGCSysSource = `
package main

import (
	"fmt"
	"runtime"
)

func main() {
	runtime.GOMAXPROCS(1)
	memstats := new(runtime.MemStats)
	runtime.GC()
	runtime.ReadMemStats(memstats)
	sys := memstats.Sys

	runtime.MemProfileRate = 0 // disable profiler

	itercount := 1000000
{{if .Short}}
	itercount = 100000
{{end}}
	for i := 0; i < itercount; i++ {
		workthegc()
	}

	// Should only be using a few MB.
	// We allocated 100 MB or (if not short) 1 GB.
	runtime.ReadMemStats(memstats)
	if sys > memstats.Sys {
		sys = 0
	} else {
		sys = memstats.Sys - sys
	}
	if sys > 16<<20 {
		fmt.Printf("using too much memory: %d bytes\n", sys)
		return
	}
	fmt.Printf("OK\n")
}

func workthegc() []byte {
	return make([]byte, 1029)
}
`

func TestGcDeepNesting(t *testing.T) {
	type T [2][2][2][2][2][2][2][2][2][2]*int
	a := new(T)

	// Prevent the compiler from applying escape analysis.
	// This makes sure new(T) is allocated on heap, not on the stack.
	t.Logf("%p", a)

	a[0][0][0][0][0][0][0][0][0][0] = new(int)
	*a[0][0][0][0][0][0][0][0][0][0] = 13
	runtime.GC()
	if *a[0][0][0][0][0][0][0][0][0][0] != 13 {
		t.Fail()
	}
}

func TestGcHashmapIndirection(t *testing.T) {
	defer debug.SetGCPercent(debug.SetGCPercent(1))
	runtime.GC()
	type T struct {
		a [256]int
	}
	m := make(map[T]T)
	for i := 0; i < 2000; i++ {
		var a T
		a.a[0] = i
		m[a] = T{}
	}
}

func TestGcArraySlice(t *testing.T) {
	type X struct {
		buf     [1]byte
		nextbuf []byte
		next    *X
	}
	var head *X
	for i := 0; i < 10; i++ {
		p := &X{}
		p.buf[0] = 42
		p.next = head
		if head != nil {
			p.nextbuf = head.buf[:]
		}
		head = p
		runtime.GC()
	}
	for p := head; p != nil; p = p.next {
		if p.buf[0] != 42 {
			t.Fatal("corrupted heap")
		}
	}
}

func TestGcRescan(t *testing.T) {
	type X struct {
		c     chan error
		nextx *X
	}
	type Y struct {
		X
		nexty *Y
		p     *int
	}
	var head *Y
	for i := 0; i < 10; i++ {
		p := &Y{}
		p.c = make(chan error)
		if head != nil {
			p.nextx = &head.X
		}
		p.nexty = head
		p.p = new(int)
		*p.p = 42
		head = p
		runtime.GC()
	}
	for p := head; p != nil; p = p.nexty {
		if *p.p != 42 {
			t.Fatal("corrupted heap")
		}
	}
}

func TestGcLastTime(t *testing.T) {
	ms := new(runtime.MemStats)
	t0 := time.Now().UnixNano()
	runtime.GC()
	t1 := time.Now().UnixNano()
	runtime.ReadMemStats(ms)
	last := int64(ms.LastGC)
	if t0 > last || last > t1 {
		t.Fatalf("bad last GC time: got %v, want [%v, %v]", last, t0, t1)
	}
	pause := ms.PauseNs[(ms.NumGC+255)%256]
	// Due to timer granularity, pause can actually be 0 on windows
	// or on virtualized environments.
	if pause == 0 {
		t.Logf("last GC pause was 0")
	} else if pause > 10e9 {
		t.Logf("bad last GC pause: got %v, want [0, 10e9]", pause)
	}
}

var hugeSink interface{}

func TestHugeGCInfo(t *testing.T) {
	// The test ensures that compiler can chew these huge types even on weakest machines.
	// The types are not allocated at runtime.
	if hugeSink != nil {
		// 400MB on 32 bots, 4TB on 64-bits.
		const n = (400 << 20) + (unsafe.Sizeof(uintptr(0))-4)<<40
		hugeSink = new([n]*byte)
		hugeSink = new([n]uintptr)
		hugeSink = new(struct {
			x float64
			y [n]*byte
			z []string
		})
		hugeSink = new(struct {
			x float64
			y [n]uintptr
			z []string
		})
	}
}

func BenchmarkSetTypeNoPtr1(b *testing.B) {
	type NoPtr1 struct {
		p uintptr
	}
	var p *NoPtr1
	for i := 0; i < b.N; i++ {
		p = &NoPtr1{}
	}
	_ = p
}
func BenchmarkSetTypeNoPtr2(b *testing.B) {
	type NoPtr2 struct {
		p, q uintptr
	}
	var p *NoPtr2
	for i := 0; i < b.N; i++ {
		p = &NoPtr2{}
	}
	_ = p
}
func BenchmarkSetTypePtr1(b *testing.B) {
	type Ptr1 struct {
		p *byte
	}
	var p *Ptr1
	for i := 0; i < b.N; i++ {
		p = &Ptr1{}
	}
	_ = p
}
func BenchmarkSetTypePtr2(b *testing.B) {
	type Ptr2 struct {
		p, q *byte
	}
	var p *Ptr2
	for i := 0; i < b.N; i++ {
		p = &Ptr2{}
	}
	_ = p
}

func BenchmarkAllocation(b *testing.B) {
	type T struct {
		x, y *byte
	}
	ngo := runtime.GOMAXPROCS(0)
	work := make(chan bool, b.N+ngo)
	result := make(chan *T)
	for i := 0; i < b.N; i++ {
		work <- true
	}
	for i := 0; i < ngo; i++ {
		work <- false
	}
	for i := 0; i < ngo; i++ {
		go func() {
			var x *T
			for <-work {
				for i := 0; i < 1000; i++ {
					x = &T{}
				}
			}
			result <- x
		}()
	}
	for i := 0; i < ngo; i++ {
		<-result
	}
}

func TestPrintGC(t *testing.T) {
	if testing.Short() {
		t.Skip("Skipping in short mode")
	}
	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(2))
	done := make(chan bool)
	go func() {
		for {
			select {
			case <-done:
				return
			default:
				runtime.GC()
			}
		}
	}()
	for i := 0; i < 1e4; i++ {
		func() {
			defer print("")
		}()
	}
	close(done)
}