Source file src/runtime/arena_test.go

Documentation: runtime

     1  // Copyright 2022 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  	"internal/goarch"
     9  	"internal/runtime/atomic"
    10  	"reflect"
    11  	. "runtime"
    12  	"runtime/debug"
    13  	"testing"
    14  	"time"
    15  	"unsafe"
    16  )
    17  
    18  type smallScalar struct {
    19  	X uintptr
    20  }
    21  type smallPointer struct {
    22  	X *smallPointer
    23  }
    24  type smallPointerMix struct {
    25  	A *smallPointer
    26  	B byte
    27  	C *smallPointer
    28  	D [11]byte
    29  }
    30  type mediumScalarEven [8192]byte
    31  type mediumScalarOdd [3321]byte
    32  type mediumPointerEven [1024]*smallPointer
    33  type mediumPointerOdd [1023]*smallPointer
    34  
    35  type largeScalar [UserArenaChunkBytes + 1]byte
    36  type largePointer [UserArenaChunkBytes/unsafe.Sizeof(&smallPointer{}) + 1]*smallPointer
    37  
    38  func TestUserArena(t *testing.T) {
    39  	// Set GOMAXPROCS to 2 so we don't run too many of these
    40  	// tests in parallel.
    41  	defer GOMAXPROCS(GOMAXPROCS(2))
    42  
    43  	// Start a subtest so that we can clean up after any parallel tests within.
    44  	t.Run("Alloc", func(t *testing.T) {
    45  		ss := &smallScalar{5}
    46  		runSubTestUserArenaNew(t, ss, true)
    47  
    48  		sp := &smallPointer{new(smallPointer)}
    49  		runSubTestUserArenaNew(t, sp, true)
    50  
    51  		spm := &smallPointerMix{sp, 5, nil, [11]byte{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11}}
    52  		runSubTestUserArenaNew(t, spm, true)
    53  
    54  		mse := new(mediumScalarEven)
    55  		for i := range mse {
    56  			mse[i] = 121
    57  		}
    58  		runSubTestUserArenaNew(t, mse, true)
    59  
    60  		mso := new(mediumScalarOdd)
    61  		for i := range mso {
    62  			mso[i] = 122
    63  		}
    64  		runSubTestUserArenaNew(t, mso, true)
    65  
    66  		mpe := new(mediumPointerEven)
    67  		for i := range mpe {
    68  			mpe[i] = sp
    69  		}
    70  		runSubTestUserArenaNew(t, mpe, true)
    71  
    72  		mpo := new(mediumPointerOdd)
    73  		for i := range mpo {
    74  			mpo[i] = sp
    75  		}
    76  		runSubTestUserArenaNew(t, mpo, true)
    77  
    78  		ls := new(largeScalar)
    79  		for i := range ls {
    80  			ls[i] = 123
    81  		}
    82  		// Not in parallel because we don't want to hold this large allocation live.
    83  		runSubTestUserArenaNew(t, ls, false)
    84  
    85  		lp := new(largePointer)
    86  		for i := range lp {
    87  			lp[i] = sp
    88  		}
    89  		// Not in parallel because we don't want to hold this large allocation live.
    90  		runSubTestUserArenaNew(t, lp, false)
    91  
    92  		sss := make([]smallScalar, 25)
    93  		for i := range sss {
    94  			sss[i] = smallScalar{12}
    95  		}
    96  		runSubTestUserArenaSlice(t, sss, true)
    97  
    98  		mpos := make([]mediumPointerOdd, 5)
    99  		for i := range mpos {
   100  			mpos[i] = *mpo
   101  		}
   102  		runSubTestUserArenaSlice(t, mpos, true)
   103  
   104  		sps := make([]smallPointer, UserArenaChunkBytes/unsafe.Sizeof(smallPointer{})+1)
   105  		for i := range sps {
   106  			sps[i] = *sp
   107  		}
   108  		// Not in parallel because we don't want to hold this large allocation live.
   109  		runSubTestUserArenaSlice(t, sps, false)
   110  
   111  		// Test zero-sized types.
