Implement shared memory WAL. (#71)

- enabled by default on 64-bit macOS and Linux (`amd64`/`arm64`)
- depends on merged but unreleased wazero
- may cause small performance regression
- users may need WithMemoryLimitPages if not enough address space available
- needs docs

.github/workflows/cross.sh

@@ -17,7 +17,9 @@ echo aix           ; GOOS=aix       GOARCH=ppc64 go build .
 echo js            ; GOOS=js        GOARCH=wasm  go build .
 echo wasip1        ; GOOS=wasip1    GOARCH=wasm  go build .
 echo darwin-flock  ; GOOS=darwin    GOARCH=amd64 go build -tags sqlite3_flock .
+echo darwin-noshm  ; GOOS=darwin    GOARCH=amd64 go build -tags sqlite3_noshm .
 echo darwin-nosys  ; GOOS=darwin    GOARCH=amd64 go build -tags sqlite3_nosys .
+echo linux-noshm   ; GOOS=linux     GOARCH=amd64 go build -tags sqlite3_noshm .
 echo linux-nosys   ; GOOS=linux     GOARCH=amd64 go build -tags sqlite3_nosys .
 echo windows-nosys ; GOOS=windows   GOARCH=amd64 go build -tags sqlite3_nosys .
 echo freebsd-nosys ; GOOS=freebsd   GOARCH=amd64 go build -tags sqlite3_nosys .

.github/workflows/test.yml

@@ -47,6 +47,10 @@ jobs:
       run: go test -v -tags sqlite3_flock ./...
       if: matrix.os == 'macos-latest'
 
+    - name: Test no shared memory
+      run: go test -v -tags sqlite3_noshm ./...
+      if: matrix.os == 'ubuntu-latest'
+
     - name: Test no locks
       run: go test -v -tags sqlite3_nosys ./tests -run TestDB_nolock
 

embed/exports.txt

@@ -1,6 +1,7 @@
 free
 malloc
 malloc_destructor
+aligned_alloc
 sqlite3_anycollseq_init
 sqlite3_backup_finish
 sqlite3_backup_init

go.mod

@@ -5,7 +5,7 @@ go 1.21
 require (
 	github.com/ncruces/julianday v1.0.0
 	github.com/psanford/httpreadat v0.1.0
-	github.com/tetratelabs/wazero v1.7.0
+	github.com/tetratelabs/wazero v1.7.1-0.20240410111357-a0fbb185447f
 	golang.org/x/crypto v0.22.0
 	golang.org/x/sync v0.7.0
 	golang.org/x/sys v0.19.0

go.sum

@@ -2,8 +2,8 @@ github.com/ncruces/julianday v1.0.0 h1:fH0OKwa7NWvniGQtxdJRxAgkBMolni2BjDHaWTxqt
 github.com/ncruces/julianday v1.0.0/go.mod h1:Dusn2KvZrrovOMJuOt0TNXL6tB7U2E8kvza5fFc9G7g=
 github.com/psanford/httpreadat v0.1.0 h1:VleW1HS2zO7/4c7c7zNl33fO6oYACSagjJIyMIwZLUE=
 github.com/psanford/httpreadat v0.1.0/go.mod h1:Zg7P+TlBm3bYbyHTKv/EdtSJZn3qwbPwpfZ/I9GKCRE=
-github.com/tetratelabs/wazero v1.7.0 h1:jg5qPydno59wqjpGrHph81lbtHzTrWzwwtD4cD88+hQ=
-github.com/tetratelabs/wazero v1.7.0/go.mod h1:ytl6Zuh20R/eROuyDaGPkp82O9C/DJfXAwJfQ3X6/7Y=
+github.com/tetratelabs/wazero v1.7.1-0.20240410111357-a0fbb185447f h1:xJ6F/f7fM1OvnPFSn7Ggf9icswSXoYOYLZbu7aJVQbA=
+github.com/tetratelabs/wazero v1.7.1-0.20240410111357-a0fbb185447f/go.mod h1:ytl6Zuh20R/eROuyDaGPkp82O9C/DJfXAwJfQ3X6/7Y=
 golang.org/x/crypto v0.22.0 h1:g1v0xeRhjcugydODzvb3mEM9SQ0HGp9s/nh3COQ/C30=
 golang.org/x/crypto v0.22.0/go.mod h1:vr6Su+7cTlO45qkww3VDJlzDn0ctJvRgYbC2NvXHt+M=
 golang.org/x/sync v0.7.0 h1:YsImfSBoP9QPYL0xyKJPq0gcaJdG3rInoqxTWbfQu9M=

go.work.sum

@@ -1,4 +1,8 @@
+golang.org/x/mod v0.8.0 h1:LUYupSeNrTNCGzR/hVBk2NHZO4hXcVaW1k4Qx7rjPx8=
 golang.org/x/mod v0.8.0/go.mod h1:iBbtSCu2XBx23ZKBPSOrRkjjQPZFPuis4dIYUhu/chs=
+golang.org/x/net v0.21.0 h1:AQyQV4dYCvJ7vGmJyKki9+PBdyvhkSd8EIx/qb0AYv4=
 golang.org/x/net v0.21.0/go.mod h1:bIjVDfnllIU7BJ2DNgfnXvpSvtn8VRwhlsaeUTyUS44=
-golang.org/x/term v0.18.0/go.mod h1:ILwASektA3OnRv7amZ1xhE/KTR+u50pbXfZ03+6Nx58=
+golang.org/x/term v0.19.0 h1:+ThwsDv+tYfnJFhF4L8jITxu1tdTWRTZpdsWgEgjL6Q=
+golang.org/x/term v0.19.0/go.mod h1:2CuTdWZ7KHSQwUzKva0cbMg6q2DMI3Mmxp+gKJbskEk=
+golang.org/x/tools v0.6.0 h1:BOw41kyTf3PuCW1pVQf8+Cyg8pMlkYB1oo9iJ6D/lKM=
 golang.org/x/tools v0.6.0/go.mod h1:Xwgl3UAJ/d3gWutnCtw505GrjyAbvKui8lOU390QaIU=

gormlite/go.mod

@@ -4,7 +4,7 @@ go 1.21
 
 require (
 	github.com/ncruces/go-sqlite3 v0.13.0
-	gorm.io/gorm v1.25.8
+	gorm.io/gorm v1.25.9
 )
 
 require (
@@ -12,5 +12,5 @@ require (
 	github.com/jinzhu/now v1.1.5 // indirect
 	github.com/ncruces/julianday v1.0.0 // indirect
 	github.com/tetratelabs/wazero v1.7.0 // indirect
-	golang.org/x/sys v0.18.0 // indirect
+	golang.org/x/sys v0.19.0 // indirect
 )

