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Mapping an array to a file via Mmap in Go

Tags:

arrays

go

mmap

I'm trying to map an array to a file via Mmap, the array could be any type, like float64. In C, I find this one. After reading some texts, I wrote this sample. I don't know if it is correct, and it is not writing the values to the file. If I increase the size of array a lot, e.g from 1000 to 10000, it crashes. If someone know how to do that in the correctly way, please, tell me.

Thanks!

like image 203
tfmoraes Avatar asked Feb 09 '12 00:02

tfmoraes


1 Answers

For example, revising your sample program,

package main

import (
    "fmt"
    "os"
    "syscall"
    "unsafe"
)

func main() {
    const n = 1e3
    t := int(unsafe.Sizeof(0)) * n

    map_file, err := os.Create("/tmp/test.dat")
    if err != nil {
        fmt.Println(err)
        os.Exit(1)
    }
    _, err = map_file.Seek(int64(t-1), 0)
    if err != nil {
        fmt.Println(err)
        os.Exit(1)
    }
    _, err = map_file.Write([]byte(" "))
    if err != nil {
        fmt.Println(err)
        os.Exit(1)
    }

    mmap, err := syscall.Mmap(int(map_file.Fd()), 0, int(t), syscall.PROT_READ|syscall.PROT_WRITE, syscall.MAP_SHARED)
    if err != nil {
        fmt.Println(err)
        os.Exit(1)
    }
    map_array := (*[n]int)(unsafe.Pointer(&mmap[0]))

    for i := 0; i < n; i++ {
        map_array[i] = i * i
    }

    fmt.Println(*map_array)

    err = syscall.Munmap(mmap)
    if err != nil {
        fmt.Println(err)
        os.Exit(1)
    }
    err = map_file.Close()
    if err != nil {
        fmt.Println(err)
        os.Exit(1)
    }
}
like image 117
peterSO Avatar answered Nov 10 '22 12:11

peterSO