[WIP] lint a bit, update deps

vendor/github.com/cockroachdb/pebble/internal/arenaskl/arena.go

@@ -18,22 +18,21 @@
 package arenaskl
 
 import (
-	"math"
 	"sync/atomic"
 	"unsafe"
 
 	"github.com/cockroachdb/errors"
+	"github.com/cockroachdb/pebble/internal/constants"
+	"github.com/cockroachdb/pebble/internal/invariants"
 )
 
 // Arena is lock-free.
 type Arena struct {
-	n   uint64
+	n   atomic.Uint64
 	buf []byte
 }
 
-const (
-	align4 = 3
-)
+const nodeAlignment = 4
 
 var (
 	// ErrArenaFull indicates that the arena is full and cannot perform any more
@@ -44,20 +43,28 @@ var (
 // NewArena allocates a new arena using the specified buffer as the backing
 // store.
 func NewArena(buf []byte) *Arena {
-	// Don't store data at position 0 in order to reserve offset=0 as a kind
-	// of nil pointer.
-	return &Arena{
-		n:   1,
+	if len(buf) > constants.MaxUint32OrInt {
+		if invariants.Enabled {
+			panic(errors.AssertionFailedf("attempting to create arena of size %d", len(buf)))
+		}
+		buf = buf[:constants.MaxUint32OrInt]
+	}
+	a := &Arena{
 		buf: buf,
 	}
+	// We don't store data at position 0 in order to reserve offset=0 as a kind of
+	// nil pointer.
+	a.n.Store(1)
+	return a
 }
 
 // Size returns the number of bytes allocated by the arena.
 func (a *Arena) Size() uint32 {
-	s := atomic.LoadUint64(&a.n)
-	if s > math.MaxUint32 {
-		// Saturate at MaxUint32.
-		return math.MaxUint32
+	s := a.n.Load()
+	if s > constants.MaxUint32OrInt {
+		// The last failed allocation can push the size higher than len(a.buf).
+		// Saturate at the maximum representable offset.
+		return constants.MaxUint32OrInt
 	}
 	return uint32(s)
 }
@@ -67,24 +74,33 @@ func (a *Arena) Capacity() uint32 {
 	return uint32(len(a.buf))
 }
 
-func (a *Arena) alloc(size, align, overflow uint32) (uint32, uint32, error) {
+// alloc allocates a buffer of the given size and with the given alignment
+// (which must be a power of 2).
+//
+// If overflow is not 0, it also ensures that many bytes after the buffer are
+// inside the arena (this is used for structures that are larger than the
+// requested size but don't use those extra bytes).
+func (a *Arena) alloc(size, alignment, overflow uint32) (uint32, uint32, error) {
+	if invariants.Enabled && (alignment&(alignment-1)) != 0 {
+		panic(errors.AssertionFailedf("invalid alignment %d", alignment))
+	}
 	// Verify that the arena isn't already full.
-	origSize := atomic.LoadUint64(&a.n)
+	origSize := a.n.Load()
 	if int(origSize) > len(a.buf) {
 		return 0, 0, ErrArenaFull
 	}
 
 	// Pad the allocation with enough bytes to ensure the requested alignment.
-	padded := uint32(size) + align
+	padded := uint64(size) + uint64(alignment) - 1
 
-	newSize := atomic.AddUint64(&a.n, uint64(padded))
-	if int(newSize)+int(overflow) > len(a.buf) {
+	newSize := a.n.Add(padded)
+	if newSize+uint64(overflow) > uint64(len(a.buf)) {
 		return 0, 0, ErrArenaFull
 	}
 
 	// Return the aligned offset.
-	offset := (uint32(newSize) - padded + align) & ^align
-	return offset, padded, nil
+	offset := (uint32(newSize) - size) & ^(alignment - 1)
+	return offset, uint32(padded), nil
 }
 
 func (a *Arena) getBytes(offset uint32, size uint32) []byte {