mirror of
https://github.com/etcd-io/etcd.git
synced 2024-09-27 06:25:44 +00:00
98 lines
2.4 KiB
Go
98 lines
2.4 KiB
Go
// Copyright 2017 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 concurrency_test
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import (
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"context"
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"fmt"
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"log"
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"math/rand"
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"sync"
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"github.com/coreos/etcd/clientv3"
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"github.com/coreos/etcd/clientv3/concurrency"
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)
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// ExampleSTM_apply shows how to use STM with a transactional
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// transfer between balances.
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func ExampleSTM_apply() {
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cli, err := clientv3.New(clientv3.Config{Endpoints: endpoints})
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if err != nil {
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log.Fatal(err)
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}
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defer cli.Close()
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// set up "accounts"
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totalAccounts := 5
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for i := 0; i < totalAccounts; i++ {
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k := fmt.Sprintf("accts/%d", i)
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if _, err = cli.Put(context.TODO(), k, "100"); err != nil {
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log.Fatal(err)
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}
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}
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exchange := func(stm concurrency.STM) error {
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from, to := rand.Intn(totalAccounts), rand.Intn(totalAccounts)
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if from == to {
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// nothing to do
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return nil
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}
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// read values
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fromK, toK := fmt.Sprintf("accts/%d", from), fmt.Sprintf("accts/%d", to)
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fromV, toV := stm.Get(fromK), stm.Get(toK)
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fromInt, toInt := 0, 0
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fmt.Sscanf(fromV, "%d", &fromInt)
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fmt.Sscanf(toV, "%d", &toInt)
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// transfer amount
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xfer := fromInt / 2
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fromInt, toInt = fromInt-xfer, toInt+xfer
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// write back
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stm.Put(fromK, fmt.Sprintf("%d", fromInt))
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stm.Put(toK, fmt.Sprintf("%d", toInt))
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return nil
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}
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// concurrently exchange values between accounts
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var wg sync.WaitGroup
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wg.Add(10)
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for i := 0; i < 10; i++ {
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go func() {
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defer wg.Done()
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if _, serr := concurrency.NewSTM(cli, exchange); serr != nil {
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log.Fatal(serr)
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}
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}()
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}
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wg.Wait()
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// confirm account sum matches sum from beginning.
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sum := 0
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accts, err := cli.Get(context.TODO(), "accts/", clientv3.WithPrefix())
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if err != nil {
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log.Fatal(err)
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}
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for _, kv := range accts.Kvs {
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v := 0
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fmt.Sscanf(string(kv.Value), "%d", &v)
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sum += v
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}
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fmt.Println("account sum is", sum)
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// Output:
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// account sum is 500
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}
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