Jos Poortvliet did an interview with me for dot KDE in this summer's aKademy and it has been online for a while now. In it we discuss things like Midgard as a storage engine for desktop applications, and Maemo's open QA process for Downloads applications. Some excepts:

At maemo.org we have an appstore for FOSS applications on the Maemo platform. This appstore is enabled by default on all Nokia N900s so we wanted to have some quality control. We had to create our own appstore approval process, compatible with the FOSS philosophy. Now any developer can submit an app, and anyone can test and vote. The whole process is completely transparent, auditable and visible. And it also provides a feedback channel from testers and users to the developers!

...

Midgard is a data storage service. Whether you write desktop or web applications, instead of coming up with your own file format, you just use Midgard. You can work more easily and object-based. Users have many different devices these days, so Midgard has strong replication features to synchronize between different systems. Midgard is built on top of GObject; we provide bindings to a bunch of different languages so developers can choose the tools they like - PHP, Python, Javascript. Currently (as in now, while we're talking) Qt bindings are being developed here at Akademy.

Read the whole interview.

I’m excited to announce I’ll be speaking at PHPNW Conference, to be held October 9th, 2010 in Manchester, UK. I’ll be doing my talk, “Developing Easily Deployable PHP Applications“, which I also did in July at OSCON. I’m working on making the talk even better based upon feedback I received, and will talk more about the various tools we use and have developed to make building SugarCRM easier.

This is my first time to this conference, but judging from the lineup of talks it is not one to miss if you are in the area. The lineup has several exciting talks about PHP development from some of the biggest names in PHP. You can register now at the conference website; early bird registration ends on September 4th.

... on contribution

Who hasn't ever started writing his own Framework/CMS? It is considered best practice for learning purposes, but going through all the security stuff can be stressful and boring at the same time. That's where most devs start to contribute to big Open Source-projects like Typo3 or the Zend Framework, because they are already experienced working with it and yet evolving another system on the market or even getting people to contribute seems like an unachievable task. Instead of wasting his time on yet another ACL implementation, the developer is taking part in making a software become even better, no matter if he delivers new features, reports / fixes bugs or works on documentation (another, yet an often underestimated part of contribution). It is also worth noting that every single Blog-entry and every HowTo thats put on the web also is a great deal of contribution that helps the software spreading. Beginners articles are important to put on the web since every one of us had it's beginnings and these are the sort of articles where many people decide to either use the software for a certain project or not.

As you might see, this article is not only a guide on contributing bugfixes, but also I want to motivate you to just give it a try.

... on Zend Framework

Having spent almost a year at the IRC support channel, I can tell they're really fun guys to hang around with. Of course, the Framework itself developed into a great piece of software. I do not want to discuss the up or downsides of a use-at-will framework, neither I want to recommend it over {put your favourite software here}. But what I can talk about is a little summary of the support channel's chatlogs. The widely annouced channel (which is #zftalk on Freenode) includes all kinds of concerns. One kind of people finds bugs, the other do have really clever ideas on improvements, but when you ask them to contribute its all the same: they either think it takes years to get into it, the others think they might be "not good enough for this". We sure won't force or threaten people to contribute, but what I can do is taking the fear out of it and demystify the thing, so later you might see that its actually just a few minutes to spend. Let me just loose a few words to the latter ones before we get into it: You can't destroy anything, and every idea of yours can also lead to a great improvement either realted to your concern or in a completely different area. We're glad that you take your time, even if you are completely new to ZF. Some beginners concerns already caused developers to write guides and articles that are still around and are linked at times in #zftalk...

... on contributing to Zend Framework

Contributing any code to ZF requires signing the CLA, which is an agreement that both you have the right to share any code you supply, and that you will not patent that code. This is to ensure that the frameworks codebase remains business friendly, and free to use for everyone. In fact you have to actually sign a paper, having done this you can just scan and mail or fax it. This is an important step, and none of your code will be used in any official package unless you did this.

The next step will be reading the coding & subversion standards. If you already had a look at actual ZF components code you should be familiar with the standards. Once you took a short insight (you probably wont be able to just remember all of this at once), you can check out the official SVN repository. Notice, that you, even having signed the CLA and being confirmed, do not have commit rights. So you might now ask yourself how to contribute then? All magic is taking place in the bugtracker, ZF's official Jira. All bug tickets, additions and improvements are filed as tickets here. So if you find a bug, report it here, and soon there will be a discussion in the comments section of a ticket.