   112  		t.Run("struct{}", func(t *testing.T) {
   113  			arena := NewUserArena()
   114  			var x any
   115  			x = (*struct{})(nil)
   116  			arena.New(&x)
   117  			if v := unsafe.Pointer(x.(*struct{})); v != ZeroBase {
   118  				t.Errorf("expected zero-sized type to be allocated as zerobase: got %x, want %x", v, ZeroBase)
   119  			}
   120  			arena.Free()
   121  		})
   122  		t.Run("[]struct{}", func(t *testing.T) {
   123  			arena := NewUserArena()
   124  			var sl []struct{}
   125  			arena.Slice(&sl, 10)
   126  			if v := unsafe.Pointer(&sl[0]); v != ZeroBase {
   127  				t.Errorf("expected zero-sized type to be allocated as zerobase: got %x, want %x", v, ZeroBase)
   128  			}
   129  			arena.Free()
   130  		})
   131  		t.Run("[]int (cap 0)", func(t *testing.T) {
   132  			arena := NewUserArena()
   133  			var sl []int
   134  			arena.Slice(&sl, 0)
   135  			if len(sl) != 0 {
   136  				t.Errorf("expected requested zero-sized slice to still have zero length: got %x, want 0", len(sl))
   137  			}
   138  			arena.Free()
   139  		})
   140  	})
   141  
   142  	// Run a GC cycle to get any arenas off the quarantine list.
   143  	GC()
   144  
   145  	if n := GlobalWaitingArenaChunks(); n != 0 {
   146  		t.Errorf("expected zero waiting arena chunks, found %d", n)
   147  	}
   148  }
   149  
   150  func runSubTestUserArenaNew[S comparable](t *testing.T, value *S, parallel bool) {
   151  	t.Run(reflect.TypeOf(value).Elem().Name(), func(t *testing.T) {
   152  		if parallel {
   153  			t.Parallel()
   154  		}
   155  
   156  		// Allocate and write data, enough to exhaust the arena.
   157  		//
   158  		// This is an underestimate, likely leaving some space in the arena. That's a good thing,
   159  		// because it gives us coverage of boundary cases.
   160  		n := int(UserArenaChunkBytes / unsafe.Sizeof(*value))
   161  		if n == 0 {
   162  			n = 1
   163  		}
   164  
   165  		// Create a new arena and do a bunch of operations on it.
   166  		arena := NewUserArena()
   167  
   168  		arenaValues := make([]*S, 0, n)
   169  		for j := 0; j < n; j++ {
   170  			var x any
   171  			x = (*S)(nil)
   172  			arena.New(&x)
   173  			s := x.(*S)
   174  			*s = *value
   175  			arenaValues = append(arenaValues, s)
   176  		}
   177  		// Check integrity of allocated data.
   178  		for _, s := range arenaValues {
   179  			if *s != *value {
   180  				t.Errorf("failed integrity check: got %#v, want %#v", *s, *value)
   181  			}
   182  		}
   183  
   184  		// Release the arena.
   185  		arena.Free()
   186  	})
   187  }
   188  
   189  func runSubTestUserArenaSlice[S comparable](t *testing.T, value []S, parallel bool) {
   190  	t.Run("[]"+reflect.TypeOf(value).Elem().Name(), func(t *testing.T) {
   191  		if parallel {
   192  			t.Parallel()
   193  		}
   194  
   195  		// Allocate and write data, enough to exhaust the arena.
   196  		//
   197  		// This is an underestimate, likely leaving some space in the arena. That's a good thing,
   198  		// because it gives us coverage of boundary cases.
   199  		n := int(UserArenaChunkBytes / (unsafe.Sizeof(*new(S)) * uintptr(cap(value))))
   200  		if n == 0 {
   201  			n = 1
   202  		}
   203  
   204  		// Create a new arena and do a bunch of operations on it.
   205  		arena := NewUserArena()
   206  
   207  		arenaValues := make([][]S, 0, n)
   208  		for j := 0; j < n; j++ {
   209  			var sl []S
   210  			arena.Slice(&sl, cap(value))
   211  			copy(sl, value)
   212  			arenaValues = append(arenaValues, sl)
   213  		}
   214  		// Check integrity of allocated data.
