I want to use Google translate's v3 PHP library to translate some text into a bunch of different languages. There may be workarounds (though none ideal that I know of), but I'm also just trying to learn.
I wanted to use using multiple calls to translateText, one call per target language. However, to make things faster, I would need to do these requests concurrently, so I was looking into some concurrency options. I was wanting to use calls to translateText instead of constructing a bunch of curl requests manually using curl multi.
I tried the first code example I found from one of the big concurrency libraries I've seen recommended, amphp. I used the function parallelMap, but I'm getting timeout errors when creating processes. I'd guess that I'm probably forking out too many processes at a time.
I'd love to learn if there is an easy way to do concurrency in PHP without having to make a bunch of decisions about how many processes to have running at a time, whether I should use threads vs processes, profiling memory usage, and what PHP thread extension is even any good / if the one I've heard of called "parallel" may be discontinued (as suggested in a comment here).
Any stack overflow post I've found so far is just a link to one giant concurrency library or another that I don't want to have to read a bunch of documentation for. I'd be interested to hear how concurrency like this is normally done / what options there are. I've found many people claim that processes aren't much slower than threads these days, and I can't find quick Google answers as to whether they take a lot more memory than threads. I'm not even positive that a lack of memory is my problem, but it probably is. There has been more complexity involved than I would have expected.
I'm wondering how this is normally handled.
Do people normally just use a pool of workers (processes by default, or threads using, say the "parallel" PHP extension) and set a max number of processes to run at a time to make concurrent requests?
If in a hurry, do people just kind of pick a number that isn't very optimized for how many worker processes to use?
It would be nice if the number of workers to use was set dynamically for you based on how much RAM was available or something, but I guess that's not realistic, since the amount of RAM available can quickly change.
So, would you just need to set up a profiler to see how much ram one worker process/thread uses, or otherwise just make some sort of educated guess as to how many worker processes/threads to use?
We are working on an image-processing application. It involves applying filters, Gaussian etc. We want to make it a highly concurrent application.
This will be on multiple single core ec2 instances.
Since Imageprocessing is an cpu intensive operation, we are thinking node.js gets blocked in event loop, so thinking to use php. We are not able to find any benchmarks in this area. Any inputs on this will be a great help.
Its a CPU-bound task. Really well optimized PHP or Node will probably perform similarly. I/O concurrency will not affect CPU bound tasks on single core. On many core the I/O may come into play, but realistically most platforms including PHP have efficient strategies for concurrent I/O now. Also you are likely to end up calling out to C or C++ code regardless.
If you really want (cost-effective) performance, drop the single core thing, put some large basically gaming or bitcoin mining PCs in the office, find a nice way to distribute the tasks among the machine(s) and a way to process multiple images concurrently on the GPUs. None of that is in actuality tied to a particular programming language.
PHP is not highly concurrent and each request will block until it's done. Node would be fine as long as it's mainly doing I/O, or waiting for another process to return, e.g. calling convert (ImageMagick), rather than doing any processing itself. The more CPU cores you have to run the actual conversion on, the better.
For image processing, I recommend to use PHP instead of Node.js because there are many great PHP packages that can help you work with images easily. Don't worry about the performance of PHP7 or HHVM :)
I have a multi-process PHP (CLI) application that runs continuously. I am trying to optimize the memory usage because the amount of memory used by each process limits the number of forks that I can run at any given time (since I have a finite amount of memory available). I have tried several approaches. For example, following the advice given by preinheimer, I re-compiled PHP, disabling all extensions and then re-enabling only those needed for my application (mysql, curl, pcntl, posix, and json). This, however, did not reduce the memory usage. It actually increased slightly.
I am nearly ready to abandon the multi-process approach, but I am making a last ditch effort to see if anyone else has any better ideas on how to reduce memory usage. I will post my alternative approach, which involves significant refactoring of my application, below.
Many thanks in advance to anyone who can help me tackle this challenge!
Mutli-process PHP applications (e.g. an application that forks itself using pcntl_fork()) are inherently inefficient in terms of memory because each child process loads an entire copy of the php executable into memory. This can easily equate to 10 MB of memory per process or more (depending on the application). Compiling extensions as shared libraries, in theory, should reduce the memory footprint, but I have had limited success with this (actually, my attempts at this made the memory usage worse for some unknown reason).
