Golang: Processing 5 huge files concurrently - go

Question

I have 5 huge (4 million rows each) logfiles that I process in Perl currently and I thought I may try to implement the same in Go and its concurrent features. So, being very inexperienced in Go, I was thinking of doing as below. Any comments on the approach will be greatly appreciated.
Some rough pseudocode:
var wg1 sync.WaitGroup
var wg2 sync.WaitGroup
func processRow (r Row) {
wg2.Add(1)
defer wg2.Done()
res = <process r>
return res
}
func processFile(f File) {
wg1.Add(1)
open(newfile File)
defer wg1.Done()
line = <row from f>
result = go processRow(line)
newFile.Println(result) // Write new processed line to newFile
wg2.Wait()
newFile.Close()
}
func main() {
for each f logfile {
go processFile(f)
}
wg1.Wait()
}
So, idea is that I process these 5 files concurrently and then all rows of each file will in turn also be processed concurrently.
Will that work?

Answer 1

You should definitely use channels to manage your processed rows. Alternatively you could also write another goroutine to handle your output.
var numGoWriters = 10
func processRow(r Row, ch chan<- string) {
res := process(r)
ch <- res
}
func writeRow(f File, ch <-chan string) {
w := bufio.NewWriter(f)
for s := range ch {
_, err := w.WriteString(s + "\n")
}
func processFile(f File) {
outFile, err := os.Create("/path/to/file.out")
if err != nil {
// handle it
}
defer outFile.Close()
var wg sync.WaitGroup
ch := make(chan string, 10) // play with this number for performance
defer close(ch) // once we're done processing rows, we close the channel
// so our worker threads exit
fScanner := bufio.NewScanner(f)
for fScanner.Scan() {
wg.Add(1)
go func() {
processRow(fScanner.Text(), ch)
wg.Done()
}()
}
for i := 0; i < numGoWriters; i++ {
go writeRow(outFile, ch)
}
wg.Wait()
}
Here we have processRow doing all the processing (I assumed to string), writeRow doing all the out I/O, and processFile tying each file together. Then all main has to do is hand off the files, spawn the goroutines, et voila.
func main() {
var wg sync.WaitGroup
filenames := [...]string{"here", "are", "some", "log", "paths"}
for fname := range filenames {
inFile, err := os.Open(fname)
if err != nil {
// handle it
}
defer inFile.Close()
wg.Add(1)
go processFile(inFile)
}
wg.Wait()