   215  		for _, sl := range arenaValues {
   216  			for i := range sl {
   217  				got := sl[i]
   218  				want := value[i]
   219  				if got != want {
   220  					t.Errorf("failed integrity check: got %#v, want %#v at index %d", got, want, i)
   221  				}
   222  			}
   223  		}
   224  
   225  		// Release the arena.
   226  		arena.Free()
   227  	})
   228  }
   229  
   230  func TestUserArenaLiveness(t *testing.T) {
   231  	t.Run("Free", func(t *testing.T) {
   232  		testUserArenaLiveness(t, false)
   233  	})
   234  	t.Run("Finalizer", func(t *testing.T) {
   235  		testUserArenaLiveness(t, true)
   236  	})
   237  }
   238  
   239  func testUserArenaLiveness(t *testing.T, useArenaFinalizer bool) {
   240  	// Disable the GC so that there's zero chance we try doing anything arena related *during*
   241  	// a mark phase, since otherwise a bunch of arenas could end up on the fault list.
   242  	defer debug.SetGCPercent(debug.SetGCPercent(-1))
   243  
   244  	// Defensively ensure that any full arena chunks leftover from previous tests have been cleared.
   245  	GC()
   246  	GC()
   247  
   248  	arena := NewUserArena()
   249  
   250  	// Allocate a few pointer-ful but un-initialized objects so that later we can
   251  	// place a reference to heap object at a more interesting location.
   252  	for i := 0; i < 3; i++ {
   253  		var x any
   254  		x = (*mediumPointerOdd)(nil)
   255  		arena.New(&x)
   256  	}
   257  
   258  	var x any
   259  	x = (*smallPointerMix)(nil)
   260  	arena.New(&x)
   261  	v := x.(*smallPointerMix)
   262  
   263  	var safeToFinalize atomic.Bool
   264  	var finalized atomic.Bool
   265  	v.C = new(smallPointer)
   266  	SetFinalizer(v.C, func(_ *smallPointer) {
   267  		if !safeToFinalize.Load() {
   268  			t.Error("finalized arena-referenced object unexpectedly")
   269  		}
   270  		finalized.Store(true)
   271  	})
   272  
   273  	// Make sure it stays alive.
   274  	GC()
   275  	GC()
   276  
   277  	// In order to ensure the object can be freed, we now need to make sure to use
   278  	// the entire arena. Exhaust the rest of the arena.
   279  
   280  	for i := 0; i < int(UserArenaChunkBytes/unsafe.Sizeof(mediumScalarEven{})); i++ {
   281  		var x any
   282  		x = (*mediumScalarEven)(nil)
   283  		arena.New(&x)
   284  	}
   285  
   286  	// Make sure it stays alive again.
   287  	GC()
   288  	GC()
   289  
   290  	v = nil
   291  
   292  	safeToFinalize.Store(true)
   293  	if useArenaFinalizer {
   294  		arena = nil
   295  
   296  		// Try to queue the arena finalizer.
   297  		GC()
   298  		GC()
   299  
   300  		// In order for the finalizer we actually want to run to execute,
   301  		// we need to make sure this one runs first.
   302  		if !BlockUntilEmptyFinalizerQueue(int64(2 * time.Second)) {
   303  			t.Fatal("finalizer queue was never emptied")
   304  		}
   305  	} else {
   306  		// Free the arena explicitly.
   307  		arena.Free()
   308  	}
   309  
   310  	// Try to queue the object's finalizer that we set earlier.
   311  	GC()
   312  	GC()
   313  
   314  	if !BlockUntilEmptyFinalizerQueue(int64(2 * time.Second)) {
   315  		t.Fatal("finalizer queue was never emptied")
   316  	}
   317  	if !finalized.Load() {
   318  		t.Error("expected arena-referenced object to be finalized")
   319  	}
   320  }
   321  
   322  func TestUserArenaClearsPointerBits(t *testing.T) {
   323  	// This is a regression test for a serious issue wherein if pointer bits
   324  	// aren't properly cleared, it's possible to allocate scalar data down
   325  	// into a previously pointer-ful area, causing misinterpretation by the GC.
   326  
   327  	// Create a large object, grab a pointer into it, and free it.
