57 lines
1.0 KiB
Go
57 lines
1.0 KiB
Go
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package mmap
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import (
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"os"
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"syscall"
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"unsafe"
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)
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// Map memory-maps a file.
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func Map(path string, sz int64) ([]byte, error) {
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fi, err := os.Stat(path)
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if err != nil {
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return nil, err
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}
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// Truncate file to size if too small.
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if fi.Size() < sz {
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if err := os.Truncate(path, sz); err != nil {
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return nil, err
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}
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} else {
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sz = fi.Size()
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}
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if sz == 0 {
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return nil, nil
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}
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f, err := os.Open(path)
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if err != nil {
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return nil, err
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}
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defer f.Close()
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lo, hi := uint32(sz), uint32(sz>>32)
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fmap, err := syscall.CreateFileMapping(syscall.Handle(f.Fd()), nil, syscall.PAGE_READONLY, hi, lo, nil)
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if err != nil {
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return nil, err
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}
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defer syscall.CloseHandle(fmap)
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ptr, err := syscall.MapViewOfFile(fmap, syscall.FILE_MAP_READ, 0, 0, uintptr(sz))
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if err != nil {
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return nil, err
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}
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data := (*[1 << 30]byte)(unsafe.Pointer(ptr))[:sz]
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return data, nil
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}
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// Unmap closes the memory-map.
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func Unmap(data []byte) error {
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if data == nil {
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return nil
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}
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return syscall.UnmapViewOfFile(uintptr(unsafe.Pointer(&data[0])))
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}
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