Async helper function for Go.

async.go

// Released under MIT License

package main

import "sync"

// asyncFn is a function that can be run asychronously by
// async.
type asyncFn func() error

// async runs many functions at the same time.
// Returns the last not-nil error.
func async(fns ...asyncFn) error {
	var errLock sync.Mutex // protects errResult
	var errResult error
	var wg sync.WaitGroup
	wg.Add(len(fns))
	for i := range fns {
		go func(i int) {
			defer wg.Done()
			if err := fns[i](); err != nil {
				errLock.Lock()
				errResult = err
				errLock.Unlock()
			}
		}(i)
	}
	wg.Wait()
	if errResult != nil {
		return errResult
	}
	return nil
}

I have an errutil.ExecParallel function that is similar, but it relies on errutil.Slice, which can turn a []error into a Multierror. This way you capture all the errors, not just the first.