   328  	x := new([8 << 20]byte)
   329  	xp := uintptr(unsafe.Pointer(&x[124]))
   330  	var finalized atomic.Bool
   331  	SetFinalizer(x, func(_ *[8 << 20]byte) {
   332  		finalized.Store(true)
   333  	})
   334  
   335  	// Write three chunks worth of pointer data. Three gives us a
   336  	// high likelihood that when we write 2 later, we'll get the behavior
   337  	// we want.
   338  	a := NewUserArena()
   339  	for i := 0; i < int(UserArenaChunkBytes/goarch.PtrSize*3); i++ {
   340  		var x any
   341  		x = (*smallPointer)(nil)
   342  		a.New(&x)
   343  	}
   344  	a.Free()
   345  
   346  	// Recycle the arena chunks.
   347  	GC()
   348  	GC()
   349  
   350  	a = NewUserArena()
   351  	for i := 0; i < int(UserArenaChunkBytes/goarch.PtrSize*2); i++ {
   352  		var x any
   353  		x = (*smallScalar)(nil)
   354  		a.New(&x)
   355  		v := x.(*smallScalar)
   356  		// Write a pointer that should not keep x alive.
   357  		*v = smallScalar{xp}
   358  	}
   359  	KeepAlive(x)
   360  	x = nil
   361  
   362  	// Try to free x.
   363  	GC()
   364  	GC()
   365  
   366  	if !BlockUntilEmptyFinalizerQueue(int64(2 * time.Second)) {
   367  		t.Fatal("finalizer queue was never emptied")
   368  	}
   369  	if !finalized.Load() {
   370  		t.Fatal("heap allocation kept alive through non-pointer reference")
   371  	}
   372  
   373  	// Clean up the arena.
   374  	a.Free()
   375  	GC()
   376  	GC()
   377  }
   378  
   379  func TestUserArenaCloneString(t *testing.T) {
   380  	a := NewUserArena()
   381  
   382  	// A static string (not on heap or arena)
   383  	var s = "abcdefghij"
   384  
   385  	// Create a byte slice in the arena, initialize it with s
   386  	var b []byte
   387  	a.Slice(&b, len(s))
   388  	copy(b, s)
   389  
   390  	// Create a string as using the same memory as the byte slice, hence in
   391  	// the arena. This could be an arena API, but hasn't really been needed
   392  	// yet.
   393  	as := unsafe.String(&b[0], len(b))
   394  
   395  	// Clone should make a copy of as, since it is in the arena.
   396  	asCopy := UserArenaClone(as)
   397  	if unsafe.StringData(as) == unsafe.StringData(asCopy) {
   398  		t.Error("Clone did not make a copy")
   399  	}
   400  
   401  	// Clone should make a copy of subAs, since subAs is just part of as and so is in the arena.
   402  	subAs := as[1:3]
   403  	subAsCopy := UserArenaClone(subAs)
   404  	if unsafe.StringData(subAs) == unsafe.StringData(subAsCopy) {
   405  		t.Error("Clone did not make a copy")
   406  	}
   407  	if len(subAs) != len(subAsCopy) {
   408  		t.Errorf("Clone made an incorrect copy (bad length): %d -> %d", len(subAs), len(subAsCopy))
   409  	} else {
   410  		for i := range subAs {
   411  			if subAs[i] != subAsCopy[i] {
   412  				t.Errorf("Clone made an incorrect copy (data at index %d): %d -> %d", i, subAs[i], subAs[i])
   413  			}
   414  		}
   415  	}
   416  
   417  	// Clone should not make a copy of doubleAs, since doubleAs will be on the heap.
   418  	doubleAs := as + as
   419  	doubleAsCopy := UserArenaClone(doubleAs)
   420  	if unsafe.StringData(doubleAs) != unsafe.StringData(doubleAsCopy) {
   421  		t.Error("Clone should not have made a copy")
   422  	}
   423  
   424  	// Clone should not make a copy of s, since s is a static string.
   425  	sCopy := UserArenaClone(s)
   426  	if unsafe.StringData(s) != unsafe.StringData(sCopy) {
   427  		t.Error("Clone should not have made a copy")
   428  	}
   429  
   430  	a.Free()
   431  }
   432  
   433  func TestUserArenaClonePointer(t *testing.T) {
   434  	a := NewUserArena()
   435  
   436  	// Clone should not make a copy of a heap-allocated smallScalar.
