Slashdot Mirror

← Back to Stories (view on slashdot.org)

Former Sun Mobile JIT Engineers Take On Mobile JavaScript/HTML Performance

Posted by samzenpus on from the point-counterpoint dept.

First time accepted submitter digiti writes "In response to Drew Crawford's article about JavaScript performance, Shai Almog wrote a piece providing a different interpretation for the performance costs (summary: it's the DOM not the script). He then gives several examples of where mobile Java performs really well on memory constrained devices. Where do you stand in the debate?"

12 of 106 comments (clear)

  1. I blame the DOM too by Anonymous Coward · · Score: 5, Interesting

    An arbitrary tree of arbitrary objects with arbitrary methods of manipulating them thanks to years of incremental changes that are never properly documented (quick! point to the document showing that a select tag has a value attribute!) and are never deprecated.

    1. Re:I blame the DOM too by maxwell+demon · · Score: 5, Funny

      (quick! point to the document showing that a select tag has a value attribute!)

      Here it is.

      --
      The Tao of math: The numbers you can count are not the real numbers.
  2. No rebuttal by arendjr · · Score: 5, Interesting

    While this post is a valuable addition to Drew's analysis, I feel it's not really a rebutal at all.

    Yes, JavaScript is slow for the reasons Drew mentioned and yes, the DOM is a nightmare to optimize for responsive UIs. They're both right.

    While this blog also provides some nice insight into how you can have acceptable performance with a GC on mobile, it's not offering any workable alternative that would work for JavaScript. So Drew's article still comes out pretty strong, IMO.

    1. Re:No rebuttal by gl4ss · · Score: 4, Interesting

      I'm just blabberfastebasted about the summary.

      first it goes on about javascript and then about mobile java performing really well on some devices.
      j2me - commonly known as mobile java, being something entirely different from javascript.. and j2me did pretty well. you could do wolfenstein clones in 128kbytes(was a common .jar size limit, earlier than that 64kbytes was pretty common) on machines with ~300-400kbytes of ram available for you.. and gc worked just fine, so long as you didn't abuse String or do shit like that - but that's a bit easier to code for in java than in javascript imho(reusing objects etc).

      dom though.. of course, it's ridiculous to use for high responsive stuff, while javascript itself can run pretty nicely, lacking real threads certainly doesn't help etc of course.. but it's pretty obvious how you can do things with canvas that would bog the dom renderer.

      the article is about how javascript on mobile should be doable ok because j2me worked remarkably well? since j2me did work remarkably well on the lower level(really, it did). what did not work out was their api jsr process for j2me which zombied the whole platform and made almost all extensions useless or half useless - had they not fucked it up like that we would not have needed android.

      funny thing about j2me is that most of the mobile stuff I have coded over last 10 years is such that you cannot go to a shop now and buy a device that would run them - except for the j2me code, I could still buy a cheapo nokia and run them.

      --
      world was created 5 seconds before this post as it is.
    2. Re:No rebuttal by slacka · · Score: 4, Interesting

      While this post is a valuable addition to Drew's analysis, I feel it's not really a rebutal at all.

      Yes, JavaScript is slow for the reasons Drew mentioned and yes, the DOM is a nightmare to optimize for responsive UIs. They're both right.

      The key issue here is that these web technologies are being shoehorned into areas they were never designed for. From Document Object Model being used for Applications to the lightweight scripting language, JavaScript, being used for heavy weight programming of course the end result is going to be a poor mobile experience.

      If W3C and WHATWG seriously want to compete with Android and iOS Apps, they should consider throwing out the DOM and CSS standards and starting over. JavaScript can be fixed, but DOM/CSS are so technically flawed to the core, the sooner they're depreciated, the sooner the web has a real chance as being a generic platform for applications.

  3. Perceived Performance by Hamfist · · Score: 4, Insightful

    I dislike the separation of 'Perceived' vs 'Actual' performance. If I perceive it to be slow, it's slow. This reminds of of the Firefox devs that spent years saying how if an add-on makes their browser a memory hog and a slowpoke, it's not their problem because their performance is fine.

    Devs.. If it's slow, it's slow. Call it perceived, call it actual, call it the Pope for all I care. It's a Slow Pope.

  4. Data vs Hand-waving by 2megs · · Score: 5, Insightful

    Crawford brought in lots of data on real-world performance. (e.g. http://sealedabstract.com/wp-content/uploads/2013/05/Screen-Shot-2013-05-14-at-10.15.29-PM.png)

    Almog's rebuttal has a lot of claims with no actual evidence. Nothing is measured; everything he says is based on how he thinks things should in theory work. But the "sufficiently smart GC" is as big a joke as the "sufficiently smart compiler", and he even says "while some of these allocation patterns were discussed by teams when I was at Sun I don't know if these were actually implemented".

