Posts Tagged Programming

One Man’s View is Another Man’s Data

I think it’s common for a developer to get the idea in his or her head that developing under an MVC (Model View Controller) paradigm is ultra cut and dry: There is one Model, one View, and one Controller for a given task. Within a given layer of the software stack this may often (or even always) be true.

However: all software produces something (in its view) which is consumed by the next higher tier of the software stack as data, and thus is only part of the model for that next stack. All software produces something to be consumed by something else. What is to you a view is to someone else data.

So it’s important to avoid thinking that there’s something special about your particular view (no matter where you are in the stack) – as if it’s somehow magical and the view. You’re never the end of the line, it doesn’t matter how far down the line you really are. The end of the line is the brain of the human who will ultimately consume this data. Even then they’re not the end of the line, they process that data, make decisions based on it, and produce some output of their own – whether it’s using it to produce new data for the next action within the application, taking that data elsewhere as an input to a different process, or storing it to memory for later use as data for a future process.

Let’s look at an example from web development. The PHP/ColdFusion/ASP.NET/Ruby/FOTM developers I know tend to think of themselves as the end of the line (and I have too to a substantial extent). They’re producing something to be consumed (as they see it) by the end user. This is the guy who gets to make the HCI (Human-Computer Interaction) interface that either creates a positive experience for the user, or a negative one. Everything past him just follows the instructions he produces. Bold this, outline that, send this data there. What’s harder to see is that he’s just following the instructions he was given by the user and producing data in a format that other software later in the stack requires of him.

What the web developer calls data is actually just a view provided by lower down in the stack (a database typically, which in turn gets a view of stuff from the filesystem which it calls data, etc). A web developer’s view (HTML typically) is just data to the web browser. The web browser’s view (graphical representation) is just data to the display driver. The display driver’s view (bits of light on a computer monitor) is just data to the user.

The software stack starts and ends with the user. If anything is sacrosanct, the ultimate MVC, it’s the user. But as I’ve already said, the user ends up just starting the cycle again, maybe she uses that data to feed the computer again, or maybe she uses that data for another purpose.

So don’t get caught up in “HTML is the view, XML/SOAP is data,” it’s all data to someone, and therefore it’s all a view to you. Don’t think there’s something special about one way to structure data vs another way to structure data. Finally don’t create different channels depending on what consumes your data. Use the same data channels (Model/Controller) and provide a different View. That is after all what the purpose of a View is all about – consumer agnosticism.

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ColdFusion Ordered Struct

As most readers probably already know, in ColdFusion, structs are associatively keyed storage structures similar to an array but where you get to use a string to key an entry rather than only a sequential number.

PHP only has array() which acts both like ColdFusion’s array and struct both. You can numerically key arrays or associatively key them, or both. One of the reasons it can get away with this is that it preserves the insert order. So if you do:


The output will be the values in the same order they were put into the structure. If you do the same thing in ColdFusion, you’ll get it back in a seemingly random order (or depending on the version some times you’ll get back in alphabetical order):

Instead if you need to preserve insert order, you can use a similar Java object from ColdFusion:

You can treat this like a struct in every way, including <cfdump>ing it (though cfdump will not show you the insert order for some reason). As you iterate over it, the contents will always come back in the same order they were inserted.

It’s important to note that LinkedHashMap keys are also case-sensitive while ColdFusion Struct keys are case insensitive. This may cause undesired results as you might have two keys that you believe are the same but differ in case; this may cause collisions when working with other objects that are not case sensitive.

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Relative CFLoop Performance for Various Loop Structures

Introduction

Jim over at Ben Nadel’s blog made the assertion that looping a list is faster than looping a struct.  It’s an interesting assertion that looping a list would be faster than looping an array.  I did a test of my own to find out.

Setup

Starting with objects with 1 entry populated, I increased the number of populated entries by 1,000 until I reached 100,001 entries in each of an Array, a List, and a Struct.

I also compared the following syntaxes:
<cfloop array=”myArray” index=”x”>
<cfloop from=”1″ to=”#ArrayLen(myArray)#” index=”x”>
<cfloop collection=”#myStruct#” item=”x”>
<cfloop from=”1″ to=”#StructCount(myStruct)#” index=”x”>
<cfloop list=”myList” index=”x”>
<cfloop from=”1″ to=”#ListLen(myList)#” index=”x”>

For each type of test, I did a <cfsavecontent> to cfoutput the relevant entries from each object without causing a ton of data to be sent back to the browser.  The actual <cfloop> and output was tight (all on one line to minimize the total content going to cfsavecontent).

I ran each incremental test 10 times to get an average duration.  I did this because my in my earliest tests it was obvious that garbage collection was causing significant variance (shorter tests often took longer than their longer brethren).  Even still it’s obvious garbage collection played a bigger factor in efficiency than the actual test results, making them somewhat difficult to decipher meaningfully.

