Refactor.

.github/workflows/repro.sh

@@ -3,13 +3,13 @@ set -euo pipefail
 
 if [[ "$OSTYPE" == "linux"* ]]; then
   WASI_SDK="https://github.com/WebAssembly/wasi-sdk/releases/download/wasi-sdk-25/wasi-sdk-25.0-x86_64-linux.tar.gz"
-  BINARYEN="https://github.com/WebAssembly/binaryen/releases/download/version_120_b/binaryen-version_120_b-x86_64-linux.tar.gz"
+  BINARYEN="https://github.com/WebAssembly/binaryen/releases/download/version_121/binaryen-version_121-x86_64-linux.tar.gz"
 elif [[ "$OSTYPE" == "darwin"* ]]; then
   WASI_SDK="https://github.com/WebAssembly/wasi-sdk/releases/download/wasi-sdk-25/wasi-sdk-25.0-arm64-macos.tar.gz"
-  BINARYEN="https://github.com/WebAssembly/binaryen/releases/download/version_120_b/binaryen-version_120_b-arm64-macos.tar.gz"
+  BINARYEN="https://github.com/WebAssembly/binaryen/releases/download/version_121/binaryen-version_121-arm64-macos.tar.gz"
 elif [[ "$OSTYPE" == "msys" || "$OSTYPE" == "cygwin" ]]; then
   WASI_SDK="https://github.com/WebAssembly/wasi-sdk/releases/download/wasi-sdk-25/wasi-sdk-25.0-x86_64-windows.tar.gz"
-  BINARYEN="https://github.com/WebAssembly/binaryen/releases/download/version_120_b/binaryen-version_120_b-x86_64-windows.tar.gz"
+  BINARYEN="https://github.com/WebAssembly/binaryen/releases/download/version_121/binaryen-version_121-x86_64-windows.tar.gz"
 fi
 
 # Download tools

.github/workflows/repro.yml

@@ -18,8 +18,6 @@ jobs:
     steps:
     - uses: ilammy/msvc-dev-cmd@v1
     - uses: actions/checkout@v4
-    - uses: actions/setup-go@v5
-      with: { go-version: stable }
 
     - name: Build
       shell: bash

README.md

@@ -74,7 +74,7 @@ This project aims for [high test coverage](https://github.com/ncruces/go-sqlite3
 It also benefits greatly from [SQLite's](https://sqlite.org/testing.html) and
 [wazero's](https://tetrate.io/blog/introducing-wazero-from-tetrate/#:~:text=Rock%2Dsolid%20test%20approach) thorough testing.
 
-Every commit is [tested](https://github.com/ncruces/go-sqlite3/wiki/Test-matrix) on
+Every commit is [tested](https://github.com/ncruces/go-sqlite3/wiki/Support-matrix) on
 Linux (amd64/arm64/386/riscv64/ppc64le/s390x), macOS (amd64/arm64),
 Windows (amd64), FreeBSD (amd64), OpenBSD (amd64), NetBSD (amd64),
 DragonFly BSD (amd64), illumos (amd64), and Solaris (amd64).

driver/driver.go

@@ -274,6 +274,7 @@ func (n *connector) Connect(ctx context.Context) (res driver.Conn, err error) {
 //	if err != nil {
 //		log.Fatal(err)
 //	}
+//	defer conn.Close()
 //
 //	err = conn.Raw(func(driverConn any) error {
 //		conn := driverConn.(driver.Conn)

driver/util.go

@@ -12,3 +12,63 @@ func namedValues(args []driver.Value) []driver.NamedValue {
 	}
 	return named
 }
+
+func notWhitespace(sql string) bool {
+	const (
+		code = iota
+		slash
+		minus
+		ccomment
+		sqlcomment
+		endcomment
+	)
+
+	state := code
+	for _, b := range ([]byte)(sql) {
+		if b == 0 {
+			break
+		}
+
+		switch state {
+		case code:
+			switch b {
+			case '/':
+				state = slash
+			case '-':
+				state = minus
+			case ' ', ';', '\t', '\n', '\v', '\f', '\r':
+				continue
+			default:
+				return true
+			}
+		case slash:
+			if b != '*' {
+				return true
+			}
+			state = ccomment
+		case minus:
+			if b != '-' {
+				return true
+			}
+			state = sqlcomment
+		case ccomment:
+			if b == '*' {
+				state = endcomment
+			}
+		case sqlcomment:
+			if b == '\n' {
+				state = code
+			}
+		case endcomment:
+			switch b {
+			case '/':
+				state = code
+			case '*':
+				state = endcomment
+			default:
+				state = ccomment
+			}
+		}
+	}
+	return state == slash || state == minus
+}

