Experiments with parallel read/write in Go without file.Sync or file.Close

parallel_rw.go

package main

// parallel_rw.go experiments with parallel read/write from a file without
// syncing (aka flushing) or closing.

import (
	"encoding/binary"
	"fmt"
	// "math/rand"
	"os"
	"runtime"
	// "time"
)

var MAX uint32 = 1000

func main() {

	runtime.GOMAXPROCS(4)

	file, err := os.Create("log")
	if err != nil {
		panic(err)
	}
	file.Close()

	done := make(chan interface{})

	go read(done)
	go write()

	<-done

}

// read reads 0..MAX integers from the log file.
func read(done chan<- interface{}) {

	file, err := os.OpenFile("log", os.O_RDONLY, 0666)
	if nil != err {
		panic(err)
	}

	var i uint32
	for i = 0; i < MAX; i = i {
		var n uint32
		err := binary.Read(file, binary.LittleEndian, &n)
		if nil != err {
			fmt.Println("\t\t\t\t\t\tError: ", err.Error())
			continue
		}
		fmt.Println("Read ", n)
		if i != n {
			fmt.Printf("Corrupted data: expected %d, was %d\n", i, n)
			os.Exit(1)
		}
		i++
	}

	done <- nil

}

// write writes 0..MAX integers into the log file.
func write() {

	file, err := os.OpenFile("log", os.O_WRONLY, 0666)
	if nil != err {
		panic(err)
	}

	var i uint32
	for i = 0; i < MAX; i++ {
		if err := binary.Write(file, binary.LittleEndian, i); nil != err {
			panic(err)
		}
		// time.Sleep(time.Duration(rand.Intn(1000)) * time.Millisecond)
		fmt.Println("\t\t\tWrite ", i)
	}

}

Execute this with:

$> rm -f log; go run parallel_rw.go

Writes and Reads occur in parallel, but if Read is called without any new data, io.EOF is returned. If no data is written for a long time, it becomes a spin loop.

With MAX set to 10, the output of a particular run looks like:

                        Error:  EOF
            Write  0
Read  0
Read  1
            Write  1
                        Error:  EOF
            Write  2
Read  2
            Write  3
Read  3
            Write  4
Read  4
            Write  5
Read  5
            Write  6
Read  6
            Write  7
Read  7
            Write  8
Read  8
            Write  9
Read  9