A better approach is to use multi-threading. In this approach, the application resides in a single process, but multiple actions can be performed *concurrently** in separate threads (i.e. multi-tasking). Traditionally PHP has not been ideal for multi-threaded applications, but recently some new extensions have made multi-threading in PHP more feasible. See for example, this answer to a question about multithreading in PHP (whose accepted answer is rather outdated).
For the above problem, I plan to refactor my application into a multi-theaded one using pthreads. This requires a significant amount of modifications, but it will (hopefully) result in a much more efficient overall architecture for the application. I will update this answer as I proceed and offer some re-factoring examples for anyone else who would like to do something similar. Others feel free to provide feedback and also update this answer with code examples!
*Footnote about concurrence: Unless one has a multi-core machine, the actions will not actually be performed concurrently. But they will be scheduled to run on the CPU in different small time slices. From the user perspective, they will appear to run concurrently.
I wish to create a background process and I have been told these are usually written in C or something of that sort. I have recently found out PHP can be used to create a daemon and I was hoping to get some advice if I should make use of PHP in this way.
Here are my requirements for a daemon.
Continuously check if a row has been
added to MySQL database table
Run FFmpeg commands on what was
retrieved from database
Insert output into MySQL table
I am not sure what else I can offer to help make this decision. Just to add, I have not done C before. Only Java and PHP and basic bash scripting.
Does it even make that much of a performance difference?
Please allow for my ignorance, I am learning! :)
Thanks all
As others have noted, various versions of PHP have issues with their garbage collectors. Of course, if you know that your version does not have such issues, you eliminate that problem. The point is, you don't know (for sure) until you write the daemon and run it through valgrind to see if the installed PHP leaks or not on any given machine. So on that hand, you may write it just to discover that what Zend thinks is fixed might still be buggy, or you are dealing with a slightly older version of PHP or some extension. Icky.
The other problem is somewhat buggy signals. In my experience, signal handlers are not always entered correctly with PHP, especially when the signal is queued instead of merged. That may not be an issue for you, i.e. if you just need to handle SIGINT/SIGUSR1/SIGUSR2/SIGHUP.
So, I suggest:
If the daemon is simple, go ahead and use PHP. If it looks like its going to get rather complex, or allocate lots of memory, you might consider writing it in C after prototyping it in PHP.
I am a pretty die hard C person. However, I see nothing wrong with hammering out something quick using PHP (beyond the cases that I explained). I also see nothing wrong with using PHP to prototype something that may or may not be later rewritten in C. For instance, handling database stuff is going to be much simpler if you use PHP, versus managing callbacks using other interfaces in C. So in that instance, for a 'one off', you will surely get it done much faster.
I would be inclined to perform this task with a cron job, rather than polling the database in a daemon.
It's likely that your FFmpeg command will take a while to do it's thing, right? In that case, is it really necessary to be constantly polling the database? Wouldn't a cronjob running each minute (or every five, ten or twenty minutes for that matter) be a simpler way to achieve the same thing?
Php isn't any better or worse for this kind of thing than any of the other common scripting languages. It has fairly complete access to all of the system calls and library utilities you would need to do this sort of work. If you are most comfortable using PHP for scripting, then php will do the job for you.
The only down side is that php is not quite as ubiquitous as, say, perl or python, which is installed on almost every flavor of unix. Php is only found on systems that are going to be serving dynamic web content. Not that a Php interpreter is too large or costly to install also, but if your biggest concern is getting your program to many systems, that may be a slight hurdle.
I'll be contrary and recommend you try the php daemon. It's apparently the language you know the best. You'll presumably incorporate a timer in any case, so you can duplicate the querying frequency on the database. There's really no penalty as long as you aren't naively looping on a query.
If it's something not executed frequently, you could alternatively run the php from cron, letting youor code drain the queue and then die.
But don't be afraid to stick with what you know best, as a first approximation.
Try not to use triggers. They'll impose unnecessary coupling, and they're no fun to test and debug.
One problem with properly daemonizing a PHP script is that PHP doesn't have interfaces to the dup() or dup2() syscalls, which are needed for detaching the file descriptors.
