goconcurrencygoroutine

How to handle errors and terminate Goroutine using WaitGroup


I have been playing around with Goroutines, Channels and WaitGroup today and I am finally starting to understand the concept, after just been reading about it for a while.

My problem is that I am unsure how I handle errors when working like this, mainly because of the WaitGroup I use. When using the WaitGroup, I start by adding the amount of goroutines that will be executed, but what if an error happens during one of these?

package main

import (
    "errors"
    "sync"
)

var waitGroup sync.WaitGroup

func main() {
    c := make(chan int, 10)

    waitGroup.Add(10)

    go doSomething(c)

    waitGroup.Wait()
}

func doSomething(c chan int) {
    for i := 0; i < 10; i++ {
        n, err := someFunctionThatCanError()

        if err != nil {
            // How do I end the routines and WaitGroups here?
        }

        c <- n
        waitGroup.Done()
    }

    close(c)    
}

func someFunctionThatCanError() (int, error) {
    return 1, errors.New("an error")
}

Playground: https://play.golang.org/p/ZLsBSqdMD49

I have tried my best to provide an example that shows what I am talking about. A loop will run 10 times in doSomething() and it will call waitGroup.Done() on every iteration, but what if an error happens during all this, like shown with someFunctionThatCanError()?

When I try to solve it now, by returning and/or cancelling the channel, I end up with deadlocks, so I am a little unsure where to go from here. I am also unsure of how to handel the WaitGroup that I assume is waiting for more things to happen.

Any help is really appreciated.


Solution

  • Use golang.org/x/sync/errgroup to wait on and handle errors from goroutines.

    package main
    
    import (
        "errors"
        "log"
        "sync"
    
        "golang.org/x/sync/errgroup"
    )
    
    func main() {
        c := make(chan int, 10)
    
        var g errgroup.Group
    
        g.Go(func() error {
            return doSomething(c)
        })
    
        // g.Wait waits for all goroutines to complete
        // and returns the first non-nil error returned
        // by one of the goroutines.
        if err := g.Wait(); err != nil {
            log.Fatal(err)
        }
    }
    
    func doSomething(c chan int) error {
        defer close(c)
        for i := 0; i < 10; i++ {
            n, err := someFunctionThatCanError()
            if err != nil {
                return err
            }
            c <- n
        }
        return nil
    }
    
    func someFunctionThatCanError() (int, error) {
        return 1, errors.New("an error")
    }
    

    Run it on the playground.