driver/util_test.go

@@ -1,9 +1,13 @@
 package driver
 
 import (
+	"context"
 	"database/sql/driver"
 	"reflect"
 	"testing"
+
+	_ "github.com/ncruces/go-sqlite3/embed"
+	_ "github.com/ncruces/go-sqlite3/internal/testcfg"
 )
 
 func Test_namedValues(t *testing.T) {
@@ -16,3 +20,67 @@ func Test_namedValues(t *testing.T) {
 		t.Errorf("got %v, want %v", got, want)
 	}
 }
+
+func Fuzz_notWhitespace(f *testing.F) {
+	f.Add("")
+	f.Add(" ")
+	f.Add(";")
+	f.Add("0")
+	f.Add("-")
+	f.Add("-0")
+	f.Add("--")
+	f.Add("--0")
+	f.Add("--\n")
+	f.Add("--0\n")
+	f.Add("/0")
+	f.Add("/*")
+	f.Add("/*/")
+	f.Add("/**")
+	f.Add("/*0")
+	f.Add("/**/")
+	f.Add("/***/")
+	f.Add("/**0/")
+	f.Add("\v")
+	f.Add(" \v")
+	f.Add("\xf0")
+	f.Add("\000")
+
+	db, err := Open(":memory:")
+	if err != nil {
+		f.Fatal(err)
+	}
+	defer db.Close()
+
+	f.Fuzz(func(t *testing.T, str string) {
+		if len(str) > 128 {
+			t.SkipNow()
+		}
+
+		c, err := db.Conn(context.Background())
+		if err != nil {
+			t.Fatal(err)
+		}
+		defer c.Close()
+
+		c.Raw(func(driverConn any) error {
+			conn := driverConn.(*conn).Conn
+			stmt, tail, err := conn.Prepare(str)
+			stmt.Close()
+
+			// It's hard to be bug for bug compatible with SQLite.
+			// We settle for somewhat less:
+			//   - if SQLite reports whitespace, we must too
+			//   - if we report whitespace, SQLite must not parse a statement
+			if notWhitespace(str) {
+				if stmt == nil && tail == "" && err == nil {
+					t.Errorf("was whitespace: %q", str)
+				}
+			} else {
+				if stmt != nil {
+					t.Errorf("was not whitespace: %q (%v)", str, err)
+				}
+			}
+			return nil
+		})
+	})
+}

driver/whitespace.go

@@ -1,61 +0,0 @@
-package driver
-
-func notWhitespace(sql string) bool {
-	const (
-		code = iota
-		slash
-		minus
-		ccomment
-		sqlcomment
-		endcomment
-	)
-
-	state := code
-	for _, b := range ([]byte)(sql) {
-		if b == 0 {
-			break
-		}
-
-		switch state {
-		case code:
-			switch b {
-			case '/':
-				state = slash
-			case '-':
-				state = minus
-			case ' ', ';', '\t', '\n', '\v', '\f', '\r':
-				continue
-			default:
-				return true
-			}
-		case slash:
-			if b != '*' {
-				return true
-			}
-			state = ccomment
-		case minus:
-			if b != '-' {
-				return true
-			}
-			state = sqlcomment
-		case ccomment:
-			if b == '*' {
-				state = endcomment
-			}
-		case sqlcomment:
-			if b == '\n' {
-				state = code
-			}
-		case endcomment:
-			switch b {
-			case '/':
-				state = code
-			case '*':
-				state = endcomment
-			default:
-				state = ccomment
-			}
-		}
-	}
-	return state == slash || state == minus
-}

