semgroup 
semgroup provides synchronization and error propagation, for groups of goroutines working on subtasks of a common task. It uses a weighted semaphore implementation to make sure that only a number of maximum tasks can be run at any time.
Unlike golang.org/x/sync/errgroup, it doesn't return the first non-nil error, rather it accumulates all errors and returns a set of errors, allowing each task to fullfil their task.
Install
go get github.com/fatih/semgroupExample
With no errors:
package main
import (
"context"
"fmt"
"github.com/fatih/semgroup"
)
func main() {
const maxWorkers = 2
s := semgroup.NewGroup(context.Background(), maxWorkers)
visitors := []int{5, 2, 10, 8, 9, 3, 1}
for _, v := range visitors {
v := v
s.Go(func() error {
fmt.Println("Visits: ", v)
return nil
})
}
// Wait for all visits to complete. Any errors are accumulated.
if err := s.Wait(); err != nil {
fmt.Println(err)
}
// Output:
// Visits: 2
// Visits: 10
// Visits: 8
// Visits: 9
// Visits: 3
// Visits: 1
// Visits: 5
}With errors:
package main
import (
"context"
"errors"
"fmt"
"github.com/fatih/semgroup"
)
func main() {
const maxWorkers = 2
s := semgroup.NewGroup(context.Background(), maxWorkers)
visitors := []int{1, 1, 1, 1, 2, 2, 1, 1, 2}
for _, v := range visitors {
v := v
s.Go(func() error {
if v != 1 {
return errors.New("only one visitor is allowed")
}
return nil
})
}
// Wait for all visits to complete. Any errors are accumulated.
if err := s.Wait(); err != nil {
fmt.Println(err)
}
// Output:
// 3 error(s) occurred:
// * only one visitor is allowed
// * only one visitor is allowed
// * only one visitor is allowed
}