Source file src/runtime/gc_test.go

Documentation: runtime

     1  // Copyright 2011 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package runtime_test
     6  
     7  import (
     8  	"fmt"
     9  	"math/bits"
    10  	"math/rand"
    11  	"os"
    12  	"reflect"
    13  	"runtime"
    14  	"runtime/debug"
    15  	"slices"
    16  	"strings"
    17  	"sync"
    18  	"sync/atomic"
    19  	"testing"
    20  	"time"
    21  	"unsafe"
    22  )
    23  
    24  func TestGcSys(t *testing.T) {
    25  	t.Skip("skipping known-flaky test; golang.org/issue/37331")
    26  	if os.Getenv("GOGC") == "off" {
    27  		t.Skip("skipping test; GOGC=off in environment")
    28  	}
    29  	got := runTestProg(t, "testprog", "GCSys")
    30  	want := "OK\n"
    31  	if got != want {
    32  		t.Fatalf("expected %q, but got %q", want, got)
    33  	}
    34  }
    35  
    36  func TestGcDeepNesting(t *testing.T) {
    37  	type T [2][2][2][2][2][2][2][2][2][2]*int
    38  	a := new(T)
    39  
    40  	// Prevent the compiler from applying escape analysis.
    41  	// This makes sure new(T) is allocated on heap, not on the stack.
    42  	t.Logf("%p", a)
    43  
    44  	a[0][0][0][0][0][0][0][0][0][0] = new(int)
    45  	*a[0][0][0][0][0][0][0][0][0][0] = 13
    46  	runtime.GC()
    47  	if *a[0][0][0][0][0][0][0][0][0][0] != 13 {
    48  		t.Fail()
    49  	}
    50  }
    51  
    52  func TestGcMapIndirection(t *testing.T) {
    53  	defer debug.SetGCPercent(debug.SetGCPercent(1))
    54  	runtime.GC()
    55  	type T struct {
    56  		a [256]int
    57  	}
    58  	m := make(map[T]T)
    59  	for i := 0; i < 2000; i++ {
    60  		var a T
    61  		a.a[0] = i
    62  		m[a] = T{}
    63  	}
    64  }
    65  
    66  func TestGcArraySlice(t *testing.T) {
    67  	type X struct {
    68  		buf     [1]byte
    69  		nextbuf []byte
    70  		next    *X
    71  	}
    72  	var head *X
    73  	for i := 0; i < 10; i++ {
    74  		p := &X{}
    75  		p.buf[0] = 42
    76  		p.next = head
    77  		if head != nil {
    78  			p.nextbuf = head.buf[:]
    79  		}
    80  		head = p
    81  		runtime.GC()
    82  	}
    83  	for p := head; p != nil; p = p.next {
    84  		if p.buf[0] != 42 {
    85  			t.Fatal("corrupted heap")
    86  		}
    87  	}
    88  }
    89  
    90  func TestGcRescan(t *testing.T) {
    91  	type X struct {
    92  		c     chan error
    93  		nextx *X
    94  	}
    95  	type Y struct {
    96  		X
    97  		nexty *Y
    98  		p     *int
    99  	}
   100  	var head *Y
   101  	for i := 0; i < 10; i++ {
   102  		p := &Y{}
   103  		p.c = make(chan error)
   104  		if head != nil {
   105  			p.nextx = &head.X
   106  		}
   107  		p.nexty = head
   108  		p.p = new(int)
   109  		*p.p = 42
   110  		head = p
   111  		runtime.GC()
   112  	}
   113  	for p := head; p != nil; p = p.nexty {
   114  		if *p.p != 42 {
   115  			t.Fatal("corrupted heap")
   116  		}
   117  	}
   118  }
   119  
   120  func TestGcLastTime(t *testing.T) {
   121  	ms := new(runtime.MemStats)
   122  	t0 := time.Now().UnixNano()
   123  	runtime.GC()
   124  	t1 := time.Now().UnixNano()
   125  	runtime.ReadMemStats(ms)
   126  	last := int64(ms.LastGC)
   127  	if t0 > last || last > t1 {
   128  		t.Fatalf("bad last GC time: got %v, want [%v, %v]", last, t0, t1)
   129  	}
   130  	pause := ms.PauseNs[(ms.NumGC+255)%256]
   131  	// Due to timer granularity, pause can actually be 0 on windows
   132  	// or on virtualized environments.
