github.com/etecs-ru/ristretto@v0.9.1/z/mmap_windows.go (about)

     1  //go:build windows
     2  // +build windows
     3  
     4  /*
     5   * Copyright 2019 Dgraph Labs, Inc. and Contributors
     6   *
     7   * Licensed under the Apache License, Version 2.0 (the "License");
     8   * you may not use this file except in compliance with the License.
     9   * You may obtain a copy of the License at
    10   *
    11   *     http://www.apache.org/licenses/LICENSE-2.0
    12   *
    13   * Unless required by applicable law or agreed to in writing, software
    14   * distributed under the License is distributed on an "AS IS" BASIS,
    15   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    16   * See the License for the specific language governing permissions and
    17   * limitations under the License.
    18   */
    19  
    20  package z
    21  
    22  import (
    23  	"fmt"
    24  	"os"
    25  	"syscall"
    26  	"unsafe"
    27  )
    28  
    29  func mmap(fd *os.File, write bool, size int64) ([]byte, error) {
    30  	protect := syscall.PAGE_READONLY
    31  	access := syscall.FILE_MAP_READ
    32  
    33  	if write {
    34  		protect = syscall.PAGE_READWRITE
    35  		access = syscall.FILE_MAP_WRITE
    36  	}
    37  	fi, err := fd.Stat()
    38  	if err != nil {
    39  		return nil, err
    40  	}
    41  
    42  	// In windows, we cannot mmap a file more than it's actual size.
    43  	// So truncate the file to the size of the mmap.
    44  	if fi.Size() < size {
    45  		if err := fd.Truncate(size); err != nil {
    46  			return nil, fmt.Errorf("truncate: %s", err)
    47  		}
    48  	}
    49  
    50  	// Open a file mapping handle.
    51  	sizelo := uint32(size >> 32)
    52  	sizehi := uint32(size) & 0xffffffff
    53  
    54  	handler, err := syscall.CreateFileMapping(syscall.Handle(fd.Fd()), nil,
    55  		uint32(protect), sizelo, sizehi, nil)
    56  	if err != nil {
    57  		return nil, os.NewSyscallError("CreateFileMapping", err)
    58  	}
    59  
    60  	// Create the memory map.
    61  	addr, err := syscall.MapViewOfFile(handler, uint32(access), 0, 0, uintptr(size))
    62  	if addr == 0 {
    63  		return nil, os.NewSyscallError("MapViewOfFile", err)
    64  	}
    65  
    66  	// Close mapping handle.
    67  	if err := syscall.CloseHandle(syscall.Handle(handler)); err != nil {
    68  		return nil, os.NewSyscallError("CloseHandle", err)
    69  	}
    70  
    71  	// Slice memory layout
    72  	// Copied this snippet from golang/sys package
    73  	sl := struct {
    74  		addr uintptr
    75  		len  int
    76  		cap  int
    77  	}{addr, int(size), int(size)}
    78  
    79  	// Use unsafe to turn sl into a []byte.
    80  	data := *(*[]byte)(unsafe.Pointer(&sl))
    81  
    82  	return data, nil
    83  }
    84  
    85  func munmap(b []byte) error {
    86  	return syscall.UnmapViewOfFile(uintptr(unsafe.Pointer(&b[0])))
    87  }
    88  
    89  func madvise(b []byte, readahead bool) error {
    90  	// Do Nothing. We don’t care about this setting on Windows
    91  	return nil
    92  }
    93  
    94  func msync(b []byte) error {
    95  	return syscall.FlushViewOfFile(uintptr(unsafe.Pointer(&b[0])), uintptr(len(b)))
    96  }