go.etcd.io/etcd@v3.3.27+incompatible/clientv3/concurrency/example_stm_test.go (about)

     1  // Copyright 2017 The etcd Authors
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package concurrency_test
    16  
    17  import (
    18  	"context"
    19  	"fmt"
    20  	"log"
    21  	"math/rand"
    22  	"sync"
    23  
    24  	"github.com/coreos/etcd/clientv3"
    25  	"github.com/coreos/etcd/clientv3/concurrency"
    26  )
    27  
    28  // ExampleSTM_apply shows how to use STM with a transactional
    29  // transfer between balances.
    30  func ExampleSTM_apply() {
    31  	cli, err := clientv3.New(clientv3.Config{Endpoints: endpoints})
    32  	if err != nil {
    33  		log.Fatal(err)
    34  	}
    35  	defer cli.Close()
    36  
    37  	// set up "accounts"
    38  	totalAccounts := 5
    39  	for i := 0; i < totalAccounts; i++ {
    40  		k := fmt.Sprintf("accts/%d", i)
    41  		if _, err = cli.Put(context.TODO(), k, "100"); err != nil {
    42  			log.Fatal(err)
    43  		}
    44  	}
    45  
    46  	exchange := func(stm concurrency.STM) error {
    47  		from, to := rand.Intn(totalAccounts), rand.Intn(totalAccounts)
    48  		if from == to {
    49  			// nothing to do
    50  			return nil
    51  		}
    52  		// read values
    53  		fromK, toK := fmt.Sprintf("accts/%d", from), fmt.Sprintf("accts/%d", to)
    54  		fromV, toV := stm.Get(fromK), stm.Get(toK)
    55  		fromInt, toInt := 0, 0
    56  		fmt.Sscanf(fromV, "%d", &fromInt)
    57  		fmt.Sscanf(toV, "%d", &toInt)
    58  
    59  		// transfer amount
    60  		xfer := fromInt / 2
    61  		fromInt, toInt = fromInt-xfer, toInt+xfer
    62  
    63  		// write back
    64  		stm.Put(fromK, fmt.Sprintf("%d", fromInt))
    65  		stm.Put(toK, fmt.Sprintf("%d", toInt))
    66  		return nil
    67  	}
    68  
    69  	// concurrently exchange values between accounts
    70  	var wg sync.WaitGroup
    71  	wg.Add(10)
    72  	for i := 0; i < 10; i++ {
    73  		go func() {
    74  			defer wg.Done()
    75  			if _, serr := concurrency.NewSTM(cli, exchange); serr != nil {
    76  				log.Fatal(serr)
    77  			}
    78  		}()
    79  	}
    80  	wg.Wait()
    81  
    82  	// confirm account sum matches sum from beginning.
    83  	sum := 0
    84  	accts, err := cli.Get(context.TODO(), "accts/", clientv3.WithPrefix())
    85  	if err != nil {
    86  		log.Fatal(err)
    87  	}
    88  	for _, kv := range accts.Kvs {
    89  		v := 0
    90  		fmt.Sscanf(string(kv.Value), "%d", &v)
    91  		sum += v
    92  	}
    93  
    94  	fmt.Println("account sum is", sum)
    95  	// Output:
    96  	// account sum is 500
    97  }