Thomas Heigl created WICKET-7041:
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Summary: 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
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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