   133  	if pause == 0 {
   134  		t.Logf("last GC pause was 0")
   135  	} else if pause > 10e9 {
   136  		t.Logf("bad last GC pause: got %v, want [0, 10e9]", pause)
   137  	}
   138  }
   139  
   140  var hugeSink any
   141  
   142  func TestHugeGCInfo(t *testing.T) {
   143  	// The test ensures that compiler can chew these huge types even on weakest machines.
   144  	// The types are not allocated at runtime.
   145  	if hugeSink != nil {
   146  		// 400MB on 32 bots, 4TB on 64-bits.
   147  		const n = (400 << 20) + (unsafe.Sizeof(uintptr(0))-4)<<40
   148  		hugeSink = new([n]*byte)
   149  		hugeSink = new([n]uintptr)
   150  		hugeSink = new(struct {
   151  			x float64
   152  			y [n]*byte
   153  			z []string
   154  		})
   155  		hugeSink = new(struct {
   156  			x float64
   157  			y [n]uintptr
   158  			z []string
   159  		})
   160  	}
   161  }
   162  
   163  func TestPeriodicGC(t *testing.T) {
   164  	if runtime.GOARCH == "wasm" {
   165  		t.Skip("no sysmon on wasm yet")
   166  	}
   167  
   168  	// Make sure we're not in the middle of a GC.
   169  	runtime.GC()
   170  
   171  	var ms1, ms2 runtime.MemStats
   172  	runtime.ReadMemStats(&ms1)
   173  
   174  	// Make periodic GC run continuously.
   175  	orig := *runtime.ForceGCPeriod
   176  	*runtime.ForceGCPeriod = 0
   177  
   178  	// Let some periodic GCs happen. In a heavily loaded system,
   179  	// it's possible these will be delayed, so this is designed to
   180  	// succeed quickly if things are working, but to give it some
   181  	// slack if things are slow.
   182  	var numGCs uint32
   183  	const want = 2
   184  	for i := 0; i < 200 && numGCs < want; i++ {
   185  		time.Sleep(5 * time.Millisecond)
   186  
   187  		// Test that periodic GC actually happened.
   188  		runtime.ReadMemStats(&ms2)
   189  		numGCs = ms2.NumGC - ms1.NumGC
   190  	}
   191  	*runtime.ForceGCPeriod = orig
   192  
   193  	if numGCs < want {
   194  		t.Fatalf("no periodic GC: got %v GCs, want >= 2", numGCs)
   195  	}
   196  }
   197  
   198  func TestGcZombieReporting(t *testing.T) {
   199  	// This test is somewhat sensitive to how the allocator works.
   200  	// Pointers in zombies slice may cross-span, thus we
   201  	// add invalidptr=0 for avoiding the badPointer check.
   202  	// See issue https://golang.org/issues/49613/
   203  	got := runTestProg(t, "testprog", "GCZombie", "GODEBUG=invalidptr=0")
   204  	want := "found pointer to free object"
   205  	if !strings.Contains(got, want) {
   206  		t.Fatalf("expected %q in output, but got %q", want, got)
   207  	}
   208  }
   209  
   210  func TestGCTestMoveStackOnNextCall(t *testing.T) {
   211  	t.Parallel()
   212  	var onStack int
   213  	// GCTestMoveStackOnNextCall can fail in rare cases if there's
   214  	// a preemption. This won't happen many times in quick
   215  	// succession, so just retry a few times.
   216  	for retry := 0; retry < 5; retry++ {
   217  		runtime.GCTestMoveStackOnNextCall()
   218  		if moveStackCheck(t, &onStack, uintptr(unsafe.Pointer(&onStack))) {
   219  			// Passed.
   220  			return
   221  		}
   222  	}
   223  	t.Fatal("stack did not move")
   224  }
   225  
   226  // This must not be inlined because the point is to force a stack
   227  // growth check and move the stack.
