src/runtime/arena_test.go - go - Git at Google

 // Copyright 2022 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 (
 	"internal/goarch"
 	"reflect"
 	. "runtime"
 	"runtime/debug"
 	"runtime/internal/atomic"
 	"testing"
 	"time"
 	"unsafe"
 )

 type smallScalar struct {
 	X uintptr
 }
 type smallPointer struct {
 	X *smallPointer
 }
 type smallPointerMix struct {
 	A *smallPointer
 	B byte
 	C *smallPointer
 	D [11]byte
 }
 type mediumScalarEven [8192]byte
 type mediumScalarOdd [3321]byte
 type mediumPointerEven [1024]*smallPointer
 type mediumPointerOdd [1023]*smallPointer

 type largeScalar [UserArenaChunkBytes + 1]byte
 type largePointer [UserArenaChunkBytes/unsafe.Sizeof(&smallPointer{}) + 1]*smallPointer

 func TestUserArena(t *testing.T) {
 	// Set GOMAXPROCS to 2 so we don't run too many of these
 	// tests in parallel.
 	defer GOMAXPROCS(GOMAXPROCS(2))

 	// Start a subtest so that we can clean up after any parallel tests within.
 	t.Run("Alloc", func(t *testing.T) {
 		ss := &smallScalar{5}
 		runSubTestUserArenaNew(t, ss, true)

 		sp := &smallPointer{new(smallPointer)}
 		runSubTestUserArenaNew(t, sp, true)

 		spm := &smallPointerMix{sp, 5, nil, [11]byte{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11}}
 		runSubTestUserArenaNew(t, spm, true)

 		mse := new(mediumScalarEven)
 		for i := range mse {
 			mse[i] = 121
 		}
 		runSubTestUserArenaNew(t, mse, true)

 		mso := new(mediumScalarOdd)
 		for i := range mso {
 			mso[i] = 122
 		}
 		runSubTestUserArenaNew(t, mso, true)

 		mpe := new(mediumPointerEven)
 		for i := range mpe {
 			mpe[i] = sp
 		}
 		runSubTestUserArenaNew(t, mpe, true)

 		mpo := new(mediumPointerOdd)
 		for i := range mpo {
 			mpo[i] = sp
 		}
 		runSubTestUserArenaNew(t, mpo, true)

 		ls := new(largeScalar)
 		for i := range ls {
 			ls[i] = 123
 		}
 		// Not in parallel because we don't want to hold this large allocation live.
 		runSubTestUserArenaNew(t, ls, false)

 		lp := new(largePointer)
 		for i := range lp {
 			lp[i] = sp
 		}
 		// Not in parallel because we don't want to hold this large allocation live.
 		runSubTestUserArenaNew(t, lp, false)

 		sss := make([]smallScalar, 25)
 		for i := range sss {
 			sss[i] = smallScalar{12}
 		}
 		runSubTestUserArenaSlice(t, sss, true)

 		mpos := make([]mediumPointerOdd, 5)
 		for i := range mpos {
 			mpos[i] = *mpo
 		}
 		runSubTestUserArenaSlice(t, mpos, true)

 		sps := make([]smallPointer, UserArenaChunkBytes/unsafe.Sizeof(smallPointer{})+1)
 		for i := range sps {
 			sps[i] = *sp
 		}
 		// Not in parallel because we don't want to hold this large allocation live.
 		runSubTestUserArenaSlice(t, sps, false)

 		// Test zero-sized types.
 		t.Run("struct{}", func(t *testing.T) {
 			arena := NewUserArena()
 			var x any
 			x = (*struct{})(nil)
 			arena.New(&x)
 			if v := unsafe.Pointer(x.(*struct{})); v != ZeroBase {
 				t.Errorf("expected zero-sized type to be allocated as zerobase: got %x, want %x", v, ZeroBase)
 			}
 			arena.Free()
 		})
 		t.Run("[]struct{}", func(t *testing.T) {
 			arena := NewUserArena()
 			var sl []struct{}
 			arena.Slice(&sl, 10)
 			if v := unsafe.Pointer(&sl[0]); v != ZeroBase {
 				t.Errorf("expected zero-sized type to be allocated as zerobase: got %x, want %x", v, ZeroBase)
 			}
 			arena.Free()
 		})
 		t.Run("[]int (cap 0)", func(t *testing.T) {
 			arena := NewUserArena()
 			var sl []int
 			arena.Slice(&sl, 0)
 			if len(sl) != 0 {
 				t.Errorf("expected requested zero-sized slice to still have zero length: got %x, want 0", len(sl))
 			}
 			arena.Free()
 		})
 	})

