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