move to separate lock file on windows

bolt_unix.go

@@ -11,7 +11,7 @@ import (
 )
 
 // flock acquires an advisory lock on a file descriptor.
-func flock(f *os.File, exclusive bool, timeout time.Duration) error {
+func flock(db *DB, mode os.FileMode, exclusive bool, timeout time.Duration) error {
 	var t time.Time
 	for {
 		// If we're beyond our timeout then return an error.
@@ -27,7 +27,7 @@ func flock(f *os.File, exclusive bool, timeout time.Duration) error {
 		}
 
 		// Otherwise attempt to obtain an exclusive lock.
-		err := syscall.Flock(int(f.Fd()), flag|syscall.LOCK_NB)
+		err := syscall.Flock(int(db.file.Fd()), flag|syscall.LOCK_NB)
 		if err == nil {
 			return nil
 		} else if err != syscall.EWOULDBLOCK {
@@ -40,8 +40,8 @@ func flock(f *os.File, exclusive bool, timeout time.Duration) error {
 }
 
 // funlock releases an advisory lock on a file descriptor.
-func funlock(f *os.File) error {
+func funlock(db *DB) error {
-	return syscall.Flock(int(f.Fd()), syscall.LOCK_UN)
+	return syscall.Flock(int(db.file.Fd()), syscall.LOCK_UN)
 }
 
 // mmap memory maps a DB's data file.

bolt_unix_solaris.go

@@ -11,7 +11,7 @@ import (
 )
 
 // flock acquires an advisory lock on a file descriptor.
-func flock(f *os.File, exclusive bool, timeout time.Duration) error {
+func flock(db *DB, mode os.FileMode, exclusive bool, timeout time.Duration) error {
 	var t time.Time
 	for {
 		// If we're beyond our timeout then return an error.
@@ -32,7 +32,7 @@ func flock(f *os.File, exclusive bool, timeout time.Duration) error {
 		} else {
 			lock.Type = syscall.F_RDLCK
 		}
-		err := syscall.FcntlFlock(f.Fd(), syscall.F_SETLK, &lock)
+		err := syscall.FcntlFlock(db.file.Fd(), syscall.F_SETLK, &lock)
 		if err == nil {
 			return nil
 		} else if err != syscall.EAGAIN {
@@ -45,13 +45,13 @@ func flock(f *os.File, exclusive bool, timeout time.Duration) error {
 }
 
 // funlock releases an advisory lock on a file descriptor.
-func funlock(f *os.File) error {
+func funlock(db *DB) error {
 	var lock syscall.Flock_t
 	lock.Start = 0
 	lock.Len = 0
 	lock.Type = syscall.F_UNLCK
 	lock.Whence = 0
-	return syscall.FcntlFlock(uintptr(f.Fd()), syscall.F_SETLK, &lock)
+	return syscall.FcntlFlock(uintptr(db.file.Fd()), syscall.F_SETLK, &lock)
 }
 
 // mmap memory maps a DB's data file.

bolt_windows.go

@@ -16,6 +16,8 @@ var (
 )
 
 const (
+	lockExt = ".lock"
+
 	// see https://msdn.microsoft.com/en-us/library/windows/desktop/aa365203(v=vs.85).aspx
 	flagLockExclusive       = 2
 	flagLockFailImmediately = 1
@@ -46,7 +48,16 @@ func fdatasync(db *DB) error {
 }
 
 // flock acquires an advisory lock on a file descriptor.
-func flock(f *os.File, exclusive bool, timeout time.Duration) error {
+func flock(db *DB, mode os.FileMode, exclusive bool, timeout time.Duration) error {
+	// Create a separate lock file on windows because a process
+	// cannot share an exclusive lock on the same file. This is
+	// needed during Tx.WriteTo().
+	f, err := os.OpenFile(db.path+lockExt, os.O_CREATE, mode)
+	if err != nil {
+		return err
+	}
+	db.lockfile = f
+
 	var t time.Time
 	for {
 		// If we're beyond our timeout then return an error.
@@ -62,7 +73,7 @@ func flock(f *os.File, exclusive bool, timeout time.Duration) error {
 			flag |= flagLockExclusive
 		}
 
-		err := lockFileEx(syscall.Handle(f.Fd()), flag, 0, 1, 0, &syscall.Overlapped{})
+		err := lockFileEx(syscall.Handle(db.lockfile.Fd()), flag, 0, 1, 0, &syscall.Overlapped{})
 		if err == nil {
 			return nil
 		} else if err != errLockViolation {
@@ -75,8 +86,11 @@ func flock(f *os.File, exclusive bool, timeout time.Duration) error {
 }
 
 // funlock releases an advisory lock on a file descriptor.
-func funlock(f *os.File) error {
+func funlock(db *DB) error {
-	return unlockFileEx(syscall.Handle(f.Fd()), 0, 1, 0, &syscall.Overlapped{})
+	err := unlockFileEx(syscall.Handle(db.lockfile.Fd()), 0, 1, 0, &syscall.Overlapped{})
+	db.lockfile.Close()
+	os.Remove(db.path+lockExt)
+	return err
 }
 
 // mmap memory maps a DB's data file.

db.go

@@ -93,6 +93,7 @@ type DB struct {
 
 	path     string
 	file     *os.File
+	lockfile *os.File // windows only
 	dataref  []byte // mmap'ed readonly, write throws SEGV
 	data     *[maxMapSize]byte
 	datasz   int
@@ -177,7 +178,7 @@ func Open(path string, mode os.FileMode, options *Options) (*DB, error) {
 	// if !options.ReadOnly.
 	// The database file is locked using the shared lock (more than one process may
 	// hold a lock at the same time) otherwise (options.ReadOnly is set).
-	if err := flock(db.file, !db.readOnly, options.Timeout); err != nil {
+	if err := flock(db, mode, !db.readOnly, options.Timeout); err != nil {
 		_ = db.close()
 		return nil, err
 	}
@@ -379,6 +380,10 @@ func (db *DB) Close() error {
 }
 
 func (db *DB) close() error {
+	if !db.opened {
+		return nil
+	}
+	
 	db.opened = false
 
 	db.freelist = nil
@@ -397,7 +402,7 @@ func (db *DB) close() error {
 		// No need to unlock read-only file.
 		if !db.readOnly {
 			// Unlock the file.
-			if err := funlock(db.file); err != nil {
+			if err := funlock(db); err != nil {
 				log.Printf("bolt.Close(): funlock error: %s", err)
 			}
 		}
@@ -824,8 +829,10 @@ func (db *DB) grow(sz int) error {
 	// Truncate and fsync to ensure file size metadata is flushed.
 	// https://github.com/boltdb/bolt/issues/284
 	if !db.NoGrowSync && !db.readOnly {
-		if err := db.file.Truncate(int64(sz)); err != nil {
+		if runtime.GOOS != "windows" {
-			return fmt.Errorf("file resize error: %s", err)
+			if err := db.file.Truncate(int64(sz)); err != nil {
+				return fmt.Errorf("file resize error: %s", err)
+			}
 		}
 		if err := db.file.Sync(); err != nil {
 			return fmt.Errorf("file sync error: %s", err)