add retry func for reconciler (#1008)

* add retry func for reconciler

* run update_deps.sh properly

* review comments

* review comments

Gopkg.lock

@@ -1393,6 +1393,7 @@
     "k8s.io/api/admissionregistration/v1beta1",
     "k8s.io/api/apps/v1",
     "k8s.io/api/authentication/v1",
+    "k8s.io/api/autoscaling/v1",
     "k8s.io/api/autoscaling/v2beta1",
     "k8s.io/api/batch/v1",
     "k8s.io/api/core/v1",
@@ -1449,6 +1450,7 @@
     "k8s.io/client-go/tools/clientcmd",
     "k8s.io/client-go/tools/metrics",
     "k8s.io/client-go/tools/record",
+    "k8s.io/client-go/util/retry",
     "k8s.io/client-go/util/workqueue",
     "k8s.io/code-generator/cmd/client-gen",
     "k8s.io/code-generator/cmd/client-gen/generators/util",

reconciler/retry.go

@@ -0,0 +1,28 @@
+/*
+Copyright 2020 The Knative Authors
+Licensed under the Apache License, Veroute.on 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+    http://www.apache.org/licenses/LICENSE-2.0
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+package reconciler
+
+import (
+	"k8s.io/client-go/util/retry"
+)
+
+// RetryUpdateConflicts retries the inner function if it returns conflict errors.
+// This can be used to retry status updates without constantly reenqueuing keys.
+func RetryUpdateConflicts(updater func(int) error) error {
+	attempts := 0
+	return retry.RetryOnConflict(retry.DefaultRetry, func() error {
+		err := updater(attempts)
+		attempts++
+		return err
+	})
+}

reconciler/retry_test.go

@@ -0,0 +1,77 @@
+/*
+Copyright 2020 The Knative Authors
+Licensed under the Apache License, Veroute.on 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+    http://www.apache.org/licenses/LICENSE-2.0
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package reconciler
+
+import (
+	"errors"
+	"testing"
+
+	apierrs "k8s.io/apimachinery/pkg/api/errors"
+
+	v1 "k8s.io/api/autoscaling/v1"
+)
+
+func TestRetryUpdateConflicts(t *testing.T) {
+	errAny := errors.New("foo")
+	errConflict := apierrs.NewConflict(v1.Resource("foo"), "bar", errAny)
+
+	tests := []struct {
+		name         string
+		returns      []error
+		want         error
+		wantAttempts int
+	}{{
+		name:         "all good",
+		returns:      []error{nil},
+		want:         nil,
+		wantAttempts: 1,
+	}, {
+		name:         "not retry on non-conflict error",
+		returns:      []error{errAny},
+		want:         errAny,
+		wantAttempts: 1,
+	}, {
+		name:         "retry up to 5 times on conflicts",
+		returns:      []error{errConflict, errConflict, errConflict, errConflict, errConflict, errConflict},
+		want:         errConflict,
+		wantAttempts: 5,
+	}, {
+		name:         "eventually succeed",
+		returns:      []error{errConflict, errConflict, nil},
+		want:         nil,
+		wantAttempts: 3,
+	}, {
+		name:         "eventually fail",
+		returns:      []error{errConflict, errConflict, errAny},
+		want:         errAny,
+		wantAttempts: 3,
+	}}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			attempts := 0
+			got := RetryUpdateConflicts(func(i int) error {
+				attempts++
+				return test.returns[i]
+			})
+
+			if got != test.want {
+				t.Errorf("RetryUpdateConflicts() = %v, want %v", got, test.want)
+			}
+			if attempts != test.wantAttempts {
+				t.Errorf("attempts = %d, want %d", attempts, test.wantAttempts)
+			}
+		})
+	}
+}