driver/whitespace_test.go

@@ -1,73 +0,0 @@
-package driver
-
-import (
-	"context"
-	"testing"
-
-	_ "github.com/ncruces/go-sqlite3/embed"
-	_ "github.com/ncruces/go-sqlite3/internal/testcfg"
-)
-
-func Fuzz_notWhitespace(f *testing.F) {
-	f.Add("")
-	f.Add(" ")
-	f.Add(";")
-	f.Add("0")
-	f.Add("-")
-	f.Add("-0")
-	f.Add("--")
-	f.Add("--0")
-	f.Add("--\n")
-	f.Add("--0\n")
-	f.Add("/0")
-	f.Add("/*")
-	f.Add("/*/")
-	f.Add("/**")
-	f.Add("/*0")
-	f.Add("/**/")
-	f.Add("/***/")
-	f.Add("/**0/")
-	f.Add("\v")
-	f.Add(" \v")
-	f.Add("\xf0")
-	f.Add("\000")
-
-	db, err := Open(":memory:")
-	if err != nil {
-		f.Fatal(err)
-	}
-	defer db.Close()
-
-	f.Fuzz(func(t *testing.T, str string) {
-		if len(str) > 128 {
-			t.SkipNow()
-		}
-
-		c, err := db.Conn(context.Background())
-		if err != nil {
-			t.Fatal(err)
-		}
-		defer c.Close()
-
-		c.Raw(func(driverConn any) error {
-			conn := driverConn.(*conn).Conn
-			stmt, tail, err := conn.Prepare(str)
-			stmt.Close()
-
-			// It's hard to be bug for bug compatible with SQLite.
-			// We settle for somewhat less:
-			//   - if SQLite reports whitespace, we must too
-			//   - if we report whitespace, SQLite must not parse a statement
-			if notWhitespace(str) {
-				if stmt == nil && tail == "" && err == nil {
-					t.Errorf("was whitespace: %q", str)
-				}
-			} else {
-				if stmt != nil {
-					t.Errorf("was not whitespace: %q (%v)", str, err)
-				}
-			}
-			return nil
-		})
-	})
-}

embed/bcw2/bcw2_test.go

@@ -32,6 +32,11 @@ func Test_bcw2(t *testing.T) {
 		t.Fatal(err)
 	}
 
+	_, err = tx.Exec(`DELETE FROM test LIMIT 1`)
+	if err != nil {
+		t.Fatal(err)
+	}
+
 	err = tx.Commit()
 	if err != nil {
 		t.Fatal(err)

embed/bcw2/build.sh

@@ -13,15 +13,14 @@ mkdir -p build/ext/
 cp "$ROOT"/sqlite3/*.[ch] build/
 cp "$ROOT"/sqlite3/*.patch build/
 
-# https://sqlite.org/src/info/08cfa7e8b3090151
-curl -# https://sqlite.org/src/tarball/sqlite.tar.gz?r=08cfa7e8 | tar xz
+# https://sqlite.org/src/info/ec5d7025cba9f4ac
+curl -# https://sqlite.org/src/tarball/sqlite.tar.gz?r=ec5d7025 | tar xz
 
 cd sqlite
 if [[ "$OSTYPE" == "msys" || "$OSTYPE" == "cygwin" ]]; then
-	MSYS_NO_PATHCONV=1 nmake /f makefile.msc sqlite3.c
+	MSYS_NO_PATHCONV=1 nmake /f makefile.msc sqlite3.c OPTS=-DSQLITE_ENABLE_UPDATE_DELETE_LIMIT
 else
-	sh configure
-	make sqlite3.c
+	sh configure --enable-update-limit && make sqlite3.c
 fi
 cd ~-
 
@@ -54,6 +53,7 @@ cd ~-
 	-Wl,--import-undefined \
 	-Wl,--initial-memory=327680 \
 	-D_HAVE_SQLITE_CONFIG_H \
+	-DSQLITE_ENABLE_UPDATE_DELETE_LIMIT \
 	-DSQLITE_CUSTOM_INCLUDE=sqlite_opt.h \
 	$(awk '{print "-Wl,--export="$0}' ../exports.txt)
 

ext/blobio/blob.go

@@ -44,6 +44,8 @@ func Register(db *sqlite3.Conn) error {
 type OpenCallback func(*sqlite3.Blob, ...sqlite3.Value) error
 
 func readblob(ctx sqlite3.Context, arg ...sqlite3.Value) {
+	_ = arg[5] // bounds check
+
 	blob, err := getAuxBlob(ctx, arg, false)
 	if err != nil {
 		ctx.ResultError(err)
@@ -78,6 +80,8 @@ func readblob(ctx sqlite3.Context, arg ...sqlite3.Value) {
 }
 
