[WICKET-7041] Reduce allocations when rendering component headers

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 9.12.0
• Fix Version/s: 10.0.0-M1, 8.15.0, 9.13.0
• Component/s: wicket-core
• Assignee: Thomas Heigl
• Reporter: Thomas Heigl
• Created: 10/Apr/23 15:04
• Updated: 23/Apr/23 13:46
• Resolved: 11/Apr/23 15:32

Description

We noticed a very substantial amount of allocations coming from Component#internalRenderHead:

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

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);
}

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.

Issue Links

• links to: GitHub Pull Request #572
• links to: GitHub Pull Request #574