 	// Run a GC cycle to get any arenas off the quarantine list.
 	GC()

 	if n := GlobalWaitingArenaChunks(); n != 0 {
 		t.Errorf("expected zero waiting arena chunks, found %d", n)
 	}
 }

 func runSubTestUserArenaNew[S comparable](t *testing.T, value *S, parallel bool) {
 	t.Run(reflect.TypeOf(value).Elem().Name(), func(t *testing.T) {
 		if parallel {
 			t.Parallel()
 		}

 		// Allocate and write data, enough to exhaust the arena.
 		//
 		// This is an underestimate, likely leaving some space in the arena. That's a good thing,
 		// because it gives us coverage of boundary cases.
 		n := int(UserArenaChunkBytes / unsafe.Sizeof(*value))
 		if n == 0 {
 			n = 1
 		}

 		// Create a new arena and do a bunch of operations on it.
 		arena := NewUserArena()

 		arenaValues := make([]*S, 0, n)
 		for j := 0; j < n; j++ {
 			var x any
 			x = (*S)(nil)
 			arena.New(&x)
 			s := x.(*S)
 			*s = *value
 			arenaValues = append(arenaValues, s)
 		}
 		// Check integrity of allocated data.
 		for _, s := range arenaValues {
 			if *s != *value {
 				t.Errorf("failed integrity check: got %#v, want %#v", *s, *value)
 			}
 		}

 		// Release the arena.
 		arena.Free()
 	})
 }

 func runSubTestUserArenaSlice[S comparable](t *testing.T, value []S, parallel bool) {
 	t.Run("[]"+reflect.TypeOf(value).Elem().Name(), func(t *testing.T) {
 		if parallel {
 			t.Parallel()
 		}

 		// Allocate and write data, enough to exhaust the arena.
 		//
 		// This is an underestimate, likely leaving some space in the arena. That's a good thing,
 		// because it gives us coverage of boundary cases.
 		n := int(UserArenaChunkBytes / (unsafe.Sizeof(*new(S)) * uintptr(cap(value))))
 		if n == 0 {
 			n = 1
 		}

 		// Create a new arena and do a bunch of operations on it.
 		arena := NewUserArena()

 		arenaValues := make([][]S, 0, n)
 		for j := 0; j < n; j++ {
 			var sl []S
 			arena.Slice(&sl, cap(value))
 			copy(sl, value)
 			arenaValues = append(arenaValues, sl)
 		}
 		// Check integrity of allocated data.
 		for _, sl := range arenaValues {
 			for i := range sl {
 				got := sl[i]
 				want := value[i]
 				if got != want {
 					t.Errorf("failed integrity check: got %#v, want %#v at index %d", got, want, i)
 				}
 			}
 		}

 		// Release the arena.
 		arena.Free()
 	})
 }

 func TestUserArenaLiveness(t *testing.T) {
 	t.Run("Free", func(t *testing.T) {
 		testUserArenaLiveness(t, false)
 	})
 	t.Run("Finalizer", func(t *testing.T) {
 		testUserArenaLiveness(t, true)
 	})
 }

 func testUserArenaLiveness(t *testing.T, useArenaFinalizer bool) {
 	// Disable the GC so that there's zero chance we try doing anything arena related *during*
 	// a mark phase, since otherwise a bunch of arenas could end up on the fault list.
 	defer debug.SetGCPercent(debug.SetGCPercent(-1))

 	// Defensively ensure that any full arena chunks leftover from previous tests have been cleared.
 	GC()
 	GC()

 	arena := NewUserArena()

 	// Allocate a few pointer-ful but un-initialized objects so that later we can
 	// place a reference to heap object at a more interesting location.
 	for i := 0; i < 3; i++ {
 		var x any
 		x = (*mediumPointerOdd)(nil)
 		arena.New(&x)
 	}

 	var x any
 	x = (*smallPointerMix)(nil)
 	arena.New(&x)
 	v := x.(*smallPointerMix)

 	var safeToFinalize atomic.Bool
 	var finalized atomic.Bool
 	v.C = new(smallPointer)
 	SetFinalizer(v.C, func(_ *smallPointer) {
 		if !safeToFinalize.Load() {
 			t.Error("finalized arena-referenced object unexpectedly")
 		}
 		finalized.Store(true)
 	})

 	// Make sure it stays alive.
 	GC()
 	GC()