   228  //
   229  //go:noinline
   230  func moveStackCheck(t *testing.T, new *int, old uintptr) bool {
   231  	// new should have been updated by the stack move;
   232  	// old should not have.
   233  
   234  	// Capture new's value before doing anything that could
   235  	// further move the stack.
   236  	new2 := uintptr(unsafe.Pointer(new))
   237  
   238  	t.Logf("old stack pointer %x, new stack pointer %x", old, new2)
   239  	if new2 == old {
   240  		// Check that we didn't screw up the test's escape analysis.
   241  		if cls := runtime.GCTestPointerClass(unsafe.Pointer(new)); cls != "stack" {
   242  			t.Fatalf("test bug: new (%#x) should be a stack pointer, not %s", new2, cls)
   243  		}
   244  		// This was a real failure.
   245  		return false
   246  	}
   247  	return true
   248  }
   249  
   250  func TestGCTestMoveStackRepeatedly(t *testing.T) {
   251  	// Move the stack repeatedly to make sure we're not doubling
   252  	// it each time.
   253  	for i := 0; i < 100; i++ {
   254  		runtime.GCTestMoveStackOnNextCall()
   255  		moveStack1(false)
   256  	}
   257  }
   258  
   259  //go:noinline
   260  func moveStack1(x bool) {
   261  	// Make sure this function doesn't get auto-nosplit.
   262  	if x {
   263  		println("x")
   264  	}
   265  }
   266  
   267  func TestGCTestIsReachable(t *testing.T) {
   268  	var all, half []unsafe.Pointer
   269  	var want uint64
   270  	for i := 0; i < 16; i++ {
   271  		// The tiny allocator muddies things, so we use a
   272  		// scannable type.
   273  		p := unsafe.Pointer(new(*int))
   274  		all = append(all, p)
   275  		if i%2 == 0 {
   276  			half = append(half, p)
   277  			want |= 1 << i
   278  		}
   279  	}
   280  
   281  	got := runtime.GCTestIsReachable(all...)
   282  	if got&want != want {
   283  		// This is a serious bug - an object is live (due to the KeepAlive
   284  		// call below), but isn't reported as such.
   285  		t.Fatalf("live object not in reachable set; want %b, got %b", want, got)
   286  	}
   287  	if bits.OnesCount64(got&^want) > 1 {
   288  		// Note: we can occasionally have a value that is retained even though
   289  		// it isn't live, due to conservative scanning of stack frames.
   290  		// See issue 67204. For now, we allow a "slop" of 1 unintentionally
   291  		// retained object.
   292  		t.Fatalf("dead object in reachable set; want %b, got %b", want, got)
   293  	}
   294  	runtime.KeepAlive(half)
   295  }
   296  
   297  var pointerClassBSS *int
   298  var pointerClassData = 42
   299  
   300  func TestGCTestPointerClass(t *testing.T) {
   301  	t.Parallel()
   302  	check := func(p unsafe.Pointer, want string) {
   303  		t.Helper()
   304  		got := runtime.GCTestPointerClass(p)
   305  		if got != want {
   306  			// Convert the pointer to a uintptr to avoid
   307  			// escaping it.
