sync_sanity_check.go

package main

import (
  "crypto/rand"
  "fmt"
  "os"
  "os/exec"
)

func main() {
  if err := os.RemoveAll("synctest.txt"); err != nil {
    panic(err)
  }
  f, err := os.OpenFile("synctest.txt", os.O_RDWR|os.O_CREATE, 0755)
  if err != nil {
    panic(err)
  }
  defer f.Close()
  buf := make([]byte, 1024*1024)
  for i := 0; i < 2; i++ {
    for j := 0; j < 256; j++ {
      n1, err := rand.Read(buf)
      if err != nil {
        panic(err)
      }
      n2, err := f.Write(buf)
      if err != nil {
        panic(err)
      }
      if n1 != n2 {
        panic(fmt.Sprintf("wrote %d bytes; expected %d", n2, n1))
      }
    }
    fmt.Printf("after batch #%d of writes: %q\n", i+1, dirtyBytes())
  }
  fmt.Printf("fsyncing: %q\n", dirtyBytes())
  if err := f.Sync(); err != nil {
    panic(err)
  }
  fmt.Printf("done fsyncing: %q\n", dirtyBytes())
}

func dirtyBytes() string {
  output, err := exec.Command("grep", "Dirty", "/proc/meminfo").CombinedOutput()
  if err != nil {
    panic(err)
  }
  return string(output)
}