 	// In order to ensure the object can be freed, we now need to make sure to use
 	// the entire arena. Exhaust the rest of the arena.

 	for i := 0; i < int(UserArenaChunkBytes/unsafe.Sizeof(mediumScalarEven{})); i++ {
 		var x any
 		x = (*mediumScalarEven)(nil)
 		arena.New(&x)
 	}

 	// Make sure it stays alive again.
 	GC()
 	GC()

 	v = nil

 	safeToFinalize.Store(true)
 	if useArenaFinalizer {
 		arena = nil

 		// Try to queue the arena finalizer.
 		GC()
 		GC()

 		// In order for the finalizer we actually want to run to execute,
 		// we need to make sure this one runs first.
 		if !BlockUntilEmptyFinalizerQueue(int64(2 * time.Second)) {
 			t.Fatal("finalizer queue was never emptied")
 		}
 	} else {
 		// Free the arena explicitly.
 		arena.Free()
 	}

 	// Try to queue the object's finalizer that we set earlier.
 	GC()
 	GC()

 	if !BlockUntilEmptyFinalizerQueue(int64(2 * time.Second)) {
 		t.Fatal("finalizer queue was never emptied")
 	}
 	if !finalized.Load() {
 		t.Error("expected arena-referenced object to be finalized")
 	}
 }

 func TestUserArenaClearsPointerBits(t *testing.T) {
 	// This is a regression test for a serious issue wherein if pointer bits
 	// aren't properly cleared, it's possible to allocate scalar data down
 	// into a previously pointer-ful area, causing misinterpretation by the GC.

 	// Create a large object, grab a pointer into it, and free it.
 	x := new([8 << 20]byte)
 	xp := uintptr(unsafe.Pointer(&x[124]))
 	var finalized atomic.Bool
 	SetFinalizer(x, func(_ *[8 << 20]byte) {
 		finalized.Store(true)
 	})

 	// Write three chunks worth of pointer data. Three gives us a
 	// high likelihood that when we write 2 later, we'll get the behavior
 	// we want.
 	a := NewUserArena()
 	for i := 0; i < int(UserArenaChunkBytes/goarch.PtrSize*3); i++ {
 		var x any
 		x = (*smallPointer)(nil)
 		a.New(&x)
 	}
 	a.Free()

 	// Recycle the arena chunks.
 	GC()
 	GC()

 	a = NewUserArena()
 	for i := 0; i < int(UserArenaChunkBytes/goarch.PtrSize*2); i++ {
 		var x any
 		x = (*smallScalar)(nil)
 		a.New(&x)
 		v := x.(*smallScalar)
 		// Write a pointer that should not keep x alive.
 		*v = smallScalar{xp}
 	}
 	KeepAlive(x)
 	x = nil

 	// Try to free x.
 	GC()
 	GC()

 	if !BlockUntilEmptyFinalizerQueue(int64(2 * time.Second)) {
 		t.Fatal("finalizer queue was never emptied")
 	}
 	if !finalized.Load() {
 		t.Fatal("heap allocation kept alive through non-pointer reference")
 	}

 	// Clean up the arena.
 	a.Free()
 	GC()
 	GC()
 }

 func TestUserArenaCloneString(t *testing.T) {
 	a := NewUserArena()

 	// A static string (not on heap or arena)
 	var s = "abcdefghij"

 	// Create a byte slice in the arena, initialize it with s
 	var b []byte
 	a.Slice(&b, len(s))
 	copy(b, s)

 	// Create a string as using the same memory as the byte slice, hence in
 	// the arena. This could be an arena API, but hasn't really been needed
 	// yet.
 	var as string
 	asHeader := (*reflect.StringHeader)(unsafe.Pointer(&as))
 	asHeader.Data = (*reflect.SliceHeader)(unsafe.Pointer(&b)).Data
 	asHeader.Len = len(b)

 	// Clone should make a copy of as, since it is in the arena.
 	asCopy := UserArenaClone(as)
 	if (*reflect.StringHeader)(unsafe.Pointer(&as)).Data == (*reflect.StringHeader)(unsafe.Pointer(&asCopy)).Data {
 		t.Error("Clone did not make a copy")
 	}

