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I recently read about http://php.net/pcntl and was woundering how good that functions works and if it would be smart to use multithreading in PHP since it isn't a core function of PHP.
I would want to trigger events that don't require feedback through it like fireing a cronjob execution manually.
All of it is supposed to run in a web app written with Zend Framework
The pcntl package works quite fine - it just uses the according unix functions. The only shortage is that you can't use them if php is invoked from a web server context. i.e. you can use it in shell scripts, but not on web pages - at least not without using a hack like calling a forking script with exec or similar.
[edit]
I just found a page explaining why mod_php cannot fork. Basically it's a security issue.
[/edit]
This is not thread control, this is process control. The library for the threads is pthreads (POSIX threads) and it's not included in PHP, so there are no multi-threading functions in PHP.
As of multiprocessing, you cannot use that in mod_php, as that would be a giant security hole (spawned process would have all the web-server's privileges).
The only possible way to have php code executing in multiple threads is to run php as a module of a threaded web server, which is useless because threads are fully isolated and your code has no control over them. As far as i know, pcntl only manages processes, not threads.
If I needed to do manual crontab executions or the like from PHP, I'd probably use a queue. Have a database table that you append jobs to. Another process, either from a cron or running as a daemon, executes the jobs as they show up.
Another way to do it is to set up a separate script and do an HTTP GET to it. It's not quite threading, but it's one way of shelling to another command in PHP.
For example, if I wanted to run /usr/bin/somescript.sh on demand, I'd have a somescript.php that did a system call. This would be on a virtual host only accessible from localhost.
I'd do a socket call to the webserver and GET the script. The key is to not read on the socket so it doesn't block. If I wanted to check the return value of somescript.php, I'd do it later in my main script to prevent blocking.
If somescript.php takes a long time to execute (longer than the calling script), you'll have to do some magic to stop apache from killing the script when the socket is closed.
Multiplatform PHP Multithreading engine
http://anton.vedeshin.com/articles/lightweight-and-multiplatform-php-multithreading-engine
Examples of multithreading working in PHP (with excerpts from their project pages):
Cron Multi-Threaded.
As of October 25th, 2011, this module has reached "end of life" and is deprecated in favor of projects such as Elysia Cron. This module wasn't completely useless in that a core patch inspired by Cron MT was committed to D7.
Boost.
... provides static page caching for Drupal enabling a very significant performance and scalability boost for sites that receive mostly anonymous traffic. For shared hosting this is your best option in terms of improving performance. On dedicated servers, you may want to consider Varnish instead.
Guys recently I decided to go back to PHP and do some more complex stuff than a simple log in page. For 3 years I've been programming with Java/JavaEE and have a good understanding of the architecture of of Java Applications. Basically, a virtual machine ( a simple OS process ) that runs compiled code called byte code. a simple Java web server is basically a java application that listens on provided TCP port for Http requests and responds accordingly of course it is more complicated than that but this is its initial work.
Now, what about PHP ? How does it work ? What, in a nutshell, is its architecture.
I googled about this question but in 90% the articles explain how to implement and construct a web application with PHP which is not what I am looking for.
The biggest difference between a Java web server and PHP is that PHP doesn't have its own built-in web server. (Well, newer versions do, but it's supposed to be for testing only, it's not a production ready web server.) PHP itself is basically one executable which reads in a source code file of PHP code and interprets/executes the commands written in that file. That's it. That's PHP's architecture in a nutshell.
That executable supports a default API which the userland PHP code can call, and it's possible to add extensions to provide more APIs. Those extensions are typically written in C and compiled together with the PHP executable at install time. Some extensions can only be added by recompiling PHP with additional flags, others can be compiled against a PHP install and activated via a configuration file after the fact. PHP offers the PEAR and PECL side projects as an effort to standardise and ease such after-the-fact installs. Userland PHP code will often also include additional third party libraries simply written in PHP code. The advantage of C extensions is their execution speed and low-level system access, the advantage of userland code libraries is their trivial inclusion. If you're administering your own PHP install, it's often simple enough to add new PHP extensions; however on the very popular shared-host model there's often a tension between what the host wants to install and what the developer needs.
In practice a web service written in PHP runs on a third party web server, very often Apache, which handles any incoming requests and invokes the PHP interpreter with the given requested PHP source code file as argument, then delivers any output of that process back to the HTTP client. This also means there's no persistent PHP process running at all times with a persistent state, like Java typically does, but each request is handled by starting up and then tearing down a new PHP instance.
