C# Blocking Queue

If you’re writing a threaded application in C# and you need to wait until a resource becomes available, you can use this class. Very handy for producer/consumer scenarios.

public class BlockingQueue<T>
    Queue<T> que = new Queue<T>();
    Semaphore sem = new Semaphore(0, Int32.MaxValue);

    public void Enqueue(T item)
        lock (que)


    public T Dequeue()

        lock (que)
            return que.Dequeue();

Django, Flatpages, Markdown, and Syntax Highlighting

For what should have been an easy task, this turned out to be extraordinarily difficult.

I assume you have Django already installed. If not, the tutorials on djangoproject.com aren’t too terrible, provided you’re not on a shared server (that’s another story!). I’m using Flatpages, but you can use whatever you want to follow along with this tutorial.

1. Install Markdown and Pygments for Python if you haven’t already. If you’re on Ubuntu, you can `sudo apt-get install python-markdown` or `easy_install Markdown` and `sudo apt-get install python-pygments`.

2. Go into your Django app and `mkdir templatetags`. This should be at the same level as `manage.py`, `settings.py` and `urls.py`. Then `cd` into that directory, and `touch __init__.py` (so that it becomes a module) and then add another file called something like `tags.py` (don’t name it “markdown.py” — that’ll bite you later). Paste this code in there:

from django import template
from django.template.defaultfilters import stringfilter

from django.conf import settings

register = template.Library()

def markdown(value, arg=''):
    Filter to create HTML out of Markdown, using custom extensions.

    The diffrence between this filter and the django-internal markdown
    filter (located in ``django/contrib/markup/templatetags/markup.py``)
    is that this filter enables extensions to be load.


        {{ object.text|markdown }}
        {{ object.text|markdown:"save" }}
        {{ object.text|markdown:"codehilite" }}
        {{ object.text|markdown:"save,codehilite" }}

    This code is taken from

        import markdown
    except ImportError:
        if settings.DEBUG:
            raise (template.TemplateSyntaxError,
                   "Error in {% markdown %} filter: "
                   + "The markdown library isn't installed.")
        else :
            from django.utils.html import escape, linebreaks
            return linebreaks(escape(value))
        if len(extensions) > 0 and extensions[0] == "safe" :
            extensions = extensions[1:]
            safe_mode = True
        else :
            safe_mode = False
        return markdown.markdown(value, extensions, safe_mode=safe_mode)

Yes, I’m leaving the link in there; I didn’t write that code.

3. Go into `settings.py` and add your app to the `INSTALLED_APPS`. You actually have to `import` your own app too; this baffled me for about an hour. My app is called `tech_eval` so my `INSTALLED_APPS` looks like this:

import tech_eval # you can put this line at the top of settings.py if you want


4. Like I said, I’m using Flatpages, so my template looks like this (I saved it to djangoproject/app/templates/flatpages/default.html).

{% load tags %}
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
    <title>{{ flatpage.title }}</title>
    <link rel="stylesheet" type="text/css" href="/tech_eval/media/css/code_style.css" />
    <h1>{{ flatpage.title }}</h1>
    {{ flatpage.content|markdown:"codehilite"|safe}}

Notice how we filter the content with markdown, make sure the codehilite extension is used, and flag it as `safe` afterwords (otherwise Django will automatically character-encode everything).

5. Hopefully this is already working for you at this point, but you probably want to add some color to your code. You can generate the appropriate css file with this:

pygmentize -f html -S default -a .codehilite >> code_style.css

Some different styles you can use (at least on my system) are:

['manni', 'colorful', 'murphy', 'autumn', 'bw', 'pastie', 'native', 'perldoc', 'borland', 'trac', 'default', 'fruity', 'emacs', 'friendly']

(stolen from here).

Or just copy and paste this CSS file if you’re lazy:

.codehilite .c { color: #408080; font-style: italic } /* Comment */
.codehilite .err { border: 1px solid #FF0000 } /* Error */
.codehilite .k { color: #008000; font-weight: bold } /* Keyword */
.codehilite .o { color: #666666 } /* Operator */
.codehilite .cm { color: #408080; font-style: italic } /* Comment.Multiline */
.codehilite .cp { color: #BC7A00 } /* Comment.Preproc */
.codehilite .c1 { color: #408080; font-style: italic } /* Comment.Single */
.codehilite .cs { color: #408080; font-style: italic } /* Comment.Special */
.codehilite .gd { color: #A00000 } /* Generic.Deleted */
.codehilite .ge { font-style: italic } /* Generic.Emph */
.codehilite .gr { color: #FF0000 } /* Generic.Error */
.codehilite .gh { color: #000080; font-weight: bold } /* Generic.Heading */
.codehilite .gi { color: #00A000 } /* Generic.Inserted */
.codehilite .go { color: #808080 } /* Generic.Output */
.codehilite .gp { color: #000080; font-weight: bold } /* Generic.Prompt */
.codehilite .gs { font-weight: bold } /* Generic.Strong */
.codehilite .gu { color: #800080; font-weight: bold } /* Generic.Subheading */
.codehilite .gt { color: #0040D0 } /* Generic.Traceback */
.codehilite .kc { color: #008000; font-weight: bold } /* Keyword.Constant */
.codehilite .kd { color: #008000; font-weight: bold } /* Keyword.Declaration */
.codehilite .kp { color: #008000 } /* Keyword.Pseudo */
.codehilite .kr { color: #008000; font-weight: bold } /* Keyword.Reserved */
.codehilite .kt { color: #B00040 } /* Keyword.Type */
.codehilite .m { color: #666666 } /* Literal.Number */
.codehilite .s { color: #BA2121 } /* Literal.String */
.codehilite .na { color: #7D9029 } /* Name.Attribute */
.codehilite .nb { color: #008000 } /* Name.Builtin */
.codehilite .nc { color: #0000FF; font-weight: bold } /* Name.Class */
.codehilite .no { color: #880000 } /* Name.Constant */
.codehilite .nd { color: #AA22FF } /* Name.Decorator */
.codehilite .ni { color: #999999; font-weight: bold } /* Name.Entity */
.codehilite .ne { color: #D2413A; font-weight: bold } /* Name.Exception */
.codehilite .nf { color: #0000FF } /* Name.Function */
.codehilite .nl { color: #A0A000 } /* Name.Label */
.codehilite .nn { color: #0000FF; font-weight: bold } /* Name.Namespace */
.codehilite .nt { color: #008000; font-weight: bold } /* Name.Tag */
.codehilite .nv { color: #19177C } /* Name.Variable */
.codehilite .ow { color: #AA22FF; font-weight: bold } /* Operator.Word */
.codehilite .w { color: #bbbbbb } /* Text.Whitespace */
.codehilite .mf { color: #666666 } /* Literal.Number.Float */
.codehilite .mh { color: #666666 } /* Literal.Number.Hex */
.codehilite .mi { color: #666666 } /* Literal.Number.Integer */
.codehilite .mo { color: #666666 } /* Literal.Number.Oct */
.codehilite .sb { color: #BA2121 } /* Literal.String.Backtick */
.codehilite .sc { color: #BA2121 } /* Literal.String.Char */
.codehilite .sd { color: #BA2121; font-style: italic } /* Literal.String.Doc */
.codehilite .s2 { color: #BA2121 } /* Literal.String.Double */
.codehilite .se { color: #BB6622; font-weight: bold } /* Literal.String.Escape */
.codehilite .sh { color: #BA2121 } /* Literal.String.Heredoc */
.codehilite .si { color: #BB6688; font-weight: bold } /* Literal.String.Interpol */
.codehilite .sx { color: #008000 } /* Literal.String.Other */
.codehilite .sr { color: #BB6688 } /* Literal.String.Regex */
.codehilite .s1 { color: #BA2121 } /* Literal.String.Single */
.codehilite .ss { color: #19177C } /* Literal.String.Symbol */
.codehilite .bp { color: #008000 } /* Name.Builtin.Pseudo */
.codehilite .vc { color: #19177C } /* Name.Variable.Class */
.codehilite .vg { color: #19177C } /* Name.Variable.Global */
.codehilite .vi { color: #19177C } /* Name.Variable.Instance */
.codehilite .il { color: #666666 } /* Literal.Number.Integer.Long */
.codehilitetable { border: 1px solid #666; width: 100%; background-color: #666; }
.codehilitetable .linenos { background-color: #666; padding: 0 5px; width: 20px; }
.codehilitetable .code { padding: 0 15px; background-color: #fff; }

And that should pretty much be it. Let me know if I missed anything or this was too difficult to follow along.

Qt + OpenGL Code Example

This article is from August 2009; please see the updated and more detailed version here.

I wanted to develop a game using OpenGL but I was having trouble deciding on a windowing library. Somebody suggested I try Qt, so I decided to give it another shot. I heard it was good, but the editor it came with was so foreign and unintuitive. Unfortunately, this overshadowed what a beautiful library Qt really is! It takes a little getting used to, but it really is well designed.
Read more Qt + OpenGL Code Example

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Not much needs to be said here.

function array_map_recursive($callback, $arr) {
    $ret = array();
    foreach($arr as $key => $val) {
        if(is_array($val)) $ret[$key] = array_map_recursive($callback, $val);
        else $ret[$key] = $callback($val);
    return $ret;

I wrote this so that I could do this…

$filters = array('htmlspecialchars', 'nl2br');
foreach($filters as $filter) $view_vars = array_map_recursive($filter, $view_vars);

Which just sanitizes my variables before I print them.

