blocks|key|2735550|text|PCNTL无法创建线程。它只“分叉”当前的PHP进程。什么意思？当您调用pcntl_fork()时，当前进程被拆分为两个进程。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2735551|一些提示：|2735552|2735553|它在默认情况下是禁用的。如果您设法启用了它，则仅为CLI启用它。永远不要将它与web服务器一起使用！它将以不确定的方式运行。它还可以使整个机器停机。请将其禁用，并且可以在进程之间读取on.|unordered-list-item|2735554|Communication，但这很可怕(通过共享内存中的序列化对象)。|2735555|文件描述符(和数据库连接)是共享的，这经常会导致问题。您必须在派生之后重新连接数据库，否则当第一个派生进程关闭时，所有派生进程都会出现类似MySQL+server+has+gone+away的错误。|BOLD|2735556|2735557|下面是from+documentation示例|2735558|<?php

$pid+=+pcntl_fork();
if+($pid+==+-1)+{
+++++die('could+not+fork');
}+else+if+($pid)+{
+++++//+we+are+the+parent
+++++pcntl_wait($status);+//Protect+against+Zombie+children
}+else+{
+++++//+we+are+the+child
}|code-block|syntax|javascript|2735559|但请记住，PHP只是一种脚本语言。它不是为并行计算而设计的。根据您的需要，同时运行CRON、消息队列或低级语言程序可以做得更好。|2735560|派生的PHP程序很难阅读，理解和调试。维护这个程序将是一场噩梦。|2735561|不要犯错，避免分叉。你不需要它。你真正需要的是异步任务运行器。好消息是，有RabbitMQ和nice+tutorial+;-)您也可以尝试使用名为Bunny的RabbitMQ库|2735562|PS:使用消息队列而不是forking会给你带来更多的好处。您可以使用多个服务器处理队列，并随着流量的增长进行水平扩展。|2735563|编辑2019-03-07|2735564|我使用过很多异步并发框架amphp，在这里我不得不提一下。如果你真的需要在单个请求中运行异步非阻塞任务，我认为amphp是目前最好的解决方案。它使用php生成器($value+=+yield+$promise)的概念来执行人类可读的代码，而无需使用类似于php的promise地狱。|2735565|https://amphp.org/|2735566|entityMap|0|LINK|mutability|MUTABLE|url|http://php.net/manual/en/function.pcntl-fork.php|1|https://www.rabbitmq.com/|2|https://www.sitepoint.com/use-rabbitmq-php/|3|https://github.com/jakubkulhan/bunny|4^0|10|C|0|0|0|0|0|R|6|1X|Q|0|0|3|I|0|0|0|0|0|11|8|1|1A|D|2|21|5|3|0|0|0|C|5|1J|5|29|N|0|0|I|4|0^^$0|@$1|2|3|4|5|6|7|1R|8|@$9|1S|A|1T|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|1U|8|@]|D|@]|E|$]]|$1|H|3|-4|5|6|7|1V|8|@]|D|@]|E|$]]|$1|I|3|J|5|K|7|1W|8|@]|D|@]|E|$]]|$1|L|3|M|5|K|7|1X|8|@]|D|@]|E|$]]|$1|N|3|O|5|K|7|1Y|8|@$9|1Z|A|20|B|P]|$9|21|A|22|B|C]]|D|@]|E|$]]|$1|Q|3|-4|5|6|7|23|8|@]|D|@]|E|$]]|$1|R|3|S|5|6|7|24|8|@]|D|@$9|25|A|26|1|27]]|E|$]]|$1|T|3|U|5|V|7|28|8|@]|D|@]|E|$W|X]]|$1|Y|3|Z|5|6|7|29|8|@]|D|@]|E|$]]|$1|10|3|11|5|6|7|2A|8|@]|D|@]|E|$]]|$1|12|3|13|5|6|7|2B|8|@]|D|@$9|2C|A|2D|1|2E]|$9|2F|A|2G|1|2H]|$9|2I|A|2J|1|2K]]|E|$]]|$1|14|3|15|5|6|7|2L|8|@]|D|@]|E|$]]|$1|16|3|17|5|6|7|2M|8|@]|D|@]|E|$]]|$1|18|3|19|5|6|7|2N|8|@$9|2O|A|2P|B|C]|$9|2Q|A|2R|B|C]|$9|2S|A|2T|B|C]]|D|@]|E|$]]|$1|1A|3|1B|5|6|7|2U|8|@]|D|@$9|2V|A|2W|1|2X]]|E|$]]|$1|1C|3|-4|5|6|7|2Y|8|@]|D|@]|E|$]]]|1D|$1E|$5|1F|1G|1H|E|$1I|1J]]|1K|$5|1F|1G|1H|E|$1I|1L]]|1M|$5|1F|1G|1H|E|$1I|1N]]|1O|$5|1F|1G|1H|E|$1I|1P]]|1Q|$5|1F|1G|1H|E|$1I|1B]]]]