 	// Clone should make a copy of subAs, since subAs is just part of as and so is in the arena.
 	subAs := as[1:3]
 	subAsCopy := UserArenaClone(subAs)
 	if (*reflect.StringHeader)(unsafe.Pointer(&subAs)).Data == (*reflect.StringHeader)(unsafe.Pointer(&subAsCopy)).Data {
 		t.Error("Clone did not make a copy")
 	}
 	if len(subAs) != len(subAsCopy) {
 		t.Errorf("Clone made an incorrect copy (bad length): %d -> %d", len(subAs), len(subAsCopy))
 	} else {
 		for i := range subAs {
 			if subAs[i] != subAsCopy[i] {
 				t.Errorf("Clone made an incorrect copy (data at index %d): %d -> %d", i, subAs[i], subAs[i])
 			}
 		}
 	}

 	// Clone should not make a copy of doubleAs, since doubleAs will be on the heap.
 	doubleAs := as + as
 	doubleAsCopy := UserArenaClone(doubleAs)
 	if (*reflect.StringHeader)(unsafe.Pointer(&doubleAs)).Data != (*reflect.StringHeader)(unsafe.Pointer(&doubleAsCopy)).Data {
 		t.Error("Clone should not have made a copy")
 	}

 	// Clone should not make a copy of s, since s is a static string.
 	sCopy := UserArenaClone(s)
 	if (*reflect.StringHeader)(unsafe.Pointer(&s)).Data != (*reflect.StringHeader)(unsafe.Pointer(&sCopy)).Data {
 		t.Error("Clone should not have made a copy")
 	}

 	a.Free()
 }

 func TestUserArenaClonePointer(t *testing.T) {
 	a := NewUserArena()

 	// Clone should not make a copy of a heap-allocated smallScalar.
 	x := Escape(new(smallScalar))
 	xCopy := UserArenaClone(x)
 	if unsafe.Pointer(x) != unsafe.Pointer(xCopy) {
 		t.Errorf("Clone should not have made a copy: %#v -> %#v", x, xCopy)
 	}

 	// Clone should make a copy of an arena-allocated smallScalar.
 	var i any
 	i = (*smallScalar)(nil)
 	a.New(&i)
 	xArena := i.(*smallScalar)
 	xArenaCopy := UserArenaClone(xArena)
 	if unsafe.Pointer(xArena) == unsafe.Pointer(xArenaCopy) {
 		t.Errorf("Clone should have made a copy: %#v -> %#v", xArena, xArenaCopy)
 	}
 	if *xArena != *xArenaCopy {
 		t.Errorf("Clone made an incorrect copy copy: %#v -> %#v", *xArena, *xArenaCopy)
 	}

 	a.Free()
 }

 func TestUserArenaCloneSlice(t *testing.T) {
 	a := NewUserArena()

 	// A static string (not on heap or arena)
 	var s = "klmnopqrstuv"

 	// Create a byte slice in the arena, initialize it with s
 	var b []byte
 	a.Slice(&b, len(s))
 	copy(b, s)

 	// Clone should make a copy of b, since it is in the arena.
 	bCopy := UserArenaClone(b)
 	if unsafe.Pointer(&b[0]) == unsafe.Pointer(&bCopy[0]) {
 		t.Errorf("Clone did not make a copy: %#v -> %#v", b, bCopy)
 	}
 	if len(b) != len(bCopy) {
 		t.Errorf("Clone made an incorrect copy (bad length): %d -> %d", len(b), len(bCopy))
 	} else {
 		for i := range b {
 			if b[i] != bCopy[i] {
 				t.Errorf("Clone made an incorrect copy (data at index %d): %d -> %d", i, b[i], bCopy[i])
 			}
 		}
 	}

 	// Clone should make a copy of bSub, since bSub is just part of b and so is in the arena.
 	bSub := b[1:3]
 	bSubCopy := UserArenaClone(bSub)
 	if unsafe.Pointer(&bSub[0]) == unsafe.Pointer(&bSubCopy[0]) {
 		t.Errorf("Clone did not make a copy: %#v -> %#v", bSub, bSubCopy)
 	}
 	if len(bSub) != len(bSubCopy) {
 		t.Errorf("Clone made an incorrect copy (bad length): %d -> %d", len(bSub), len(bSubCopy))
 	} else {
 		for i := range bSub {
 			if bSub[i] != bSubCopy[i] {
 				t.Errorf("Clone made an incorrect copy (data at index %d): %d -> %d", i, bSub[i], bSubCopy[i])
 			}
 		}
 	}

