Add utility function for errors that runs multiple functions that errors

as goroutines, blocks until they're all done executing, and combines the
results into an Aggregate error.

pkg/util/errors/errors.go

@@ -131,3 +131,20 @@ func Flatten(agg Aggregate) Aggregate {
 	}
 	return NewAggregate(result)
 }
+
+// AggregateGoroutines runs the provided functions in parallel, stuffing all
+// non-nil errors into the returned Aggregate.
+// Returns nil if all the functions complete successfully.
+func AggregateGoroutines(funcs ...func() error) Aggregate {
+	errChan := make(chan error, len(funcs))
+	for _, f := range funcs {
+		go func(f func() error) { errChan <- f() }(f)
+	}
+	errs := make([]error, 0)
+	for i := 0; i < cap(errChan); i++ {
+		if err := <-errChan; err != nil {
+			errs = append(errs, err)
+		}
+	}
+	return NewAggregate(errs)
+}

pkg/util/errors/errors_test.go

@@ -221,3 +221,66 @@ func TestFlatten(t *testing.T) {
 		}
 	}
 }
+
+func TestAggregateGoroutines(t *testing.T) {
+	testCases := []struct {
+		errs     []error
+		expected map[string]bool // can't compare directly to Aggregate due to non-deterministic ordering
+	}{
+		{
+			[]error{},
+			nil,
+		},
+		{
+			[]error{nil},
+			nil,
+		},
+		{
+			[]error{nil, nil},
+			nil,
+		},
+		{
+			[]error{fmt.Errorf("1")},
+			map[string]bool{"1": true},
+		},
+		{
+			[]error{fmt.Errorf("1"), nil},
+			map[string]bool{"1": true},
+		},
+		{
+			[]error{fmt.Errorf("1"), fmt.Errorf("267")},
+			map[string]bool{"1": true, "267": true},
+		},
+		{
+			[]error{fmt.Errorf("1"), nil, fmt.Errorf("1234")},
+			map[string]bool{"1": true, "1234": true},
+		},
+		{
+			[]error{nil, fmt.Errorf("1"), nil, fmt.Errorf("1234"), fmt.Errorf("22")},
+			map[string]bool{"1": true, "1234": true, "22": true},
+		},
+	}
+	for i, testCase := range testCases {
+		funcs := make([]func() error, len(testCase.errs))
+		for i := range testCase.errs {
+			err := testCase.errs[i]
+			funcs[i] = func() error { return err }
+		}
+		agg := AggregateGoroutines(funcs...)
+		if agg == nil {
+			if len(testCase.expected) > 0 {
+				t.Errorf("%d: expected %v, got nil", i, testCase.expected)
+			}
+			continue
+		}
+		if len(agg.Errors()) != len(testCase.expected) {
+			t.Errorf("%d: expected %d errors in aggregate, got %v", i, len(testCase.expected), agg)
+			continue
+		}
+		for _, err := range agg.Errors() {
+			if !testCase.expected[err.Error()] {
+				t.Errorf("%d: expected %v, got aggregate containing %v", i, testCase.expected, err)
+			}
+		}
+	}
+}