foo := make([]Foo, someLen)
// jobs preparation... each job fills one item in []foo
if err := thread.Parallelize(
  ctx,
  jobs,
  thread.ParallelizeWithCancel(cancelGetBlobs), // if one job fails, stop all jobs
); err != nil {
  return nil, err
}
// at this point the user could assume that if no errors happened, then []foo was successfully
// populated... well, if the ctx was cancelled, some/all items in []foo might be empty/nil.
// Even if the ctx was cancelled not by an error trying to fill []foo, but upstream from
// another caller.