five/hbrdd/dbf/locks_windows.go

// Copyright (c) 2026 Charles KWON OhJun (charleskwonohjun@gmail.com)
// All rights reserved.

//go:build windows

// Windows file locking for DBF shared mode.
// Uses kernel32 LockFileEx / UnlockFileEx for byte-range exclusive locks,
// matching Harbour's hb_fsLockLarge on Windows.
//
// Lock region layout (identical to the POSIX implementation):
//   - FLOCK:  [0, HeaderLen+1)            file-wide exclusive
//   - RLOCK:  [RecordOffset(n), RecordLen) per-record exclusive
//
// Non-blocking: LOCKFILE_FAIL_IMMEDIATELY returns immediately if another
// process holds a conflicting lock — matching Clipper FLOCK() → .F.

package dbf

import (
	"fmt"
	"syscall"
	"unsafe"
)

const flockOffset = int64(0)

func flockLen(a *DBFArea) int64 {
	return int64(a.header.HeaderLen) + 1
}

var (
	modkernel32      = syscall.NewLazyDLL("kernel32.dll")
	procLockFileEx   = modkernel32.NewProc("LockFileEx")
	procUnlockFileEx = modkernel32.NewProc("UnlockFileEx")
)

// Windows constants
const (
	_LOCKFILE_EXCLUSIVE_LOCK   = 0x00000002
	_LOCKFILE_FAIL_IMMEDIATELY = 0x00000001
	_ERROR_LOCK_VIOLATION      = 33
)

func splitOffset(off int64) (lo, hi uint32) {
	return uint32(off & 0xFFFFFFFF), uint32(off >> 32)
}

// tryLock acquires an exclusive byte-range lock via LockFileEx.
// Non-blocking: returns (false, nil) on contention.
func tryLock(handle syscall.Handle, start, length int64) (bool, error) {
	oLo, oHi := splitOffset(start)
	lLo, lHi := splitOffset(length)
	ol := &syscall.Overlapped{
		Offset:     oLo,
		OffsetHigh: oHi,
	}
	flags := uint32(_LOCKFILE_EXCLUSIVE_LOCK | _LOCKFILE_FAIL_IMMEDIATELY)
	r1, _, err := procLockFileEx.Call(
		uintptr(handle),
		uintptr(flags),
		0, // reserved
		uintptr(lLo),
		uintptr(lHi),
		uintptr(unsafe.Pointer(ol)),
	)
	if r1 == 0 {
		// Call failed
		if errno, ok := err.(syscall.Errno); ok && errno == _ERROR_LOCK_VIOLATION {
			return false, nil // another process holds it
		}
		return false, err
	}
	return true, nil
}

// unlockRange releases a previously acquired byte-range lock via UnlockFileEx.
func unlockRange(handle syscall.Handle, start, length int64) error {
	oLo, oHi := splitOffset(start)
	lLo, lHi := splitOffset(length)
	ol := &syscall.Overlapped{
		Offset:     oLo,
		OffsetHigh: oHi,
	}
	r1, _, err := procUnlockFileEx.Call(
		uintptr(handle),
		0, // reserved
		uintptr(lLo),
		uintptr(lHi),
		uintptr(unsafe.Pointer(ol)),
	)
	if r1 == 0 {
		return err
	}
	return nil
}

// winHandle returns the Windows HANDLE for the data file.
func (a *DBFArea) winHandle() syscall.Handle {
	return syscall.Handle(a.dataFile.Fd())
}

// LockFile tries to acquire an exclusive FLOCK on the DBF file.
func (a *DBFArea) LockFile() (bool, error) {
	if a.dataFile == nil {
		return false, fmt.Errorf("file not open")
	}
	if a.fileLocked {
		return true, nil
	}
	ok, err := tryLock(a.winHandle(), flockOffset, flockLen(a))
	if err != nil {
		return false, err
	}
	if ok {
		a.fileLocked = true
	}
	return ok, nil
}

// UnlockFile releases the file-wide lock held by this workarea.
func (a *DBFArea) UnlockFile() error {
	if a.dataFile == nil || !a.fileLocked {
		return nil
	}
	if err := unlockRange(a.winHandle(), flockOffset, flockLen(a)); err != nil {
		return err
	}
	a.fileLocked = false
	return nil
}

// LockRecord tries to acquire an exclusive lock on a single record.
func (a *DBFArea) LockRecord(recNo uint32) (bool, error) {
	if a.dataFile == nil {
		return false, fmt.Errorf("file not open")
	}
	if recNo == 0 {
		recNo = a.recNo
	}
	if recNo == 0 {
		return false, nil
	}
	if a.lockedRecs != nil && a.lockedRecs[recNo] {
		return true, nil
	}
	start := a.header.RecordOffset(recNo)
	length := int64(a.header.RecordLen)
	ok, err := tryLock(a.winHandle(), start, length)
	if err != nil {
		return false, err
	}
	if ok {
		if a.lockedRecs == nil {
			a.lockedRecs = make(map[uint32]bool, 16)
		}
		a.lockedRecs[recNo] = true
	}
	return ok, nil
}

// UnlockRecord releases a single record lock. recNo == 0 unlocks ALL.
func (a *DBFArea) UnlockRecord(recNo uint32) error {
	if a.dataFile == nil {
		return nil
	}
	if recNo == 0 {
		if a.lockedRecs == nil {
			return nil
		}
		length := int64(a.header.RecordLen)
		for r := range a.lockedRecs {
			start := a.header.RecordOffset(r)
			_ = unlockRange(a.winHandle(), start, length)
		}
		a.lockedRecs = nil
		return nil
	}
	if a.lockedRecs == nil || !a.lockedRecs[recNo] {
		return nil
	}
	start := a.header.RecordOffset(recNo)
	length := int64(a.header.RecordLen)
	if err := unlockRange(a.winHandle(), start, length); err != nil {
		return err
	}
	delete(a.lockedRecs, recNo)
	return nil
}

// releaseAllLocks is called on Close to release any held locks.
func (a *DBFArea) releaseAllLocks() {
	_ = a.UnlockFile()
	_ = a.UnlockRecord(0)
}