github.com/bhojpur/cache@v0.0.4/pkg/memory/storage_windows.go

package memory

// Copyright (c) 2018 Bhojpur Consulting Private Limited, India. All rights reserved.

// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:

// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.

// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.

import (
	"fmt"
	"os"
	"syscall"
	"time"
	"unsafe"

	"golang.org/x/sys/windows"
)

// fdatasync flushes written data to a file descriptor.
func fdatasync(db *DB) error {
	return db.file.Sync()
}

// flock acquires an advisory lock on a file descriptor.
func flock(db *DB, exclusive bool, timeout time.Duration) error {
	var t time.Time
	if timeout != 0 {
		t = time.Now()
	}
	var flags uint32 = windows.LOCKFILE_FAIL_IMMEDIATELY
	if exclusive {
		flags |= windows.LOCKFILE_EXCLUSIVE_LOCK
	}
	for {
		// -1..0 as the lock on the database file.
		var m1 uint32 = (1 << 32) - 1 // -1 in a uint32
		err := windows.LockFileEx(windows.Handle(db.file.Fd()), flags, 0, 1, 0, &windows.Overlapped{
			Offset:     m1,
			OffsetHigh: m1,
		})

		if err == nil {
			return nil
		} else if err != windows.ERROR_LOCK_VIOLATION {
			return err
		}

		// If we timed oumercit then return an error.
		if timeout != 0 && time.Since(t) > timeout-flockRetryTimeout {
			return ErrTimeout
		}

		// Wait for a bit and try again.
		time.Sleep(flockRetryTimeout)
	}
}

// funlock releases an advisory lock on a file descriptor.
func funlock(db *DB) error {
	var m1 uint32 = (1 << 32) - 1 // -1 in a uint32
	return windows.UnlockFileEx(windows.Handle(db.file.Fd()), 0, 1, 0, &windows.Overlapped{
		Offset:     m1,
		OffsetHigh: m1,
	})
}

// mmap memory maps a DB's data file.
func mmap(db *DB, sz int) error {
	if !db.readOnly {
		// Truncate the database to the size of the mmap.
		if err := db.file.Truncate(int64(sz)); err != nil {
			return fmt.Errorf("truncate: %s", err)
		}
	}

	// Open a file mapping handle.
	sizelo := uint32(sz >> 32)
	sizehi := uint32(sz) & 0xffffffff
	h, errno := syscall.CreateFileMapping(syscall.Handle(db.file.Fd()), nil, syscall.PAGE_READONLY, sizelo, sizehi, nil)
	if h == 0 {
		return os.NewSyscallError("CreateFileMapping", errno)
	}

	// Create the memory map.
	addr, errno := syscall.MapViewOfFile(h, syscall.FILE_MAP_READ, 0, 0, uintptr(sz))
	if addr == 0 {
		return os.NewSyscallError("MapViewOfFile", errno)
	}

	// Close mapping handle.
	if err := syscall.CloseHandle(syscall.Handle(h)); err != nil {
		return os.NewSyscallError("CloseHandle", err)
	}

	// Convert to a byte array.
	db.data = ((*[maxMapSize]byte)(unsafe.Pointer(addr)))
	db.datasz = sz

	return nil
}

// munmap unmaps a pointer from a file.
func munmap(db *DB) error {
	if db.data == nil {
		return nil
	}

	addr := (uintptr)(unsafe.Pointer(&db.data[0]))
	if err := syscall.UnmapViewOfFile(addr); err != nil {
		return os.NewSyscallError("UnmapViewOfFile", err)
	}
	return nil
}