Mostly all of these people, being listed by their reallife names, are also to be found on different names in the support channel, so feel free to ask them any ticket-related stuff.

The code itself will be submitted as a patch file (svn diff > patchFile), and uploaded in the Jira-Ticket. This might also be done by people who do have commit rights, but one might not be sure how to fix a problem, or any question might be left. This method of code management then leaves it to the original package developer to decide whether a change should be made or it should be thought over again (might have side effects on other packages and so on).

The last yet very important point is unit tests. ZF makes heavy use of th

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I don’t want to be too alarmist, but try running the following PHP code on your system:

<?php
$date = '2040-02-01';
$format = 'l d F Y H:i';

$mydate1 = strtotime($date);
echo '<p>', date($format, $mydate1), '</p>';
?>

With luck, you’ll see “Wednesday 1 February 2040 00:00″ displayed in your browser. If you’re seeing a date in the late 60’s or early 70’s, your PHP application may be at risk from the Y2K38 bug!

What’s the Y2K38 bug?

Y2K38, or the Unix Millennium Bug, affects PHP and many other languages and systems which use a signed 32-bit integer to represent dates as the number of seconds since 00:00:00 UTC on 1 January 1970. The furthest date which can be stored is 03:14:07 UTC on 19 January 2038. Beyond that, the left-most bit is set and the integer becomes a negative decimal number — or a time prior to the epoch.

Yes, it’s 28 years away and I’m sure many of you think it’s ridiculous to worry about it now. However, developers thought that way about the Millennium bug the 1970’s and 80’s. Also, any web application which handles long-term future events could be at risk. For example, a typical mortgage runs for 25 years. Pensions and savings plans can be far longer.

Will 64-bit save us?

Probably. If you’re using a 64-bit OS with a compiled 64-bit edition of PHP, your application shouldn’t be affected. I’d recommend you test it, though. A signed 64-bit number gives a maximum future date which is 21 times greater than the current age of the universe — 292 billion years, give or take a day or two.

You can probably sleep at night if you’re convinced your financial application will always be installed on a 64-bit system.

Are there alternative options?

Fortunately, PHP introduced a new DateTime class in version 5.2 (experimental support was available in 5.1 and be aware that some methods were introduced in 5.3)…

<?php
$date = '2040-02-01';
$format = 'l j F Y H:i';

$mydate2 = new DateTime($date);
echo '<p>', $mydate2->format($format), '</p>';
?>

DateTime does not suffer from Y2K38 problems and will happily handle dates up to December 31, 9999. I might have paid off my mortgage by then!

It may not be worth upgrading existing applications, but you should certainly consider the DateTime class when planning your next project.

Has you experienced Y2K38 problems in your application? How did you fix it?

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jQuery is a popular JavaScript library which is used by many developers and applications. While using jQuery you need to write less code, writing functions is less complex and there are a lot of plugins you can use for free in your web application. Even if you code everything by yourself, you need only a few rows of code to create nice and powerful features for your website. If you’re in hurry check the jQuery demo page.

Populate select menus with jQuery and Ajax

One of the most powerful jQuery function is the Ajax Suite. This example shows how-to populate a second select menu based on the option from the first select menu.

Just in case we have this select menu with the main categories:

<form>
        <label for="category">Choose: </label>
        <select id="category" name="category">
                <option value="fruit">Fruit</option>
                <option value="grain">Grains</option>
                <option value="vegetables">Vegetables</option>
        </select>
</form>

If someone has changed the value for this select menu, we want to show the equivalent menu inside the span element with the ID “subcat”. To do this we use this jQuery snippet that makes an Ajax request to a PHP file called “getSubCat.php”. After the select menu is changed a loading image will show up (in case of slow Internet connections), the PHP script is called and the sub-select menu becomes visible.

$(document).ready(function() {
        $('#category').change(function() {
                var category = $(this).val

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This year’s Vermont Code Camp will be on Saturday, September 11th, 2010 at Kalkin Hall on the University of Vermont campus. Last year’s event was a big success with 85 attendees and 19 sessions and this one promises to be even bigger and better! The second annual Vermont Code Camp will be a full day event bringing together technology community members, students, and professionals from around Vermont and beyond.