Execution

Early on, I dropped the final test (which involved ListGetAt() for the output portion) since while the others were still taking a few milliseconds, this test was already taking multiple seconds.

It should be no surprise that 1 entry of each took no measurable time (getTickCount() had not incremented).

At 10,001 entries, <cfloop array> and <cfloop list> took 5 and 4 milliseconds respectively, but at 11,001 (the next level up), it was 3 and 7 milliseconds respectively – neck and neck, looking in favor of <cfloop array>.  <cfloop ArrayLen()> was taking 9 and 6 seconds, <cfloop collection> 21 and 17 seconds, and <cfloop StructCount()> waas taking 21 and 14.  At this level we could say <cfloop array> and <cfloop list> were close, while the others were not.

At 50,001 entries, <cfloop array> and <cfloop list> are still neck and neck.  They reported identical times of 11.00 milliseconds.  <cfloop ArrayLen()> weighed in at 56.10ms, <cfloop collection> at 126.2ms, and <cfloop StructCount()> at 91.2ms.

By the final test of 100,001 entries, <cfloop array> and <cfloop list> had finally started to show a real difference.  <cfloop array> pulled ahead as the clear winner, with at least a 10ms margin on all but one of the the 10 tests leading up to 100,001.

Cfloop Performance Comparison
(Click for full version)

So what causes such a performance difference?

<cfloop ListLen()> was the clear loser by a wide margin.  ListGetAt() is horribly inefficient.  Each time you call it, it has to consume the string from the start, counting delimiters until it reaches position-1, then continue consuming until it reaches position.  This is no surprise at all.

<cfloop collection> was the clear next-to-last-place loser.  The most likely reason for this to me is that internally it needs to loop over some other type of object (in this case, most likely an array of struct keys), then needs to do a lookup within the actual structure itself (a HashMap of some form).

<cfloop StructCount()> came next.  This was a bit of an non-real world scenario.  We didn’t have to loop over a collection of struct keys, we knew what the struct keys were and were able to perform the loop itself in a faster fashion than looking up keys.  But to output the value, we still needed to do HashMap lookups on the keys themselves.

<cfloop ArrayLen()> won the bronze.  Seems to me that this is because we have to do a positional lookup to output the value for each entry.  That shouldn’t be huge because internally this should be represented as a vector of pointers to the actual entries, and since each vector has a fixed memory size, we take ArrayMemoryStartPoint + position * sizeof(vector).  Well, would be nice if that’s the case, but it’s not quite that simple since these arrays are dynamically sized.  We actually have to do a bit of work with a table of memory references, blah blah blah.  Point is we have to do a lookup (albeit cheaper than a struct lookup) to find the correct entry.

<cfloop list> took the silver.  This makes sense, the iterator involved in the cfloop can remember where it left off, and each time through the loop only has to consume up to the next delimiter.  It knows what the index of the previous delimiter is, and so the only lookup it has to do at all is collecting the characters from offset A to offset B (which it could actually have kept track of while it was consuming).

<cfloop array> took the gold, but not by a large margin.  This also makes sense because it has the same sort of performance gain that <cfloop list> has (already knowing its current offset for the next time through the loop), and all it has to do is return a pointer to the next element in the vector.  The vector iterator handles this stuff at a lower level and is able to make the best use of its own internal structures to make this as fast as possible.

Conclusion

<cfloop array> and <cfloop list> are pretty interchangeable even though the former wins the contest.

All of this being said, we are still looking at loop overhead of less than 300 milliseconds even for the slowest (other than <cfloop ListLen()>) loop type for 100,000 records.  This is incredibly trivial overhead for that amount of data.  So in reality which type you use probably depends more on what structures you’re already using – trying to convert to a different data container for your loop will probably cost you as many or more cycles than using the native loop type associated with wherever your data currently is.

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Established Programmers Getting Started in Web Development

An acquaintance of mine has recently graduated from college with a degree in computer science.  Where he went, apparently they stressed theory over practice.  He’s got some C++, Lisp, Java, and MySQL experience, but has never touched web development (neither HTML, nor even viewed source on a web page).

He’s hoping to get a job with a company that has him supporting Java applications with web front ends, so to do that he’ll need to get at least tolerable with HTML.  He’s willing to go to training if there’s a course that’ll help, but the obvious concern is that he goes to a 5 day training and spends a significant amount of time covering “Web pages are viewed in web browsers” type material – that is to say, he’s concerned that intro to web development courses are going to be tailored to people looking to set up a family-newsletter or small-business-created-by-the-owner type site.

I’m recommending he start with the W3C tutorials: http://www.w3.org/2002/03/tutorials , which should get him a functional early level of knowledge.  I suggested he could start out trying to make a personal site in HTML w/o leaning on a HTML editor, hopefully this gets him the rudimentary skills he needs.  Other suggestions are welcome!

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