gormlite/go.sum

@@ -8,9 +8,9 @@ github.com/ncruces/julianday v1.0.0 h1:fH0OKwa7NWvniGQtxdJRxAgkBMolni2BjDHaWTxqt
 github.com/ncruces/julianday v1.0.0/go.mod h1:Dusn2KvZrrovOMJuOt0TNXL6tB7U2E8kvza5fFc9G7g=
 github.com/tetratelabs/wazero v1.7.0 h1:jg5qPydno59wqjpGrHph81lbtHzTrWzwwtD4cD88+hQ=
 github.com/tetratelabs/wazero v1.7.0/go.mod h1:ytl6Zuh20R/eROuyDaGPkp82O9C/DJfXAwJfQ3X6/7Y=
-golang.org/x/sys v0.18.0 h1:DBdB3niSjOA/O0blCZBqDefyWNYveAYMNF1Wum0DYQ4=
-golang.org/x/sys v0.18.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
+golang.org/x/sys v0.19.0 h1:q5f1RH2jigJ1MoAWp2KTp3gm5zAGFUTarQZ5U386+4o=
+golang.org/x/sys v0.19.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
 golang.org/x/text v0.14.0 h1:ScX5w1eTa3QqT8oi6+ziP7dTV1S2+ALU0bI+0zXKWiQ=
 golang.org/x/text v0.14.0/go.mod h1:18ZOQIKpY8NJVqYksKHtTdi31H5itFRjB5/qKTNYzSU=
-gorm.io/gorm v1.25.8 h1:WAGEZ/aEcznN4D03laj8DKnehe1e9gYQAjW8xyPRdeo=
-gorm.io/gorm v1.25.8/go.mod h1:hbnx/Oo0ChWMn1BIhpy1oYozzpM15i4YPuHDmfYtwg8=
+gorm.io/gorm v1.25.9 h1:wct0gxZIELDk8+ZqF/MVnHLkA1rvYlBWUMv2EdsK1g8=
+gorm.io/gorm v1.25.9/go.mod h1:hbnx/Oo0ChWMn1BIhpy1oYozzpM15i4YPuHDmfYtwg8=

gormlite/test.sh

@@ -7,7 +7,7 @@ rm -rf gorm/ tests/
 go work use -r .
 go test
 
-git clone --branch v1.25.8 --filter=blob:none https://github.com/go-gorm/gorm.git
+git clone --branch v1.25.9 --filter=blob:none https://github.com/go-gorm/gorm.git
 mv gorm/tests tests
 rm -rf gorm/
 

internal/util/alloc.go

@@ -0,0 +1,81 @@
+//go:build unix
+
+package util
+
+import (
+	"math"
+
+	"github.com/tetratelabs/wazero/experimental"
+	"golang.org/x/sys/unix"
+)
+
+func mmappedAllocator(min, cap, max uint64) experimental.MemoryBuffer {
+	// Round up to the page size.
+	rnd := uint64(unix.Getpagesize() - 1)
+	max = (max + rnd) &^ rnd
+	cap = (cap + rnd) &^ rnd
+
+	if max > math.MaxInt {
+		// This ensures int(max) overflows to a negative value,
+		// and unix.Mmap returns EINVAL.
+		max = 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(max), unix.PROT_NONE, unix.MAP_PRIVATE|unix.MAP_ANON)
+	if err != nil {
+		panic(err)
+	}
+	// Commit the initial cap bytes of memory.
+	err = unix.Mprotect(b[:cap], unix.PROT_READ|unix.PROT_WRITE)
+	if err != nil {
+		unix.Munmap(b)
+		panic(err)
+	}
+	return &mmappedBuffer{
+		buf: b[:cap],
+		cur: min,
+	}
+}
+
+// The slice covers the entire mmapped memory:
+//   - len(buf) is the already committed memory,
+//   - cap(buf) is the reserved address space,
+//   - cur is the already requested size.
+type mmappedBuffer struct {
+	buf []byte
+	cur uint64
+}
+
+func (m *mmappedBuffer) Buffer() []byte {
+	// Limit capacity because bytes beyond len(m.buf)
+	// have not yet been committed.
+	return m.buf[:m.cur:len(m.buf)]
+}
+
+func (m *mmappedBuffer) Grow(size uint64) []byte {
+	if com := uint64(len(m.buf)); com < size {
+		// Round up to the page size.
+		rnd := uint64(unix.Getpagesize() - 1)
+		new := (size + rnd) &^ rnd
+
+		// Commit additional memory up to new bytes.
+		err := unix.Mprotect(m.buf[com:new], unix.PROT_READ|unix.PROT_WRITE)
+		if err != nil {
+			panic(err)
+		}
+
+		// Update commited memory.
+		m.buf = m.buf[:new]
+	}
+	m.cur = size
+	return m.Buffer()
+}
+
+func (m *mmappedBuffer) Free() {
+	err := unix.Munmap(m.buf[:cap(m.buf)])
+	if err != nil {
+		panic(err)
+	}
+	m.buf = nil
+}

internal/util/handle.go

@@ -3,21 +3,11 @@ package util
 import (
 	"context"
 	"io"
-
-	"github.com/tetratelabs/wazero/experimental"
 )
 
-type handleKey struct{}
 type handleState struct {
 	handles []any
-	empty   int
-}
-
-func NewContext(ctx context.Context) context.Context {
-	state := new(handleState)
-	ctx = experimental.WithCloseNotifier(ctx, state)
-	ctx = context.WithValue(ctx, handleKey{}, state)
-	return ctx
+	holes   int
 }
 
 func (s *handleState) CloseNotify(ctx context.Context, exitCode uint32) {
@@ -27,14 +17,14 @@ func (s *handleState) CloseNotify(ctx context.Context, exitCode uint32) {
 		}
 	}
 	s.handles = nil
-	s.empty = 0
+	s.holes = 0
 }
 
 func GetHandle(ctx context.Context, id uint32) any {
 	if id == 0 {
 		return nil
 	}
-	s := ctx.Value(handleKey{}).(*handleState)
+	s := ctx.Value(moduleKey{}).(*moduleState)
 	return s.handles[^id]
 }
 
@@ -42,10 +32,10 @@ func DelHandle(ctx context.Context, id uint32) error {
 	if id == 0 {
 		return nil
 	}
-	s := ctx.Value(handleKey{}).(*handleState)
+	s := ctx.Value(moduleKey{}).(*moduleState)
 	a := s.handles[^id]
 	s.handles[^id] = nil
-	s.empty++
+	s.holes++
 	if c, ok := a.(io.Closer); ok {
 		return c.Close()
 	}
@@ -56,13 +46,13 @@ func AddHandle(ctx context.Context, a any) (id uint32) {
 	if a == nil {
 		panic(NilErr)
 	}
-	s := ctx.Value(handleKey{}).(*handleState)
+	s := ctx.Value(moduleKey{}).(*moduleState)
 
 	// Find an empty slot.
-	if s.empty > cap(s.handles)-len(s.handles) {
+	if s.holes > cap(s.handles)-len(s.handles) {
 		for id, h := range s.handles {
 			if h == nil {
-				s.empty--
+				s.holes--
 				s.handles[id] = a
 				return ^uint32(id)
 			}

