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example_zpop_test.go
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example_zpop_test.go
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// Copyright 2013 Gary Burd
//
// 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 redis_test
import (
"context"
"fmt"
"github.com/weiwenchen2022/go-redis"
)
// zpop pops a value from the ZSET key using WATCH/MULTI/EXEC commands.
func zpop(ctx context.Context, rdb *redis.Client, key string) (result string, err error) {
// Loop until transaction is successful.
for {
err = rdb.Watch(ctx, func(tx *redis.Tx) error {
members, err := tx.Do(ctx, "ZRANGE", key, 0, 0).Strings()
if err != nil {
return err
}
if len(members) != 1 {
return redis.ErrNil
}
_, err = tx.TxPipelined(ctx, func(pipe redis.Pipeliner) error {
pipe.Send("ZREM", key, members[0])
return nil
})
if err == nil {
result = members[0]
}
return err
}, key)
switch err {
default:
// Return any other error.
return "", err
case nil:
// Success.
return result, nil
case redis.TxFailedErr:
// Optimistic lock lost. Retry.
}
}
}
// zpopScript pops a value from a ZSET.
var zpopScript = redis.NewScript(`
local r = redis.call('ZRANGE', KEYS[1], 0, 0)
if r ~= nil then
r = r[1]
redis.call('ZREM', KEYS[1], r)
end
return r
`)
// This example implements ZPOP as described at
// http://redis.io/topics/transactions using WATCH/MULTI/EXEC and scripting.
func Example_zpop() {
var (
ctx = context.Background()
rdb = redis.NewClient(&redis.Options{
Addr: "localhost:6379",
})
)
// Add test data using a pipeline.
if _, err := rdb.Pipelined(ctx, func(pipe redis.Pipeliner) error {
for i, member := range []string{"red", "blue", "green"} {
pipe.Send("ZADD", "zset", i, member)
}
return nil
}); err != nil {
panic(err)
}
// Pop using WATCH/MULTI/EXEC
v, err := zpop(ctx, rdb, "zset")
if err != nil {
panic(err)
}
fmt.Println(v)
// Pop using a script.
v, err = zpopScript.Run(ctx, rdb, []string{"zset"}).String()
if err != nil {
panic(err)
}
fmt.Println(v)
// Output:
// red
// blue
}