   437  	x := Escape(new(smallScalar))
   438  	xCopy := UserArenaClone(x)
   439  	if unsafe.Pointer(x) != unsafe.Pointer(xCopy) {
   440  		t.Errorf("Clone should not have made a copy: %#v -> %#v", x, xCopy)
   441  	}
   442  
   443  	// Clone should make a copy of an arena-allocated smallScalar.
   444  	var i any
   445  	i = (*smallScalar)(nil)
   446  	a.New(&i)
   447  	xArena := i.(*smallScalar)
   448  	xArenaCopy := UserArenaClone(xArena)
   449  	if unsafe.Pointer(xArena) == unsafe.Pointer(xArenaCopy) {
   450  		t.Errorf("Clone should have made a copy: %#v -> %#v", xArena, xArenaCopy)
   451  	}
   452  	if *xArena != *xArenaCopy {
   453  		t.Errorf("Clone made an incorrect copy copy: %#v -> %#v", *xArena, *xArenaCopy)
   454  	}
   455  
   456  	a.Free()
   457  }
   458  
   459  func TestUserArenaCloneSlice(t *testing.T) {
   460  	a := NewUserArena()
   461  
   462  	// A static string (not on heap or arena)
   463  	var s = "klmnopqrstuv"
   464  
   465  	// Create a byte slice in the arena, initialize it with s
   466  	var b []byte
   467  	a.Slice(&b, len(s))
   468  	copy(b, s)
   469  
   470  	// Clone should make a copy of b, since it is in the arena.
   471  	bCopy := UserArenaClone(b)
   472  	if unsafe.Pointer(&b[0]) == unsafe.Pointer(&bCopy[0]) {
   473  		t.Errorf("Clone did not make a copy: %#v -> %#v", b, bCopy)
   474  	}
   475  	if len(b) != len(bCopy) {
   476  		t.Errorf("Clone made an incorrect copy (bad length): %d -> %d", len(b), len(bCopy))
   477  	} else {
   478  		for i := range b {
   479  			if b[i] != bCopy[i] {
   480  				t.Errorf("Clone made an incorrect copy (data at index %d): %d -> %d", i, b[i], bCopy[i])
   481  			}
   482  		}
   483  	}
   484  
   485  	// Clone should make a copy of bSub, since bSub is just part of b and so is in the arena.
   486  	bSub := b[1:3]
   487  	bSubCopy := UserArenaClone(bSub)
   488  	if unsafe.Pointer(&bSub[0]) == unsafe.Pointer(&bSubCopy[0]) {
   489  		t.Errorf("Clone did not make a copy: %#v -> %#v", bSub, bSubCopy)
   490  	}
   491  	if len(bSub) != len(bSubCopy) {
   492  		t.Errorf("Clone made an incorrect copy (bad length): %d -> %d", len(bSub), len(bSubCopy))
   493  	} else {
   494  		for i := range bSub {
   495  			if bSub[i] != bSubCopy[i] {
   496  				t.Errorf("Clone made an incorrect copy (data at index %d): %d -> %d", i, bSub[i], bSubCopy[i])
   497  			}
   498  		}
   499  	}
   500  
   501  	// Clone should not make a copy of bNotArena, since it will not be in an arena.
   502  	bNotArena := make([]byte, len(s))
   503  	copy(bNotArena, s)
   504  	bNotArenaCopy := UserArenaClone(bNotArena)
   505  	if unsafe.Pointer(&bNotArena[0]) != unsafe.Pointer(&bNotArenaCopy[0]) {
   506  		t.Error("Clone should not have made a copy")
   507  	}
   508  
   509  	a.Free()
   510  }
   511  
   512  func TestUserArenaClonePanic(t *testing.T) {
   513  	var s string
   514  	func() {
   515  		x := smallScalar{2}
   516  		defer func() {
   517  			if v := recover(); v != nil {
   518  				s = v.(string)
   519  			}
   520  		}()
   521  		UserArenaClone(x)
   522  	}()
   523  	if s == "" {
   524  		t.Errorf("expected panic from Clone")
   525  	}
   526  }
   527  

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