forked from restic/restic
/
parallel.go
71 lines (57 loc) · 1.25 KB
/
parallel.go
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package repository
import (
"sync"
"github.com/restic/restic/backend"
)
func closeIfOpen(ch chan struct{}) {
// only close ch when it is not already closed, in which the case statement runs.
select {
case <-ch:
return
default:
close(ch)
}
}
// ParallelWorkFunc gets one file ID to work on. If an error is returned,
// processing stops. If done is closed, the function should return.
type ParallelWorkFunc func(id string, done <-chan struct{}) error
// FilesInParallel runs n workers of f in parallel, on the IDs that
// repo.List(t) yield. If f returns an error, the process is aborted and the
// first error is returned.
func FilesInParallel(repo backend.Lister, t backend.Type, n uint, f ParallelWorkFunc) error {
done := make(chan struct{})
defer closeIfOpen(done)
wg := &sync.WaitGroup{}
ch := repo.List(t, done)
errors := make(chan error, n)
for i := 0; uint(i) < n; i++ {
wg.Add(1)
go func() {
defer wg.Done()
for {
select {
case id, ok := <-ch:
if !ok {
return
}
err := f(id, done)
if err != nil {
closeIfOpen(done)
errors <- err
return
}
case <-done:
return
}
}
}()
}
wg.Wait()
select {
case err := <-errors:
return err
default:
break
}
return nil
}