 	// Clone should not make a copy of bNotArena, since it will not be in an arena.
 	bNotArena := make([]byte, len(s))
 	copy(bNotArena, s)
 	bNotArenaCopy := UserArenaClone(bNotArena)
 	if unsafe.Pointer(&bNotArena[0]) != unsafe.Pointer(&bNotArenaCopy[0]) {
 		t.Error("Clone should not have made a copy")
 	}

 	a.Free()
 }

 func TestUserArenaClonePanic(t *testing.T) {
 	var s string
 	func() {
 		x := smallScalar{2}
 		defer func() {
 			if v := recover(); v != nil {
 				s = v.(string)
 			}
 		}()
 		UserArenaClone(x)
 	}()
 	if s == "" {
 		t.Errorf("expected panic from Clone")
 	}
 }
	// Copyright 2022 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 (
	"internal/goarch"
	"reflect"
	. "runtime"
	"runtime/debug"
	"runtime/internal/atomic"
	"testing"
	"time"
	"unsafe"
	)

	type smallScalar struct {
	X uintptr
	}
	type smallPointer struct {
	X *smallPointer
	}
	type smallPointerMix struct {
	A *smallPointer
	B byte
	C *smallPointer
	D [11]byte
	}
	type mediumScalarEven [8192]byte
	type mediumScalarOdd [3321]byte
	type mediumPointerEven [1024]*smallPointer
	type mediumPointerOdd [1023]*smallPointer

	type largeScalar [UserArenaChunkBytes + 1]byte
	type largePointer [UserArenaChunkBytes/unsafe.Sizeof(&smallPointer{}) + 1]*smallPointer

	func TestUserArena(t *testing.T) {
	// Set GOMAXPROCS to 2 so we don't run too many of these
	// tests in parallel.
	defer GOMAXPROCS(GOMAXPROCS(2))

	// Start a subtest so that we can clean up after any parallel tests within.
	t.Run("Alloc", func(t *testing.T) {
	ss := &smallScalar{5}
	runSubTestUserArenaNew(t, ss, true)

	sp := &smallPointer{new(smallPointer)}
	runSubTestUserArenaNew(t, sp, true)

	spm := &smallPointerMix{sp, 5, nil, [11]byte{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11}}
	runSubTestUserArenaNew(t, spm, true)

	mse := new(mediumScalarEven)
	for i := range mse {
	mse[i] = 121
	}
	runSubTestUserArenaNew(t, mse, true)

	mso := new(mediumScalarOdd)
	for i := range mso {
	mso[i] = 122
	}
	runSubTestUserArenaNew(t, mso, true)

	mpe := new(mediumPointerEven)
	for i := range mpe {
	mpe[i] = sp
	}
	runSubTestUserArenaNew(t, mpe, true)

	mpo := new(mediumPointerOdd)
	for i := range mpo {
	mpo[i] = sp
	}
	runSubTestUserArenaNew(t, mpo, true)

	ls := new(largeScalar)
	for i := range ls {
	ls[i] = 123
	}
	// Not in parallel because we don't want to hold this large allocation live.
	runSubTestUserArenaNew(t, ls, false)

	lp := new(largePointer)
	for i := range lp {
	lp[i] = sp
	}
	// Not in parallel because we don't want to hold this large allocation live.
	runSubTestUserArenaNew(t, lp, false)

	sss := make([]smallScalar, 25)
	for i := range sss {
	sss[i] = smallScalar{12}
	}
	runSubTestUserArenaSlice(t, sss, true)

	mpos := make([]mediumPointerOdd, 5)
	for i := range mpos {
	mpos[i] = *mpo
	}
	runSubTestUserArenaSlice(t, mpos, true)

	sps := make([]smallPointer, UserArenaChunkBytes/unsafe.Sizeof(smallPointer{})+1)
	for i := range sps {
	sps[i] = *sp
	}
	// Not in parallel because we don't want to hold this large allocation live.
	runSubTestUserArenaSlice(t, sps, false)

	// Test zero-sized types.
	t.Run("struct{}", func(t *testing.T) {
	arena := NewUserArena()
	var x any
	x = (*struct{})(nil)
	arena.New(&x)
	if v := unsafe.Pointer(x.(*struct{})); v != ZeroBase {
	t.Errorf("expected zero-sized type to be allocated as zerobase: got %x, want %x", v, ZeroBase)
	}
	arena.Free()
	})
	t.Run("[]struct{}", func(t *testing.T) {
	arena := NewUserArena()
	var sl []struct{}
	arena.Slice(&sl, 10)
	if v := unsafe.Pointer(&sl[0]); v != ZeroBase {
	t.Errorf("expected zero-sized type to be allocated as zerobase: got %x, want %x", v, ZeroBase)
	}
	arena.Free()
	})
	t.Run("[]int (cap 0)", func(t *testing.T) {
	arena := NewUserArena()
	var sl []int
	arena.Slice(&sl, 0)
	if len(sl) != 0 {
	t.Errorf("expected requested zero-sized slice to still have zero length: got %x, want 0", len(sl))
	}
	arena.Free()
	})
	})

