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main.go
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main.go
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/*
* Copyright (c) 2008-2023, Hazelcast, Inc. All Rights Reserved.
*
* 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 main
import (
"context"
"fmt"
"log"
"math/rand"
"sync"
"time"
"github.com/hazelcast/hazelcast-go-client"
)
// lockAndIncrement locks the given key, reads the value from it and sets back the incremented value.
func lockAndIncrement(myMap *hazelcast.Map, key string, wg *sync.WaitGroup) {
// Signal completion before this goroutine exits.
defer wg.Done()
intValue := int64(0)
// Create a new unique lock context.
lockCtx := hazelcast.NewLockContext(context.Background())
// Lock the key.
// The key cannot be unlocked without the same lock context.
if err := myMap.Lock(lockCtx, key); err != nil {
panic(err)
}
// Remember to unlock the key, otherwise it won't be accessible elsewhere.
defer myMap.Unlock(lockCtx, key)
// The same lock context, or a derived one from that lock context must be used,
// otherwise the Get operation below will block.
v, err := myMap.Get(lockCtx, key)
if err != nil {
panic(err)
}
// If v is not nil, then there's already a value for the key.
if v != nil {
intValue = v.(int64)
}
// Increment and set the value back.
intValue++
// The same lock context, or a derived one from that lock context must be used,
// otherwise the Set operation below will block.
if err = myMap.Set(lockCtx, key, intValue); err != nil {
panic(err)
}
}
func main() {
const goroutineCount = 100
const key = "counter"
// Start the client with defaults
ctx := context.TODO()
client, err := hazelcast.StartNewClient(ctx)
if err != nil {
log.Fatal(err)
}
// Get a random map.
rand.Seed(time.Now().Unix())
mapName := fmt.Sprintf("sample-%d", rand.Int())
myMap, err := client.GetMap(ctx, mapName)
if err != nil {
log.Fatal(err)
}
// Lock and increment the value stored in key for goroutineCount times.
wg := &sync.WaitGroup{}
wg.Add(goroutineCount)
for i := 0; i < goroutineCount; i++ {
go lockAndIncrement(myMap, key, wg)
}
// Wait for all goroutines to complete.
wg.Wait()
// Retrieve the final value.
// A lock context is not needed, since the key is unlocked.
if lastValue, err := myMap.Get(context.Background(), key); err != nil {
panic(err)
} else {
fmt.Println("lastValue", lastValue)
}
// Shutdown client
client.Shutdown(ctx)
}