A profiling tool can provide valuable information about bottlenecks in your code. I believe profiling is a critical aspect of optimizing because it will tell you about your real code bottlenecks as opposed to your perceived bottlenecks. This enables you to focus your resources on areas that will provide the most performance benefit for your effort. Most programming languages and environments have one or more profiling tools available and PHP is no exception.

Xdebug is a PHP extension that provides valuable debugging information such as stack traces, functions traces, profiling, code coverage analysis, etc. There is another PHP tool called DBG that has similar functionality but this post will focus on using Xdebug.

Setup Xdebug

Xdebug is a PECL module and can be installed using the PECL installation instructions in one of my previous posts.

• If you have already setup PEAR you just need to run the following from a shell:

  sudo pecl install xdebug

  sudo pecl install xdebug

  If everything goes well Xdebug should download, build, and install. You may get a message telling you:

  You should add "extension=xdebug.so" to php.ini

  Go ahead and add the line. On an Ubuntu server you will probably find the php.ini file here: /etc/php5/apache2/php.ini

• Restart Apache, or whatever web server you are using, so the change will take effect.
  If you are running Apache on Ubuntu it would be:

  sudo /etc/init.d/apache2 restart

  sudo /etc/init.d/apache2 restart

• Write a phpinfo.php page with the following code and then point a browser at it. It should show the Xdebug module there in addition to many other things:

  <?php phpinfo(); ?>

  <?php phpinfo(); ?>

At this point the Xdebug extension should be installed. For more detailed instructions on a PECL extension install see my post: How to install a PHP PECL extension/module on Ubuntu. Note that there is a problem running the Xdebug extension with Zend Studio since it has it’s own debugger.

Enable Xdebug profiling

• By default, profiling is disable in Xdebug. Enable it by adding the following entry to the php.ini file:

  xdebug.profiler_enable=On

  xdebug.profiler_enable=On

  On on a linux box there is often a php.d or conf.d folder that holds additional .ini file settings PHP will use. On Ubuntu the path for this folder is “/etc/php5/apache2/conf.d”. To prevent further cluttering my php.ini file with Xdebug settings, I created a xdebug.ini file to store all my Xdebug .ini file settings. This file is located in the “/etc/php5/apache2/conf.d” so it is automatically scanned when Apache is restarted.

  Now you might be tempted to enable the profiler in your script using the ini_set() function which, normally allows you to temporarily set a .ini setting for only the current script execution. Unfortunately this does not work. You must set it in the php.ini or a sub .ini file and restart the web server.

• Restart your web server (I.e. Apache) once you have “xdebug.profiler_enable” set to “On”.

By default, Xdebug will write a cachegrind.out file to the /tmp folder. It will be named something like cachegrind.out.22373 where the number at the end is the ID of the process that was profiled. If you are using Windows you will probably need to change the default folder. Also by default, this file will be overwritten by each script execution so you don’t have to worry about it getting too big. The output file behavior is highly customizable and a complete list of Xdebug settings can be found here.

Call your script and display the analysis

With Xdebug enabled, pull up the page in your browser that you want to profile. If everything is working OK a cachegrind.out file should show up in the /tmp folder.

There are a couple programs you can use to open and analyze the cachegrind file:

• WinCacheGrind (for Windows)
• KCacheGrind (for Linux)

WinCacheGrind

WinCacheGrind is not very featured but it will tell you the main thing you need to know, which is where your PHP application is spending its time. Click on the screen shot below to see the full output of my test script:

The script makes an external call to example.com using a file_get_contents() function. Based on this analysis I might try caching the call results and only make the call at some interval to keep the cache updated. This would eliminate almost 75% of the application’s overhead and is just one example of an easy-to-fix bottleneck that profiling will help identify.

KCacheGrind

KCacheGrind does essentially the same thing as WinCacheGrind but it is geared for the Linux desktop and has quite a few more bells and whistles:

KCacheGrind includes a map feature that graphically represents the percentages of where the test application spent the time:

KCacheGrind also includes a graph feature with an export option that displays a tree diagram of the linkage between all the includes and functions:

That’s it for this post. Have fun profiling!

In a previous post I talked about using the HttpRequest object and functions in the PECL_HTTP extension to make HTTP requests from PHP. In some cases you may be limited to using functionality built into the PHP core. The file_get_contents() function has less features than the PECL_HTTP extension but it is built into PHP 4.3 and up. Here is an example of using it to retrieve the landing page at www.example.com:

<?php
 
echo file_get_contents("http://www.example.com");
 
?>

Someone hit that easy button.

The file_get_contents() functions as well as many other PHP file functions implement a streams abstraction layer largely conceived by Mr. Wez Furlong. This abstraction layer is what enables many of the PHP file functions to access network resources. Given this functionality “file” seems a misnomer.

The file_get_contents() function uses an HTTP GET request but what if you want to do a POST without using cURL or the PECL_HTTP extension? Furlong posted an article here on how to do just that.

