Intranet Journal - E-business: Reshaping the Application Server Market

What's New in PHP4?

By Christophe Lauer, Head of R&D (clauer@techmetrix.net)

This article is a follow-up to Free Software Profile: PHP, which did not deal with PHP4's new features.

The long-awaited PHP4 version has been available since the end of May 2000. After having acquired successively Beta-test and Release Candidate status, the final version which can be used for real-world site production is today a reality.

The questions that come up systematically with each new version of a software program are, 'What's new in this version?' and 'Which of these new features are truly useful?' These are certainly legitimate questions, as the simple availability of a new version does not justify migration to it. The thing is that behind what seems to be a simple update looms a myriad of potential problems that must be zeroed in on before moving forward, especially because once updated, there's often no turning back.

I'd like to take a minute to point out that if you are currently questioning the availability date of PHP4 support by your favorite host, it is important to know that such a task represents a considerable amount of work.

In this article, we'll take a quick look at PHP4's new features, which will allow you to appreciate the tremendous work that has been carried out by Zeev Suraski and Andi Gutmans, as well as all of the other contributors.

What's the difference between PHP3 and PHP4?

PHP4 is a complete rewrite of PHP3 at the heart of the language's engine. But why did the language's authors decide to completely rewrite it?

The manner in which PHP3's scripting engine works is not adapted to the execution of rich, large-scale applications such as Phorum or KeyStone. Indeed, this engine reads PHP script instructions line-by-line and then executes them one-by-one, which enables PHP3 to obtain good performance with short and simple scripts, but yields rather mediocre performance with larger applications. It is important to understand that PHP3 was not designed to execute such applications.

It is for this reason that PHP3's two creators decided to implement a scripting engine that would be capable of reading all PHP code and "compiling" it before executing it: Zend. This was not an easy task. Although incompatibilities could be conceived at the time of migration from PHP2 to PHP3, such differences had to be limited as much as possible between PHP3 and PHP4 due to the installed base and the number of PHP3 scripts already in use. We can congratulate PHP4's authors on a job well done because the incompatibilities that do exist are only minor.

Although Zend is an integral part of PHP4, it is in fact a scripting/runtime engine that is independent of the PHP language. On this account, it is possible to use Zend in MySQL as the basis for the development of a stored procedure language specific to this database system.

Without going into the details of internal implementation, we can point out a few things about the Zend/PHP4 couple.

PHP4's new architecture allowed its authors to add an abstraction layer in relation to the Web server at the heart of its language. Up until now with PHP3, we had the choice between using it as a specific module for the Apache server or in CGI mode for all other HTTP servers. With PHP4 it is now possible to imagine better integration with Web servers other than Apache. In fact, this is the case for Microsoft's HTTP server, IIS. PHP4 now works as an ISAPI filter for Microsoft's IIS server. For this reason, different parts of PHP4 code had to be made compliant with use in a multi-thread environment (PHP4 is "thread-safe").

There are many new features concerning PHP4's internal implementation, but they don't really concern PHP programmers directly. Nonetheless, it is worth noting one of the most important points: memory allocation and reference counting mechanisms, in other words those mechanisms that free up resources which were no longer used, were completely rethought. Performance and memory use are thus improved, especially for objects and tables. The more data the variables contain, the more memory is saved.

A Developer's View

What are the major differences between PHP3 and PHP4 from a user's (a PHP4 designer/developer) point of view?

Sessions
One of PHP4's most anticipated functions is native session support. Indeed, nothing in the language's base functions provided for management of user sessions, in other words all of the values and variables that are linked to a user and can be transferred from page to page within the same application.

With PHP3, it was necessary to build a session system manually by using cookies, by making an identifier a parameter, or by using PHPLib. PHPLib can still be used with PHP4 because it offers other functionalities besides session management.

In PHP4, a whole group of configuration features and directives in the php.ini file take the burden of session and user context management off of the programmer. PHP4 session variables can be stored in a simple ASCII file or in a relational database. All of these features are now documented in the official PHP manual.

