[jira] [Resolved] (WICKET-7041) Reduce allocations when rendering component headers

["Thomas Heigl (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/WICKET-7041?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Thomas Heigl resolved WICKET-7041.
----------------------------------
    Resolution: Fixed

> Reduce allocations when rendering component headers
> ---------------------------------------------------
>
>                 Key: WICKET-7041
>                 URL: https://issues.apache.org/jira/browse/WICKET-7041
>             Project: Wicket
>          Issue Type: Improvement
>          Components: wicket-core
>    Affects Versions: 9.12.0
>            Reporter: Thomas Heigl
>            Assignee: Thomas Heigl
>            Priority: Major
>             Fix For: 10.0.0, 9.13.0
>
>         Attachments: image-2023-04-10-16-56-52-061.png
>
>
> We noticed a *very* substantial amount of allocations coming from Component#internalRenderHead:
> !image-2023-04-10-16-56-52-061.png|width=716,height=612!
> This is the relevant part of the code:
> https://github.com/apache/wicket/blame/9b4c5fe9a26174a06d612837297eca90ef8711cc/wicket-core/src/main/java/org/apache/wicket/Component.java#L2642
> {code:java}
> StringResponse markupHeaderResponse = new StringResponse();
> Response oldResponse = getResponse();
> RequestCycle.get().setResponse(markupHeaderResponse);
> try
> {
> 	// Make sure the markup source strategy contributes to the header first
> 	// to be backward compatible. WICKET-3761
> 	getMarkupSourcingStrategy().renderHead(this, container);
> 	CharSequence headerContribution = markupHeaderResponse.getBuffer();
> 	if (Strings.isEmpty(headerContribution) == false)
> 	{
> 		response.render(StringHeaderItem.forString(headerContribution));
> 	}
> }
> finally
> {
> 	RequestCycle.get().setResponse(oldResponse);
> }
> {code}
> The code *always* allocates a new StringResponse for rendering potential markup header contributions. Internally, this creates a new AppendingStringBuffer with capacity 128.
> In my application, we do not use <wicket:head> tags at all. So 99.9% of these allocations are completely unnecessary.
> Ideally, I'd like to get rid of the temporary StringResponse, but I don't know if thats possible without breaking things.
> Another solution would be to create a LazyStringResponse that initializes the internal String buffer on first use.



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