Windows blocking locks. (#200)

README.md

@@ -10,7 +10,7 @@ as well as direct access to most of the [C SQLite API](https://sqlite.org/cintro
 
 It wraps a [Wasm](https://webassembly.org/) [build](embed/) of SQLite,
 and uses [wazero](https://wazero.io/) as the runtime.\
-Go, wazero and [`x/sys`](https://pkg.go.dev/golang.org/x/sys) are the _only_ runtime dependencies.
+Go, wazero and [`x/sys`](https://pkg.go.dev/golang.org/x/sys) are the _only_ direct dependencies.
 
 ### Getting started
 

go.work.sum

@@ -10,5 +10,6 @@ golang.org/x/term v0.23.0/go.mod h1:DgV24QBUrK6jhZXl+20l6UWznPlwAHm1Q1mGHtydmSk=
 golang.org/x/term v0.24.0/go.mod h1:lOBK/LVxemqiMij05LGJ0tzNr8xlmwBRJ81PX6wVLH8=
 golang.org/x/term v0.25.0/go.mod h1:RPyXicDX+6vLxogjjRxjgD2TKtmAO6NZBsBRfrOLu7M=
 golang.org/x/term v0.26.0/go.mod h1:Si5m1o57C5nBNQo5z1iq+XDijt21BDBDp2bK0QI8e3E=
+golang.org/x/term v0.27.0/go.mod h1:iMsnZpn0cago0GOrHO2+Y7u7JPn5AylBrcoWkElMTSM=
 golang.org/x/tools v0.6.0/go.mod h1:Xwgl3UAJ/d3gWutnCtw505GrjyAbvKui8lOU390QaIU=
 golang.org/x/tools v0.21.1-0.20240508182429-e35e4ccd0d2d/go.mod h1:aiJjzUbINMkxbQROHiO6hDPo2LHcIPhhQsa9DLh0yGk=

util/osutil/open_windows.go

@@ -101,6 +101,9 @@ func syscallOpen(path string, mode int, perm uint32) (fd Handle, err error) {
 		const _FILE_FLAG_WRITE_THROUGH = 0x80000000
 		attrs |= _FILE_FLAG_WRITE_THROUGH
 	}
+	if mode&O_NONBLOCK != 0 {
+		attrs |= FILE_FLAG_OVERLAPPED
+	}
 	return CreateFile(pathp, access, sharemode, sa, createmode, attrs, 0)
 }
 

vfs/os_windows.go

@@ -3,7 +3,6 @@
 package vfs
 
 import (
-	"math/rand"
 	"os"
 	"time"
 
@@ -46,7 +45,7 @@ func osGetExclusiveLock(file *os.File, state *LockLevel) _ErrorCode {
 	osUnlock(file, _SHARED_FIRST, _SHARED_SIZE)
 
 	// Acquire the EXCLUSIVE lock.
-	rc := osWriteLock(file, _SHARED_FIRST, _SHARED_SIZE, time.Millisecond)
+	rc := osWriteLock(file, _SHARED_FIRST, _SHARED_SIZE, 0)
 
 	if rc != _OK {
 		// Reacquire the SHARED lock.
@@ -123,29 +122,40 @@ func osLock(file *os.File, flags, start, len uint32, timeout time.Duration, def
 	var err error
 	switch {
 	case timeout == 0:
-		err = osLockEx(file, flags|windows.LOCKFILE_FAIL_IMMEDIATELY, start, len)
+		err = osLockEx(file, flags|windows.LOCKFILE_FAIL_IMMEDIATELY, start, len, 0)
 	case timeout < 0:
-		err = osLockEx(file, flags, start, len)
+		err = osLockEx(file, flags, start, len, 0)
 	default:
-		before := time.Now()
-		for {
-			err = osLockEx(file, flags|windows.LOCKFILE_FAIL_IMMEDIATELY, start, len)
-			if errno, _ := err.(windows.Errno); errno != windows.ERROR_LOCK_VIOLATION {
-				break
+		var event windows.Handle
+		event, err = windows.CreateEvent(nil, 1, 0, nil)
+		if err != nil {
+			break
+		}
+		defer windows.CloseHandle(event)
+
+		err = osLockEx(file, flags, start, len, event)
+		if err == windows.ERROR_IO_PENDING {
+			rc, serr := windows.WaitForSingleObject(event, uint32(timeout/time.Millisecond))
+			if rc == windows.WAIT_OBJECT_0 {
+				return _OK
 			}
-			if time.Since(before) > timeout {
-				break
+			if serr != nil {
+				err = serr
+			} else {
+				err = windows.Errno(rc)
 			}
-			const sleepIncrement = 1024*1024 - 1 // power of two, ~1ms
-			time.Sleep(time.Duration(rand.Int63() & sleepIncrement))
+			windows.CancelIo(windows.Handle(file.Fd()))
 		}
 	}
 	return osLockErrorCode(err, def)
 }
 
