RabbitMq初探——消息确认

消息确认机制

前言

消息队列的下游，业务逻辑可能复杂，处理任务可能花费很长时间。若在一条消息到达它的下游，任务刚处理了一半，由于不确定因素，下游的任务处理进程

被kill掉啦，导致任务无法执行完成。而沿用我们前面几章的消息删除【消息一旦抛给下游，就立马从队列删除】，这可能会引发问题——消息没有处理完，但是队列

里的消息已经被删除了。

因此，rabbitmq内含消息确认机制【Message acknowledgment】，简称ack。rabbitmq将消息发送给consumer，此刻消息不会从队列删除，consumer消费完毕消息后，

给rabbitmq发送一条ack，在rabbitmq收到ack后，才从队列里删除。

代码

在consumer层的代码，需要修改两步。

一、添加ack代码

$msg->delivery_info['channel']->basic_ack($msg->delivery_info['delivery_tag']);

二、开启消息确认机制

$channel->basic_consume('task_queue', '', false, false, false, false, $callback); //basic_consume第四个参数置成false，no_ack=false

整体代码见下

生产者sender.php

<?php
/**
 * sender.php
 * Created by PhpStorm.
 * User: wangdaxi
 * Date: 2017/10/18
 * Time: 14:26
 */
require_once __DIR__ . '/vendor/autoload.php';
use PhpAmqpLib\Connection\AMQPStreamConnection;
use PhpAmqpLib\Message\AMQPMessage;

$connection = new AMQPStreamConnection('127.0.0.1', 5672, 'guest', 'guest');
$channel = $connection->channel();


$channel->queue_declare('hello', false, false, false, false);

$data = implode(" ", array_slice($argv, 1));
empty($data) && $data = "Hello World!";

$msg = new AMQPMessage($data);

$channel->basic_publish($msg, '', 'hello');

echo " [x] Sent '$data'\n";

//close the channel and connection;
$channel->close();
$connection->close();

消费者receive.php

<?php
/**
 * receive.php
 * Created by PhpStorm.
 * User: wangdaxi
 * Date: 2017/10/18
 * Time: 14:34
 */
require_once __DIR__ . '/vendor/autoload.php';
use PhpAmqpLib\Connection\AMQPStreamConnection;

$connection = new AMQPStreamConnection('127.0.0.1', 5672, 'guest', 'guest');
$channel = $connection->channel();

$channel->queue_declare('hello', false, false, false, false);
echo ' [*] Waiting for messages. To exit press CTRL+C', "\n";

$callback = function($msg) {
    echo "[x] Received ", $msg->body, "\n";
    sleep(substr_count($msg->body, '.'));
    echo "[x] Done\n";
    //消息确认
    $msg->delivery_info['channel']->basic_ack($msg->delivery_info['delivery_tag']);
};
$channel->basic_consume('hello', '', false, false, false, false, $callback);

while(count($channel->callbacks)) {
    $channel->wait();
}