PHP：为什么msg_receive（）收到错误的类型？

Question

我使用以下代码在PHP中测试msg队列。

<?php

$mq = msg_get_queue(3141592653589793238);

while (true)
{
    $msg_type = null;
    $msg = null;
    $max_msg_size = 32;

    msg_receive($mq, 1, $msg_type, $max_msg_size, $msg);
    print "receive: $msg ($msg_type)\n";
}

?>

根据手册，如果需要的类型（此处，= 1）为正，则接收的类型应与所需类型相同。但是当我运行代码时，输​​出如下所示。此外，它是非阻塞的，并且在之前没有发送任何内容时继续接收空消息。

receive:  (0)
receive:  (0)
receive:  (0)
receive:  (0)
receive:  (0)
receive:  (0)
receive:  (0)
receive:  (0)
receive:  (0)
receive:  (0)
receive:  (0)

那么这里有什么问题？