Don't panic on overallocation and remove mux (#8)

allocator/nonmoving_other.go

@@ -4,7 +4,7 @@ package allocator
 
 import "github.com/tetratelabs/wazero/experimental"
 
-var pageSize = 0 // used only for test
+var pageSize = uint64(0) // used only for test
 
 func alloc(cap, max uint64) experimental.LinearMemory {
 	return sliceAlloc(cap, max)

allocator/nonmoving_slice.go

@@ -17,8 +17,5 @@ type sliceBuffer struct {
 func (b *sliceBuffer) Free() {}
 
 func (b *sliceBuffer) Reallocate(size uint64) []byte {
-	if int(size) > cap(b.buf) {
-		panic(errInvalidReallocation)
-	}
 	return b.buf[:size]
 }

allocator/nonmoving_test.go

@@ -11,7 +11,7 @@ func TestNonMoving(t *testing.T) {
 	tests := []struct {
 		name string
 		mem  experimental.LinearMemory
-		cap  int
+		cap  uint64
 	}{
 		{
 			name: "native",
@@ -36,7 +36,7 @@ func TestNonMoving(t *testing.T) {
 
 			buf := mem.Reallocate(5)
 			require.Len(t, buf, 5)
-			require.Equal(t, tc.cap, cap(buf))
+			require.EqualValues(t, tc.cap, cap(buf))
 			base := &buf[0]
 
 			buf = mem.Reallocate(5)
@@ -50,8 +50,6 @@ func TestNonMoving(t *testing.T) {
 			buf = mem.Reallocate(20)
 			require.Len(t, buf, 20)
 			require.Equal(t, base, &buf[0])
-
-			require.PanicsWithError(t, errInvalidReallocation.Error(), func() { mem.Reallocate(21) })
 		})
 	}
 }

allocator/nonmoving_unix.go

@@ -5,68 +5,55 @@ package allocator
 import (
 	"fmt"
 	"math"
-	"sync"
 
 	"github.com/tetratelabs/wazero/experimental"
 	"golang.org/x/sys/unix"
 )
 
-var pageSize = unix.Getpagesize()
+var pageSize = uint64(unix.Getpagesize())
 
 func alloc(_, max uint64) experimental.LinearMemory {
 	// Round up to the page size because recommitting must be page-aligned.
 	// In practice, the WebAssembly page size should be a multiple of the system
 	// page size on most if not all platforms and rounding will never happen.
-	rnd := uint64(pageSize - 1)
-	reserved := (max + rnd) &^ rnd
+	rnd := pageSize - 1
+	res := (max + rnd) &^ rnd
 
-	if reserved > math.MaxInt {
+	if res > math.MaxInt {
 		// This ensures int(max) overflows to a negative value,
 		// and unix.Mmap returns EINVAL.
-		reserved = math.MaxUint64
+		res = math.MaxUint64
 	}
 
 	// Reserve max bytes of address space, to ensure we won't need to move it.
 	// A protected, private, anonymous mapping should not commit memory.
-	b, err := unix.Mmap(-1, 0, int(reserved), unix.PROT_NONE, unix.MAP_PRIVATE|unix.MAP_ANON)
+	b, err := unix.Mmap(-1, 0, int(res), unix.PROT_NONE, unix.MAP_PRIVATE|unix.MAP_ANON)
 	if err != nil {
 		panic(fmt.Errorf("allocator_unix: failed to reserve memory: %w", err))
 	}
-	return &mmappedMemory{buf: b[:0], max: max}
+	return &mmappedMemory{buf: b[:0]}
 }
 
 // The slice covers the entire mmapped memory:
 //   - len(buf) is the already committed memory,
 //   - cap(buf) is the reserved address space, which is max rounded up to a page.
 type mmappedMemory struct {
 	buf []byte
-	max uint64
-
-	// Any reasonable Wasm implementation will take a lock before calling Grow, but this
-	// is invisible to Go's race detector so it can still detect raciness when we updated
-	// buf. We go ahead and take a lock when mutating since the performance effect should
-	// be negligible in practice and it will help the race detector confirm the safety.
-	mu sync.Mutex
 }
 
 func (m *mmappedMemory) Reallocate(size uint64) []byte {
-	if size > m.max {
-		panic(errInvalidReallocation)
-	}
-
-	m.mu.Lock()
-	defer m.mu.Unlock()
-
 	com := uint64(len(m.buf))
-	if com < size {
+	res := uint64(cap(m.buf))
+
+	if com < size && size <= res {
 		// Round up to the page size.
-		rnd := uint64(unix.Getpagesize() - 1)
+		rnd := pageSize - 1
 		newCap := (size + rnd) &^ rnd
 
