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Use the right sized byte array for large indexes #301

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Mar 14, 2018
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Use the right sized byte array for large indexes #301

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10 changes: 6 additions & 4 deletions fileutil/mmap_windows.go
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Original file line number Diff line number Diff line change
Expand Up @@ -19,14 +19,16 @@ import (
"unsafe"
)

func mmap(f *os.File, sz int) ([]byte, error) {
low, high := uint32(sz), uint32(sz>>32)
const maxMapSize = 0xFFFFFFFFFFFF // 256TB

func mmap(f *os.File, size int) ([]byte, error) {
low, high := uint32(size), uint32(size>>32)
h, errno := syscall.CreateFileMapping(syscall.Handle(f.Fd()), nil, syscall.PAGE_READONLY, high, low, nil)
if h == 0 {
return nil, os.NewSyscallError("CreateFileMapping", errno)
}

addr, errno := syscall.MapViewOfFile(h, syscall.FILE_MAP_READ, 0, 0, uintptr(sz))
addr, errno := syscall.MapViewOfFile(h, syscall.FILE_MAP_READ, 0, 0, uintptr(size))
if addr == 0 {
return nil, os.NewSyscallError("MapViewOfFile", errno)
}
Expand All @@ -35,7 +37,7 @@ func mmap(f *os.File, sz int) ([]byte, error) {
return nil, os.NewSyscallError("CloseHandle", err)
}

return (*[1 << 30]byte)(unsafe.Pointer(addr))[:sz], nil
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sz is just size? Can we name it like that? (maybe just for master)

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Also I have stupid question. I have never used mmap before, but... why don't we cast to just [sz]byte here?

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I was thinking the same thing and tried it but casting to an array requires a constant for the array size as this is evaluated at compile time

  • return (*[sz]byte)(unsafe.Pointer(addr))[:sz], nil = non-constant array bound

return (*[maxMapSize]byte)(unsafe.Pointer(addr))[:size], nil
}

func munmap(b []byte) error {
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