You are dealing in double digit nano differences on an IO call - it makes no
difference. Use whichever code is easier to work with and understand.
> On May 30, 2020, at 4:45 AM, amarjeetanandsi...@gmail.com wrote:
>
>
> Hi
>
> I have a db package, which needs to return a slice of struct(of user,order
> etc type).
> In the user pkg, I want the slice of user. To achieve this, I have tried 4
> ways, As shown below.
>
>
> Attempt 1: Create a callback func using reflection
>
> create the user obj & callBack func using reflection & call the callback func
> with new doc as parameter. This way looks clean to use in user pkg but using
> reflection is costly. (please see the benchmark @ bottom of this mail)
> package db
>
> func QueryResults_CallBack_ReflectionFunc(callBackFuncI interface{}) error {
> defer client.Close()
>
> funcType := reflect.TypeOf(callBackFuncI)
> docType := funcType.In(0).Elem()
> callBackFunc := reflect.ValueOf(callBackFuncI)
> arg := make([]reflect.Value, 1)
>
> doc := reflect.New(docType)
> for client.HasMore() {
> if err := client.ReadDocument(doc.Interface()); err != nil {
> return err
> }
> arg[0] = doc
> callBackFunc.Call(arg)
> }
>
> return nil
> }
>
>
> and at the user pkg side just pass a call back function like...
> package user
>
> func GetUsers_CallBack_ReflectionFunc() []User {
> users := make([]User, 0, 5)
> db.QueryResults_CallBack_ReflectionFunc(func(user *User) {
> users = append(users, *user)
> })
> return users
> }
>
>
>
>
> Attempt 2: Pass the callback func & user object
>
> Pass the callback func & user object from user to db pkg, so that, the db
> pkg doesn't have to create one using reflection, thus saving cost of using
> reflection
> package db
>
> func QueryResults_CallBack_ObjNFunc(doc interface{}, callBackFunc
> func(interface{})) error {
> defer client.Close()
>
> for client.HasMore() {
> if err := client.ReadDocument(doc); err != nil {
> return err
> }
> callBackFunc(doc)
> }
> return nil
> }
>
>
>
> and in user package it can be used as -
> package user
>
> func GetUsers_CallBack_ObjNFunc() []User {
> users := make([]User, 0, 5)
> db.QueryResults_CallBack_ObjNFunc(&User{}, func(userI interface{}) {
> u := userI.(*User)
> users = append(users, *u)
> })
> return users
> }
>
>
> Attempt 3: Pass the db client in a callback func
> package db
>
> func QueryResults_CallBack_DBClient(callBackFunc func(DbClient) error) error {
> defer client.Close()
>
> for client.HasMore() {
> if err := callBackFunc(client); err != nil {
> return err
> }
> }
> return nil
> }
>
>
> and in user pkg, it can be used as -
> package user
>
> func GetUsers_CallBack_DBClient() []User {
> users := make([]User, 0, 5)
> db.QueryResults_CallBack_DBClient(func(client db.DbClient) error {
> user := User{}
> if err := client.ReadDocument(&user); err != nil {
> return err
> }
> users = append(users, user)
> return nil
> })
>
> return users
> }
>
>
>
>
> Attempt 4: Expose the db client
>
> package db
>
> func QueryResults_ExposeClient() DbClient {
> return client
> }
>
>
> and in user package, handle the read document logic like...
> package user
>
> func GetUsers_ExposeClient() []User {
> users := make([]User, 0, 5)
>
> client := db.QueryResults_ExposeClient()
> for client.HasMore() {
> user := User{}
> client.ReadDocument(&user)
> users = append(users, user)
> }
> client.Close() // responsibility of caller to close the client
>
> return users
> }
>
>
> Benchmark
> ~/go/src/testReflection master* 5s ❯ go test ./user -cpuprofile cpu.prof
> -memprofile mem.prof -bench='BenchmarkGetUser*' -run=^a -benchmem
>
> BenchmarkGetUsers_CallBackReflectionFunc-12 4426987 263
> ns/op 432 B/op 4 allocs/op
>
> BenchmarkGetUsers_CallBack_ObjNFunc-12 6293131 186
> ns/op 384 B/op 2 allocs/op
>
> BenchmarkGetUsers_CallBackClient-12 7858377 147
> ns/op 320 B/op 1 allocs/op
>
> BenchmarkGetUsers_ExposeClient-12 10273468 106
> ns/op 320 B/op 1 allocs/op
>
>
>
> PProf svg
> https://raw.githubusercontent.com/amarjeetanandsingh/go_reflection_test/master/pprof_cpu.svg
> https://raw.githubusercontent.com/amarjeetanandsingh/go_reflection_test/master/pprof_mem.svg
>
>
> Source Code
> You can find the code at
> https://github.com/amarjeetanandsingh/go_reflection_test
>
>
>
> Based on the performance which approach would you suggest?
> Or any optimisation you can suggest for CallBack_ReflectionFunc()?
> Or maybe you can purpose a better way?
>
>
>
>
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