   308  			t.Errorf("for %#x, want class %s, got %s", uintptr(p), want, got)
   309  		}
   310  	}
   311  	var onStack int
   312  	var notOnStack int
   313  	check(unsafe.Pointer(&onStack), "stack")
   314  	check(unsafe.Pointer(runtime.Escape(&notOnStack)), "heap")
   315  	check(unsafe.Pointer(&pointerClassBSS), "bss")
   316  	check(unsafe.Pointer(&pointerClassData), "data")
   317  	check(nil, "other")
   318  }
   319  
   320  func BenchmarkAllocation(b *testing.B) {
   321  	type T struct {
   322  		x, y *byte
   323  	}
   324  	ngo := runtime.GOMAXPROCS(0)
   325  	work := make(chan bool, b.N+ngo)
   326  	result := make(chan *T)
   327  	for i := 0; i < b.N; i++ {
   328  		work <- true
   329  	}
   330  	for i := 0; i < ngo; i++ {
   331  		work <- false
   332  	}
   333  	for i := 0; i < ngo; i++ {
   334  		go func() {
   335  			var x *T
   336  			for <-work {
   337  				for i := 0; i < 1000; i++ {
   338  					x = &T{}
   339  				}
   340  			}
   341  			result <- x
   342  		}()
   343  	}
   344  	for i := 0; i < ngo; i++ {
   345  		<-result
   346  	}
   347  }
   348  
   349  func TestPrintGC(t *testing.T) {
   350  	if testing.Short() {
   351  		t.Skip("Skipping in short mode")
   352  	}
   353  	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(2))
   354  	done := make(chan bool)
   355  	go func() {
   356  		for {
   357  			select {
   358  			case <-done:
   359  				return
   360  			default:
   361  				runtime.GC()
   362  			}
   363  		}
   364  	}()
   365  	for i := 0; i < 1e4; i++ {
   366  		func() {
   367  			defer print("")
   368  		}()
   369  	}
   370  	close(done)
   371  }
   372  
   373  func testTypeSwitch(x any) error {
   374  	switch y := x.(type) {
   375  	case nil:
   376  		// ok
   377  	case error:
   378  		return y
   379  	}
   380  	return nil
   381  }
   382  
   383  func testAssert(x any) error {
   384  	if y, ok := x.(error); ok {
   385  		return y
   386  	}
   387  	return nil
   388  }
   389  
   390  func testAssertVar(x any) error {
   391  	var y, ok = x.(error)
   392  	if ok {
   393  		return y
   394  	}
   395  	return nil
   396  }
   397  
   398  var a bool
   399  
   400  //go:noinline
   401  func testIfaceEqual(x any) {
   402  	if x == "abc" {
   403  		a = true
   404  	}
   405  }
   406  
   407  func TestPageAccounting(t *testing.T) {
   408  	// Grow the heap in small increments. This used to drop the
   409  	// pages-in-use count below zero because of a rounding
   410  	// mismatch (golang.org/issue/15022).
   411  	const blockSize = 64 << 10
   412  	blocks := make([]*[blockSize]byte, (64<<20)/blockSize)
   413  	for i := range blocks {
   414  		blocks[i] = new([blockSize]byte)
   415  	}
   416  
   417  	// Check that the running page count matches reality.
   418  	pagesInUse, counted := runtime.CountPagesInUse()
   419  	if pagesInUse != counted {
   420  		t.Fatalf("mheap_.pagesInUse is %d, but direct count is %d", pagesInUse, counted)
   421  	}
   422  }
   423  
   424  func init() {
   425  	// Enable ReadMemStats' double-check mode.
   426  	*runtime.DoubleCheckReadMemStats = true
   427  }
   428  
   429  func TestReadMemStats(t *testing.T) {
   430  	base, slow := runtime.ReadMemStatsSlow()
   431  	if base != slow {
   432  		logDiff(t, "MemStats", reflect.ValueOf(base), reflect.ValueOf(slow))
   433  		t.Fatal("memstats mismatch")
   434  	}
   435  }
   436  
   437  func logDiff(t *testing.T, prefix string, got, want reflect.Value) {
   438  	typ := got.Type()
   439  	switch typ.Kind() {
   440  	case reflect.Array, reflect.Slice:
   441  		if got.Len() != want.Len() {
   442  			t.Logf("len(%s): got %v, want %v", prefix, got, want)
   443  			return
   444  		}
   445  		for i := 0; i < got.Len(); i++ {
   446  			logDiff(t, fmt.Sprintf("%s[%d]", prefix, i), got.Index(i), want.Index(i))
   447  		}
   448  	case reflect.Struct:
   449  		for i := 0; i < typ.NumField(); i++ {
   450  			gf, wf := got.Field(i), want.Field(i)
   451  			logDiff(t, prefix+"."+typ.Field(i).Name, gf, wf)
   452  		}
   453  	case reflect.Map:
   454  		t.Fatal("not implemented: logDiff for map")
   455  	default:
   456  		if got.Interface() != want.Interface() {
   457  			t.Logf("%s: got %v, want %v", prefix, got, want)
   458  		}
   459  	}
   460  }
   461  
   462  func BenchmarkReadMemStats(b *testing.B) {
   463  	var ms runtime.MemStats
   464  	const heapSize = 100 << 20
   465  	x := make([]*[1024]byte, heapSize/1024)
   466  	for i := range x {
   467  		x[i] = new([1024]byte)
   468  	}
   469  
   470  	b.ResetTimer()
   471  	for i := 0; i < b.N; i++ {
   472  		runtime.ReadMemStats(&ms)
   473  	}
   474  
   475  	runtime.KeepAlive(x)
   476  }
   477  
   478  func applyGCLoad(b *testing.B) func() {
   479  	// We’ll apply load to the runtime with maxProcs-1 goroutines
   480  	// and use one more to actually benchmark. It doesn't make sense
   481  	// to try to run this test with only 1 P (that's what
   482  	// BenchmarkReadMemStats is for).
