[jira] [Commented] (WICKET-5243) JS: High stack size in Function Executor causes "too much recursion"

["Martin Grigorov (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/WICKET-5243?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13919371#comment-13919371 ] 

Martin Grigorov commented on WICKET-5243:
-----------------------------------------

I have an idea how to simplify Wicket's code.
First let me reproduce the problem with FunctionExecuter involved.

> JS: High stack size in Function Executor causes "too much recursion"
> --------------------------------------------------------------------
>
>                 Key: WICKET-5243
>                 URL: https://issues.apache.org/jira/browse/WICKET-5243
>             Project: Wicket
>          Issue Type: Bug
>          Components: wicket
>    Affects Versions: 6.8.0
>         Environment: Tested on Firefox
>            Reporter: Tobias Haupt
>              Labels: javascript, perfomance
>         Attachments: WICKET-5243-avoid-recursion.patch, response.xml
>
>
> The Function Executor in wicket-ajax-jquery.js uses recursion and deferred calls to the notify() function to ensure synchronous execution of all tasks contained in an AjaxResponse.
> Each task calls notif() when it is finished. This causes a recursive call to processNext() thus raising the stack for each execution. If there are a lot of task to handle, the stack size will increase beyond the possible stack size in the client causing a "too much recursion" exception and increasingly low performance.
> The deferred execution of notify is only necessary if the task executor has to wait for long running tasks to finish at some uncertain point in the future. Examples: downloading of external resources (js, css, images). These task can call back the executor as soon as they are really finished (e.g. load event triggerd).
> The problem is that the majority of tasks don't need to wait but return instantly instead. Examples: exchanging components, executing custom javascripts that do not use the "|-syntax" to include the notify callback.
> Current fix: The depth of the stack is counted and if a depth of >= 1000 is reached, a timeout will interrupt the synchronous task queue execution. A new executor will continue with an empty stack.
> Problems with that approach: 
> - why 1000?
> - several ajax requests might interrupt each other because the synchronous execution is broken.
> - if an executed custom javascript creates a big stack itself (e.g. by using jquery a lot) the stack will add to the stack used by the Function Executor so that it may still be too big.
> Proposal to fix this: see also the attached patch.
> Another callback notifyContinue() is supported that can be called whenever the task will return instantly. This callback avoids the recursive call to processNext and continues in a simple loop over all the tasks.



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