PHP: A jump in performance for free

Not often I just post a link to another blog, but Lorna Jane has some very interesting numbers on PHP versions:
  http://www.lornajane.net/posts/2013/php-version-adoption

But what is even more interesting is the benchmarks of each PHP version which I'm going to reproduce here:

• 5.2.17: 3.77 seconds
• 5.3.23: 2.63 seconds
• 5.4.15: 1.98 seconds
• 5.5RC1: 2.11 seconds

Assuming that benchmark accurately reflects your own application, then your code on php 5.4 will run in 75% of the time it previously took on 5.3.  (PHP 5.5 appears to only be 80% of php 5.3 speed; not sure if the slowdown was due to working with a release candidate, rather than the final release?)

(PHP 5.5 stops supporting Windows XP and Windows 2003, and adds nothing that caught my interest. PHP 5.4 on the other hand had some interesting features, and now I see a worthwhile speed-up I will target that for new projects.)

node.js: Good Tutorial

Chatting with a friend at the weekend, node.js came up; I'd only vaguely heard of it, but apparently it is what all the kewl kids are into. Server-side javascript, right up my street.

I took a very quick look yesterday, and it sounded interesting: especially for speed-critical websites. So, today I took a deeper look. First up you should know the official website has a documentation link that only goes to the API documentation. In real terms that means node.js is officially undocumented. Then from the Wiki I found a link to a free e-book called Mastering Node. I won't give the link as it is (currently) over-priced: poorly organized and unfinished.

I was  getting a bit demoralized when a search found http://www.nodebeginner.org/. Now this is more like it. In fact this is an excellent tutorial, that goes right from raw beginner to a reasonably complex mini-application. (I read it in HTML format, but as an ebook it is 60 pages, so you can get an idea of how involved it is going to get.)

I followed along, and it was fairly easy, though I did have a lot of trouble outputting the POST-ed data. It always said "undefined" in my browser. I could do a console.log() of the variable just before and just after writing it to the browser and it was set correctly. I cleared the cache repeatedly, and tried a second browser. Annoyingly I didn't solve that problem in the end.

The main point of this blog post is to recommend the above tutorial/ebook if you're interested in getting a feel for node.js, but What Do I Think About node.js?

Hhhmmm. First and foremost, it should only be used by expert programmers. It is a bit like C++ in that it is going to be easy to shoot yourself in the foot. Asynchronous programming is hard. But if you use a synchronous programming-style you will lock up the whole server. I'm thinking in terms of the web server example application here (which is the use-case I had in mind for it). Asynchronous programming is hard. Yes, I know I already said that but I don't think you thought through what that means in the Real World. What will happen is programmers will take a short-cut: they'll use little bits of synchronous code for jobs they know are so quick that no-one will notice. (Even the above tutorial does this: fs.renameSync)  The problem is any job involving any I/O device (like a hard disk file system or a TCP/IP socket) will take 10 times longer to finish than average, about 1% of the time. (I made that statistic up, but the principle is true, so stay with me...)

What does that mean? When that happens it will lock the whole web server up, and all the other requests will block. Take the extreme case of doing a sync action that results in a time-out because the resource has gone offline. If the time-out is 30 seconds, the whole web server is down for 30 seconds. All of your customers are getting time-outs. Every image comes up broken.

Another nice thing about the Node Beginner tutorial is the links to deeper information... and nested in one of the comments is a link to a paper comparing threads and events: Why Events Are A Bad Idea  Well, their conclusion is in the title, but if you look at their charts the important thing to learn is that well-written event handling code and well-written threading code are basically as quick as each other. (You won't ever reach the right-side of the charts in a real website on a single server; their example is just serving a static image. So the differences are only of interest to academics.)

But, although dealing with threads is hard, asynchronous programming is even harder, IMHO.

Now, if node.js had a web server module where it maintained a thread pool and each new request got its own thread, then I could program in a synchronous style in my thread, happy in the knowledge I won't break the web server, and also happy I'll be able to meet my deadlines...

Rcpp: embedding C++ in R scripts

Rcpp is an R package to aid in making R extensions written in C++. It also includes a side-project for embedding R code in a C++ program (including being able to use all the R packages), but most amazing of all is the integration with R's inline package. Let me show you a minimal (but complete) script:

library('inline')
src='Rcpp::List output(1);output[0]="Hello World";return output;'
fun=cxxfunction(signature(),src,plugin="Rcpp")
fun()

Yes, it is the classic Hello World script, the output looks like:

[[1]]
[1] "Hello World"

What do I call this amazing? The contents of src is the body of a C++ function. The cxxfunction takes your C++ code, sends it to your C++ compiler, compiles it with the necessary headers, and finally embeds it in your R session as an R extension. It just works, there is no catch (*).

(I could have used a character object instead of a list. The Rcpp::List is just like an R list, meaning each element can be of a different type. If you've always wanted something like this in C++, also take a look at boost::any.)

The cxxfunction() call takes 1.9s to run on my machine, so the overhead to start-up the compiler and run the compilation process is not too bad.

Okay, not a motivating example, but the Rcpp project is not just technically amazing, it is also well documented. You can find some more interesting examples in the documentation, and if this has got your interest you will enjoy this video (1.5hrs) of a talk the Rcpp main authors did at Google.

By the way, if anyone knows of a PHP project for embedding C++ like this, please let me know!

*: You need to install the Rcpp and inline packages, and you need R version 2.12.0 or later. If you are using Ubuntu and your default version of R is too old, there are good instructions here on getting the latest R version as a deb package.