internal/util/mmap.go

@@ -0,0 +1,105 @@
+//go:build (linux || darwin) && (amd64 || arm64) && !sqlite3_flock && !sqlite3_noshm && !sqlite3_nosys
+
+package util
+
+import (
+	"context"
+	"os"
+	"unsafe"
+
+	"github.com/tetratelabs/wazero/api"
+	"github.com/tetratelabs/wazero/experimental"
+	"golang.org/x/sys/unix"
+)
+
+type mmapState struct {
+	regions []*MappedRegion
+	enabled bool
+}
+
+func (s *mmapState) init(ctx context.Context, enabled bool) context.Context {
+	if s.enabled = enabled; enabled {
+		return experimental.WithMemoryAllocator(ctx, mmappedAllocator)
+	}
+	return ctx
+}
+
+func CanMap(ctx context.Context) bool {
+	s := ctx.Value(moduleKey{}).(*moduleState)
+	return s.mmapState.enabled
+}
+
+func (s *mmapState) new(ctx context.Context, mod api.Module, size uint32) *MappedRegion {
+	// Find unused region.
+	for _, r := range s.regions {
+		if !r.used && r.size == size {
+			return r
+		}
+	}
+
+	// Allocate page aligned memmory.
+	alloc := mod.ExportedFunction("aligned_alloc")
+	stack := [2]uint64{
+		uint64(unix.Getpagesize()),
+		uint64(size),
+	}
+	if err := alloc.CallWithStack(ctx, stack[:]); err != nil {
+		panic(err)
+	}
+	if stack[0] == 0 {
+		panic(OOMErr)
+	}
+
+	// Save the newly allocated region.
+	ptr := uint32(stack[0])
+	buf := View(mod, ptr, uint64(size))
+	addr := uintptr(unsafe.Pointer(&buf[0]))
+	s.regions = append(s.regions, &MappedRegion{
+		Ptr:  ptr,
+		addr: addr,
+		size: size,
+	})
+	return s.regions[len(s.regions)-1]
+}
+
+type MappedRegion struct {
+	addr uintptr
+	Ptr  uint32
+	size uint32
+	used bool
+}
+
+func MapRegion(ctx context.Context, mod api.Module, f *os.File, offset int64, size uint32) (*MappedRegion, error) {
+	s := ctx.Value(moduleKey{}).(*moduleState)
+	r := s.new(ctx, mod, size)
+	err := r.mmap(f, offset)
+	if err != nil {
+		return nil, err
+	}
+	return r, nil
+}
+
+func (r *MappedRegion) Unmap() error {
+	// We can't munmap the region, otherwise it could be remaped.
+	// Instead, convert it to a protected, private, anonymous mapping.
+	// If successful, it can be reused for a subsequent mmap.
+	_, err := mmap(r.addr, uintptr(r.size),
+		unix.PROT_NONE, unix.MAP_PRIVATE|unix.MAP_ANON|unix.MAP_FIXED,
+		-1, 0)
+	r.used = err != nil
+	return err
+}
+
+func (r *MappedRegion) mmap(f *os.File, offset int64) error {
+	_, err := mmap(r.addr, uintptr(r.size),
+		unix.PROT_READ|unix.PROT_WRITE, unix.MAP_SHARED|unix.MAP_FIXED,
+		int(f.Fd()), offset)
+	r.used = err == nil
+	return err
+}
+
+//go:linkname mmap syscall.mmap
+func mmap(addr, length uintptr, prot, flag, fd int, pos int64) (*byte, error)
+
+//go:linkname munmap syscall.munmap
+func munmap(addr, length uintptr) error

internal/util/mmap_other.go

@@ -0,0 +1,15 @@
+//go:build !(linux || darwin) || !(amd64 || arm64) || sqlite3_flock || sqlite3_noshm || sqlite3_nosys
+
+package util
+
+import "context"
+
+type mmapState struct{}
+
+func (s *mmapState) init(ctx context.Context, _ bool) context.Context {
+	return ctx
+}
+
+func CanMap(ctx context.Context) bool {
+	return false
+}

internal/util/module.go

@@ -0,0 +1,21 @@
+package util
+
+import (
+	"context"
+
+	"github.com/tetratelabs/wazero/experimental"
+)
+
+type moduleKey struct{}
+type moduleState struct {
+	handleState
+	mmapState
+}
+
+func NewContext(ctx context.Context, mappableMemory bool) context.Context {
+	state := new(moduleState)
+	ctx = context.WithValue(ctx, moduleKey{}, state)
+	ctx = experimental.WithCloseNotifier(ctx, state)
+	ctx = state.mmapState.init(ctx, mappableMemory)
+	return ctx
+}

sqlite.go

@@ -85,7 +85,7 @@ func instantiateSQLite() (sqlt *sqlite, err error) {
 	}
 
 	sqlt = new(sqlite)
-	sqlt.ctx = util.NewContext(context.Background())
+	sqlt.ctx = util.NewContext(context.Background(), vfs.SupportsSharedMemory)
 
 	sqlt.mod, err = instance.runtime.InstantiateModule(sqlt.ctx,
 		instance.compiled, wazero.NewModuleConfig())

sqlite3/vfs.c

@@ -13,7 +13,7 @@ int go_sleep(sqlite3_vfs *, int microseconds);
 int go_current_time_64(sqlite3_vfs *, sqlite3_int64 *);
 
 int go_open(sqlite3_vfs *, sqlite3_filename zName, sqlite3_file *, int flags,
-            int *pOutFlags);
+            int *pOutFlags, int *pOutVFS);
 int go_delete(sqlite3_vfs *, const char *zName, int syncDir);
 int go_access(sqlite3_vfs *, const char *zName, int flags, int *pResOut);
 int go_full_pathname(sqlite3_vfs *, const char *zName, int nOut, char *zOut);
@@ -32,29 +32,55 @@ int go_lock(sqlite3_file *, int eLock);
 int go_unlock(sqlite3_file *, int eLock);
 int go_check_reserved_lock(sqlite3_file *, int *pResOut);
 
+int go_shm_map(sqlite3_file *, int iPg, int pgsz, int, void volatile **);
+int go_shm_lock(sqlite3_file *, int offset, int n, int flags);
+int go_shm_unmap(sqlite3_file *, int deleteFlag);
+void go_shm_barrier(sqlite3_file *);
+
 static int go_open_wrapper(sqlite3_vfs *vfs, sqlite3_filename zName,
                            sqlite3_file *file, int flags, int *pOutFlags) {
-  static const sqlite3_io_methods os_io = {
-      .iVersion = 1,
-      .xClose = go_close,
-      .xRead = go_read,
-      .xWrite = go_write,
-      .xTruncate = go_truncate,
-      .xSync = go_sync,
-      .xFileSize = go_file_size,
-      .xLock = go_lock,
-      .xUnlock = go_unlock,
-      .xCheckReservedLock = go_check_reserved_lock,
-      .xFileControl = go_file_control,
-      .xSectorSize = go_sector_size,
-      .xDeviceCharacteristics = go_device_characteristics,
-  };
+  static const sqlite3_io_methods go_io[2] = {
+      {
+          .iVersion = 1,
+          .xClose = go_close,
+          .xRead = go_read,
+          .xWrite = go_write,
+          .xTruncate = go_truncate,
+          .xSync = go_sync,
+          .xFileSize = go_file_size,
+          .xLock = go_lock,
+          .xUnlock = go_unlock,
+          .xCheckReservedLock = go_check_reserved_lock,
+          .xFileControl = go_file_control,
+          .xSectorSize = go_sector_size,
+          .xDeviceCharacteristics = go_device_characteristics,
+      },
+      {
+          .iVersion = 2,
+          .xClose = go_close,
+          .xRead = go_read,
+          .xWrite = go_write,
+          .xTruncate = go_truncate,
+          .xSync = go_sync,
+          .xFileSize = go_file_size,
+          .xLock = go_lock,
+          .xUnlock = go_unlock,
+          .xCheckReservedLock = go_check_reserved_lock,
+          .xFileControl = go_file_control,
+          .xSectorSize = go_sector_size,
+          .xDeviceCharacteristics = go_device_characteristics,
+          .xShmMap = go_shm_map,
+          .xShmLock = go_shm_lock,
+          .xShmBarrier = go_shm_barrier,
+          .xShmUnmap = go_shm_unmap,
+      }};
+  int vfsID = 0;
   memset(file, 0, vfs->szOsFile);
-  int rc = go_open(vfs, zName, file, flags, pOutFlags);
+  int rc = go_open(vfs, zName, file, flags, pOutFlags, &vfsID);
   if (rc) {
     return rc;
   }
-  file->pMethods = &os_io;
+  file->pMethods = &go_io[vfsID];
   return SQLITE_OK;
 }
 

tests/parallel/parallel_test.go

@@ -12,9 +12,16 @@ import (
 
 	"github.com/ncruces/go-sqlite3"
 	_ "github.com/ncruces/go-sqlite3/embed"
+	"github.com/ncruces/go-sqlite3/vfs"
 	"github.com/ncruces/go-sqlite3/vfs/memdb"
+	"github.com/tetratelabs/wazero"
 )
 