There will be four rooms with sessions on .NET, PHP, Ruby, Python, Java, and more. Two of the rooms will have .NET topics and another will have sessions on free/open source software. There will be a fourth room where developers will be introduced to various technologies that they may not use every day. For example, are you a .NET developer? Come and learn about PHP, Ruby, Python, or Java. A Ruby developer? Learn about .NET, PHP, Python, or Java. You get the idea.

Vermont Code Camp is a great way to bring together technology user groups from around Vermont. The Vermont.NET User Group is the primary organizer of the event but we hope to see others from the Burlington, VT PHP Users Group (which I organize), the Vermont Ruby On Rails User Group, the Vermont Area Group of Unix Enthusiasts (VAGUE), the Green Mountain Oracle Users Group, the New England Adobe User Group, and the VT SQL Server Users Group there. Do you know of any other Vermont technology user groups? Please let me know so that we can invite them!

In case you ever heard me talking about PHP internals I certainly mentioned something along the lines of "Everything in PHP is a HashTable" that's not true, but next to a zval the HashTable is one of the most important structures in PHP. While preparing my "PHP Under The Hood" talk for the Dutch PHP Conference there was a question on IRC about extension_loaded() being faster than function_exists(), which might be strange as both of them are simple hash lookups and a hash lookup is said to be O(1). I started to write some slides for it but figured out that I won't have the time to go through it during that presentation, so I'm doing this now, here:

You all should know PHP arrays. They allow you to create a list of elements where every element may be identified by a key. This key may either be an integer or a string. Now we need a way to store this association in an effective way in memory. An efficient way to store a collection of data in memory is a "real" array, an array of elements indexed by a sequence of numbers, starting at 0, up to n. As memory is essentially a sequence of numbered storage blocks (this obviously is simplified, there might be segments and offsets, there might be virtual pages, etc.) we can efficiently access an element by knowing the address of the first element, the size of the elements (we assume all have the same size, which is the case here), and the index: The address of the n-th element is start_address + (n * size_of_element). That's basically what C arrays are.

Now we're not dealing with C and C arrays but also want to use string offsets so we need a function to calculate a numeric value, a hash, for each key. An hash function you most likely know is MD5, MD5 is creating a 128 bit numeric value which is often represented using 32 hexadecimal characters. For our purpose 128 bit is a bit much and MD5 is too slow so the PHP developers have chosen the "DJBX33A (Daniel J. Bernstein, Times 33 with Addition)" algorithm. This hash function is relatively fast and gives us an integer of the value, the trouble with this algorithm is that it is more likely to produce conflicts, that means to string values which create the same numeric value.

Now back to our C array: For being able to safely read any element, to see whether it is used, we need to pre-allocate the entire array with space for all possible elements. Given our hash function returning a system dependent (32 bit or 64 bit) integer this is quite a lot (size of an element multiplied wit the max int value), so PHP does another trick: It throws some digits away. For this a table mask is calculated. The a table mask is a number which is a power of two and then one subtracted and ideally higher than the number elements in the hash table. If one looks at this in binary representation this is a number where all bits are set. Doing a binary AND operation of our hash value and the table this gives us a number which is smaller than our table mask. Let's look at an example: The hash value of "foobar" equals, in decimal digits, to 3127933054. We assume a table mask of 2047 (2¹¹-1).

  3127933054    10111010011100000111100001111110
&       2047    00000000000000000000011111111111
=        126    00000000000000000000000001111110

Wonderful - we have an array Index, 126, for this string and can set the value in memory!

If life were that easy. Remember: We used a hashing function which is by far not collision free and then dropped almost two thirds of the binary digits by using the table mask. This makes it rather likely that some collisions appear. These collisions are handled by storing values with the same hash in a linked list. So for accessing the an element one has to

1. Calculate the hash
2. Apply the table mask
3. locate the memory offset
4. check whether this is the element we need, traverse the linked list.

Now the question initially asked was why extension_loaded() might be faster than function_exists() and we can tell: For many random reasons and since you have chosen a value which probably conflicts in the first, not in the second. So now the question is how often such collisions happen for this I did a quick analysis: Given the function table of a random PHP build of mine with 1106 functions listed I have 634 unique hash values and 210 hash values calculated from different functions. Worst is the value of 471 which represents 6 functions.

Full results are

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