 func writeblob(ctx sqlite3.Context, arg ...sqlite3.Value) {
+	_ = arg[5] // bounds check
+
 	blob, err := getAuxBlob(ctx, arg, true)
 	if err != nil {
 		ctx.ResultError(err)

ext/regexp/regexp.go

@@ -76,6 +76,7 @@ func load(ctx sqlite3.Context, i int, expr string) (*regexp.Regexp, error) {
 }
 
 func regex(ctx sqlite3.Context, arg ...sqlite3.Value) {
+	_ = arg[1] // bounds check
 	re, err := load(ctx, 0, arg[0].Text())
 	if err != nil {
 		ctx.ResultError(err)
@@ -165,6 +166,8 @@ func regexInstr(ctx sqlite3.Context, arg ...sqlite3.Value) {
 }
 
 func regexReplace(ctx sqlite3.Context, arg ...sqlite3.Value) {
+	_ = arg[2] // bounds check
+
 	re, err := load(ctx, 1, arg[1].Text())
 	if err != nil {
 		ctx.ResultError(err)

ext/unicode/unicode.go

@@ -189,6 +189,7 @@ func like(ctx sqlite3.Context, arg ...sqlite3.Value) {
 			return
 		}
 	}
+	_ = arg[1] // bounds check
 
 	type likeData struct {
 		*regexp.Regexp

internal/dotlk/dotlk.go

@@ -0,0 +1,29 @@
+package dotlk
+
+import (
+	"errors"
+	"io/fs"
+	"os"
+)
+
+// LockShm creates a directory on disk to prevent SQLite
+// from using this path for a shared memory file.
+func LockShm(name string) error {
+	err := os.Mkdir(name, 0777)
+	if errors.Is(err, fs.ErrExist) {
+		s, err := os.Lstat(name)
+		if err == nil && s.IsDir() {
+			return nil
+		}
+	}
+	return err
+}
+
+// Unlock removes the lock or shared memory file.
+func Unlock(name string) error {
+	err := os.Remove(name)
+	if errors.Is(err, fs.ErrNotExist) {
+		return nil
+	}
+	return err
+}

internal/dotlk/dotlk_other.go

@@ -0,0 +1,13 @@
+//go:build !unix
+
+package dotlk
+
+import "os"
+
+// TryLock returns nil if it acquired the lock,
+// fs.ErrExist if another process has the lock.
+func TryLock(name string) error {
+	f, err := os.OpenFile(name, os.O_RDWR|os.O_CREATE|os.O_EXCL, 0666)
+	f.Close()
+	return err
+}

internal/dotlk/dotlk_unix.go

@@ -0,0 +1,50 @@
+//go:build unix
+
+package dotlk
+
+import (
+	"errors"
+	"io/fs"
+	"os"
+	"strconv"
+
+	"golang.org/x/sys/unix"
+)
+
+// TryLock returns nil if it acquired the lock,
+// fs.ErrExist if another process has the lock.
+func TryLock(name string) error {
+	for retry := true; retry; retry = false {
+		f, err := os.OpenFile(name, os.O_RDWR|os.O_CREATE|os.O_EXCL, 0666)
+		if err == nil {
+			f.WriteString(strconv.Itoa(os.Getpid()))
+			f.Close()
+			return nil
+		}
+		if !errors.Is(err, fs.ErrExist) {
+			return err
+		}
+		if !removeStale(name) {
+			break
+		}
+	}
+	return fs.ErrExist
+}
+
+func removeStale(name string) bool {
+	buf, err := os.ReadFile(name)
+	if err != nil {
+		return errors.Is(err, fs.ErrNotExist)
+	}
+
+	pid, err := strconv.Atoi(string(buf))
+	if err != nil {
+		return false
+	}
+	if unix.Kill(pid, 0) == nil {
+		return false
+	}
+
+	err = os.Remove(name)
+	return err == nil || errors.Is(err, fs.ErrNotExist)
+}

internal/util/mmap_unix.go

@@ -39,13 +39,13 @@ func (s *mmapState) new(ctx context.Context, mod api.Module, size int32) *Mapped
 	// Save the newly allocated region.
 	ptr := uint32(stack[0])
 	buf := View(mod, ptr, uint64(size))
-	addr := unsafe.Pointer(&buf[0])
-	s.regions = append(s.regions, &MappedRegion{
+	res := &MappedRegion{
 		Ptr:  ptr,
-		addr: addr,
 		size: size,
-	})
-	return s.regions[len(s.regions)-1]
+		addr: unsafe.Pointer(&buf[0]),
+	}
+	s.regions = append(s.regions, res)
+	return res
 }
 
