rabbitmq 延迟队列的实现（PHP）http://blog.yuhai.win

参考文献：
1、https://wenku.baidu.com/view/0108202e3b3567ec102d8ab0.html

实现原理：
1、rabbitmq 可以针对 Queue和Message 设置  x-message-ttl 来控制消息的生存时间，如果超时，消息变为  dead letter
2、rabbitmq 的queue 可以配置 x-dead-letter-exchange 和 x-dead-letter-routing(可选)
两个参数，来控制队列出现  dead letter 的时候，重新发送消息的目的地

注意事项：
1、设置了  x-dead-letter-exchange 和 x-dead-letter-routing 后的队列是根据
队列入队的顺序进行消费，即使到了过期时间也不会触发x-dead-letter-exchange
因为过期时间是在消息出队列的时候进行判断的
2、所以当队列没有设过期时间时，插入一个没有过期时间的消息会导致 x-dead-letter-exchange 队列永远不会被消费

方案一： 对message设置TTL

1、对queue设置最大过期时间
2、对发送的每个Message 设置过期时间

优点
1、发送时可以自定义延迟时间
缺点
1、需要升级客户端，对客户端不透明
2、需要针对建立不同的延迟每个队列队列 带延迟参数的send方法容易误用，很难发现

存在问题：
如果插入一个过期时间很长的队列可能会照成队列堵住，过期了的消息不能被消费。

send.php

use PhpAmqpLib\Connection\AMQPStreamConnection;
use PhpAmqpLib\Message\AMQPMessage;
use PhpAmqpLib\Wire\AMQPTable;

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

$channel->exchange_declare('delay_exchange', 'direct',false,false,false);
$channel->exchange_declare('cache_exchange', 'direct',false,false,false);

$tale = new AMQPTable();
$tale->set('x-dead-letter-exchange', 'delay_exchange');
$tale->set('x-dead-letter-routing-key','delay_exchange');
$tale->set('x-message-ttl',10000);

$channel->queue_declare('cache_queue',false,true,false,false,false,$tale);
$channel->queue_bind('cache_queue', 'cache_exchange','cache_exchange');

$channel->queue_declare('delay_queue',false,true,false,false,false);
$channel->queue_bind('delay_queue', 'delay_exchange','delay_exchange');

$msg = new AMQPMessage('Hello World'.$argv[1],array(
'expiration' => intval($argv[1]),
'delivery_mode' => AMQPMessage::DELIVERY_MODE_PERSISTENT

));

$channel->basic_publish($msg,'cache_exchange','cache_exchange');
echo date('Y-m-d H:i:s')." [x] Sent 'Hello World!' ".PHP_EOL;

$channel->close();
$connection->close();

receive.php

use PhpAmqpLib\Connection\AMQPStreamConnection;
use PhpAmqpLib\Wire\AMQPTable;
$connection = new AMQPStreamConnection('127.0.0.1', 5672, 'guest', 'guest');
$channel = $connection->channel();

$channel->exchange_declare('delay_exchange', 'direct',false,false,false);
$channel->exchange_declare('cache_exchange', 'direct',false,false,false);

$channel->queue_declare('delay_queue',false,true,false,false,false);
$channel->queue_bind('delay_queue', 'delay_exchange','delay_exchange');

echo ' [*] Waiting for message. To exit press CTRL+C '.PHP_EOL;

$callback = function ($msg){
echo date('Y-m-d H:i:s')." [x] Received",$msg->body,PHP_EOL;

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

};

//只有consumer已经处理并确认了上一条message时queue才分派新的message给它
$channel->basic_qos(null, 1, null);
$channel->basic_consume('delay_queue','',false,false,false,false,$callback);

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

方案二 对queque 设置过期时间

优点：
1、维护简单
2、客户端完全透明
3、针对建立一个延迟队每个延迟时间列
缺点：
1、发送方无法自定义延迟时间
2、延迟时间在建Queue时确定，修改不便 修改延迟时间需要在MQ集群重新进行配置

send.php

use PhpAmqpLib\Connection\AMQPStreamConnection;
use PhpAmqpLib\Message\AMQPMessage;
use PhpAmqpLib\Wire\AMQPTable;

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

if (isset($argv[1])){
$expiration =  intval($argv[1]);
}else{
$expiration = 1000;
}

$cache_exchange_name = 'cache_exchange'.$expiration;
$cache_queue_name = 'cache_queue'.$expiration;

$channel->exchange_declare('delay_exchange', 'direct',false,false,false);
$channel->exchange_declare($cache_exchange_name, 'direct',false,false,false);

$tale = new AMQPTable();
$tale->set('x-dead-letter-exchange', 'delay_exchange');
$tale->set('x-dead-letter-routing-key','delay_exchange');
$tale->set('x-message-ttl',$expiration);
$channel->queue_declare($cache_queue_name,false,true,false,false,false,$tale);
$channel->queue_bind($cache_queue_name, $cache_exchange_name,'');

$channel->queue_declare('delay_queue',false,true,false,false,false);
$channel->queue_bind('delay_queue', 'delay_exchange','delay_exchange');

$msg = new AMQPMessage('Hello World'.$argv[1],array(
'delivery_mode' => AMQPMessage::DELIVERY_MODE_PERSISTENT,
));

$channel->basic_publish($msg,$cache_exchange_name,'');
echo date('Y-m-d H:i:s')." [x] Sent 'Hello World!' ".PHP_EOL;

$channel->close();
$connection->close();

receive.php

use PhpAmqpLib\Connection\AMQPStreamConnection;
use PhpAmqpLib\Wire\AMQPTable;
$connection = new AMQPStreamConnection('127.0.0.1', 5672, 'guest', 'guest');
$channel = $connection->channel();

$channel->exchange_declare('delay_exchange', 'direct',false,false,false);
$channel->exchange_declare('cache_exchange', 'direct',false,false,false);

$channel->queue_declare('delay_queue',false,true,false,false,false);
$channel->queue_bind('delay_queue', 'delay_exchange','delay_exchange');

echo ' [*] Waiting for message. To exit press CTRL+C '.PHP_EOL;

$callback = function ($msg){
echo date('Y-m-d H:i:s')." [x] Received",$msg->body,PHP_EOL;

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

};

//只有consumer已经处理并确认了上一条message时queue才分派新的message给它
$channel->basic_qos(null, 1, null);
$channel->basic_consume('delay_queue','',false,false,false,false,$callback);

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