+func TestMain(m *testing.M) {
+	sqlite3.RuntimeConfig = wazero.NewRuntimeConfig().WithMemoryLimitPages(1024)
+	os.Exit(m.Run())
+}
+
 func TestParallel(t *testing.T) {
 	var iter int
 	if testing.Short() {
@@ -32,6 +39,20 @@ func TestParallel(t *testing.T) {
 	testIntegrity(t, name)
 }
 
+func TestWAL(t *testing.T) {
+	if !vfs.SupportsSharedMemory {
+		t.Skip("skipping without shared memory")
+	}
+
+	name := "file:" +
+		filepath.Join(t.TempDir(), "test.db") +
+		"?_pragma=busy_timeout(10000)" +
+		"&_pragma=journal_mode(wal)" +
+		"&_pragma=synchronous(off)"
+	testParallel(t, name, 1000)
+	testIntegrity(t, name)
+}
+
 func TestMemory(t *testing.T) {
 	var iter int
 	if testing.Short() {

tests/wal_test.go

@@ -0,0 +1,33 @@
+package tests
+
+import (
+	"path/filepath"
+	"testing"
+
+	"github.com/ncruces/go-sqlite3"
+)
+
+func TestWAL_enter_exit(t *testing.T) {
+	t.Parallel()
+
+	file := filepath.Join(t.TempDir(), "test.db")
+
+	db, err := sqlite3.Open(file)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer db.Close()
+
+	err = db.Exec(`
+		CREATE TABLE test (col);
+		PRAGMA journal_mode=WAL;
+		SELECT * FROM test;
+		PRAGMA journal_mode=DELETE;
+		SELECT * FROM test;
+		PRAGMA journal_mode=WAL;
+		SELECT * FROM test;
+	`)
+	if err != nil {
+		t.Fatal(err)
+	}
+}

vfs/const.go

@@ -37,6 +37,10 @@ const (
 	_IOERR_CHECKRESERVEDLOCK _ErrorCode = util.IOERR_CHECKRESERVEDLOCK
 	_IOERR_LOCK              _ErrorCode = util.IOERR_LOCK
 	_IOERR_CLOSE             _ErrorCode = util.IOERR_CLOSE
+	_IOERR_SHMOPEN           _ErrorCode = util.IOERR_SHMOPEN
+	_IOERR_SHMSIZE           _ErrorCode = util.IOERR_SHMSIZE
+	_IOERR_SHMLOCK           _ErrorCode = util.IOERR_SHMLOCK
+	_IOERR_SHMMAP            _ErrorCode = util.IOERR_SHMMAP
 	_IOERR_SEEK              _ErrorCode = util.IOERR_SEEK
 	_IOERR_DELETE_NOENT      _ErrorCode = util.IOERR_DELETE_NOENT
 	_IOERR_BEGIN_ATOMIC      _ErrorCode = util.IOERR_BEGIN_ATOMIC
@@ -44,6 +48,7 @@ const (
 	_IOERR_ROLLBACK_ATOMIC   _ErrorCode = util.IOERR_ROLLBACK_ATOMIC
 	_CANTOPEN_FULLPATH       _ErrorCode = util.CANTOPEN_FULLPATH
 	_CANTOPEN_ISDIR          _ErrorCode = util.CANTOPEN_ISDIR
+	_READONLY_CANTINIT       _ErrorCode = util.READONLY_CANTINIT
 	_OK_SYMLINK              _ErrorCode = util.OK_SYMLINK
 )
 
@@ -213,3 +218,13 @@ const (
 	_FCNTL_CKSM_FILE             _FcntlOpcode = 41
 	_FCNTL_RESET_CACHE           _FcntlOpcode = 42
 )
+
+// https://sqlite.org/c3ref/c_shm_exclusive.html
+type _ShmFlag uint32
+
+const (
+	_SHM_UNLOCK    _ShmFlag = 1
+	_SHM_LOCK      _ShmFlag = 2
+	_SHM_SHARED    _ShmFlag = 4
+	_SHM_EXCLUSIVE _ShmFlag = 8
+)

vfs/file.go

@@ -130,6 +130,7 @@ type vfsFile struct {
 	keepWAL  bool
 	syncDir  bool
 	psow     bool
+	shm      vfsShm
 }
 
 var (
@@ -141,6 +142,11 @@ var (
 	_ FilePowersafeOverwrite = &vfsFile{}
 )
 
+func (f *vfsFile) Close() error {
+	f.shm.Close()
+	return f.File.Close()
+}
+
 func (f *vfsFile) Sync(flags SyncFlag) error {
 	dataonly := (flags & SYNC_DATAONLY) != 0
 	fullsync := (flags & 0x0f) == SYNC_FULL

vfs/lock.go

@@ -1,7 +1,17 @@
+//go:build (linux || darwin || windows || freebsd || openbsd || netbsd || dragonfly || illumos) && !sqlite3_nosys
+
 package vfs
 
 import "github.com/ncruces/go-sqlite3/internal/util"
 
+// SupportsFileLocking is false on platforms that do not support file locking.
+// To open a database file on those platforms,
+// you need to use the [nolock] or [immutable] URI parameters.
+//
+// [nolock]: https://sqlite.org/uri.html#urinolock
+// [immutable]: https://sqlite.org/uri.html#uriimmutable
+const SupportsFileLocking = true
+
 const (
 	_PENDING_BYTE  = 0x40000000
 	_RESERVED_BYTE = (_PENDING_BYTE + 1)

vfs/lock_other.go

@@ -0,0 +1,23 @@
+//go:build !(linux || darwin || windows || freebsd || openbsd || netbsd || dragonfly || illumos) || sqlite3_nosys
+
+package vfs
+
+// SupportsFileLocking is false on platforms that do not support file locking.
+// To open a database file on those platforms,
+// you need to use the [nolock] or [immutable] URI parameters.
+//
+// [nolock]: https://sqlite.org/uri.html#urinolock
+// [immutable]: https://sqlite.org/uri.html#uriimmutable
+const SupportsFileLocking = false
+
+func (f *vfsFile) Lock(LockLevel) error {
+	return _IOERR_LOCK
+}
+
+func (f *vfsFile) Unlock(LockLevel) error {
+	return _IOERR_UNLOCK
+}
+
+func (f *vfsFile) CheckReservedLock() (bool, error) {
+	return false, _IOERR_CHECKRESERVEDLOCK
+}

vfs/lock_test.go

@@ -33,7 +33,7 @@ func Test_vfsLock(t *testing.T) {
 		pOutput = 32
 	)
 	mod := wazerotest.NewModule(wazerotest.NewMemory(wazerotest.PageSize))
-	ctx := util.NewContext(context.TODO())
+	ctx := util.NewContext(context.TODO(), false)
 
 	vfsFileRegister(ctx, mod, pFile1, &vfsFile{File: file1})
 	vfsFileRegister(ctx, mod, pFile2, &vfsFile{File: file2})

vfs/os_bsd.go

@@ -32,14 +32,14 @@ func osWriteLock(file *os.File, _ /*start*/, _ /*len*/ int64, _ /*timeout*/ time
 	return osLock(file, unix.LOCK_EX|unix.LOCK_NB, _IOERR_LOCK)
 }
 