 type MappedRegion struct {

sqlite.go

@@ -265,10 +265,11 @@ func (a *arena) mark() (reset func()) {
 	ptrs := len(a.ptrs)
 	next := a.next
 	return func() {
-		for _, ptr := range a.ptrs[ptrs:] {
+		rest := a.ptrs[ptrs:]
+		for _, ptr := range a.ptrs[:ptrs] {
 			a.sqlt.free(ptr)
 		}
-		a.ptrs = a.ptrs[:ptrs]
+		a.ptrs = rest
 		a.next = next
 	}
 }

vfs/README.md

@@ -48,11 +48,6 @@ On Unix, this package may use `mmap` to implement
 [shared-memory for the WAL-index](https://sqlite.org/wal.html#implementation_of_shared_memory_for_the_wal_index),
 like SQLite.
 
-With [BSD locks](https://man.freebsd.org/cgi/man.cgi?query=flock&sektion=2)
-a WAL database can only be accessed by a single proccess.
-Other processes that attempt to access a database locked with BSD locks,
-will fail with the [`SQLITE_PROTOCOL`](https://sqlite.org/rescode.html#protocol) error code.
-
 On Windows, this package may use `MapViewOfFile`, like SQLite.
 
 You can also opt into a cross-platform, in-process, memory sharing implementation

vfs/lock.go

@@ -20,12 +20,10 @@ const (
 )
 
 func (f *vfsFile) Lock(lock LockLevel) error {
-	// Argument check. SQLite never explicitly requests a pending lock.
-	if lock != LOCK_SHARED && lock != LOCK_RESERVED && lock != LOCK_EXCLUSIVE {
-		panic(util.AssertErr())
-	}
-
 	switch {
+	case lock != LOCK_SHARED && lock != LOCK_RESERVED && lock != LOCK_EXCLUSIVE:
+		// Argument check. SQLite never explicitly requests a pending lock.
+		panic(util.AssertErr())
 	case f.lock < LOCK_NONE || f.lock > LOCK_EXCLUSIVE:
 		// Connection state check.
 		panic(util.AssertErr())
@@ -87,13 +85,12 @@ func (f *vfsFile) Lock(lock LockLevel) error {
 }
 
 func (f *vfsFile) Unlock(lock LockLevel) error {
-	// Argument check.
-	if lock != LOCK_NONE && lock != LOCK_SHARED {
+	switch {
+	case lock != LOCK_NONE && lock != LOCK_SHARED:
+		// Argument check.
 		panic(util.AssertErr())
-	}
-
-	// Connection state check.
-	if f.lock < LOCK_NONE || f.lock > LOCK_EXCLUSIVE {
+	case f.lock < LOCK_NONE || f.lock > LOCK_EXCLUSIVE:
+		// Connection state check.
 		panic(util.AssertErr())
 	}
 

vfs/os_bsd.go

@@ -9,11 +9,11 @@ import (
 )
 
 func osGetSharedLock(file *os.File) _ErrorCode {
-	return osLock(file, unix.LOCK_SH|unix.LOCK_NB, _IOERR_RDLOCK)
+	return osFlock(file, unix.LOCK_SH|unix.LOCK_NB, _IOERR_RDLOCK)
 }
 
 func osGetReservedLock(file *os.File) _ErrorCode {
-	rc := osLock(file, unix.LOCK_EX|unix.LOCK_NB, _IOERR_LOCK)
+	rc := osFlock(file, unix.LOCK_EX|unix.LOCK_NB, _IOERR_LOCK)
 	if rc == _BUSY {
 		// The documentation states that a lock is upgraded by
 		// releasing the previous lock, then acquiring the new lock.
@@ -37,7 +37,7 @@ func osGetExclusiveLock(file *os.File, state *LockLevel) _ErrorCode {
 }
 
 func osDowngradeLock(file *os.File, _ LockLevel) _ErrorCode {
-	rc := osLock(file, unix.LOCK_SH|unix.LOCK_NB, _IOERR_RDLOCK)
+	rc := osFlock(file, unix.LOCK_SH|unix.LOCK_NB, _IOERR_RDLOCK)
 	if rc == _BUSY {
 		// The documentation states that a lock is downgraded by
 		// releasing the previous lock then acquiring the new lock.
@@ -66,7 +66,36 @@ func osCheckReservedLock(file *os.File) (bool, _ErrorCode) {
 	return lock == unix.F_WRLCK, rc
 }
 
