rclone/lib/mmap/mmap_windows.go

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// Package mmap implements a large block memory allocator using
// anonymous memory maps.
// +build windows
package mmap
import (
"reflect"
"unsafe"
"github.com/pkg/errors"
"golang.org/x/sys/windows"
)
// Alloc allocates size bytes and returns a slice containing them. If
// the allocation fails it will return with an error. This is best
// used for allocations which are a multiple of the PageSize.
func Alloc(size int) ([]byte, error) {
p, err := windows.VirtualAlloc(0, uintptr(size), windows.MEM_COMMIT, windows.PAGE_READWRITE)
if err != nil {
return nil, errors.Wrap(err, "mmap: failed to allocate memory for buffer")
}
var mem []byte
sh := (*reflect.SliceHeader)(unsafe.Pointer(&mem))
sh.Data = p
sh.Len = size
sh.Cap = size
return mem, nil
}
// Free frees buffers allocated by Alloc. Note it should be passed
// the same slice (not a derived slice) that Alloc returned. If the
// free fails it will return with an error.
func Free(mem []byte) error {
sh := (*reflect.SliceHeader)(unsafe.Pointer(&mem))
err := windows.VirtualFree(sh.Data, 0, windows.MEM_RELEASE)
if err != nil {
return errors.Wrap(err, "mmap: failed to unmap memory")
}
return nil
}