   483  	maxProcs := runtime.GOMAXPROCS(-1)
   484  	if maxProcs == 1 {
   485  		b.Skip("This benchmark can only be run with GOMAXPROCS > 1")
   486  	}
   487  
   488  	// Code to build a big tree with lots of pointers.
   489  	type node struct {
   490  		children [16]*node
   491  	}
   492  	var buildTree func(depth int) *node
   493  	buildTree = func(depth int) *node {
   494  		tree := new(node)
   495  		if depth != 0 {
   496  			for i := range tree.children {
   497  				tree.children[i] = buildTree(depth - 1)
   498  			}
   499  		}
   500  		return tree
   501  	}
   502  
   503  	// Keep the GC busy by continuously generating large trees.
   504  	done := make(chan struct{})
   505  	var wg sync.WaitGroup
   506  	for i := 0; i < maxProcs-1; i++ {
   507  		wg.Add(1)
   508  		go func() {
   509  			defer wg.Done()
   510  			var hold *node
   511  		loop:
   512  			for {
   513  				hold = buildTree(5)
   514  				select {
   515  				case <-done:
   516  					break loop
   517  				default:
   518  				}
   519  			}
   520  			runtime.KeepAlive(hold)
   521  		}()
   522  	}
   523  	return func() {
   524  		close(done)
   525  		wg.Wait()
   526  	}
   527  }
   528  
   529  func BenchmarkReadMemStatsLatency(b *testing.B) {
   530  	stop := applyGCLoad(b)
   531  
   532  	// Spend this much time measuring latencies.
   533  	latencies := make([]time.Duration, 0, 1024)
   534  
   535  	// Run for timeToBench hitting ReadMemStats continuously
   536  	// and measuring the latency.
   537  	b.ResetTimer()
   538  	var ms runtime.MemStats
   539  	for i := 0; i < b.N; i++ {
   540  		// Sleep for a bit, otherwise we're just going to keep
   541  		// stopping the world and no one will get to do anything.
   542  		time.Sleep(100 * time.Millisecond)
   543  		start := time.Now()
   544  		runtime.ReadMemStats(&ms)
   545  		latencies = append(latencies, time.Since(start))
   546  	}
   547  	// Make sure to stop the timer before we wait! The load created above
   548  	// is very heavy-weight and not easy to stop, so we could end up
   549  	// confusing the benchmarking framework for small b.N.
   550  	b.StopTimer()
   551  	stop()
   552  
   553  	// Disable the default */op metrics.
   554  	// ns/op doesn't mean anything because it's an average, but we
   555  	// have a sleep in our b.N loop above which skews this significantly.
   556  	b.ReportMetric(0, "ns/op")
   557  	b.ReportMetric(0, "B/op")
   558  	b.ReportMetric(0, "allocs/op")
   559  
   560  	// Sort latencies then report percentiles.
   561  	slices.Sort(latencies)
   562  	b.ReportMetric(float64(latencies[len(latencies)*50/100]), "p50-ns")
   563  	b.ReportMetric(float64(latencies[len(latencies)*90/100]), "p90-ns")
   564  	b.ReportMetric(float64(latencies[len(latencies)*99/100]), "p99-ns")
   565  }
   566  
   567  func TestUserForcedGC(t *testing.T) {
   568  	// Test that runtime.GC() triggers a GC even if GOGC=off.