-func osLock(file *os.File, how int, def _ErrorCode) _ErrorCode {
+func osFlock(file *os.File, how int, def _ErrorCode) _ErrorCode {
 	err := unix.Flock(int(file.Fd()), how)
 	return osLockErrorCode(err, def)
 }
+
+func osReadLock(file *os.File, start, len int64) _ErrorCode {
+	return osLock(file, unix.F_RDLCK, start, len, _IOERR_RDLOCK)
+}
+
+func osWriteLock(file *os.File, start, len int64) _ErrorCode {
+	return osLock(file, unix.F_WRLCK, start, len, _IOERR_LOCK)
+}
+
+func osLock(file *os.File, typ int16, start, len int64, def _ErrorCode) _ErrorCode {
+	err := unix.FcntlFlock(file.Fd(), unix.F_SETLK, &unix.Flock_t{
+		Type:  typ,
+		Start: start,
+		Len:   len,
+	})
+	return osLockErrorCode(err, def)
+}
+
+func osUnlock(file *os.File, start, len int64) _ErrorCode {
+	err := unix.FcntlFlock(file.Fd(), unix.F_SETLK, &unix.Flock_t{
+		Type:  unix.F_UNLCK,
+		Start: start,
+		Len:   len,
+	})
+	if err != nil {
+		return _IOERR_UNLOCK
+	}
+	return _OK
+}

vfs/os_dotlk.go

@@ -7,6 +7,8 @@ import (
 	"io/fs"
 	"os"
 	"sync"
+
+	"github.com/ncruces/go-sqlite3/internal/dotlk"
 )
 
 var (
@@ -28,12 +30,10 @@ func osGetSharedLock(file *os.File) _ErrorCode {
 	name := file.Name()
 	locker := vfsDotLocks[name]
 	if locker == nil {
-		f, err := os.OpenFile(name+".lock", os.O_RDWR|os.O_CREATE|os.O_EXCL, 0666)
-		f.Close()
-		if errors.Is(err, fs.ErrExist) {
-			return _BUSY // Another process has the lock.
-		}
-		if err != nil {
+		if err := dotlk.TryLock(name + ".lock"); err != nil {
+			if errors.Is(err, fs.ErrExist) {
+				return _BUSY // Another process has the lock.
+			}
 			return _IOERR_LOCK
 		}
 		locker = &vfsDotLocker{}
@@ -114,8 +114,7 @@ func osReleaseLock(file *os.File, state LockLevel) _ErrorCode {
 	}
 
 	if locker.shared == 1 {
-		err := os.Remove(name + ".lock")
-		if err != nil && !errors.Is(err, fs.ErrNotExist) {
+		if err := dotlk.Unlock(name + ".lock"); err != nil {
 			return _IOERR_UNLOCK
 		}
 		delete(vfsDotLocks, name)

vfs/shm_bsd.go

@@ -4,7 +4,9 @@ package vfs
 
 import (
 	"context"
+	"errors"
 	"io"
+	"io/fs"
 	"os"
 	"sync"
 
@@ -20,7 +22,7 @@ type vfsShmParent struct {
 
 	refs int // +checklocks:vfsShmListMtx
 
-	lock [_SHM_NLOCK]int16 // +checklocks:Mutex
+	lock [_SHM_NLOCK]int8 // +checklocks:Mutex
 	sync.Mutex
 }
 
@@ -71,23 +73,21 @@ func (s *vfsShm) shmOpen() _ErrorCode {
 		return _OK
 	}
 
-	// Always open file read-write, as it will be shared.
-	f, err := os.OpenFile(s.path,
-		os.O_RDWR|os.O_CREATE|_O_NOFOLLOW, 0666)
-	if err != nil {
-		return _CANTOPEN
-	}
-	// Closes file if it's not nil.
+	var f *os.File
+	// Close file on error.
+	// Keep this here to avoid confusing checklocks.
 	defer func() { f.Close() }()
 