	// Run a GC cycle to get any arenas off the quarantine list.
	GC()

	if n := GlobalWaitingArenaChunks(); n != 0 {
	t.Errorf("expected zero waiting arena chunks, found %d", n)
	}
	}

	func runSubTestUserArenaNew[S comparable](t testing.T, value S, parallel bool) {
	t.Run(reflect.TypeOf(value).Elem().Name(), func(t *testing.T) {
	if parallel {
	t.Parallel()
	}

	// Allocate and write data, enough to exhaust the arena.
	//
	// This is an underestimate, likely leaving some space in the arena. That's a good thing,
	// because it gives us coverage of boundary cases.
	n := int(UserArenaChunkBytes / unsafe.Sizeof(*value))
	if n == 0 {
	n = 1
	}

	// Create a new arena and do a bunch of operations on it.
	arena := NewUserArena()

	arenaValues := make([]*S, 0, n)
	for j := 0; j < n; j++ {
	var x any
	x = (*S)(nil)
	arena.New(&x)
	s := x.(*S)
	s = value
	arenaValues = append(arenaValues, s)
	}
	// Check integrity of allocated data.
	for _, s := range arenaValues {
	if s != value {
	t.Errorf("failed integrity check: got %#v, want %#v", s, value)
	}
	}

	// Release the arena.
	arena.Free()
	})
	}

	func runSubTestUserArenaSlice[S comparable](t *testing.T, value []S, parallel bool) {
	t.Run("[]"+reflect.TypeOf(value).Elem().Name(), func(t *testing.T) {
	if parallel {
	t.Parallel()
	}

	// Allocate and write data, enough to exhaust the arena.
	//
	// This is an underestimate, likely leaving some space in the arena. That's a good thing,
	// because it gives us coverage of boundary cases.
	n := int(UserArenaChunkBytes / (unsafe.Sizeof(new(S)) uintptr(cap(value))))
	if n == 0 {
	n = 1
	}

	// Create a new arena and do a bunch of operations on it.
	arena := NewUserArena()

	arenaValues := make([][]S, 0, n)
	for j := 0; j < n; j++ {
	var sl []S
	arena.Slice(&sl, cap(value))
	copy(sl, value)
	arenaValues = append(arenaValues, sl)
	}
	// Check integrity of allocated data.
	for _, sl := range arenaValues {
	for i := range sl {
	got := sl[i]
	want := value[i]
	if got != want {
	t.Errorf("failed integrity check: got %#v, want %#v at index %d", got, want, i)
	}
	}
	}

	// Release the arena.
	arena.Free()
	})
	}

	func TestUserArenaLiveness(t *testing.T) {
	t.Run("Free", func(t *testing.T) {
	testUserArenaLiveness(t, false)
	})
	t.Run("Finalizer", func(t *testing.T) {
	testUserArenaLiveness(t, true)
	})
	}

	func testUserArenaLiveness(t *testing.T, useArenaFinalizer bool) {
	// Disable the GC so that there's zero chance we try doing anything arena related during
	// a mark phase, since otherwise a bunch of arenas could end up on the fault list.
	defer debug.SetGCPercent(debug.SetGCPercent(-1))

	// Defensively ensure that any full arena chunks leftover from previous tests have been cleared.
	GC()
	GC()

	arena := NewUserArena()

	// Allocate a few pointer-ful but un-initialized objects so that later we can
	// place a reference to heap object at a more interesting location.
	for i := 0; i < 3; i++ {
	var x any
	x = (*mediumPointerOdd)(nil)
	arena.New(&x)
	}

	var x any
	x = (*smallPointerMix)(nil)
	arena.New(&x)
	v := x.(*smallPointerMix)

	var safeToFinalize atomic.Bool
	var finalized atomic.Bool
	v.C = new(smallPointer)
	SetFinalizer(v.C, func(_ *smallPointer) {
	if !safeToFinalize.Load() {
	t.Error("finalized arena-referenced object unexpectedly")
	}
	finalized.Store(true)
	})

	// Make sure it stays alive.
	GC()
	GC()