 		// Commit additional memory up to new bytes.
 		err := unix.Mprotect(m.buf[com:newCap], unix.PROT_READ|unix.PROT_WRITE)
 		if err != nil {
-			panic(fmt.Errorf("allocator_unix: failed to commit memory: %w", err))
+			return nil
 		}
 
 		// Update committed memory.
@@ -78,9 +65,6 @@ func (m *mmappedMemory) Reallocate(size uint64) []byte {
 }
 
 func (m *mmappedMemory) Free() {
-	m.mu.Lock()
-	defer m.mu.Unlock()
-
 	err := unix.Munmap(m.buf[:cap(m.buf)])
 	if err != nil {
 		panic(fmt.Errorf("allocator_unix: failed to release memory: %w", err))

allocator/nonmoving_windows.go

@@ -5,37 +5,36 @@ package allocator
 import (
 	"fmt"
 	"math"
-	"sync"
 	"unsafe"
 
 	"github.com/tetratelabs/wazero/experimental"
 	"golang.org/x/sys/windows"
 )
 
-var pageSize = windows.Getpagesize()
+var pageSize = uint64(windows.Getpagesize())
 
 func alloc(_, max uint64) experimental.LinearMemory {
 	// Round up to the page size because recommitting must be page-aligned.
 	// In practice, the WebAssembly page size should be a multiple of the system
 	// page size on most if not all platforms and rounding will never happen.
-	rnd := uint64(pageSize) - 1
-	reserved := (max + rnd) &^ rnd
+	rnd := pageSize - 1
+	res := (max + rnd) &^ rnd
 
-	if reserved > math.MaxInt {
+	if res > math.MaxInt {
 		// This ensures uintptr(max) overflows to a large value,
 		// and windows.VirtualAlloc returns an error.
-		reserved = math.MaxUint64
+		res = math.MaxUint64
 	}
 
 	// Reserve max bytes of address space, to ensure we won't need to move it.
 	// This does not commit memory.
-	r, err := windows.VirtualAlloc(0, uintptr(reserved), windows.MEM_RESERVE, windows.PAGE_READWRITE)
+	r, err := windows.VirtualAlloc(0, uintptr(res), windows.MEM_RESERVE, windows.PAGE_READWRITE)
 	if err != nil {
 		panic(fmt.Errorf("allocator_windows: failed to reserve memory: %w", err))
 	}
 
-	buf := unsafe.Slice((*byte)(unsafe.Pointer(r)), int(reserved))
-	return &virtualMemory{buf: buf[:0], addr: r, max: max}
+	buf := unsafe.Slice((*byte)(unsafe.Pointer(r)), int(res))
+	return &virtualMemory{buf: buf[:0], addr: r}
 }
 
 // The slice covers the entire mmapped memory:
@@ -44,33 +43,21 @@ func alloc(_, max uint64) experimental.LinearMemory {
 type virtualMemory struct {
 	buf  []byte
 	addr uintptr
-	max  uint64
-
-	// Any reasonable Wasm implementation will take a lock before calling Grow, but this
-	// is invisible to Go's race detector so it can still detect raciness when we updated
-	// buf. We go ahead and take a lock when mutating since the performance effect should
-	// be negligible in practice and it will help the race detector confirm the safety.
-	mu sync.Mutex
 }
 
 func (m *virtualMemory) Reallocate(size uint64) []byte {
-	if size > m.max {
-		panic(errInvalidReallocation)
-	}
-
-	m.mu.Lock()
-	defer m.mu.Unlock()
-
 	com := uint64(len(m.buf))
-	if com < size {
+	res := uint64(cap(m.buf))
+
+	if com < size && size <= res {
 		// Round up to the page size.
-		rnd := uint64(pageSize) - 1
+		rnd := pageSize - 1
 		newCap := (size + rnd) &^ rnd
 
 		// Commit additional memory up to new bytes.
 		_, err := windows.VirtualAlloc(m.addr, uintptr(newCap), windows.MEM_COMMIT, windows.PAGE_READWRITE)
 		if err != nil {
-			panic(fmt.Errorf("allocator_windows: failed to commit memory: %w", err))
+			return nil
 		}
 
 		// Update committed memory.
@@ -82,9 +69,6 @@ func (m *virtualMemory) Reallocate(size uint64) []byte {
 }
 
 func (m *virtualMemory) Free() {
-	m.mu.Lock()
-	defer m.mu.Unlock()
-
 	err := windows.VirtualFree(m.addr, 0, windows.MEM_RELEASE)
 	if err != nil {
 		panic(fmt.Errorf("allocator_windows: failed to release memory: %w", err))