TIL: it's possible to open the same path twice (even on Windows!) - it might not be a good idea, though.

001_concurrent_writes.go

package main

import (
	"io/ioutil"
	"log"
	"os"
)

func main() {
	path := "sample.txt"
	weirdWrites(path)
	read(path)
}

func weirdWrites(path string) {
	f1, err := os.OpenFile(path, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0644)
	if err != nil {
		log.Fatal(err)
	}

	f2, err := os.OpenFile(path, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0644)
	if err != nil {
		log.Fatal(err)
	}

	_, err = f1.Write([]byte("one"))
	if err != nil {
		log.Fatal(err)
	}

	_, err = f2.Write([]byte("two two"))
	if err != nil {
		log.Fatal(err)
	}

	err = f2.Close()
	if err != nil {
		log.Fatal(err)
	}

	_, err = f1.Write([]byte("extra one"))
	if err != nil {
		log.Fatal(err)
	}

	err = f1.Close()
	if err != nil {
		log.Fatal(err)
	}
}

func read(path string) {
	bytes, err := ioutil.ReadFile(path)
	if err != nil {
		log.Fatal(err)
	}

	log.Print(string(bytes))
}

002_sample_output_linux.txt

2016/12/31 16:24:44 twoextra one

003_sample_output_windows.txt

2016/12/31 15:25:46 twoextra one