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jQuery Select Table Column or Row

Table rows are pretty easy to work as all the td elements are contained within one tr, but how would you grab all the tds in a single column? Why, by using these selectors of course!

$.fn.row = function(i) {
    return $('tr:nth-child('+(i+1)+') td', this);
$.fn.column = function(i) {
    return $('tr td:nth-child('+(i+1)+')', this);

// example - this will make the first column of every table red
$(document).ready(function() {

I like my selectors zero-based, but you can get rid of the +1 if you don’t like it.

SQL Injection Safe Queries Redux

function mysql_safe_string($value) {
    if(is_numeric($value))      return $value;
    elseif(empty($value))       return 'NULL';
    elseif(is_string($value))   return '\''.mysql_real_escape_string($value).'\'';
    elseif(is_array($value))    return implode(',',array_map('mysql_safe_string',$value));

function mysql_safe_query($format) {
    $args = array_slice(func_get_args(),1);
    $args = array_map('mysql_safe_string',$args);
    $query = vsprintf($format,$args);
    $result = mysql_query($query);
    if($result === false) echo '<div class="mysql-error"><strong>Error: </strong>',mysql_error(),'<br/><strong>Query: </strong>',$query,'</div>';
    return $result;

// example
$result = mysql_safe_query('SELECT * FROM users WHERE username=%s', $username);

Just use mysql_safe_query in place of mysql_query and you should be safe from SQL injection attacks. Use %s in place of any variables, and append them as arguments. Don’t quote your strings, it’ll be done for you automatically. Arrays will be flattened for you automatically and concatenated with commas. You can delete the error-echoing line if you want, but I find it useful for development.

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Facebook PHP API: Get the names of all your friends

If you didn’t already know, Facebook has an API that exposes quite a darn bit information. You can easily query this data using their API, but each request takes a fair bit of time. Typically, to get the names of all your friends, first you have to grab a list of the user ids of all your friends, and then query each and every single one to get their names. For me, that’s about 300 cross-server requests, which will almost certainly cause my server to time out, and probably force Facebook to reject me. Fortunately, Facebook has also created their own MySQL-like language, FQL (I pronounce it feequel), which lets you do some of these “complicated” queries in a single call. Here’s a simple example I wrote:

require_once 'facebook-platform/php/facebook.php';

$appapikey = 'yourapikeyhere';
$appsecret = 'yoursecretkey';
$facebook = new Facebook($appapikey, $appsecret);
$user_id = $facebook->require_login();

$result = fql_query('SELECT name FROM user WHERE uid IN (SELECT uid2 FROM friend WHERE uid1=%s)', $user_id);

function fql_query($query) {
    global $facebook;
    $args = array_slice(func_get_args(), 1);
    return $facebook->api_client->fql_query(vsprintf($query, $args));

function pr($arr) {
    echo '<pre>';
    echo '</pre>';

You’ll notice I’ve included two of my favorite wrapper functions. You can unroll them if you want. Anyway, just thought I’d share 🙂 I prefer writing FQL than trying to remember all their API calls anyway.

Oh… and just FYI, this prints out something like this:

    [0] => Array
            [name] => Mark Zuckerberg

    [1] => Array
            [name] => Tom Riddle

I hate it when people leave it a mystery what exactly their example is doing!

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Get Domain & Subdomain from URL

preg_match('/^(?:www\.)?(?:(.+)\.)?(.+\..+)$/i', $_SERVER['HTTP_HOST'], $matches);

define('PROTOCOL', strtolower(substr($_SERVER['SERVER_PROTOCOL'],0,strpos($_SERVER['SERVER_PROTOCOL'],'/'))).'://');
define('SUBDOMAIN', $matches[1]);
define('DOMAIN', $matches[2]);
define('HERE', $_SERVER['REQUEST_URI']);

If you’re at http://www.sub.domain.com/page, then:

PROTOCOL = http://
DOMAIN = domain.com
HERE = /page

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Insert into MySQL datetime column from PHP

You can use this simple function to convert a unix timestamp (like the one obtained from time()) to MySQL datetime format:

function mysql_datetime($timestamp = null) {
    if(!isset($timestamp)) $timestamp = time();
    return date('Y-m-d H:i:s', $timestamp);

I’m using this instead of MySQL’s NOW() function because my MySQL server isn’t localized to my timezone, but my PHP is by usage of date_default_timezone_set.

Edit: And you can use this function to convert back the other way (you can do this directly in the SQL too, but just in case)

function datetime_to_unix($datetime) {
    list($date, $time) = explode(' ', $datetime);
    list($year, $month, $day) = explode('-', $date);
    list($hour, $minute, $second) = explode(':', $time);
    return mktime($hour, $minute, $second, $month, $day, $year);