-	fi, err := f.Stat()
-	if err != nil {
-		return _IOERR_FSTAT
-	}
-
 	vfsShmListMtx.Lock()
 	defer vfsShmListMtx.Unlock()
 
+	// Stat file without opening it.
+	// Closing it would release all POSIX locks on it.
+	fi, err := os.Stat(s.path)
+	if err != nil && !errors.Is(err, fs.ErrNotExist) {
+		return _IOERR_FSTAT
+	}
+
 	// Find a shared file, increase the reference count.
 	for _, g := range vfsShmList {
 		if g != nil && os.SameFile(fi, g.info) {
@@ -97,13 +97,33 @@ func (s *vfsShm) shmOpen() _ErrorCode {
 		}
 	}
 
-	// Lock and truncate the file.
-	// The lock is only released by closing the file.
-	if rc := osLock(f, unix.LOCK_EX|unix.LOCK_NB, _IOERR_LOCK); rc != _OK {
+	// Always open file read-write, as it will be shared.
+	f, err = os.OpenFile(s.path,
+		os.O_RDWR|os.O_CREATE|_O_NOFOLLOW, 0666)
+	if err != nil {
+		return _CANTOPEN
+	}
+
+	// Dead man's switch.
+	if lock, rc := osTestLock(f, _SHM_DMS, 1); rc != _OK {
+		return _IOERR_LOCK
+	} else if lock == unix.F_WRLCK {
+		return _BUSY
+	} else if lock == unix.F_UNLCK {
+		if rc := osWriteLock(f, _SHM_DMS, 1); rc != _OK {
+			return rc
+		}
+		if err := f.Truncate(0); err != nil {
+			return _IOERR_SHMOPEN
+		}
+	}
+	if rc := osReadLock(f, _SHM_DMS, 1); rc != _OK {
 		return rc
 	}
-	if err := f.Truncate(0); err != nil {
-		return _IOERR_SHMOPEN
+
+	fi, err = f.Stat()
+	if err != nil {
+		return _IOERR_FSTAT
 	}
 
 	// Add the new shared file.
@@ -157,7 +177,42 @@ func (s *vfsShm) shmMap(ctx context.Context, mod api.Module, id, size int32, ext
 func (s *vfsShm) shmLock(offset, n int32, flags _ShmFlag) _ErrorCode {
 	s.Lock()
 	defer s.Unlock()
-	return s.shmMemLock(offset, n, flags)
+
+	// Check if we could obtain/release the lock locally.
+	rc := s.shmMemLock(offset, n, flags)
+	if rc != _OK {
+		return rc
+	}
+
+	// Obtain/release the appropriate file locks.
+	switch {
+	case flags&_SHM_UNLOCK != 0:
+		begin, end := offset, offset+n
+		for i := begin; i < end; i++ {
+			if s.vfsShmParent.lock[i] != 0 {
+				if i > begin {
+					rc |= osUnlock(s.File, _SHM_BASE+int64(begin), int64(i-begin))
+				}
+				begin = i + 1
+			}
+		}
+		if end > begin {
+			rc |= osUnlock(s.File, _SHM_BASE+int64(begin), int64(end-begin))
+		}
+		return rc
+	case flags&_SHM_SHARED != 0:
+		rc = osReadLock(s.File, _SHM_BASE+int64(offset), int64(n))
+	case flags&_SHM_EXCLUSIVE != 0:
+		rc = osWriteLock(s.File, _SHM_BASE+int64(offset), int64(n))
+	default:
+		panic(util.AssertErr())
+	}
+
+	// Release the local lock we had acquired.
+	if rc != _OK {
+		s.shmMemLock(offset, n, flags^(_SHM_UNLOCK|_SHM_LOCK))
+	}
+	return rc
 }
 
 func (s *vfsShm) shmUnmap(delete bool) {

vfs/shm_dotlk.go

@@ -6,11 +6,11 @@ import (
 	"context"
 	"errors"
 	"io/fs"
-	"os"
 	"sync"
 
 	"github.com/tetratelabs/wazero/api"
 
+	"github.com/ncruces/go-sqlite3/internal/dotlk"
 	"github.com/ncruces/go-sqlite3/internal/util"
 )
 
@@ -18,7 +18,7 @@ type vfsShmParent struct {
 	shared [][_WALINDEX_PGSZ]byte
 	refs   int // +checklocks:vfsShmListMtx
 