A cron-job would probably work just fine, if near-instant actions is not required.
I'm just about to put live, a system I've built, based on the queueing daemon 'beanstalkd'. I send various small messages from (in this case, PHP) webpage calls to the daemon, and a PHP script then picks them up from the queue and performs various tasks, such as resizing images or checking databases (often passing info back via a Memcache-based store).
To avoid long-running processes, I've wrapped it in a BASH script, that, depending on the value returned from the script ("exit(1);") will restart the script, for every (say) 50 tasks it's performed. If it's restarting because I plan it to, it will do so instantly, any other exit value (the default is 0, so I don't use that) would pause a few seconds before it was restarted.
Running as a cron job with sensibly determined periodicity, a PHP script can do the job, and production stability is certainly achievable. You might want to limit the number of simultaneous FFMpeg instances, and be sure to have complete application logging and exception handling. I have implemented continuously running polling processes in Java, as well as the every-ten-minute cron'd PHP script, and both do the job nicely.
You might want to consider making a mysql trigger that executes a system command (i.e. FFmpeg) instead of a daemon. If some lag isn't a problem, you could also put something in cron that executes every few minutes to check. Cron would be my choice, if it is an option.
To answer your question, php is perfectly fine to run as a daemon. It does not have to be done in C.
If you combine the answers from Kent Fredric, tokenmacguy and Domster you get something useful.
php is probably not good for long execution times,
so let's keep every execution cycle short and make sure the OS takes care of the cleanup of any memoryleaks.
As a tool to start your php script cron can be a good tool.
And if you do it like that, there is not much difference between languages.
However, the question still stands.
Is php even capable to run as a normal daemon for long times (some years)?
Or will assorted memoryleaks eat up all your ram and kill the system?
/Johan
If you do so, pay attention to memory leaks. PHP 5.2 has some problems with its garbage collector, according to this (fixed in 5.3). Perhaps its better to use cron, so the script starts clean every run.
For what you've described, I would go with a daemon. Make sure that you stick a sleep in the poll loop, so that you don't bombard the database when there are no new tasks. A cronjob works better for workflow/report type of jobs, where there isn't some particular event that triggers the next run.
As mentioned, PHP has some problems with memory management. You need to be sure that you test your code for memory leaks, since these would build up over time, in a long running script. PHP doesn't have real garbage collection - It relies on reference counting, which means that cyclic references will cause leaks. If you're aware of this, you can code around it.
If you do decided to go down the daemon route, there is a great PEAR module called System_Daemon which I've recently used successfully on a PHP v5.3.0 installation. It is documented on the authors blog: http://kevin.vanzonneveld.net/techblog/article/create_daemons_in_php
If you have PEAR installed, you can install this module using:
pear install -f System_Daemon
You will also need to create a initialisation script: /etc/init.d/<your_daemon_name>
Then you can:
Start Daemon: /etc/init.d/projNotifMailDaemon start
Stop Daemon: /etc/init.d/projNotifMailDaemon stop
Logs are kept at: /var/log/<your_daemon_name>.log
I wouldn't recommend it. PHP is not designed for longterm execution. Its designed primarily with short lived pages.
In my experience PHP can have problems with leaking memory for some of the larger tasks.
A cron job and a little bit of bash scripting should be everything you need by the sounds of it. You can do things like:
$file=`mysqlquery -h server < "select file from table;"`
ffmpeg $file -fps 50 output.a etc.
so bash would be easier to write, port and maintain IMHO than to use PHP.
If you know what you are doing sure. You need to understand your operating system well. PHP generally isn't suited for most daemons because it isn't threaded and doesn't have a decent event based system for all tasks. However if it suits your needs then no problem. Modern PHP (5.3+) is really stable and doesn't have any memory leaks. As long as you enable the GC and don't implement your own memory leaks, etc you'll be fine.
Here are the stats for one daemon I am running:
uptime 17 days (last restart due to PHP upgrade).
bytes written: 200GB
connections: hundreds
connections handled, hundreds of thousands
items/requests processed: millions
node.js is generally better suited although has some minor annoyances. Some attempts to improve PHP in the same areas have been made but they aren't really that great.
