lib/mmap: library to do memory allocation with anonymous memory maps

lib/mmap/mmap_windows.go

@@ -0,0 +1,42 @@
+// 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
+}