-func osCheckLock(file *os.File, start, len int64) (bool, _ErrorCode) {
+func osGetLock(file *os.File, start, len int64) (int16, _ErrorCode) {
 	lock := unix.Flock_t{
-		Type:  unix.F_RDLCK,
+		Type:  unix.F_WRLCK,
 		Start: start,
 		Len:   len,
 	}
 	if unix.FcntlFlock(file.Fd(), unix.F_GETLK, &lock) != nil {
-		return false, _IOERR_CHECKRESERVEDLOCK
+		return 0, _IOERR_CHECKRESERVEDLOCK
 	}
-	return lock.Type != unix.F_UNLCK, _OK
+	return lock.Type, _OK
 }

vfs/os_darwin.go

@@ -95,14 +95,14 @@ func osWriteLock(file *os.File, start, len int64, timeout time.Duration) _ErrorC
 	return osLock(file, unix.F_WRLCK, start, len, timeout, _IOERR_LOCK)
 }
 
-func osCheckLock(file *os.File, start, len int64) (bool, _ErrorCode) {
+func osGetLock(file *os.File, start, len int64) (int16, _ErrorCode) {
 	lock := unix.Flock_t{
-		Type:  unix.F_RDLCK,
+		Type:  unix.F_WRLCK,
 		Start: start,
 		Len:   len,
 	}
 	if unix.FcntlFlock(file.Fd(), _F_OFD_GETLK, &lock) != nil {
-		return false, _IOERR_CHECKRESERVEDLOCK
+		return 0, _IOERR_CHECKRESERVEDLOCK
 	}
-	return lock.Type != unix.F_UNLCK, _OK
+	return lock.Type, _OK
 }

vfs/os_nolock.go

@@ -1,41 +0,0 @@
-//go:build !(linux || darwin || windows || freebsd || openbsd || netbsd || dragonfly || illumos) || sqlite3_nosys
-
-package vfs
-
-import "os"
-
-// SupportsFileLocking is false on platforms that do not support file locking.
-// To open a database file in one such platform,
-// you need to use the [nolock] or [immutable] URI parameters.
-//
-// [nolock]: https://sqlite.org/uri.html#urinolock
-// [immutable]: https://sqlite.org/uri.html#uriimmutable
-const SupportsFileLocking = false
-
-func osGetSharedLock(_ *os.File) _ErrorCode {
-	return _IOERR_RDLOCK
-}
-
-func osGetReservedLock(_ *os.File) _ErrorCode {
-	return _IOERR_LOCK
-}
-
-func osGetPendingLock(_ *os.File, _ bool) _ErrorCode {
-	return _IOERR_LOCK
-}
-
-func osGetExclusiveLock(_ *os.File, _ bool) _ErrorCode {
-	return _IOERR_LOCK
-}
-
-func osDowngradeLock(_ *os.File, _ LockLevel) _ErrorCode {
-	return _IOERR_RDLOCK
-}
-
-func osReleaseLock(_ *os.File, _ LockLevel) _ErrorCode {
-	return _IOERR_UNLOCK
-}
-
-func osCheckReservedLock(_ *os.File) (bool, _ErrorCode) {
-	return false, _IOERR_CHECKRESERVEDLOCK
-}

vfs/os_ofd.go

@@ -57,14 +57,14 @@ func osWriteLock(file *os.File, start, len int64, timeout time.Duration) _ErrorC
 	return osLock(file, unix.F_WRLCK, start, len, timeout, _IOERR_LOCK)
 }
 
-func osCheckLock(file *os.File, start, len int64) (bool, _ErrorCode) {
+func osGetLock(file *os.File, start, len int64) (int16, _ErrorCode) {
 	lock := unix.Flock_t{
-		Type:  unix.F_RDLCK,
+		Type:  unix.F_WRLCK,
 		Start: start,
 		Len:   len,
 	}
 	if unix.FcntlFlock(file.Fd(), unix.F_OFD_GETLK, &lock) != nil {
-		return false, _IOERR_CHECKRESERVEDLOCK
+		return 0, _IOERR_CHECKRESERVEDLOCK
 	}
-	return lock.Type != unix.F_UNLCK, _OK
+	return lock.Type, _OK
 }

vfs/os_unix_lock.go

@@ -9,17 +9,9 @@ import (
 	"golang.org/x/sys/unix"
 )
 
-// SupportsFileLocking is false on platforms that do not support file locking.
-// To open a database file in one such platform,
-// you need to use the [nolock] or [immutable] URI parameters.
-//
-// [nolock]: https://sqlite.org/uri.html#urinolock
-// [immutable]: https://sqlite.org/uri.html#uriimmutable
-const SupportsFileLocking = true
-
 func osGetSharedLock(file *os.File) _ErrorCode {
 	// Test the PENDING lock before acquiring a new SHARED lock.
-	if pending, _ := osCheckLock(file, _PENDING_BYTE, 1); pending {
+	if lock, _ := osGetLock(file, _PENDING_BYTE, 1); lock == unix.F_WRLCK {
 		return _BUSY
 	}
 	// Acquire the SHARED lock.
@@ -72,7 +64,8 @@ func osReleaseLock(file *os.File, _ LockLevel) _ErrorCode {
 
 func osCheckReservedLock(file *os.File) (bool, _ErrorCode) {
 	// Test the RESERVED lock.
-	return osCheckLock(file, _RESERVED_BYTE, 1)
+	lock, rc := osGetLock(file, _RESERVED_BYTE, 1)
+	return lock == unix.F_WRLCK, rc
 }
 
 func osLockErrorCode(err error, def _ErrorCode) _ErrorCode {

vfs/os_windows.go

@@ -9,18 +9,9 @@ import (
 	"golang.org/x/sys/windows"
 )
 
-// SupportsFileLocking is false on platforms that do not support file locking.
-// To open a database file in one such platform,
-// you need to use the [nolock] or [immutable] URI parameters.
-//
-// [nolock]: https://sqlite.org/uri.html#urinolock
-// [immutable]: https://sqlite.org/uri.html#uriimmutable
-const SupportsFileLocking = true
-
 func osGetSharedLock(file *os.File) _ErrorCode {
 	// Acquire the PENDING lock temporarily before acquiring a new SHARED lock.
 	rc := osReadLock(file, _PENDING_BYTE, 1, 0)
-
 	if rc == _OK {
 		// Acquire the SHARED lock.
 		rc = osReadLock(file, _SHARED_FIRST, _SHARED_SIZE, 0)
@@ -104,7 +95,15 @@ func osReleaseLock(file *os.File, state LockLevel) _ErrorCode {
 
 func osCheckReservedLock(file *os.File) (bool, _ErrorCode) {
 	// Test the RESERVED lock.
-	return osCheckLock(file, _RESERVED_BYTE, 1)
+	rc := osLock(file, 0, _RESERVED_BYTE, 1, 0, _IOERR_CHECKRESERVEDLOCK)
+	if rc == _BUSY {
+		return true, _OK
+	}
+	if rc == _OK {
+		// Release the RESERVED lock.
+		osUnlock(file, _RESERVED_BYTE, 1)
+	}
+	return false, rc
 }
 
 func osUnlock(file *os.File, start, len uint32) _ErrorCode {
@@ -155,17 +154,6 @@ func osWriteLock(file *os.File, start, len uint32, timeout time.Duration) _Error
 	return osLock(file, windows.LOCKFILE_EXCLUSIVE_LOCK, start, len, timeout, _IOERR_LOCK)
 }
 
