Flex Life Cycle
After working 10 years with Flash and 3 years with Flex I am still not convinced that the Flex Life Cycle is necessary.
I discussed this topic already with many developers but nobody could really give me a satisfying answer.
So I spread out my thoughts now to the public in the hope to get some valuable feedback.
Of course I am familiar with the concept of the Flex Life Cycle and the “elastic racetrack” behavior of the Flash Player.
The reason why I am not a friend of this concept is because it introduces an asynchronous code execution where a synchronous code execution would be much easier and faster.
In all my ActionScript based projects it was never necessary to use this pattern and defer code execution to another frame (or Render Event).
At bwin we have built a similar application as the current Flex-based Live Betting application previously in AS2, with a lot of complex components and auto layout containers, without running into any serious problems.
And to be honest the performance of the AS2 project felt somehow the same as the Flex version. But AS3 is about 10 times faster (of course that´s a bit too simple said and we did not measure the difference, but I am not the only one complaining about poor Flex Performance).
So isn´t it valid to question the concepts Flex is based on?
I am sure the architects at Adobe have had good reasons why they decided to introduce this pattern.
In the Docs and Blogosphere one can find several papers about it, but none of these explanations satisfied me, and some are not telling the full truth (that code execution is deferred to another frame).
So I try to discuss some assumptions for possible reasons:
- Avoid Performance bottlenecks
- Keep the Frame-rendering fluidly
- Avoid Performance penalty from unintended repeated method (setter) calls
- Pattern for separating different concerns
- Problems with reading out the measurements of DisplayObjects before they are rendered on screen
- Problems with complex execution flow from auto-layout containers code
So let me add my thought to these points:
Avoid Performance bottlenecks
That was my first assumption when I started with Flex, that this pattern is used to avoid performance bottlenecks. First I thought there is a hidden mechanism for detecting code execution which is running too long and delay this execution to the next frame. After checking out the SDK code I found out that it is simply delaying the 3 phases to 3 “half-frames” (Render Events and Enter Frame Events). So if you have really heavy code your player is still freezing up for a certain time and the Life Cycle does not give you any support for solving this problem.
That leads to the next argument:
Keep the Frame-rendering fluidly
Delaying the render code to the next frame helps the Flash Player running more smoothly and fluidly. That is basically true, but in my opinion 90% of the time the Life Cycle is wasting performance. For me it is a bad trade to get maybe at startup time some more fluidly running pre-loader animation but startup time takes much longer.
Why the Life Cycle is wasting Performance?
Because code which normally would be executed in one frame is now executed over 2 frames (or more).
There is another related issue with performance:
Avoid Performance penalty from unintended repeated method (setter) calls
Assume that in a large project it could be hard to control the execution flow so that it could happen that setting a text or layout property to a component is not only applied once but unintended multiple times.
For this scenario the Life Cycle helps because the call to the setter of the property is relatively cheap, so if the setter is called 10 times instead of once it will not hurt much. Then at commitProperties the property is only applied once to the component.
Again some weird scenarios with multiple invocations of commitProperties will not hurt much because the applying of the property to the component should be protected by a “changed” flag (see best practice with the Flex Life Cycle).
Also if you need for layout code some measurements the pattern helps to avoid unnecessary and repeated code executions.
BUT – is poorly written code really the reason why this pattern was introduced? It is true that it gives you some kind of fault tolerance, performance-wise. I guess this argument should not count in professional software development, and in fact it is dangerous because it could hide some deeper problems. If your setters are called more then once, why not look for the reason and clean it up?
I know in complex situations this could be sometimes hard, and under real life circumstances and time pressure you have to deal with something like this. But it should not count as a criteria for such a basic framework design decision.
I made also some measurements to check out the performance penalties for repeatedly called setters:
With 100 000 iterations applying a changing text to a TextField (in a AS3 project) I got these results:
Setting the text property to a variable in a loop and then applying the already stored text to the TextField again in a loop:
[code lang="actionscript3"]setText(): 119ms applyStoredText(): 481ms [/code]
In contrast to applying the property directly to the TextField:
[code lang="actionscript3"] setAndApplyText(): 2879ms [/code]
So you can see it is much slower in the 2. Case, so the Life Cycle really helps here, because it only applies the last stored property and not the changing values in between. But again – setting multiple times unnecessary property values is another problem.
The same test with setting the x position does not deliver such a big difference, in fact it is nearly the same time consumed (40+52 vs. 114)
[code lang="actionscript3"]setXPos(): 40ms applyStoredXPos(): 52ms setAndApplyXPos(): 114ms [/code]
Let´s continue with the next point:
Pattern for separating different concerns
To have a kind of pattern which separates different concerns is basically a cool thing. So you have your code block for setting properties, another method where the properties are applied to the component, a method where the measurement is defined and another one for the layout code.
I have no really argument against this pattern, but I don´t know why it is necessary to defer some code of these phases to the next Frame. The execution of the Life Cycle methods could have been triggered also at the Render Event, then there would not have been any delay to another frame, even it still would add this nasty asynchrony.
So this pattern could make development easier but introduce asynchronous behavior where we lived in a beautiful synchronous Flash world before. In my opinion: Not a good trade.
Problems with reading out the measurements of DisplayObjects before they are rendered on screen
Remembering back to some of my Flash projects I have had sometimes strange problems with TextFields and measurement when setting text and using autosize. But I could not reproduce these problems in a test case anymore. So I am not sure if that was caused by some other stuff or maybe by differences in some older Flash Player versions? But at least in my situations these problems could always be solved without deferring code to another Frame. But at this point I am not sure if there are certain use cases where you cannot read out the size of a DisplayObject (TextField) before it is actually rendered to the screen. If there are such cases this would be a valid argument, but then I am wondering why this could not be solved on the Flash Player level instead of solving this problem at a Framework level.
And my last point:
Problems with complex execution flow from auto-layout containers code
I can imagine that complex situations with nested auto layout containers could be sometimes really tricky to handle. To avoid recursions or unnecessary calls for any possible situation in a generic framework is a tough challenge.
But also in complex situations it is a deterministic behavior, so it should be possible to solve this without the Life Cycle pattern as well. From my experience there was no problems with auto layout containers, but of course in normal project development you have limited use cases and we were not forced to deal with all the possible use cases, like Flex has to do as a generic framework.
So finally I don´t have any idea for the real reason why Adobe has introduced the Life Cycle.
Maybe it seemed that it could help solving a lot of tricky problems (auto layout containers, mixing MXML with AS code,…) and was considered as a good pattern to make development easier. Maybe the fact that Flash has a strong support for Event driven programming and the Flash developers are already used to handle this asynchrony, led to this decision?
Maybe is was a strategic decision to make Flex easier for new developers without Flash background, who were not familiar with the Flash Players frame-based execution model?
I don´t know. I really would appreciate if someone from the Flex Team could illuminate this topic.
I just have made the experience that many things where much more transparent, cleaner and faster in pure ActionScript then in Flex, and i think the Life Cycle is one of the reasons for that.
I really like the API of Flex but I am wondering why Adobe don´t give more attention to performance, specially for large scale applications.
Any comments or insights are highly appreciated!
P.S.: Just found an interesting post related to this. I 100% agree what Paul Taylor says about UIComponent, but that is another story. Ever heard about Reflex? Sounds pretty promising!
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Made Wednesday, 23 of March , 2011 at 23:47
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