-	lock [_SHM_NLOCK]int16 // +checklocks:Mutex
+	lock [_SHM_NLOCK]int8 // +checklocks:Mutex
 	sync.Mutex
 }
 
@@ -58,8 +58,7 @@ func (s *vfsShm) Close() error {
 		return nil
 	}
 
-	err := os.Remove(s.path)
-	if err != nil && !errors.Is(err, fs.ErrNotExist) {
+	if err := dotlk.Unlock(s.path); err != nil {
 		return _IOERR_UNLOCK
 	}
 	delete(vfsShmList, s.path)
@@ -82,9 +81,8 @@ func (s *vfsShm) shmOpen() _ErrorCode {
 		return _OK
 	}
 
-	// Create a directory on disk to ensure only this process
-	// uses this path to register a shared memory.
-	err := os.Mkdir(s.path, 0777)
+	// Dead man's switch.
+	err := dotlk.LockShm(s.path)
 	if errors.Is(err, fs.ErrExist) {
 		return _BUSY
 	}

vfs/shm_memlk.go

@@ -10,9 +10,6 @@ func (s *vfsShm) shmMemLock(offset, n int32, flags _ShmFlag) _ErrorCode {
 	case flags&_SHM_UNLOCK != 0:
 		for i := offset; i < offset+n; i++ {
 			if s.lock[i] {
-				if s.vfsShmParent.lock[i] == 0 {
-					panic(util.AssertErr())
-				}
 				if s.vfsShmParent.lock[i] <= 0 {
 					s.vfsShmParent.lock[i] = 0
 				} else {
@@ -23,20 +20,21 @@ func (s *vfsShm) shmMemLock(offset, n int32, flags _ShmFlag) _ErrorCode {
 		}
 	case flags&_SHM_SHARED != 0:
 		for i := offset; i < offset+n; i++ {
-			if s.lock[i] {
-				panic(util.AssertErr())
-			}
-			if s.vfsShmParent.lock[i]+1 <= 0 {
+			if !s.lock[i] &&
+				s.vfsShmParent.lock[i]+1 <= 0 {
 				return _BUSY
 			}
 		}
 		for i := offset; i < offset+n; i++ {
-			s.vfsShmParent.lock[i]++
-			s.lock[i] = true
+			if !s.lock[i] {
+				s.vfsShmParent.lock[i]++
+				s.lock[i] = true
+			}
 		}
 	case flags&_SHM_EXCLUSIVE != 0:
 		for i := offset; i < offset+n; i++ {
 			if s.lock[i] {
+				// SQLite never requests an exclusive lock that it already holds.
 				panic(util.AssertErr())
 			}
 			if s.vfsShmParent.lock[i] != 0 {

vfs/shm_ofd.go

@@ -110,7 +110,12 @@ func (s *vfsShm) shmMap(ctx context.Context, mod api.Module, id, size int32, ext
 
 func (s *vfsShm) shmLock(offset, n int32, flags _ShmFlag) _ErrorCode {
 	// Argument check.
-	if n <= 0 || offset < 0 || offset+n > _SHM_NLOCK {
+	switch {
+	case n <= 0:
+		panic(util.AssertErr())
+	case offset < 0 || offset+n > _SHM_NLOCK:
+		panic(util.AssertErr())
+	case n != 1 && flags&_SHM_EXCLUSIVE == 0:
 		panic(util.AssertErr())
 	}
 	switch flags {
@@ -123,9 +128,6 @@ func (s *vfsShm) shmLock(offset, n int32, flags _ShmFlag) _ErrorCode {
 	default:
 		panic(util.AssertErr())
 	}
-	if n != 1 && flags&_SHM_EXCLUSIVE == 0 {
-		panic(util.AssertErr())
-	}
 
 	var timeout time.Duration
 	if s.blocking {

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

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:32dfb1b76b5cf71cb7610a7cb34ec3d9b68fcea5e54d734e35ae6b649c923c7a
-size 477479
+oid sha256:e20f37d94223a88d8f94b3a20177c0fbf53392df2f9c59a28cc7f1f2b5d3de81
+size 477370

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

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:a0d0b42fe3120de55da71dae0b2aa6ae5b4888593d2129e651590f12555ecdf3
-size 491151
+oid sha256:eebe395695c739a24e9cded13553b97d232eb268a5bc36f10f27cc13945e78cd
+size 491003