mirror of
https://github.com/etcd-io/etcd.git
synced 2024-09-27 06:25:44 +00:00
81 lines
2.2 KiB
Go
81 lines
2.2 KiB
Go
// Copyright 2016 The etcd Authors
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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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"context"
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"fmt"
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v3 "go.etcd.io/etcd/clientv3"
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"go.etcd.io/etcd/mvcc/mvccpb"
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)
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// PriorityQueue implements a multi-reader, multi-writer distributed queue.
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type PriorityQueue struct {
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client *v3.Client
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ctx context.Context
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key string
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}
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// NewPriorityQueue creates an etcd priority queue.
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func NewPriorityQueue(client *v3.Client, key string) *PriorityQueue {
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return &PriorityQueue{client, context.TODO(), key + "/"}
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}
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// Enqueue puts a value into a queue with a given priority.
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func (q *PriorityQueue) Enqueue(val string, pr uint16) error {
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prefix := fmt.Sprintf("%s%05d", q.key, pr)
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_, err := newSequentialKV(q.client, prefix, val)
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return err
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}
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// Dequeue returns Enqueue()'d items in FIFO order. If the
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// queue is empty, Dequeue blocks until items are available.
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func (q *PriorityQueue) 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.key, v3.WithFirstKey()...)
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if err != nil {
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return "", err
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}
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kv, err := claimFirstKey(q.client, resp.Kvs)
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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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} 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 to dequeue; wait on items
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ev, err := WaitPrefixEvents(
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q.client,
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q.key,
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resp.Header.Revision,
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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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ok, err := deleteRevKey(q.client, string(ev.Kv.Key), ev.Kv.ModRevision)
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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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