   569  	defer debug.SetGCPercent(debug.SetGCPercent(-1))
   570  
   571  	var ms1, ms2 runtime.MemStats
   572  	runtime.ReadMemStats(&ms1)
   573  	runtime.GC()
   574  	runtime.ReadMemStats(&ms2)
   575  	if ms1.NumGC == ms2.NumGC {
   576  		t.Fatalf("runtime.GC() did not trigger GC")
   577  	}
   578  	if ms1.NumForcedGC == ms2.NumForcedGC {
   579  		t.Fatalf("runtime.GC() was not accounted in NumForcedGC")
   580  	}
   581  }
   582  
   583  func writeBarrierBenchmark(b *testing.B, f func()) {
   584  	runtime.GC()
   585  	var ms runtime.MemStats
   586  	runtime.ReadMemStats(&ms)
   587  	//b.Logf("heap size: %d MB", ms.HeapAlloc>>20)
   588  
   589  	// Keep GC running continuously during the benchmark, which in
   590  	// turn keeps the write barrier on continuously.
   591  	var stop uint32
   592  	done := make(chan bool)
   593  	go func() {
   594  		for atomic.LoadUint32(&stop) == 0 {
   595  			runtime.GC()
   596  		}
   597  		close(done)
   598  	}()
   599  	defer func() {
   600  		atomic.StoreUint32(&stop, 1)
   601  		<-done
   602  	}()
   603  
   604  	b.ResetTimer()
   605  	f()
   606  	b.StopTimer()
   607  }
   608  
   609  func BenchmarkWriteBarrier(b *testing.B) {
   610  	if runtime.GOMAXPROCS(-1) < 2 {
   611  		// We don't want GC to take our time.
   612  		b.Skip("need GOMAXPROCS >= 2")
   613  	}
   614  
   615  	// Construct a large tree both so the GC runs for a while and
   616  	// so we have a data structure to manipulate the pointers of.
   617  	type node struct {
   618  		l, r *node
   619  	}
   620  	var wbRoots []*node
   621  	var mkTree func(level int) *node
   622  	mkTree = func(level int) *node {
   623  		if level == 0 {
   624  			return nil
   625  		}
   626  		n := &node{mkTree(level - 1), mkTree(level - 1)}
   627  		if level == 10 {
   628  			// Seed GC with enough early pointers so it
   629  			// doesn't start termination barriers when it
   630  			// only has the top of the tree.
   631  			wbRoots = append(wbRoots, n)
   632  		}
   633  		return n
   634  	}
   635  	const depth = 22 // 64 MB
   636  	root := mkTree(22)
   637  
   638  	writeBarrierBenchmark(b, func() {
   639  		var stack [depth]*node
   640  		tos := -1
   641  
   642  		// There are two write barriers per iteration, so i+=2.
   643  		for i := 0; i < b.N; i += 2 {
   644  			if tos == -1 {
   645  				stack[0] = root
   646  				tos = 0
   647  			}
   648  
   649  			// Perform one step of reversing the tree.
   650  			n := stack[tos]
   651  			if n.l == nil {
   652  				tos--
   653  			} else {
   654  				n.l, n.r = n.r, n.l
   655  				stack[tos] = n.l
   656  				stack[tos+1] = n.r
   657  				tos++
   658  			}
   659  
   660  			if i%(1<<12) == 0 {
   661  				// Avoid non-preemptible loops (see issue #10958).
   662  				runtime.Gosched()
   663  			}
   664  		}
   665  	})
   666  
   667  	runtime.KeepAlive(wbRoots)
   668  }
   669  
   670  func BenchmarkBulkWriteBarrier(b *testing.B) {
   671  	if runtime.GOMAXPROCS(-1) < 2 {
   672  		// We don't want GC to take our time.
   673  		b.Skip("need GOMAXPROCS >= 2")
   674  	}
   675  
   676  	// Construct a large set of objects we can copy around.