While Java simply saves persistent data in memory, data persistence between requests in PHP is handled via a number of methods like memcache, sessions, databases, files etc.; depending on the specific needs of the situation. PHP does have opcode cache addons, which kind of work like Java byte code, simply so PHP doesn't have to repeat the same parse and compile process every single time it's executing the same file.
Do keep in mind that it's entirely feasible to write a persistent PHP program which keeps running just like Java, it's simply not PHP's default modus operandi. Personally I'm quite a fan of writing workers for specific tasks on Gearman or ZMQ which run persistently, and have some ephemeral scripts running on the web server as "frontend" which delegate work to those workers as needed.
If this sounds like a typical PHP app is much more of a glued-together accumulation of several disparate components, you'd be correct. Java is pretty self-contained, except for external products like RDBMS servers. PHP on the other hand often tends to rely on a bunch of third party products; which can work to its advantage in the sense that you can use best-of-breed products for specific tasks, but also requires more overhead of dealing with different systems.
This is how does PHP work:
(one of the best over the Internet)
In general terms, PHP as an engine interprets the content of PHP files (typically *.php, although alternative extensions are used occasionally) into an abstract syntax tree. The PHP engine then processes the translated AST and then returns the result given whatever inputs and processing are required.
Below image will depict more information
Source: freecodecamp.org
I'm building a script to generate thousands of PDF pages but the memory consuming will affect the server's perfomance. As this is not a prioritary task (this generation can take hours, as long as it doesn't affect the webserver) what is the best approach for this problem?
I've seen some implementations of pthread but I would have to install also the ZTS. pthreadPHP
Don't really know if this is the right approach for my problem.
Thanks all
If you want to avoid installing pcntl or pthread, simply move the operation to a cron job (with file locking to prevent duplicate processes from running) or a never ending service to process them. Your main application would leave behind the meta data needed to generate the PD while the service runs separately from your main app and can be throttled.
Another option would be to use Gearman which can allow you to offload the PDF generation process to a completely separate server (or group of servers, gearmand itself is really just a job dispatcher). The worker scripts can be written in many different languages, including PHP (so if you're already using some PDF Generation library written in PHP, you can still use it). See also http://gearman.org/
I am currently trying to implement a job queue in php. The queue will then be processed as a batch job and should be able to process some jobs in parallel.
I already did some research and found several ways to implement it, but I am not really aware of their advantages and disadvantages.
E.g. doing the parallel processing by calling a script several times through fsockopen like explained here:
Easy parallel processing in PHP
Another way I found was using the curl_multi functions.
curl_multi_exec PHP docs
But I think those 2 ways will add pretty much overhead for creating batch processing on a queue that should mainly run on the background?
I also read about pcntl_fork which also seems to be a way to handle the problem. But that looks like it can get really messy if you don't really know what you are doing (like me at the moment).
I also had a look at Gearman, but there I would also need to spawn the worker threads dynamically as needed and not just run a few and let the gearman job server then sent it to the free workers. Especially because the threads should be exit cleanly after one job has been executed, to not run into eventual memory leaks (code may not be perfect in that issue).
Gearman Getting Started
So my question is, how do you handle parallel processing in PHP? And why do you choose your method, which advantages/disadvantages may the different methods have?
i use exec(). Its easy and clean. You basically need to build a thread manager, and thread scripts, that will do what you need.
I dont like fsockopen() because it will open a server connection, that will build up and may hit the apache's connection limit
I dont like curl functions for the same reason
I dont like pnctl because it needs the pnctl extension available, and you have to keep track of parent/child relations.
never played with gearman...
Well I guess we have 3 options there:
A. Multi-Thread:
PHP does not support multithread natively.
But there is one PHP extension (experimental) called pthreads (https://github.com/krakjoe/pthreads) that allows you to do just that.
B. Multi-Process:
This can be done in 3 ways:
Forking
Executing Commands
Piping
C. Distributed Parallel Processing:
How it works:
The Client App sends data (AKA message) “can be JSON formatted” to the Engine (MQ Engine) “can be local or external a web service”
The MQ Engine stores the data “mostly in Memory and optionally in Database” inside a queues (you can define the queue name)
The Client App asks the MQ Engine for a data (message) to be processed them in order (FIFO or based on priority) “you can also request data from specific queue".
