Wait result of multiple goroutines

Question

I am searching a way to execute asynchronously two functions in go which returns different results and errors, wait for them to finish and print both results. Also if one of function returned error I do not want to wait for another function, and just print the error. For example, I have this functions:

func methodInt(error bool) (int, error) {
    <-time.NewTimer(time.Millisecond * 100).C
    if error {
        return 0, errors.New("Some error")
    } else {
        return 1, nil
    }
}

func methodString(error bool) (string, error) {
    <-time.NewTimer(time.Millisecond * 120).C
    if error {
        return "", errors.New("Some error")
    } else {
        return "Some result", nil
    }
}

Here https://play.golang.org/p/-8StYapmlg is how I implemented it, but it has too much code I think. It can be simplified by using interface{} but I don't want to go this way. I want something simpler as, for example, can be implemented in C# with async/await. Probably there is some library that simplifies such operation.

Answer 1

You should create two channels for errors and results, then first read errors if no erorrs then read the results, this sample should works for your use case:

package main

import (
    "errors"
    "sync"
)

func test(i int) (int, error) {
    if i > 2 {
        return 0, errors.New("test error")
    }
    return i + 5, nil
}

func test2(i int) (int, error) {
    if i > 3 {
        return 0, errors.New("test2 error")
    }
    return i + 7, nil
}

func main() {
    results := make(chan int, 2)
    errors := make(chan error, 2)
    var wg sync.WaitGroup
    wg.Add(1)
    go func() {
        defer wg.Done()
        result, err := test(3)
        if err != nil {
            errors <- err
            return
        }
        results <- result
    }()
    wg.Add(1)
    go func() {
        defer wg.Done()
        result, err := test2(3)
        if err != nil {
            errors <- err
            return
        }
        results <- result
    }()

    // here we wait in other goroutine to all jobs done and close the channels
    go func() {
        wg.Wait()
        close(results)
        close(errors)
    }()
    for err := range errors {
        // here error happend u could exit your caller function
        println(err.Error())
        return

    }
    for res := range results {
        println("--------- ", res, " ------------")
    }
}