如何使用videlalvaro/php-amqplib完成阻塞的basic_get调用

Question

我正在使用https://github.com/videlalvaro/php-amqplib做一些rabbitmq工作：

我正在尝试创建一个阻塞版本的basic_get (或者是一个可以重复调用的basic_consume版本，每次只能得到一个msg )，它将阻塞，直到消息就绪，如果队列中没有消息，则返回它，而不是返回null。

当我试图用basic_consume抓取一条消息时，事情变得一团糟，我最终得到了一堆“未准备好”但未确认的消息。(如果我只用这种方式抓取一条消息，它每次都可以工作，如果我试图获取两条消息，它有时会挂起，而其他消息则可以工作)

class Foo {
    ...
    private function blockingGet() {
            /*
                queue: Queue from where to get the messages
                consumer_tag: Consumer identifier
                no_local: Don't receive messages published by this consumer.
                no_ack: Tells the server if the consumer will acknowledge the messages.
                exclusive: Request exclusive consumer access, meaning only this consumer can access the queue
                nowait:
                callback: A PHP Callback
             */
            $this->ch->basic_consume($this->queueName, "consumer_".$this->consumerNum++, false, false, false, false, function($msg) {
                    $this->msgCache = json_decode($msg->body);
                    $this->ch->basic_ack($msg->delivery_info['delivery_tag']);
                    $this->ch->basic_cancel($msg->delivery_info['consumer_tag']);
            });
            while (count($this->ch->callbacks)) {
                    $this->ch->wait();
            }
            return $this->msgCache;
    }
}

$q = new Foo();
for ($i = 0; $i < 5; $i++) {
    print $q->blockingGet();
}

Answer 1

我实现了与这里类似的功能，方法是将接收到的消息保存在传递给$channel->basic_consume()回调参数的闭包中，然后在$channel->wait()调用之后处理它，因为如果接收到消息(或者设置了timeout参数并达到超时)，wait()将返回控制权。尝试如下所示：

class Foo {
    // ...
    public function __construct() {
        $this->ch->basic_consume($this->queueName, "", false, false, false, false, function($msg) {
                $this->msgCache = json_decode($msg->body);
                $this->ch->basic_ack($msg->delivery_info['delivery_tag']);
        });
    }
    // ...
    private function blockingGet() {
        $this->ch->wait();
        if ($this->msgCache) {
            $msgCache = $this->msgCache;
            $this->msgCache = null;
            return $msgCache;
        }
        return null;
    }
}

$q = new Foo();
for ($i = 0; $i < 5; $i++) {
    print $q->blockingGet();
}