I have a resourceId
array which I need loop in parallel. And generate URL
for each resource and then put inside a map which is key (resourcId) and value is url.
I got below code which does the job but I am not sure if this is the right way to do it. I am using sizedwaitgroup here to parallelize the resourceId
list. And also using lock on map while writing the data to it. I am sure this isn't efficient code as using lock and then using sizedwaitgroup will have some performance problem.
What is the best and efficient way to do this? Should I use channels here? I want to control the parallelism on how much I should have instead of running length of resourceId
list. If any resourceId
url generation fails, I want to log that as an error for that resourceId
but do not disrupt other go routine running in parallel to get the url generated for other resourceId
.
For example: If there are 10 resources, and 2 fails then log error for those 2 and map should have entry for remaining 8.
// running 20 threads in parallel
swg := sizedwaitgroup.New(20)
var mutex = &sync.Mutex{}
start := time.Now()
m := make(map[string]*customerPbV1.CustomerResponse)
for _, resources := range resourcesList {
swg.Add()
go func(resources string) {
defer swg.Done()
customerUrl, err := us.GenerateUrl(clientId, resources, appConfig)
if err != nil {
errs.NewWithCausef(err, "Could not generate the url for %s", resources)
}
mutex.Lock()
m[resources] = customerUrl
mutex.Unlock()
}(resources)
}
swg.Wait()
elapsed := time.Since(start)
fmt.Println(elapsed)
Note: Above code will be called at high throughput from multiple reader threads so it needs to perform well.
CodePudding user response:
I'm not sure what sizedwaitgroup
is and it's not explained, but overall this approach doesn't look very typical of Go. For that matter, "best" is a matter of opinion, but the most typical approach in Go would be something along these lines:
func main() {
wg := new(sync.WaitGroup)
start := time.Now()
numWorkers := 20
m := make(map[string]*customerPbV1.CustomerResponse)
work := make(chan string)
results := make(chan result)
for i := 0; i < numWorkers; i {
wg.Add(1)
go worker(work, results)
}
for _, resources := range resourcesList {
work <- resources
}
close(work)
go func() {
wg.Wait()
close(results)
}()
for result := range results {
m[result.resources] = result.response
}
elapsed := time.Since(start)
fmt.Println(elapsed)
}
type result struct {
resources string
response *customerPbV1.CustomerResponse
}
func worker(ch chan string, r chan result) {
for w := range ch {
customerUrl, err := us.GenerateUrl(clientId, w, appConfig)
if err != nil {
errs.NewWithCausef(err, "Could not generate the url for %s", resources)
continue
}
r <- result{w, customerUrl}
}
}
(Though, based on the name, I would assume errs.NewWithCause
doesn't actually handle errors, but returns one, in which case the current code is dropping them on the floor, and a proper solution would have an additional chan error
for handling errors:
func main() {
wg := new(sync.WaitGroup)
start := time.Now()
numWorkers := 20
m := make(map[string]*customerPbV1.CustomerResponse)
work := make(chan string)
results := make(chan result)
errors := make(chan error)
for i := 0; i < numWorkers; i {
wg.Add(1)
go worker(work, results, errors)
}
for _, resources := range resourcesList {
work <- resources
}
close(work)
go func() {
wg.Wait()
close(results)
close(errors)
}()
go func() {
for err := range errors {
// Do something with err
}
}()
for result := range results {
m[result.resources] = result.response
}
elapsed := time.Since(start)
fmt.Println(elapsed)
}
type result struct {
resources string
response *customerPbV1.CustomerResponse
}
func worker(ch chan string, r chan result, errs chan error) {
for w := range ch {
customerUrl, err := us.GenerateUrl(clientId, w, appConfig)
if err != nil {
errs <- errs.NewWithCausef(err, "Could not generate the url for %s", resources)
continue
}
r <- result{w, customerUrl}
}
}
CodePudding user response:
Don't set map in goroutine.
I have create example code with comment. please read the comment.
note: query function will sleep in 1 second.
package main
import (
"errors"
"fmt"
"log"
"math/rand"
"runtime"
"strconv"
"sync"
"time"
)
type Result struct {
resource string
val int
err error
}
/*
CHANGE Result struct to this
result struct will collect all you need to create map
type Result struct {
resources string
customerUrl *customerPbV1.CustomerResponse
err error
}
*/
// const numWorker = 8
func main() {
now := time.Now()
rand.Seed(time.Now().UnixNano())
m := make(map[string]int)
// m := make(map[string]*customerPbV1.CustomerResponse) // CHANGE TO THIS
numWorker := runtime.NumCPU()
fmt.Println(numWorker)
chanResult := make(chan Result)
go func() {
for i := 0; i < 20; i {
/*
customerUrl, err := us.GenerateUrl(clientId, resources, appConfig)
we asume i is resources
chanResult <- Result {resource: strconv.Itoa(i)}
*/
chanResult <- Result{ // this will block until chanResult is consume in line 68
resource: strconv.Itoa(i),
}
}
close(chanResult)
}()
var wg sync.WaitGroup
cr := make(chan Result)
wg.Add(numWorker)
go func() {
wg.Wait()
close(cr) // NOTE: don't forget to close cr
}()
go func() {
for i := 0; i < numWorker; i { // this for loop will run goroutine
go func(x int) {
for job := range chanResult { // unblock chan on line 49
log.Println("worker", x, "working on", job.resource)
x, err := query(job.resource) // TODO: customerUrl, err := us.GenerateUrl(clientId, resources, appConfig)
cr <- Result{ // send to channel, will block until it consume. Consume is in MAIN goroutine "line 84"
resource: job.resource,
val: x,
err: err,
}
}
wg.Done()
}(i)
}
}()
counterTotal := 0
counterSuccess := 0
for res := range cr { // will unblock channel in line 71
if res.err != nil {
log.Printf("error found %s. stack trace: %s", res.resource, res.err)
} else {
m[res.resource] = res.val // NOTE: save to map
counterSuccess
}
counterTotal
}
log.Printf("%d/%d of total job run", counterSuccess, counterTotal)
fmt.Println("final :", m)
fmt.Println("len m", len(m))
fmt.Println(runtime.NumGoroutine())
fmt.Println(time.Since(now))
}
func query(s string) (int, error) {
time.Sleep(time.Second)
i, err := strconv.Atoi(s)
if err != nil {
return 0, err
}
if i%3 == 0 {
return 0, errors.New("i divided by 3")
}
ms := i 500 rand.Intn(500)
return ms, nil
}
playground : https://go.dev/play/p/LeyE9n1hh81