Some MQ Engines:
ZeroMQ (good option, hard to use)
a message orientated IPC Library, is a Message Queue Server in Erlang, stores jobs in memory. It is a socket library that acts as a concurrency framework. Faster than TCP for clustered products and supercomputing.
RabbitMQ (good option, easy to use)
self hosted, Enterprise Message Queues, Not really a work queue - but rather a message queue that can be used as a work queue but requires additional semantics.
Beanstalkd (best option, easy to use)
(Laravel built in support, built by facebook, for work queue) - has a "Beanstalkd console" tool which is very nice
Gearman
(problem: centralized broker system for distributed processing)
Apache ActiveMQ
the most popular open source message broker in Java, (problem: lot of bugs and problems)
Amazon SQS
(Laravel built in support, Hosted - so no administration is required. Not really a work queue thus will require extra work to handle semantics such as burying a job)
IronMQ
(Laravel built in support, Written in Go, Available both as cloud version and on-premise)
Redis
(Laravel built in support, not that fast as its not designed for that)
Sparrow
(written in Ruby that based on memcache)
Starling
(written in Ruby that based on memcache, built in twitter)
Kestrel
(just another QM)
Kafka
(Written at LinkedIn in Scala)
EagleMQ
open source, high-performance and lightweight queue manager (Written in C)
More of them can be foun here: http://queues.io
If your application is going to run under a unix/linux enviroment I would suggest you go with the forking option. It's basically childs play to get it working. I have used it for a Cron manager and had code for it to revert to a Windows friendly codepath if forking was not an option.
The options of running the entire script several times do, as you state, add quite a bit of overhead. If your script is small it might not be a problem. But you will probably get used to doing parallel processing in PHP by the way you choose to go. And next time when you have a job that uses 200mb of data it might very well be a problem. So you'd be better of learning a way that you can stick with.
I have also tested Gearman and I like it a lot. There are a few thing to think about but as a whole it offers a very good way to distribute works to different servers running different applications written in different languages. Besides setting it up, actually using it from within PHP, or any other language for that matter, is... once again... childs play.
It could very well be overkill for what you need to do. But it will open your eyes to new possibilities when it comes to handling data and jobs, so I would recommend you to try Gearman for that fact alone.
Here's a summary of a few options for parallel processing in PHP.
AMP
Checkout Amp - Asynchronous concurrency made simple - this looks to be the most mature PHP library I've seen for parallel processing.
Peec's Process Class
This class was posted in the comments of PHP's exec() function and provides a real simple starting point for forking new processes and keeping track of them.
Example:
// You may use status(), start(), and stop(). notice that start() method gets called automatically one time.
$process = new Process('ls -al');
// or if you got the pid, however here only the status() metod will work.
$process = new Process();
$process.setPid(my_pid);
// Then you can start/stop/check status of the job.
$process.stop();
$process.start();
if ($process.status()) {
echo "The process is currently running";
} else {
echo "The process is not running.";
}
Other Options Compared
There's also a great article Async processing or multitasking in PHP that explains the pros and cons of various approaches:
pthreads extension (see also this SitePoint article)
Amp\Thread Library
hack's async (requires running Facebook's HHVM)
pcntl_fork
popen
fopen/curl/fsockopen
Doorman
Then, there's also this simple tutorial which was wrapped up into a little library called Doorman.
Hope these links provide a useful starting point for more research.
First of all, this answer is based on the linux OS env.
Yet another pecl extension is parallel,you can install it by issuing pecl install parallel，but it has some prerequisities：
Installing ZTS(Zend Thread safety) Build PHP 7.2+ version
if you build this extension by source, you should check the php.ini like config file,then add extension=parallel.so to it
then see the full example gist :https://gist.github.com/krakjoe/0ee02b887288720d9b785c9f947f3a0a
or the php official site url:https://www.php.net/manual/en/book.parallel.php
Use native PHP (7.2+) Parallel , i.e.:
use \parallel\Runtime;
$sampleFunc = function($num, $param2, $param3) {
echo "[Start: $num]";
sleep(rand(1,3) );
echo "[end:$num]";
};
for($i = 0; $i < 11; $i++) {
\parallel\run($sampleFunc, [$param1=$i, $param2=null, $param3="blabla"] );
}
for ($i = 0; $i < 11; $i++) {
echo " <REGULAR_CODE> ";
sleep(1);
}
(BTW, you will need to go through hard path to install PHP with ZTS support, and then enable parallel. I recommend phpbrew to do that.)