   677  	const heapSize = 64 << 20
   678  	type obj [16]*byte
   679  	ptrs := make([]*obj, heapSize/unsafe.Sizeof(obj{}))
   680  	for i := range ptrs {
   681  		ptrs[i] = new(obj)
   682  	}
   683  
   684  	writeBarrierBenchmark(b, func() {
   685  		const blockSize = 1024
   686  		var pos int
   687  		for i := 0; i < b.N; i += blockSize {
   688  			// Rotate block.
   689  			block := ptrs[pos : pos+blockSize]
   690  			first := block[0]
   691  			copy(block, block[1:])
   692  			block[blockSize-1] = first
   693  
   694  			pos += blockSize
   695  			if pos+blockSize > len(ptrs) {
   696  				pos = 0
   697  			}
   698  
   699  			runtime.Gosched()
   700  		}
   701  	})
   702  
   703  	runtime.KeepAlive(ptrs)
   704  }
   705  
   706  func BenchmarkScanStackNoLocals(b *testing.B) {
   707  	var ready sync.WaitGroup
   708  	teardown := make(chan bool)
   709  	for j := 0; j < 10; j++ {
   710  		ready.Add(1)
   711  		go func() {
   712  			x := 100000
   713  			countpwg(&x, &ready, teardown)
   714  		}()
   715  	}
   716  	ready.Wait()
   717  	b.ResetTimer()
   718  	for i := 0; i < b.N; i++ {
   719  		b.StartTimer()
   720  		runtime.GC()
   721  		runtime.GC()
   722  		b.StopTimer()
   723  	}
   724  	close(teardown)
   725  }
   726  
   727  func BenchmarkMSpanCountAlloc(b *testing.B) {
   728  	// Allocate one dummy mspan for the whole benchmark.
   729  	s := runtime.AllocMSpan()
   730  	defer runtime.FreeMSpan(s)
   731  
   732  	// n is the number of bytes to benchmark against.
   733  	// n must always be a multiple of 8, since gcBits is
   734  	// always rounded up 8 bytes.
   735  	for _, n := range []int{8, 16, 32, 64, 128} {
   736  		b.Run(fmt.Sprintf("bits=%d", n*8), func(b *testing.B) {
   737  			// Initialize a new byte slice with pseduo-random data.
   738  			bits := make([]byte, n)
   739  			rand.Read(bits)
   740  
   741  			b.ResetTimer()
   742  			for i := 0; i < b.N; i++ {
   743  				runtime.MSpanCountAlloc(s, bits)
   744  			}
   745  		})
   746  	}
   747  }
   748  
   749  func countpwg(n *int, ready *sync.WaitGroup, teardown chan bool) {
   750  	if *n == 0 {
   751  		ready.Done()
   752  		<-teardown
   753  		return
   754  	}
   755  	*n--
   756  	countpwg(n, ready, teardown)
   757  }
   758  
   759  func TestMemoryLimit(t *testing.T) {
   760  	if testing.Short() {
   761  		t.Skip("stress test that takes time to run")
   762  	}
   763  	if runtime.NumCPU() < 4 {
   764  		t.Skip("want at least 4 CPUs for this test")
   765  	}
   766  	got := runTestProg(t, "testprog", "GCMemoryLimit")
   767  	want := "OK\n"
   768  	if got != want {
   769  		t.Fatalf("expected %q, but got %q", want, got)
   770  	}
   771  }
   772  
   773  func TestMemoryLimitNoGCPercent(t *testing.T) {
   774  	if testing.Short() {
   775  		t.Skip("stress test that takes time to run")
   776  	}
   777  	if runtime.NumCPU() < 4 {
   778  		t.Skip("want at least 4 CPUs for this test")
   779  	}
   780  	got := runTestProg(t, "testprog", "GCMemoryLimitNoGCPercent")
   781  	want := "OK\n"
   782  	if got != want {
   783  		t.Fatalf("expected %q, but got %q", want, got)
   784  	}
   785  }
   786  
   787  func TestMyGenericFunc(t *testing.T) {
   788  	runtime.MyGenericFunc[int]()
   789  }
   790  

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