-func osCheckLock(file *os.File, start, len uint32) (bool, _ErrorCode) {
-	rc := osLock(file, 0, start, len, 0, _IOERR_CHECKRESERVEDLOCK)
-	if rc == _BUSY {
-		return true, _OK
-	}
-	if rc == _OK {
-		osUnlock(file, start, len)
-	}
-	return false, rc
-}
-
 func osLockErrorCode(err error, def _ErrorCode) _ErrorCode {
 	if err == nil {
 		return _OK

vfs/shm.go

@@ -0,0 +1,144 @@
+//go:build (linux || darwin) && (amd64 || arm64) && !sqlite3_flock && !sqlite3_noshm && !sqlite3_nosys
+
+package vfs
+
+import (
+	"context"
+	"io"
+	"os"
+
+	"github.com/ncruces/go-sqlite3/internal/util"
+	"github.com/tetratelabs/wazero/api"
+	"golang.org/x/sys/unix"
+)
+
+// SupportsSharedMemory is true on platforms that support shared memory.
+// To enable shared memory support on those platforms,
+// you need to set the appropriate [wazero.RuntimeConfig];
+// otherwise, [EXCLUSIVE locking mode] is activated automatically
+// to use [WAL without shared-memory].
+//
+// [WAL without shared-memory]: https://sqlite.org/wal.html#noshm
+// [EXCLUSIVE locking mode]: https://sqlite.org/pragma.html#pragma_locking_mode
+const SupportsSharedMemory = true
+
+type vfsShm struct {
+	*os.File
+	regions []*util.MappedRegion
+}
+
+const (
+	_SHM_NLOCK = 8
+	_SHM_BASE  = 120
+	_SHM_DMS   = _SHM_BASE + _SHM_NLOCK
+)
+
+func (f *vfsFile) shmMap(ctx context.Context, mod api.Module, id, size uint32, extend bool) (uint32, error) {
+	// Ensure size is a multiple of the OS page size.
+	if int(size)&(unix.Getpagesize()-1) != 0 {
+		return 0, _IOERR_SHMMAP
+	}
+
+	if f.shm.File == nil {
+		var flag int
+		if f.readOnly {
+			flag = unix.O_RDONLY | unix.O_NOFOLLOW
+		} else {
+			flag = unix.O_RDWR | unix.O_CREAT | unix.O_NOFOLLOW
+		}
+		s, err := os.OpenFile(f.Name()+"-shm", flag, 0666)
+		if err != nil {
+			return 0, _CANTOPEN
+		}
+		f.shm.File = s
+	}
+
+	// Dead man's switch.
+	if lock, rc := osGetLock(f.shm.File, _SHM_DMS, 1); rc != _OK {
+		return 0, _IOERR_LOCK
+	} else if lock == unix.F_WRLCK {
+		return 0, _BUSY
+	} else if lock == unix.F_UNLCK {
+		if f.readOnly {
+			return 0, _READONLY_CANTINIT
+		}
+		if rc := osWriteLock(f.shm.File, _SHM_DMS, 1, 0); rc != _OK {
+			return 0, rc
+		}
+		if err := f.shm.Truncate(0); err != nil {
+			return 0, _IOERR_SHMOPEN
+		}
+	}
+	if rc := osReadLock(f.shm.File, _SHM_DMS, 1, 0); rc != _OK {
+		return 0, rc
+	}
+
+	// Check if file is big enough.
+	s, err := f.shm.Seek(0, io.SeekEnd)
+	if err != nil {
+		return 0, _IOERR_SHMSIZE
+	}
+	if n := (int64(id) + 1) * int64(size); n > s {
+		if !extend {
+			return 0, nil
+		}
+		err := osAllocate(f.shm.File, n)
+		if err != nil {
+			return 0, _IOERR_SHMSIZE
+		}
+	}
+
+	r, err := util.MapRegion(ctx, mod, f.shm.File, int64(id)*int64(size), size)
+	if err != nil {
+		return 0, err
+	}
+	f.shm.regions = append(f.shm.regions, r)
+	return r.Ptr, nil
+}
+
+func (f *vfsFile) shmLock(offset, n uint32, flags _ShmFlag) error {
+	// Argument check.
+	if n == 0 || offset+n > _SHM_NLOCK {
+		panic(util.AssertErr())
+	}
+	switch flags {
+	case
+		_SHM_LOCK | _SHM_SHARED,
+		_SHM_LOCK | _SHM_EXCLUSIVE,
+		_SHM_UNLOCK | _SHM_SHARED,
+		_SHM_UNLOCK | _SHM_EXCLUSIVE:
+		//
+	default:
+		panic(util.AssertErr())
+	}
+	if n != 1 && flags&_SHM_EXCLUSIVE == 0 {
+		panic(util.AssertErr())
+	}
+
+	switch {
+	case flags&_SHM_UNLOCK != 0:
+		return osUnlock(f.shm.File, _SHM_BASE+int64(offset), int64(n))
+	case flags&_SHM_SHARED != 0:
+		return osReadLock(f.shm.File, _SHM_BASE+int64(offset), int64(n), 0)
+	case flags&_SHM_EXCLUSIVE != 0:
+		return osWriteLock(f.shm.File, _SHM_BASE+int64(offset), int64(n), 0)
+	default:
+		panic(util.AssertErr())
+	}
+}
+
+func (f *vfsFile) shmUnmap(delete bool) {
+	// Unmap regions.
+	for _, r := range f.shm.regions {
+		r.Unmap()
+	}
+	clear(f.shm.regions)
+	f.shm.regions = f.shm.regions[:0]
+
+	// Close the file.
+	if delete && f.shm.File != nil {
+		os.Remove(f.shm.Name())
+	}
+	f.shm.Close()
+	f.shm.File = nil
+}

vfs/shm_other.go

@@ -0,0 +1,17 @@
+//go:build !(linux || darwin) || !(amd64 || arm64) || sqlite3_flock || sqlite3_noshm || sqlite3_nosys
+
+package vfs
+
+// SupportsSharedMemory is true on platforms that support shared memory.
+// To enable shared memory support on those platforms,
+// you need to set the appropriate [wazero.RuntimeConfig];
+// otherwise, [EXCLUSIVE locking mode] is activated automatically
+// to use [WAL without shared-memory].
+//
+// [WAL without shared-memory]: https://sqlite.org/wal.html#noshm
+// [EXCLUSIVE locking mode]: https://sqlite.org/pragma.html#pragma_locking_mode
+const SupportsSharedMemory = false
+
+type vfsShm struct{}
+
+func (vfsShm) Close() error { return nil }

vfs/tests/mptest/mptest_test.go

@@ -92,7 +92,7 @@ func system(ctx context.Context, mod api.Module, ptr uint32) uint32 {
 
 	cfg := config(ctx).WithArgs(args...)
 	go func() {
-		ctx := util.NewContext(ctx)
+		ctx := util.NewContext(ctx, true)
 		mod, _ := rt.InstantiateModule(ctx, module, cfg)
 		mod.Close(ctx)
 	}()
@@ -100,7 +100,7 @@ func system(ctx context.Context, mod api.Module, ptr uint32) uint32 {
 }
 
 func Test_config01(t *testing.T) {
-	ctx := util.NewContext(newContext(t))
+	ctx := util.NewContext(newContext(t), false)
 	name := filepath.Join(t.TempDir(), "test.db")
 	cfg := config(ctx).WithArgs("mptest", name, "config01.test")
 	mod, err := rt.InstantiateModule(ctx, module, cfg)
@@ -118,7 +118,7 @@ func Test_config02(t *testing.T) {
 		t.Skip("skipping in CI")
 	}
 