I prefer exec() and gearman.
exec() is easy and no connection and less memory consuming.
gearman should need a socket connection and the worker should take some memory.
But gearman is more flexible and faster than exec(). And the most important is that it can deploy the worker in other server. If the work is time and resource consuming.
I'm using gearman in my current project.
I use PHP's pnctl - it is good as long as you know what you do. I understand you situation but I don't think it's something difficult to understand our code, we just have to be little more conscious than ever when implementing JOB queue or Parallel process.
I feel as long as you code it perfectly and make sure the flow is perfect off-course you should keep PARALLEL PROCESS in mind when you implement.
Where you could do mistakes:
Loops - should be able to handle by GLOBAL vars.
Processing some set of transactions - again as long as you define the sets proper, you should be able to get it done.
Take a look at this example - https://github.com/rakesh-sankar/Tools/blob/master/PHP/fork-parallel-process.php.
Hope it helps.
The method described in 'Easy parallel processing in PHP' is downright scary - the principle is OK - but the implementation??? As you've already pointed out the curl_multi_ fns provide a much better way of implementing this approach.
But I think those 2 ways will add pretty much overhead
Yes, you probably don't need a client and server HTTP stack for handing off the job - but unless you're working for Google, your development time is much more expensive than your hardware costs - and there are plenty of tools for managing HTTP/analysing performance - and there is a defined standard covering stuff such as status notifications and authentication.
A lot of how you implement the solution depends on the level transactional integrity you require and whether you require in-order processing.
Out of the approaches you mention I'd recommend focussing on the HTTP request method using curl_multi_ . But if you need good transactional control / in order delivery then you should definitely run a broker daemon between the source of the messages and the processing agents (there is a well written single threaded server suitable for use as a framework for the broker here). Note that the processing agents should process a single message at a time.
If you need a highly scalable solution, then take a look at a proper message queuing system such as RabbitMQ.
HTH
C.
I recently read about http://php.net/pcntl and was woundering how good that functions works and if it would be smart to use multithreading in PHP since it isn't a core function of PHP.
I would want to trigger events that don't require feedback through it like fireing a cronjob execution manually.
All of it is supposed to run in a web app written with Zend Framework
The pcntl package works quite fine - it just uses the according unix functions. The only shortage is that you can't use them if php is invoked from a web server context. i.e. you can use it in shell scripts, but not on web pages - at least not without using a hack like calling a forking script with exec or similar.
[edit]
I just found a page explaining why mod_php cannot fork. Basically it's a security issue.
[/edit]
This is not thread control, this is process control. The library for the threads is pthreads (POSIX threads) and it's not included in PHP, so there are no multi-threading functions in PHP.
As of multiprocessing, you cannot use that in mod_php, as that would be a giant security hole (spawned process would have all the web-server's privileges).
The only possible way to have php code executing in multiple threads is to run php as a module of a threaded web server, which is useless because threads are fully isolated and your code has no control over them. As far as i know, pcntl only manages processes, not threads.
If I needed to do manual crontab executions or the like from PHP, I'd probably use a queue. Have a database table that you append jobs to. Another process, either from a cron or running as a daemon, executes the jobs as they show up.
Another way to do it is to set up a separate script and do an HTTP GET to it. It's not quite threading, but it's one way of shelling to another command in PHP.
For example, if I wanted to run /usr/bin/somescript.sh on demand, I'd have a somescript.php that did a system call. This would be on a virtual host only accessible from localhost.
I'd do a socket call to the webserver and GET the script. The key is to not read on the socket so it doesn't block. If I wanted to check the return value of somescript.php, I'd do it later in my main script to prevent blocking.
If somescript.php takes a long time to execute (longer than the calling script), you'll have to do some magic to stop apache from killing the script when the socket is closed.
Multiplatform PHP Multithreading engine
http://anton.vedeshin.com/articles/lightweight-and-multiplatform-php-multithreading-engine
Examples of multithreading working in PHP (with excerpts from their project pages):
Cron Multi-Threaded.
As of October 25th, 2011, this module has reached "end of life" and is deprecated in favor of projects such as Elysia Cron. This module wasn't completely useless in that a core patch inspired by Cron MT was committed to D7.
Boost.
... provides static page caching for Drupal enabling a very significant performance and scalability boost for sites that receive mostly anonymous traffic. For shared hosting this is your best option in terms of improving performance. On dedicated servers, you may want to consider Varnish instead.