PCNTL can not make threads. It only "forks" current PHP process. What does it mean? When you call <code>pcntl_fork()</code>, current process is split into two processes. Whole namespace of parent process is copied into the child and both processes continue with execution in parallel with only one difference: <code>pcntl_fork()</code> returns child's PID in parent and <code>0</code> in child.

Some hints:

<ul>
<li>It is disabled by default. If you manage to enable it, then do it for CLI only. Never ever use it with web server! It will behave in non-deterministic way. It can also bring whole machine down. Please, leave it disabled and read on.</li>
<li>Communication between processes is possible but horrible (via
serialized object in shared memory). </li>
<li>File descriptors (and database
connections) are shared, this causes problems very often. You have to reconnect your DB after forking or you will get errors like <code>MySQL server has gone away</code> from all forked processes when first of them closes the connection.</li>
<li>Parent process have to wait for children to finish or it will leave zombie
processes consuming system resources behind.</li>
</ul>

Here's example <a href="http://php.net/manual/en/function.pcntl-fork.php" rel="noreferrer">from documentation</a>:

<pre><code>&lt;?php

$pid = pcntl_fork();
if ($pid == -1) {
 die('could not fork');
} else if ($pid) {
 // we are the parent
 pcntl_wait($status); //Protect against Zombie children
} else {
 // we are the child
}
</code></pre>

But remember, PHP is just scripting language. It's not designed for parallel computing. You could do better job with simultaneously running CRONs, message queues or program in lower-level language, depending on your needs.

Forked PHP program is very hard to read, understand and debug. Maintaining that program will be a nightmare.

Don't make mistake and avoid forking. You don't need it. What you really need is asynchronous task runner. Good news, there is <a href="https://www.rabbitmq.com/" rel="noreferrer">RabbitMQ</a> and <a href="https://www.sitepoint.com/use-rabbitmq-php/" rel="noreferrer">nice tutorial</a> ;-) You can also try promising RabbitMQ library called <a href="https://github.com/jakubkulhan/bunny" rel="noreferrer">Bunny</a>

PS: Using message queues instead of forking gives you one more advantage. You can process the queue with multiple servers and scale horizontally as your traffic grows.

EDIT 2019-03-07

I have played a lot with asynchronous concurrency framework <code>amphp</code> and I have to mention it here. If you really need to run async non-blocking tasks in single request, I consider <code>amphp</code> to be the best solution today. It uses concept of php generators (<code>$value = yield $promise</code>) to execute human-readable code without reactphp-like promise hell.

<a href="https://amphp.org/" rel="noreferrer">https://amphp.org/</a>

I'm confused about <a href="http://php.net/pcntl_fork" rel="noreferrer"><code>pcntl_fork</code></a> in PHP.

I think it does multi-threading, but how does it work and how would I use it in a script?

How does pcntl_fork work in PHP?

消息队列

数据库

服务器

MySQL

我对PHP中的感到困惑。我认为它支持多线程，但是它是如何工作的，我该如何在脚本中使用它呢？

问pcntl_fork在PHP中是如何工作的？
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