    Also:

    (in fact game programmers NEVER allocate during game level execution)....This isn't really hard, you just make sure that while you are performing an animation or within a game level you don't make any allocations.

    I'm a professional game programmer, and I'm laughing at this. If you're making Space Invaders, and there's a fixed board and a fixed number of invaders, that statement is true. If you're making a game for this decade, with meaningful AI, an open world that's continuously streamed in and out of memory, and dynamic, emergent, or player-driven events, that's just silly. For Mr. Almog to even say that shows how much he doesn't know about the subject.

  5. Throughput, latency, and latency hiding by tepples · · Score: 4, Interesting

    Perhaps it's a difference between throughput and latency. Nine moms can make nine babies in nine months, offering nine times the throughput of one mom, but each baby still takes nine months from conception to completion. Users tend to notice latency more than throughput unless an operation already takes long enough to need a progress bar. Some algorithms have a tradeoff between throughput and latency, which need fine tuning to make things feel fast enough.

    There are also a few ways to psychologically hide latency even if you can't eliminate it. The "door opening" transition screen in Resident Evil is one example, hiding a load from disc, as are some of the transitions used by online photo albums to slowly open a viewer window while the photo downloads.

    1. Re:Throughput, latency, and latency hiding by aliquis · · Score: 4, Funny

      Or you sit there like:

      "Stupid animation just show me the content."

  6. Re:My guarantee by i+kan+reed · · Score: 4, Funny

    For the 3 seconds before your battery runs out.

  7. I didn't post a rebuttal by Shai+Almog · · Score: 5, Interesting

    I actually agree with almost everything Drew wrote with the exception of his GC statements, I worked for an EA contractor in the 90's doing large scale terrain streaming on what today would be a a computer less powerful than an iPhone so while my game programming experience might be outdated its still valid. Saying that I don't know if its actually implemented only referred to the last section. Like I said, I actually worked on the VM code as well as the elements on top of it. As I said in the comments to the article never might have been harsh but I pretty much stand by it. If you use a GC you need to program with that in mind and design the times where GC occurs (level loading). Most of your dynamic memory would be textures anyway which are outside the domain of the GC altogether and shouldn't trigger GC activity. To avoid overhead in a very large or infinite world you swap objects in place by using a pool, no its not ideal and you do need to program "around" the GC in that regard. OTOH when we programmed games in C++ we did exactly the same thing, no one would EVER allocate dynamic memory during gameplay to avoid framerate cost.

  8. Re:friggen dummies... by Anonymous Coward · · Score: 5, Insightful

    You're wrong. But not in the way you think. The ability to write abstractions, and an obsession with design patterns, often results in needless abstraction and a loss of focus.

    Libraries like C++ STL and Java Collections only make this worse. Why? Because your application is basically one giant data structure. I forgot whether it was Dennis Ritchie, or Ken Thompson, or whomever, but it was once that said good programming is about implementing the correct data structures. Note that this doesn't mean reusing generic data structures; it means drawing upon the universe of conceptual data structures to craft a narrowly focus data structure and algorithm that fits your problem.

    If you start out with generic data structures, then you end up working backwards. You have lots of boilerplate code just to use those generic data structures, which you then aggregate and glue together in the same way you would have done from scratch, but with far less code. Programming is not about splicing hash tables together with trees ad hoc. This is a ridiculously reductive perspective on what is programming and how good programs are written.

    This is why, almost without fail, real-world applications developed in high-level languages tend to have ridiculously high source line counts. People get carried away with abstraction, including the language implementors with their plethora of generic data structure libraries.

    IME, C is *the* sweet spot, if you had to pick a single language. However, you can do better by mixing and matching different languages, especially where they offer unique characteristics--functions as first-class objects + real closures (i.e. not C++ lambdas), coroutines, exceptional optimizing support (e.g. Fortran for iterative numerical algorithms), and functional language characteristics which make is easier to express some kinds of data structures and algorithms. This is why I stay away from C++; it's too much of a pain to mix C++ with various other languages, where almost every language in existence has strong C support.

    If people spent as much time maintaing proficiency in different languages instead of trying to do everything in a single language (and grappling with the inevitably cognitive dissonance when defending their choices on web forums), then the world would be a far more efficienct and less bug-prone place.