In the event the cache does not contain data for the given cache ID (or it is expired), start() will return an empty string and begin an output buffer to capture the generated output. After the output has been generated, the end() method must be called to actually display the generated content and save the content to the cache.

The end() method accepts an optional parameterthe amount of time, in seconds, before the cached version of the content expires. The result to the end user is that the page is displayed as usual; however, from an optimization standpoint the benefits are indisputable.

Caching Function Calls

Beyond caching entire dynamically generated HTML documents, the PEAR cache also has facilities to cache smaller portions of your PHP scripts, such as the results from particularly expensive function calls. For instance, consider the following function, which uses the GD library to generate an image ():

Listing 10.8. Image Generation Function Example

<?php

     define('FONT', 4);
     function make_image_word($wordfile, $width, $height) {

          $words = array_flip(file($wordfile));
          $word = trim(array_rand($words));

          $img = imagecreate($width, $height);

          $black = imagecolorallocate($img, 0x00, 0x00, 0x00);
          $white = imagecolorallocate($img, 0xFF, 0xFF, 0xFF);
          imagefill($img, 0, 0, $white);
          for($i = 0; $i < 20; $i++) {

               $start_x = rand(0, $width);
               $start_y = rand(0, $height);
               $c_width   = rand(0, $width/2);
               $c_height = rand(0, $height/2);
               $color   = imagecolorallocate($img, rand(0x00, 0xFF),
                                         rand(0x00, 0xFF), rand(0x00, 0xFF));

               imageellipse($img, $start_x, $start_y,
                                        $c_width, $c_height, $color);

          }

          return $data;

     }

     $data = make_image_word("/usr/share/dict/words", 100, 50);
?>

This function is a particularly expensive operation that returns an image with a word in an array suitable for preventing autoregistration by Web bots. To cache the data generated by this function, we'll use the PEAR function cache as shown in (assume the function is still defined):

Listing 10.9. Caching Function Calls Using PEAR

 <?php
     require_once('Cache/Function.php');
     define('CACHE_EXPIRE', 30);
     $cache = new Cache_Function('file',
                                    array('cache_dir'       => '.',
                                          'filename_prefix' => 'cache_'),
                                    CACHE_EXPIRE);
     $data = $cache->call('make_image_word', '/usr/share/dict/words', 100, 50);
?>

As you can see, caching the results of a function call is a very straightforward process. Unlike the output cache example in , the Cache_Function class requires not only a container and its parameters, but takes a third parameter representing the time in seconds to cache the function result. Furthermore, unlike the Output Cache function, caches do not have any sort of unique cache identifier associated with them. Rather, the function name and its parameters are automatically used. Calling the function using the PEAR function cache is done using the call() method of the Cache_Function class, where the first parameter is the name of the function, and each following parameter represents the parameters to pass to the function being called.

Now that you have an idea of how caching functions works, let's take a look at the performance gains by profiling the standard function call against the cached version:

Method one took 6.4777460098267 seconds.
Method two took 0.78488004207611 seconds.

Method two was faster than Method one by 87.88%

As is quite clear by the profiling statistics, caching provides staggering gains (nearly 90% faster) for high-cost operations.

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