This next code example uses the file_get_contents() function again but this time a few options are set first using the stream_context_create() function:

<?php
 
$http_options = stream_context_create(array(
    'http' => array(
        'user_agent' => "Mark's Browser",
        'max_redirects' => 3)));
echo file_get_contents("http://www.example.com", false, $http_options);
 
?>

Note that the array passed to the stream_context_create() function can also be used to specify a POST method, which is how Furlong does so in his blog post.

There is still yet another way to make an HTTP request from PHP that I haven’t covered yet using the PHP built-in cURL functions. I will cover these in a separate blog post.

The very informative phpinfo() function

The phpinfo() function displays just about everything you want to know about your PHP installation. It includes info on all your PECL and PEAR modules so it is a quick way to check what’s installed. It will also tell you useful web server information including any query strings you pass. To display all this good info just point your browser at a page on your server that contains the following code:

<?php
 
phpinfo();
 
?>

That’s it!

Automatic dependency checking

The phpinfo() function will give us a page that displays a lot of info. You can pass it bitwise constants to narrow down the information displayed but what if we want to check for specific items?

In my humble opinion, when developing software or anything in general, it is a good idea to design things so that the end user will not even need a manual because the user interface is obvious. When something doesn’t work, it should be equally obvious how to fix it.

If you write a PHP application that others will install and use, it is a good idea to check for dependencies when they try to use the application. This way even if they don’t read your documentation they will quickly know why the software is not working.

Using phpversion(), PHP_VERSION, and version_compare() to check the PHP verson

To get the core PHP version you can use either of the following methods:

<?php
 
echo phpversion();
echo "<br/>or<br/>";
echo PHP_VERSION;
 
?>

The above code should output something like this:

If you are using Ubunto or some other distribution, you will note that some additional stuff is tack on to the version number (I.e. “-2ubuntu4”). This makes a comparison to your expected version a little tricky but you can use a substr()/strpos() combo to get what you need. There is an easier way to do the comparison though. The version_compare() function is “PHP-standardized” version aware. So we can do something like this:

<?php
 
if (version_compare(PHP_VERSION, '5.0.0', '<')) {
    echo 'You are using PHP version ' . PHP_VERSION . 
      'This program requires PHP version 5.0.0 or higher.';
} else {
    echo 'You are using PHP 5.0.0 or higher. You are all set!';
}
 
?>

Now you can check the PHP version and notify the user if it is not the minimum required version.

The PHP function documentation for each function at www.php.net include the PHP versions that contain the function in the upper left hand corner:

You can use this to learn what versions of PHP include the functions you are using in your code to help identify your minimum PHP version requirement.

Using get_loaded_extensions() to check for extensions

The get_loaded_extensions() function will return an array of PHP extensions that you can use to check if a specific extension is installed. Use it in combination with with the in_array() function to check if the extension you require is loaded. In this example I check if the PECL_HTTP module is installed:

<?php
 
if (in_array("http",get_loaded_extensions())){
    echo 'The PECL_HTTP module is installed. '.
      'You are all set!';
} else {
    echo 'The PECL_HTTP module is not installed. '.
      'Please install it.';
}
 
?>

You can use the phpversion() function to check if extension is listed and if so, its version. This code example not only checks if the PECL_HTTP module is installed, but also checks it’s version:

<?php
 
if (!phpversion('http')){
    echo 'The PECL_HTTP module is not installed. '.
      'Please download it from '.
      '<a href="http://pecl.php.net/package/pecl_http">here</a> '.
      ' and install it.';
} else {
    if (version_compare(phpversion('http'),'1.6.0','>=')){
        echo 'The PECL_HTTP extension is installed and '.
          'version 1.6.0 or higher. You are all set!';
    } else {
        echo 'Please upgrade your PECL_HTTP extension to '.
          'version 1.6.0 or higher. You can download it '.
          '<a href="http://pecl.php.net/package/pecl_http">here'.
          '</a>.';
    }
}
 
?>

Use function_exists() to check for individual functions

So far the methods for checking dependencies have been somewhat broad. They check that the script has a certain version of PHP or extensions installed and that will likely be good enough in most cases. If you really want to be thorough you can also check if specific functions are available using the function_exists() method. In this example I check that the http_request() module, which is part of the PECL_HTTP extension, is there before I use it. If it is not, I use the less featured, built in, file_get_contents() function.

<?php
 
if (function_exists("http_get")) {
    echo 'Using the http_get():<br/>' .
        http_parse_message(http_get("http://www.example.com"))->body;
} else {
    echo 'Using the file_get_contents():<br/>' . 
        file_get_contents("http://www.example.com");
}
 
?>

Check for include files

Here is a simple way to check for include files. It doesn’t verify their content but you can at least make sure they are there:

<?php
 
if (!file_exists('httptest.php')){
    die('The httptest.php include file is missing.');
} else {
    require_once('httptest.php');
}
 
?>

Wrap up

Checking dependencies is an important part of building robust software and hopefully the above techniques will help accomplish that. Even if your end user is a very technical they will likely appreciate a good dependency checking mechanism that quickly tells them whats missing to save them time. If your software will be used by non-technical users you might want to automatically and gracefully downgrade your software feature set instead of generating errors and asking them for something they won’t know how to do. Usability is king!