2016-05-13 06:51:48 +03:00
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// Copyright 2016 The etcd Authors
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2016-01-04 22:13:43 +03:00
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package recipe
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import (
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2017-09-07 00:57:25 +03:00
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"context"
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2019-05-29 00:59:02 +03:00
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v3 "go.etcd.io/etcd/clientv3"
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"go.etcd.io/etcd/mvcc/mvccpb"
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2016-01-04 22:13:43 +03:00
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)
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// Queue implements a multi-reader, multi-writer distributed queue.
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type Queue struct {
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client *v3.Client
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ctx context.Context
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2016-01-04 22:13:43 +03:00
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keyPrefix string
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}
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2016-02-21 03:07:22 +03:00
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func NewQueue(client *v3.Client, keyPrefix string) *Queue {
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2016-02-25 09:49:24 +03:00
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return &Queue{client, context.TODO(), keyPrefix}
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}
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func (q *Queue) Enqueue(val string) error {
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2016-10-27 22:02:58 +03:00
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_, err := newUniqueKV(q.client, q.keyPrefix, val)
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return err
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}
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2016-02-01 08:42:39 +03:00
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// Dequeue returns Enqueue()'d elements in FIFO order. If the
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// queue is empty, Dequeue blocks until elements are available.
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func (q *Queue) Dequeue() (string, error) {
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// TODO: fewer round trips by fetching more than one key
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resp, err := q.client.Get(q.ctx, q.keyPrefix, v3.WithFirstRev()...)
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if err != nil {
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return "", err
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}
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2016-02-25 09:49:24 +03:00
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kv, err := claimFirstKey(q.client, resp.Kvs)
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2016-01-04 22:13:43 +03:00
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if err != nil {
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return "", err
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} else if kv != nil {
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return string(kv.Value), nil
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2016-06-02 23:43:40 +03:00
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} else if resp.More {
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// missed some items, retry to read in more
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return q.Dequeue()
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}
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// nothing yet; wait on elements
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ev, err := WaitPrefixEvents(
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q.client,
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q.keyPrefix,
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resp.Header.Revision,
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2016-04-25 22:32:58 +03:00
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[]mvccpb.Event_EventType{mvccpb.PUT})
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if err != nil {
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return "", err
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}
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2016-02-25 09:49:24 +03:00
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ok, err := deleteRevKey(q.client, string(ev.Kv.Key), ev.Kv.ModRevision)
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2016-01-04 22:13:43 +03:00
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if err != nil {
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return "", err
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} else if !ok {
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return q.Dequeue()
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}
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return string(ev.Kv.Value), err
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}
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