114 lines
2.3 KiB
Go
114 lines
2.3 KiB
Go
// Copyright 2013 Gary Burd
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//
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// Licensed under the Apache License, Version 2.0 (the "License"): you may
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// not use this file except in compliance with the License. You may obtain
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// 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, WITHOUT
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// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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// License for the specific language governing permissions and limitations
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// under the License.
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package redis_test
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import (
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"fmt"
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"github.com/garyburd/redigo/redis"
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)
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// zpop pops a value from the ZSET key using WATCH/MULTI/EXEC commands.
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func zpop(c redis.Conn, key string) (result string, err error) {
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defer func() {
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// Return connection to normal state on error.
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if err != nil {
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c.Do("DISCARD")
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}
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}()
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// Loop until transaction is successful.
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for {
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if _, err := c.Do("WATCH", key); err != nil {
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return "", err
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}
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members, err := redis.Strings(c.Do("ZRANGE", key, 0, 0))
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if err != nil {
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return "", err
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}
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if len(members) != 1 {
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return "", redis.ErrNil
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}
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c.Send("MULTI")
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c.Send("ZREM", key, members[0])
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queued, err := c.Do("EXEC")
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if err != nil {
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return "", err
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}
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if queued != nil {
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result = members[0]
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break
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}
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}
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return result, nil
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}
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// zpopScript pops a value from a ZSET.
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var zpopScript = redis.NewScript(1, `
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local r = redis.call('ZRANGE', KEYS[1], 0, 0)
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if r ~= nil then
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r = r[1]
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redis.call('ZREM', KEYS[1], r)
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end
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return r
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`)
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// This example implements ZPOP as described at
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// http://redis.io/topics/transactions using WATCH/MULTI/EXEC and scripting.
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func Example_zpop() {
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c, err := dial()
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if err != nil {
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fmt.Println(err)
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return
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}
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defer c.Close()
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// Add test data using a pipeline.
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for i, member := range []string{"red", "blue", "green"} {
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c.Send("ZADD", "zset", i, member)
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}
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if _, err := c.Do(""); err != nil {
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fmt.Println(err)
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return
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}
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// Pop using WATCH/MULTI/EXEC
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v, err := zpop(c, "zset")
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if err != nil {
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fmt.Println(err)
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return
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}
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fmt.Println(v)
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// Pop using a script.
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v, err = redis.String(zpopScript.Do(c, "zset"))
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if err != nil {
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fmt.Println(err)
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return
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}
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fmt.Println(v)
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// Output:
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// red
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// blue
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}
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