	// In order to ensure the object can be freed, we now need to make sure to use
	// the entire arena. Exhaust the rest of the arena.

	for i := 0; i < int(UserArenaChunkBytes/unsafe.Sizeof(mediumScalarEven{})); i++ {
	var x any
	x = (*mediumScalarEven)(nil)
	arena.New(&x)
	}

	// Make sure it stays alive again.
	GC()
	GC()

	v = nil

	safeToFinalize.Store(true)
	if useArenaFinalizer {
	arena = nil

	// Try to queue the arena finalizer.
	GC()
	GC()

	// In order for the finalizer we actually want to run to execute,
	// we need to make sure this one runs first.
	if !BlockUntilEmptyFinalizerQueue(int64(2 * time.Second)) {
	t.Fatal("finalizer queue was never emptied")
	}
	} else {
	// Free the arena explicitly.
	arena.Free()
	}

	// Try to queue the object's finalizer that we set earlier.
	GC()
	GC()

	if !BlockUntilEmptyFinalizerQueue(int64(2 * time.Second)) {
	t.Fatal("finalizer queue was never emptied")
	}
	if !finalized.Load() {
	t.Error("expected arena-referenced object to be finalized")
	}
	}

	func TestUserArenaClearsPointerBits(t *testing.T) {
	// This is a regression test for a serious issue wherein if pointer bits
	// aren't properly cleared, it's possible to allocate scalar data down
	// into a previously pointer-ful area, causing misinterpretation by the GC.

	// Create a large object, grab a pointer into it, and free it.
	x := new([8 << 20]byte)
	xp := uintptr(unsafe.Pointer(&x[124]))
	var finalized atomic.Bool
	SetFinalizer(x, func(_ *[8 << 20]byte) {
	finalized.Store(true)
	})

	// Write three chunks worth of pointer data. Three gives us a
	// high likelihood that when we write 2 later, we'll get the behavior
	// we want.
	a := NewUserArena()
	for i := 0; i < int(UserArenaChunkBytes/goarch.PtrSize*3); i++ {
	var x any
	x = (*smallPointer)(nil)
	a.New(&x)
	}
	a.Free()

	// Recycle the arena chunks.
	GC()
	GC()

	a = NewUserArena()
	for i := 0; i < int(UserArenaChunkBytes/goarch.PtrSize*2); i++ {
	var x any
	x = (*smallScalar)(nil)
	a.New(&x)
	v := x.(*smallScalar)
	// Write a pointer that should not keep x alive.
	*v = smallScalar{xp}
	}
	KeepAlive(x)
	x = nil

	// Try to free x.
	GC()
	GC()

	if !BlockUntilEmptyFinalizerQueue(int64(2 * time.Second)) {
	t.Fatal("finalizer queue was never emptied")
	}
	if !finalized.Load() {
	t.Fatal("heap allocation kept alive through non-pointer reference")
	}

	// Clean up the arena.
	a.Free()
	GC()
	GC()
	}

	func TestUserArenaCloneString(t *testing.T) {
	a := NewUserArena()

	// A static string (not on heap or arena)
	var s = "abcdefghij"

	// Create a byte slice in the arena, initialize it with s
	var b []byte
	a.Slice(&b, len(s))
	copy(b, s)

	// Create a string as using the same memory as the byte slice, hence in
	// the arena. This could be an arena API, but hasn't really been needed
	// yet.
	var as string
	asHeader := (*reflect.StringHeader)(unsafe.Pointer(&as))
	asHeader.Data = (*reflect.SliceHeader)(unsafe.Pointer(&b)).Data
	asHeader.Len = len(b)

	// Clone should make a copy of as, since it is in the arena.
	asCopy := UserArenaClone(as)
	if (reflect.StringHeader)(unsafe.Pointer(&as)).Data == (reflect.StringHeader)(unsafe.Pointer(&asCopy)).Data {
	t.Error("Clone did not make a copy")
	}

	// Clone should make a copy of subAs, since subAs is just part of as and so is in the arena.
	subAs := as[1:3]
	subAsCopy := UserArenaClone(subAs)
	if (reflect.StringHeader)(unsafe.Pointer(&subAs)).Data == (reflect.StringHeader)(unsafe.Pointer(&subAsCopy)).Data {
	t.Error("Clone did not make a copy")
	}
	if len(subAs) != len(subAsCopy) {
	t.Errorf("Clone made an incorrect copy (bad length): %d -> %d", len(subAs), len(subAsCopy))
	} else {
	for i := range subAs {
	if subAs[i] != subAsCopy[i] {
	t.Errorf("Clone made an incorrect copy (data at index %d): %d -> %d", i, subAs[i], subAs[i])
	}
	}
	}