-	ctx := util.NewContext(newContext(t))
+	ctx := util.NewContext(newContext(t), false)
 	name := filepath.Join(t.TempDir(), "test.db")
 	cfg := config(ctx).WithArgs("mptest", name, "config02.test")
 	mod, err := rt.InstantiateModule(ctx, module, cfg)
@@ -136,7 +136,7 @@ func Test_crash01(t *testing.T) {
 		t.Skip("skipping in CI")
 	}
 
-	ctx := util.NewContext(newContext(t))
+	ctx := util.NewContext(newContext(t), false)
 	name := filepath.Join(t.TempDir(), "test.db")
 	cfg := config(ctx).WithArgs("mptest", name, "crash01.test")
 	mod, err := rt.InstantiateModule(ctx, module, cfg)
@@ -151,7 +151,7 @@ func Test_multiwrite01(t *testing.T) {
 		t.Skip("skipping in short mode")
 	}
 
-	ctx := util.NewContext(newContext(t))
+	ctx := util.NewContext(newContext(t), false)
 	name := filepath.Join(t.TempDir(), "test.db")
 	cfg := config(ctx).WithArgs("mptest", name, "multiwrite01.test")
 	mod, err := rt.InstantiateModule(ctx, module, cfg)
@@ -162,7 +162,7 @@ func Test_multiwrite01(t *testing.T) {
 }
 
 func Test_config01_memory(t *testing.T) {
-	ctx := util.NewContext(newContext(t))
+	ctx := util.NewContext(newContext(t), false)
 	cfg := config(ctx).WithArgs("mptest", "/test.db", "config01.test",
 		"--vfs", "memdb")
 	mod, err := rt.InstantiateModule(ctx, module, cfg)
@@ -177,7 +177,7 @@ func Test_multiwrite01_memory(t *testing.T) {
 		t.Skip("skipping in short mode")
 	}
 
-	ctx := util.NewContext(newContext(t))
+	ctx := util.NewContext(newContext(t), false)
 	cfg := config(ctx).WithArgs("mptest", "/test.db", "multiwrite01.test",
 		"--vfs", "memdb")
 	mod, err := rt.InstantiateModule(ctx, module, cfg)
@@ -187,6 +187,59 @@ func Test_multiwrite01_memory(t *testing.T) {
 	mod.Close(ctx)
 }
 
+func Test_config01_wal(t *testing.T) {
+	ctx := util.NewContext(newContext(t), true)
+	name := filepath.Join(t.TempDir(), "test.db")
+	cfg := config(ctx).WithArgs("mptest", name, "config01.test",
+		"--journalmode", "wal")
+	mod, err := rt.InstantiateModule(ctx, module, cfg)
+	if err != nil {
+		t.Fatal(err)
+	}
+	mod.Close(ctx)
+}
+
+func Test_crash01_wal(t *testing.T) {
+	if testing.Short() {
+		t.Skip("skipping in short mode")
+	}
+	if os.Getenv("CI") != "" {
+		t.Skip("skipping in CI")
+	}
+	if !vfs.SupportsSharedMemory {
+		t.Skip("skipping without shared memory")
+	}
+
+	ctx := util.NewContext(newContext(t), true)
+	name := filepath.Join(t.TempDir(), "test.db")
+	cfg := config(ctx).WithArgs("mptest", name, "crash01.test",
+		"--journalmode", "wal")
+	mod, err := rt.InstantiateModule(ctx, module, cfg)
+	if err != nil {
+		t.Fatal(err)
+	}
+	mod.Close(ctx)
+}
+
+func Test_multiwrite01_wal(t *testing.T) {
+	if testing.Short() {
+		t.Skip("skipping in short mode")
+	}
+	if !vfs.SupportsSharedMemory {
+		t.Skip("skipping without shared memory")
+	}
+
+	ctx := util.NewContext(newContext(t), true)
+	name := filepath.Join(t.TempDir(), "test.db")
+	cfg := config(ctx).WithArgs("mptest", name, "multiwrite01.test",
+		"--journalmode", "wal")
+	mod, err := rt.InstantiateModule(ctx, module, cfg)
+	if err != nil {
+		t.Fatal(err)
+	}
+	mod.Close(ctx)
+}
+
 func newContext(t *testing.T) context.Context {
 	return context.WithValue(context.Background(), logger{}, &testWriter{T: t})
 }

vfs/tests/mptest/testdata/build.sh

@@ -21,7 +21,8 @@ WASI_SDK="$ROOT/tools/wasi-sdk-21.0/bin"
 	-DSQLITE_DEFAULT_LOCKING_MODE=0 \
 	-DHAVE_USLEEP -DSQLITE_NO_SYNC \
 	-DSQLITE_THREADSAFE=0 -DSQLITE_OMIT_LOAD_EXTENSION \
-	-D_WASI_EMULATED_GETPID -lwasi-emulated-getpid
+	-D_WASI_EMULATED_GETPID -lwasi-emulated-getpid \
+	-Wl,--export=aligned_alloc
 
 "$BINARYEN/wasm-opt" -g --strip --strip-producers -c -O3 \
 	mptest.wasm -o mptest.tmp \

vfs/tests/mptest/testdata/mptest.wasm.bz2

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:b5f4778b49a6b99a1be11db5cb07e3c5b52f91a932a97e33c895f52c6f54bf57
-size 469149
+oid sha256:523b3640c6de9accf3f6b01e7da2098faba12eec0168b67a78c56fef0716c7ae
+size 469261

vfs/tests/speedtest1/speedtest1_test.go

@@ -84,7 +84,7 @@ func initFlags() {
 
 func Benchmark_speedtest1(b *testing.B) {
 	output.Reset()
-	ctx := util.NewContext(context.Background())
+	ctx := util.NewContext(context.Background(), false)
 	name := filepath.Join(b.TempDir(), "test.db")
 	args := append(options, "--size", strconv.Itoa(b.N), name)
 	cfg := wazero.NewModuleConfig().

vfs/tests/speedtest1/testdata/build.sh

@@ -16,7 +16,8 @@ WASI_SDK="$ROOT/tools/wasi-sdk-21.0/bin"
 	-fno-stack-protector -fno-stack-clash-protection \
 	-Wl,--stack-first \
 	-Wl,--import-undefined \
-	-D_HAVE_SQLITE_CONFIG_H
+	-D_HAVE_SQLITE_CONFIG_H \
+	-Wl,--export=aligned_alloc
 
