github.com/coocood/badger@v1.5.1-0.20200528065104-c02ac3616d04/y/mmap_windows.go (about)

     1  // +build windows
     2  
     3  /*
     4   * Copyright 2017 Dgraph Labs, Inc. and Contributors
     5   *
     6   * Licensed under the Apache License, Version 2.0 (the "License");
     7   * you may not use this file except in compliance with the License.
     8   * You may obtain a copy of the License at
     9   *
    10   *     http://www.apache.org/licenses/LICENSE-2.0
    11   *
    12   * Unless required by applicable law or agreed to in writing, software
    13   * distributed under the License is distributed on an "AS IS" BASIS,
    14   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    15   * See the License for the specific language governing permissions and
    16   * limitations under the License.
    17   */
    18  
    19  package y
    20  
    21  import (
    22  	"fmt"
    23  	"os"
    24  	"syscall"
    25  	"unsafe"
    26  )
    27  
    28  func Mmap(fd *os.File, write bool, size int64) ([]byte, error) {
    29  	protect := syscall.PAGE_READONLY
    30  	access := syscall.FILE_MAP_READ
    31  
    32  	if write {
    33  		protect = syscall.PAGE_READWRITE
    34  		access = syscall.FILE_MAP_WRITE
    35  	}
    36  	fi, err := fd.Stat()
    37  	if err != nil {
    38  		return nil, err
    39  	}
    40  
    41  	// Truncate the database to the size of the mmap.
    42  	if fi.Size() < size {
    43  		if err := fd.Truncate(size); err != nil {
    44  			return nil, fmt.Errorf("truncate: %s", err)
    45  		}
    46  	}
    47  
    48  	// Open a file mapping handle.
    49  	sizelo := uint32(size >> 32)
    50  	sizehi := uint32(size) & 0xffffffff
    51  
    52  	handler, err := syscall.CreateFileMapping(syscall.Handle(fd.Fd()), nil,
    53  		uint32(protect), sizelo, sizehi, nil)
    54  	if err != nil {
    55  		return nil, os.NewSyscallError("CreateFileMapping", err)
    56  	}
    57  
    58  	// Create the memory map.
    59  	addr, err := syscall.MapViewOfFile(handler, uint32(access), 0, 0, uintptr(size))
    60  	if addr == 0 {
    61  		return nil, os.NewSyscallError("MapViewOfFile", err)
    62  	}
    63  
    64  	// Close mapping handle.
    65  	if err := syscall.CloseHandle(syscall.Handle(handler)); err != nil {
    66  		return nil, os.NewSyscallError("CloseHandle", err)
    67  	}
    68  
    69  	// Slice memory layout
    70  	// Copied this snippet from golang/sys package
    71  	var sl = struct {
    72  		addr uintptr
    73  		len  int
    74  		cap  int
    75  	}{addr, int(size), int(size)}
    76  
    77  	// Use unsafe to turn sl into a []byte.
    78  	data := *(*[]byte)(unsafe.Pointer(&sl))
    79  
    80  	return data, nil
    81  }
    82  
    83  func Munmap(b []byte) error {
    84  	return syscall.UnmapViewOfFile(uintptr(unsafe.Pointer(&b[0])))
    85  }
    86  
    87  func Madvise(b []byte, readahead bool) error {
    88  	// Do Nothing. We don’t care about this setting on Windows
    89  	return nil
    90  }