Cron job? Yes.
Daemon which runs forever? No.
PHP does not have a garbage collector (or at least, last time I checked it did not). Therefore, if you create a circular reference, it NEVER gets cleaned up - at least not until the main script execution finishes. In daemon process this is approximately never.
If they've added a GC in new versions, then yes you can.
Go for it. I had to do it once also.
Like others said, it's not ideal but it'll get-er-done. Using Windows, right? Good.
If you only need it to run occasionally (Once per hour, etc).
Make a new shortcut to your firefox, place it somewhere relevant.
Open up the properties for the shortcut, change "Target" to:
"C:\Program Files\Mozilla Firefox\firefox.exe" http://localhost/path/to/script.php
Go to Control Panel>Scheduled Tasks
Point your new scheduled task at the shortcut.
If you need it to run constantly or pseudo-constantly, you'll need to spice the script up a bit.
Start your script with
set_time_limit(0);
ob_implicit_flush(true);
If the script uses a loop (like while) you have to clear the buffer:
$i=0;
while($i<sizeof($my_array)){
//do stuff
flush();
ob_clean();
sleep(17);
$i++;
}
Most of my application is written in PHP ((Front and Back ends).
There is a part that works too slowly and I will need to rewrite it, probably not in PHP.
What will give me the following:
1. Most speed
2. Fastest development
3. Easily maintained.
I have in my mind to rewrite this piece of code in CPP as a PHP extension, but may be I am locked on this solution and misses some simpler/better solutions?
The algorithm is PorterStemmerAlgorithm on several MB of data each time it is run.
The answer really depends on what kind of process it is.
If it is a long running process (at least seconds) then perhaps an external program written in C++ would be super easy. It would not have the complexities of a PHP extension and it's stability would not affect PHP/apache. You could communicate over pipes, shared memory, or the sort...
If it is a short running process (measured in ms) then you will most likely need to write a PHP extension. That would allow it to be invoked VERY fast with almost no per-call overhead.
Another possibility is a custom server which listens on a Unix Domain Socket and will quickly respond to PHP when PHP asks for information. Then your per-call overhead is basically creating a socket (not bad). The server could be in any language (c, c++, python, erlang, etc...), and the client could be a 50 line PHP class that uses the socket_*() functions.
A lot of information needs evaluated before making this decision. PHP does not typically show slowdowns until you get into really tight loops or thousands of repeated function calls. In other words, the overhead of the HTTP request and network delays usually make PHP delays insignificant (unless the above applies)
Perhaps there is a better way to write it in PHP?
Are you database bound?
Is it CPU bound, Network bound, or IO bound?
Can the result be cached?
Does a library already exist which will do the heavy lifting.
By committing to a custom PHP extension, you add significantly to the base of knowledge required to maintain it (even above C++). But it is a great option when necessary.
Feel free to update your question with more details, and I'm sure Stack Overflow will be happy to help out.
Suggestion
The PorterStemmerAlgorithm has a C implementation available at http://tartarus.org/~martin/PorterStemmer/c.txt
It should be an easy matter to tie this C program into your data sources and make it a stand alone executable. Then you could simply invoke it from PHP with one of the proc functions, such as proc_open()
Unless you need to invoke this program many times PER php request, then this approach should save you the effort of building and integrating a PHP extension, not to mention that the hard work (in c) is already done.
Am not sure about what the PorterStemmerAlgorithm is. However if you could make your process run in parallel and collect the information together , you could look at parallel running processes easily implemented in JAVA. Not sure how you could call it in PHP, but definitely maintainable.
You can have a look at this framework. Looks simple to implement
https://computefarm.dev.java.net/
Regards,
Franklin.
If you absolutely need to rewrite in a different language for speed reasons then I think gahooa's answer covers the options nicely. However, before you do, are you absolutely sure you've done everything you can to improve the performance if the PHP implementation?
Is caching the output viable in your situation? Could you get away with running the algorithm once and caching the output rather than on every page load?
Have you tried profiling the code to ensure there's no unnecessary work being done (db queries in an inner loop and the like). Xdebug can help here.
Are there other stemming algorithms available which might perform better on your dataset?