	// Clone should not make a copy of doubleAs, since doubleAs will be on the heap.
	doubleAs := as + as
	doubleAsCopy := UserArenaClone(doubleAs)
	if (reflect.StringHeader)(unsafe.Pointer(&doubleAs)).Data != (reflect.StringHeader)(unsafe.Pointer(&doubleAsCopy)).Data {
	t.Error("Clone should not have made a copy")
	}

	// Clone should not make a copy of s, since s is a static string.
	sCopy := UserArenaClone(s)
	if (reflect.StringHeader)(unsafe.Pointer(&s)).Data != (reflect.StringHeader)(unsafe.Pointer(&sCopy)).Data {
	t.Error("Clone should not have made a copy")
	}

	a.Free()
	}

	func TestUserArenaClonePointer(t *testing.T) {
	a := NewUserArena()

	// Clone should not make a copy of a heap-allocated smallScalar.
	x := Escape(new(smallScalar))
	xCopy := UserArenaClone(x)
	if unsafe.Pointer(x) != unsafe.Pointer(xCopy) {
	t.Errorf("Clone should not have made a copy: %#v -> %#v", x, xCopy)
	}

	// Clone should make a copy of an arena-allocated smallScalar.
	var i any
	i = (*smallScalar)(nil)
	a.New(&i)
	xArena := i.(*smallScalar)
	xArenaCopy := UserArenaClone(xArena)
	if unsafe.Pointer(xArena) == unsafe.Pointer(xArenaCopy) {
	t.Errorf("Clone should have made a copy: %#v -> %#v", xArena, xArenaCopy)
	}
	if xArena != xArenaCopy {
	t.Errorf("Clone made an incorrect copy copy: %#v -> %#v", xArena, xArenaCopy)
	}

	a.Free()
	}

	func TestUserArenaCloneSlice(t *testing.T) {
	a := NewUserArena()

	// A static string (not on heap or arena)
	var s = "klmnopqrstuv"

	// Create a byte slice in the arena, initialize it with s
	var b []byte
	a.Slice(&b, len(s))
	copy(b, s)

	// Clone should make a copy of b, since it is in the arena.
	bCopy := UserArenaClone(b)
	if unsafe.Pointer(&b[0]) == unsafe.Pointer(&bCopy[0]) {
	t.Errorf("Clone did not make a copy: %#v -> %#v", b, bCopy)
	}
	if len(b) != len(bCopy) {
	t.Errorf("Clone made an incorrect copy (bad length): %d -> %d", len(b), len(bCopy))
	} else {
	for i := range b {
	if b[i] != bCopy[i] {
	t.Errorf("Clone made an incorrect copy (data at index %d): %d -> %d", i, b[i], bCopy[i])
	}
	}
	}

	// Clone should make a copy of bSub, since bSub is just part of b and so is in the arena.
	bSub := b[1:3]
	bSubCopy := UserArenaClone(bSub)
	if unsafe.Pointer(&bSub[0]) == unsafe.Pointer(&bSubCopy[0]) {
	t.Errorf("Clone did not make a copy: %#v -> %#v", bSub, bSubCopy)
	}
	if len(bSub) != len(bSubCopy) {
	t.Errorf("Clone made an incorrect copy (bad length): %d -> %d", len(bSub), len(bSubCopy))
	} else {
	for i := range bSub {
	if bSub[i] != bSubCopy[i] {
	t.Errorf("Clone made an incorrect copy (data at index %d): %d -> %d", i, bSub[i], bSubCopy[i])
	}
	}
	}

	// Clone should not make a copy of bNotArena, since it will not be in an arena.
	bNotArena := make([]byte, len(s))
	copy(bNotArena, s)
	bNotArenaCopy := UserArenaClone(bNotArena)
	if unsafe.Pointer(&bNotArena[0]) != unsafe.Pointer(&bNotArenaCopy[0]) {
	t.Error("Clone should not have made a copy")
	}

	a.Free()
	}

	func TestUserArenaClonePanic(t *testing.T) {
	var s string
	func() {
	x := smallScalar{2}
	defer func() {
	if v := recover(); v != nil {
	s = v.(string)
	}
	}()
	UserArenaClone(x)
	}()
	if s == "" {
	t.Errorf("expected panic from Clone")
	}
	}