-func osLockEx(file *os.File, flags, start, len uint32) error {
+func osLockEx(file *os.File, flags, start, len uint32, event windows.Handle) error {
 	return windows.LockFileEx(windows.Handle(file.Fd()), flags,
-		0, len, 0, &windows.Overlapped{Offset: start})
+		0, len, 0, &windows.Overlapped{
+			Offset: start,
+			HEvent: event,
+		})
 }
 
 func osReadLock(file *os.File, start, len uint32, timeout time.Duration) _ErrorCode {
@@ -166,7 +176,8 @@ func osLockErrorCode(err error, def _ErrorCode) _ErrorCode {
 		case
 			windows.ERROR_LOCK_VIOLATION,
 			windows.ERROR_IO_PENDING,
-			windows.ERROR_OPERATION_ABORTED:
+			windows.ERROR_OPERATION_ABORTED,
+			windows.WAIT_TIMEOUT:
 			return _BUSY
 		}
 	}

vfs/shm_bsd.go

@@ -73,7 +73,7 @@ func (s *vfsShm) shmOpen() _ErrorCode {
 
 	// Always open file read-write, as it will be shared.
 	f, err := os.OpenFile(s.path,
-		unix.O_RDWR|unix.O_CREAT|unix.O_NOFOLLOW, 0666)
+		os.O_RDWR|os.O_CREATE|_O_NOFOLLOW, 0666)
 	if err != nil {
 		return _CANTOPEN
 	}

vfs/shm_ofd.go

@@ -20,6 +20,7 @@ type vfsShm struct {
 	path     string
 	regions  []*util.MappedRegion
 	readOnly bool
+	fileLock bool
 	blocking bool
 	sync.Mutex
 }
@@ -29,17 +30,20 @@ var _ blockingSharedMemory = &vfsShm{}
 func (s *vfsShm) shmOpen() _ErrorCode {
 	if s.File == nil {
 		f, err := os.OpenFile(s.path,
-			unix.O_RDWR|unix.O_CREAT|unix.O_NOFOLLOW, 0666)
+			os.O_RDWR|os.O_CREATE|_O_NOFOLLOW, 0666)
 		if err != nil {
 			f, err = os.OpenFile(s.path,
-				unix.O_RDONLY|unix.O_CREAT|unix.O_NOFOLLOW, 0666)
+				os.O_RDONLY|os.O_CREATE|_O_NOFOLLOW, 0666)
 			s.readOnly = true
 		}
 		if err != nil {
 			return _CANTOPEN
 		}
 		s.File = f
 	}
+	if s.fileLock {
+		return _OK
+	}
 
 	// Dead man's switch.
 	if lock, rc := osTestLock(s.File, _SHM_DMS, 1); rc != _OK {
@@ -64,7 +68,9 @@ func (s *vfsShm) shmOpen() _ErrorCode {
 			return _IOERR_SHMOPEN
 		}
 	}
-	return osReadLock(s.File, _SHM_DMS, 1, time.Millisecond)
+	rc := osReadLock(s.File, _SHM_DMS, 1, time.Millisecond)
+	s.fileLock = rc == _OK
+	return rc
 }
 
 func (s *vfsShm) shmMap(ctx context.Context, mod api.Module, id, size int32, extend bool) (uint32, _ErrorCode) {

vfs/shm_windows.go

@@ -7,6 +7,7 @@ import (
 	"io"
 	"os"
 	"sync"
+	"syscall"
 	"time"
 
 	"github.com/tetratelabs/wazero/api"
@@ -27,6 +28,7 @@ type vfsShm struct {
 	shadow   [][_WALINDEX_PGSZ]byte
 	ptrs     []uint32
 	stack    [1]uint64
+	fileLock bool
 	blocking bool
 	sync.Mutex
 }
@@ -46,12 +48,16 @@ func (s *vfsShm) Close() error {
 
 func (s *vfsShm) shmOpen() _ErrorCode {
 	if s.File == nil {
-		f, err := osutil.OpenFile(s.path, os.O_RDWR|os.O_CREATE, 0666)
+		f, err := osutil.OpenFile(s.path,
+			os.O_RDWR|os.O_CREATE|syscall.O_NONBLOCK, 0666)
 		if err != nil {
 			return _CANTOPEN
 		}
 		s.File = f
 	}
+	if s.fileLock {
+		return _OK
+	}
 
 	// Dead man's switch.
 	if rc := osWriteLock(s.File, _SHM_DMS, 1, 0); rc == _OK {
@@ -61,7 +67,9 @@ func (s *vfsShm) shmOpen() _ErrorCode {
 			return _IOERR_SHMOPEN
 		}
 	}
-	return osReadLock(s.File, _SHM_DMS, 1, time.Millisecond)
+	rc := osReadLock(s.File, _SHM_DMS, 1, time.Millisecond)
+	s.fileLock = rc == _OK
+	return rc
 }
 
 func (s *vfsShm) shmMap(ctx context.Context, mod api.Module, id, size int32, extend bool) (_ uint32, rc _ErrorCode) {