 "$BINARYEN/wasm-opt" -g --strip --strip-producers -c -O3 \
 	speedtest1.wasm -o speedtest1.tmp \

vfs/tests/speedtest1/testdata/speedtest1.wasm.bz2

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:06882576fdea2c8e164dd2d97dce394dc825dca3cee30c9efc9601b84de92865
-size 483191
+oid sha256:855720cce2881c98d09c15eddf9cab0d5974a2a82f7f67987a28b97414629345
+size 483463

vfs/vfs.go

@@ -6,6 +6,7 @@ import (
 	"io"
 	"net/url"
 	"reflect"
+	"sync"
 	"time"
 
 	"github.com/ncruces/go-sqlite3/internal/util"
@@ -27,7 +28,7 @@ func ExportHostFunctions(env wazero.HostModuleBuilder) wazero.HostModuleBuilder
 	util.ExportFuncIIIII(env, "go_full_pathname", vfsFullPathname)
 	util.ExportFuncIIII(env, "go_delete", vfsDelete)
 	util.ExportFuncIIIII(env, "go_access", vfsAccess)
-	util.ExportFuncIIIIII(env, "go_open", vfsOpen)
+	util.ExportFuncIIIIIII(env, "go_open", vfsOpen)
 	util.ExportFuncII(env, "go_close", vfsClose)
 	util.ExportFuncIIIIJ(env, "go_read", vfsRead)
 	util.ExportFuncIIIIJ(env, "go_write", vfsWrite)
@@ -40,6 +41,10 @@ func ExportHostFunctions(env wazero.HostModuleBuilder) wazero.HostModuleBuilder
 	util.ExportFuncIII(env, "go_lock", vfsLock)
 	util.ExportFuncIII(env, "go_unlock", vfsUnlock)
 	util.ExportFuncIII(env, "go_check_reserved_lock", vfsCheckReservedLock)
+	util.ExportFuncIIIIII(env, "go_shm_map", vfsShmMap)
+	util.ExportFuncIIIII(env, "go_shm_lock", vfsShmLock)
+	util.ExportFuncIII(env, "go_shm_unmap", vfsShmUnmap)
+	util.ExportFuncVI(env, "go_shm_barrier", vfsShmBarrier)
 	return env
 }
 
@@ -129,7 +134,7 @@ func vfsAccess(ctx context.Context, mod api.Module, pVfs, zPath uint32, flags Ac
 	return vfsErrorCode(err, _IOERR_ACCESS)
 }
 
-func vfsOpen(ctx context.Context, mod api.Module, pVfs, zPath, pFile uint32, flags OpenFlag, pOutFlags uint32) _ErrorCode {
+func vfsOpen(ctx context.Context, mod api.Module, pVfs, zPath, pFile uint32, flags OpenFlag, pOutFlags, pOutVFS uint32) _ErrorCode {
 	vfs := vfsGet(mod, pVfs)
 
 	var path string
@@ -165,6 +170,9 @@ func vfsOpen(ctx context.Context, mod api.Module, pVfs, zPath, pFile uint32, fla
 	if pOutFlags != 0 {
 		util.WriteUint32(mod, pOutFlags, uint32(flags))
 	}
+	if pOutVFS != 0 && util.CanMap(ctx) {
+		util.WriteUint32(mod, pOutVFS, 1)
+	}
 	vfsFileRegister(ctx, mod, pFile, file)
 	return _OK
 }
@@ -348,6 +356,35 @@ func vfsDeviceCharacteristics(ctx context.Context, mod api.Module, pFile uint32)
 	return file.DeviceCharacteristics()
 }
 
+var shmBarrier sync.Mutex
+
+func vfsShmMap(ctx context.Context, mod api.Module, pFile, iRegion, szRegion, bExtend, pp uint32) _ErrorCode {
+	file := vfsFileGet(ctx, mod, pFile).(fileShm)
+	p, err := file.shmMap(ctx, mod, iRegion, szRegion, bExtend != 0)
+	if err != nil {
+		return vfsErrorCode(err, _IOERR_SHMMAP)
+	}
+	util.WriteUint32(mod, pp, p)
+	return _OK
+}
+
+func vfsShmLock(ctx context.Context, mod api.Module, pFile, offset, n uint32, flags _ShmFlag) _ErrorCode {
+	file := vfsFileGet(ctx, mod, pFile).(fileShm)
+	err := file.shmLock(offset, n, flags)
+	return vfsErrorCode(err, _IOERR_SHMLOCK)
+}
+
+func vfsShmUnmap(ctx context.Context, mod api.Module, pFile, bDelete uint32) _ErrorCode {
+	file := vfsFileGet(ctx, mod, pFile).(fileShm)
+	file.shmUnmap(bDelete != 0)
+	return _OK
+}
+
+func vfsShmBarrier(ctx context.Context, mod api.Module, pFile uint32) {
+	shmBarrier.Lock()
+	defer shmBarrier.Unlock()
+}
+
 func vfsURIParameters(ctx context.Context, mod api.Module, zPath uint32, flags OpenFlag) url.Values {
 	if flags&OPEN_URI == 0 {
 		return nil
@@ -428,3 +465,9 @@ func vfsErrorCode(err error, def _ErrorCode) _ErrorCode {
 	}
 	return def
 }
+
+type fileShm interface {
+	shmMap(context.Context, api.Module, uint32, uint32, bool) (uint32, error)
+	shmLock(uint32, uint32, _ShmFlag) error
+	shmUnmap(bool)
+}

vfs/vfs_test.go

@@ -209,10 +209,10 @@ func Test_vfsAccess(t *testing.T) {
 
 func Test_vfsFile(t *testing.T) {
 	mod := wazerotest.NewModule(wazerotest.NewMemory(wazerotest.PageSize))
-	ctx := util.NewContext(context.TODO())
+	ctx := util.NewContext(context.TODO(), false)
 
 	// Open a temporary file.
-	rc := vfsOpen(ctx, mod, 0, 0, 4, OPEN_CREATE|OPEN_EXCLUSIVE|OPEN_READWRITE|OPEN_DELETEONCLOSE, 0)
+	rc := vfsOpen(ctx, mod, 0, 0, 4, OPEN_CREATE|OPEN_EXCLUSIVE|OPEN_READWRITE|OPEN_DELETEONCLOSE, 0, 0)
 	if rc != _OK {
 		t.Fatal("returned", rc)
 	}
@@ -281,10 +281,10 @@ func Test_vfsFile(t *testing.T) {
 
 func Test_vfsFile_psow(t *testing.T) {
 	mod := wazerotest.NewModule(wazerotest.NewMemory(wazerotest.PageSize))
-	ctx := util.NewContext(context.TODO())
+	ctx := util.NewContext(context.TODO(), false)
 
 	// Open a temporary file.
-	rc := vfsOpen(ctx, mod, 0, 0, 4, OPEN_CREATE|OPEN_EXCLUSIVE|OPEN_READWRITE|OPEN_DELETEONCLOSE, 0)
+	rc := vfsOpen(ctx, mod, 0, 0, 4, OPEN_CREATE|OPEN_EXCLUSIVE|OPEN_READWRITE|OPEN_DELETEONCLOSE, 0, 0)
 	if rc != _OK {
 		t.Fatal("returned", rc)
 	}