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mmap_windows.go (1712B)

      1 // Copyright 2011 The Go Authors.  All rights reserved.
      2 // Use of this source code is governed by a BSD-style
      3 // license that can be found in the LICENSE file.
      4 
      5 package mmap
      6 
      7 import (
      8 	"fmt"
      9 	"os"
     10 	"syscall"
     11 	"unsafe"
     12 
     13 	"golang.org/x/sys/windows"
     14 )
     15 
     16 func mmapFile(f *os.File) (*Data, error) {
     17 	st, err := f.Stat()
     18 	if err != nil {
     19 		return nil, err
     20 	}
     21 	size := st.Size()
     22 	if size == 0 {
     23 		return &Data{f, nil, nil}, nil
     24 	}
     25 	// set the min and max sizes to zero to map the whole file, as described in
     26 	// https://learn.microsoft.com/en-us/windows/win32/memory/creating-a-file-mapping-object#file-mapping-size
     27 	h, err := windows.CreateFileMapping(windows.Handle(f.Fd()), nil, syscall.PAGE_READWRITE, 0, 0, nil)
     28 	if err != nil {
     29 		return nil, fmt.Errorf("CreateFileMapping %s: %w", f.Name(), err)
     30 	}
     31 	// the mapping extends from zero to the end of the file mapping
     32 	// https://learn.microsoft.com/en-us/windows/win32/api/memoryapi/nf-memoryapi-mapviewoffile
     33 	addr, err := windows.MapViewOfFile(h, syscall.FILE_MAP_READ|syscall.FILE_MAP_WRITE, 0, 0, 0)
     34 	if err != nil {
     35 		return nil, fmt.Errorf("MapViewOfFile %s: %w", f.Name(), err)
     36 	}
     37 	// Note: previously, we called windows.VirtualQuery here to get the exact
     38 	// size of the memory mapped region, but VirtualQuery reported sizes smaller
     39 	// than the actual file size (hypothesis: VirtualQuery only reports pages in
     40 	// a certain state, and newly written pages may not be counted).
     41 	return &Data{f, unsafe.Slice((*byte)(unsafe.Pointer(addr)), size), h}, nil
     42 }
     43 
     44 func munmapFile(d *Data) error {
     45 	err := windows.UnmapViewOfFile(uintptr(unsafe.Pointer(&d.Data[0])))
     46 	x, ok := d.Windows.(windows.Handle)
     47 	if ok {
     48 		windows.CloseHandle(x)
     49 	}
     50 	d.f.Close()
     51 	return err
     52 }