Output Buffering
With PHP3 all of the content produced by echo () or print() was directly sent to the server. In PHP4 an intermediate storage layer makes it possible to defer the sending the Web server's output flow. In order to do this, new features, which haven't been documented yet, are available:

ob_start(): activates output buffering
ob_end_flush(): sends the contents of the output buffer and deactivates buffering
ob_end_clean(): empties the output buffer and deactivates buffering
ob_get_contents(): returns the output buffer contents

These functionalities make it possible to prepare the contents that are displayed via complex processes requiring several database queries, for example, and the sending of results only when all of the queries have been carried out successfully. In the opposite case, you can empty the output buffer contents and display an error message in its place. The example below shows a typical case of how these functionalities are used:

<?php
// activate output buffers
ob_start();
// the output is not displayed, it enters the buffer print "Hello, world!";
// read buffer contents
$output = ob_get_contents();
// deactivate the buffer, empty the buffer
ob_end_clean();
// display contents
print $output;
?>

Evaluate for Identical Operator
A new evaluate for identical operator makes its debut in PHP4. This operator makes it possible to test the equality of the values and types of two different variables or expressions. With implicit PHP-type conversions,the value 5 could be compared with the string containing the character "5." These two values were considered equal in a comparison. The new operator is represented by the three equal signs ("= = =") and only sends back TRUE if the variable type and value are identical. Thus, in the following example, the four tests using the equality operator with the numbers 1 to 4 are true, while with the following four, which use the evaluate for identical operator, only tests 5 and 8 are true.

$valint1 = 1;
$valint2 = 2;
$valint3 = 3;

$valfloat1 = 1.0;
$valfloat2 = 2.0;
$valfloat3 = 3.0;

$valstr3 = '3';

$res = (($valint1+$valint2)==$valint3) ? ('TRUE'):('FALSE') ;
print " TEST 1 : " . $res . " \n";

$res = ($valint3==$valfloat3) ? ('TRUE') : ('FALSE') ; print " TEST 2 : " . $res . " \n";

$res = ($valstr3==$valint3) ? ('TRUE') : ('FALSE') ; print " TEST 3 : " . $res . " \n";

$res = (($valfloat1+$valfloat2)==$valfloat3) ? ('TRUE') : ('FALSE') ; print " TEST 4 : " . $res . " \n ";

"; $res = (($valint1+$valint2)===$valint3) ? ('TRUE') : ('FALSE') ;
print " TEST 5 : " . $res . " \n";

$res = ($valint3===$valfloat3) ? ('TRUE') : ('FALSE') ; print " TEST 6 : " . $res . " \n";

$res = ($valstr3===$valint3) ? ('TRUE') : ('FALSE') ; print " TEST 7 : " . $res . " \n";

$res = (($valfloat1+$valfloat2)===$valfloat3) ? ('TRUE') : ('FALSE') ; print " TEST 8 : " . $res . " \n";

In passing, it is worth noting that PHP4 now includes Boolean-type data.

COM support on Windows
On Windows platforms, PHP4 now offers support for COM components. This means that practically all Windows applications can be manipulated from PHP4. The COM model that is at the heart of Microsoft's architecture is such that any Windows application can provide a certain number of components and exposed methods, which are entry points for manipulating applications from other applications.

Since a few lines of code tend to be more useful than a long description, let's look at the following example. The code below does nothing less than boot Word, create a new document from it, add text to this document, and then save everything on the disk before quitting.

<?php
$word = new COM("word.application") or
die("Impossible to instantiate WordApp");
print "Word is running, version {$word->Version}\n";

$word->Visible=1;

$word->Documents->Add();
$word->Selection->TypeText("This is a test..."); $word->Documents[1]->SaveAs("test_com_php.doc"); $word->Quit();
?>

Displaying portions of raw HTML code
Another newcomer to PHP4 is a new syntax that is modeled after Perl's "here printing." It is possible to display complete portions of HTML code by flanking them with either a print or echo instruction and an end label. Unlike Perl, the operator used is not a double less than sign (<<), but a triple less than sign (<<<) so as to distinguish it from the binary shift operator. For example:

<?php

$version = phpversion();
$valstr = "Example of HerePrinting\n";

echo "<hr> /n";

print <<< mylabel

<h4>PHP's New Features</h4>
<ul>
<li>ISAPI support
<li>COM support on Win32
<li>Java and servlets support
</ul>

$valstr Tested on PHP version $version

mylabel;

echo "<hr> /n";
?>

Onto Page II: Java Support

TechMetrix Research is a technically focused analyst firm focused on e-business application development needs. Based in Boston, Mass., the firm publishes comparison reports and product reviews designed to aid enterprises with decision making and to keep pace with the fast-moving e-business market.

TechMetrix is a U.S.-based subsidiary of SQLI, a European company that offers on-site development services to international organizations. SQLI specializes in e-business project development.