`Dialog.shortenText` performs badly with huge inputs

[FlorianKroiss]

Let's make sure issue is not already fixed in latest builds first.

• I verified I can reproduce this issue against latest Integration Build of Eclipse SDK

Steps to reproduce

1. Make sure the Progress view open
2. Start a Job that produces an enormous error message, e.g.,

final Job j = new Job("test") {

    @Override
    protected IStatus run(final IProgressMonitor monitor) {
        return Status.error("There was an Error\n".repeat(2000000));
    }
};
j.schedule();

3. The application freezes, because Dialog.shortenText is trying to reduce this large error message down to a string which can be displayed.

Excerpt from main-Thread Stack:

OS.DrawText(long, char[], int, RECT, int) line: not available [native method]	
GC.textExtentInPixels(String, int) line: 5832	
GC.textExtent(String) line: 5773	
Dialog.shortenText(String, Control) line: 361	
ProgressInfoItem.updateText(String, Link) line: 812	
ProgressInfoItem.setLinkText(Job, String, int) line: 741	
ProgressInfoItem.refresh() line: 528	
ProgressInfoItem.createChildren() line: 271	
ProgressInfoItem.<init>(Composite, int, JobTreeElement) line: 197	
DetailedProgressViewer.createNewItem(JobTreeElement) line: 220	
DetailedProgressViewer.reorderControls(Object[]) line: 481	
DetailedProgressViewer.updateItems(Set<JobTreeElement>) line: 189	
DetailedProgressViewer.add(JobTreeElement...) line: 173	
DetailedProgressViewer.internalRefresh(Object) line: 367	
DetailedProgressViewer(StructuredViewer).internalRefresh(Object, boolean) line: 1249	
DetailedProgressViewer(StructuredViewer).lambda$3(Object, boolean) line: 1485	
Lambda.run() line: not available	
DetailedProgressViewer(StructuredViewer).preservingSelection(Runnable, boolean) line: 1391	
DetailedProgressViewer(StructuredViewer).preservingSelection(Runnable) line: 1352	
DetailedProgressViewer(StructuredViewer).refresh(Object, boolean) line: 1485	
ProgressViewerContentProvider.refresh(JobTreeElement...) line: 75	
ProgressViewUpdater.update() line: 299
[...]

Possible fixes for Dialog.shortenText:

• Add a hard limit to the length of the input String at which point we don't even try to shorten the string
• Perform some kind of binary-search when trying to determine start and end instead of moving each limit by 1 in each iteration of the for loop.

Relevant code:

eclipse.platform.ui/bundles/org.eclipse.jface/src/org/eclipse/jface/dialogs/Dialog.java

Lines 357 to 386 in 343fd57

	public static String shortenText(String textValue, Control control) {
	if (textValue == null) {
	return null;
	}
	GC gc = new GC(control);
	int maxWidth = control.getBounds().width - 5;
	int maxExtent = gc.textExtent(textValue).x;
	if (maxExtent < maxWidth) {
	gc.dispose();
	return textValue;
	}
	int length = textValue.length();
	int charsToClip = Math.round(0.95f*length * (1 - ((float)maxWidth/maxExtent)));
	int pivot = length / 2;
	int start = pivot - (charsToClip/2);
	int end = pivot + (charsToClip/2) + 1;
	while (start >= 0 && end < length) {
	String s1 = textValue.substring(0, start);
	String s2 = textValue.substring(end, length);
	String s = s1 + ELLIPSIS + s2;
	int l = gc.textExtent(s).x;
	if (l < maxWidth) {
	gc.dispose();
	return s;
	}
	start--;
	end++;
	}
	gc.dispose();
	return textValue;

[iloveeclipse]

Add a hard limit to the length of the input String at which point we don't even try to shorten the string

Hard limit, substring to that limit and start shortening. One can assume the text to be readable needs at least 3 pixel per character.
So limit would be maxWidth / 3.

Perform some kind of binary-search when trying to determine start and end instead of moving each limit by 1 in each iteration of the for loop.

Could be done, but assuming the shortening would first cut the string to hard limit, probably not needed.