[GTK3] Fix ToolBar.computeSize 60 Hz repaint loop with SWT.WRAP

[vogella]

Summary

• Remove the gtk_toolbar_set_show_arrow toggle workaround in ToolBar.computeSizeInPixels that caused two GTK invalidation cycles per measurement call
• This workaround was added in 2012 (Bug 46025) for GTK 3.4 and is no longer needed on modern GTK 3.24
• When a SWT.WRAP ToolBar sits inside a frequently-measured parent (e.g. CTabFolder.setTopRight), the toggle created a self-sustaining ~60 Hz repaint loop burning 10-25% CPU while idle
• Add Snippet394 to verify ToolBar sizing works correctly without the workaround

Test plan

• Run Snippet394 on GTK3 to verify both WRAP and non-WRAP toolbars report similar widths
• Run the reproducer from [GTK3] ToolBar.computeSize with SWT.WRAP causes self-sustaining 60 Hz repaint loop in CTabFolder.setTopRight #3236 with SWT.WRAP and confirm CPU stays at 0% on idle
• Verify SWT.WRAP toolbar overflow behavior still works correctly (items hidden behind chevron when toolbar is too narrow)
• Test in Eclipse IDE with CTabFolder top-right toolbars

Fixes #3236

🤖 Generated with Claude Code

[akurtakov]

Very good catch. The snippet is good for testing but it is not smth that any SWT user can use as an example so it shouldn't end up in snippets whenever the PR is merged.

[github-actions]

Test Results

  182 files  ±0    182 suites  ±0   27m 43s ⏱️ + 2m 59s
4 701 tests ±0  4 680 ✅ ±0   21 💤 ±0  0 ❌ ±0 
6 704 runs  ±0  6 546 ✅ ±0  158 💤 ±0  0 ❌ ±0 

Results for commit 29468e1. ± Comparison against base commit dbac219.

[akurtakov]

With the requested changes in Toolbar GTK3.gtk_toolbar_set_show_arrow will no longer be needed so it can be removed too.

[vogella]

/*******************************************************************************
 * Copyright (c) 2026 Eclipse Foundation and others.
 *
 * This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License 2.0
 * which accompanies this distribution, and is available at
 * https://www.eclipse.org/legal/epl-2.0/
 *
 * SPDX-License-Identifier: EPL-2.0
 *
 * Contributors:
 *     Eclipse Foundation - initial API and implementation
 *******************************************************************************/
package org.eclipse.swt.snippets;

import org.eclipse.swt.*;
import org.eclipse.swt.graphics.*;
import org.eclipse.swt.layout.*;
import org.eclipse.swt.widgets.*;

/**
 * ToolBar computeSize test: verify whether the GTK3 toolbar sizing bug
 * (toolbar reports only the overflow arrow width when show_arrow is enabled)
 * is still present.
 *
 * <p>This snippet creates a ToolBar with several items and compares the
 * computed size with and without the SWT.WRAP style. If the GTK bug is fixed,
 * both sizes should be similar. If the bug is still present, the WRAP toolbar
 * will report a much smaller width (just the arrow).
 *
 * <p>See https://github.com/eclipse-platform/eclipse.platform.swt/issues/3236
 *
 * <p>For a list of all SWT example snippets see
 * https://eclipse.dev/eclipse/swt/snippets/
 */
public class Snippet395 {

public static void main(String[] args) {
	Display display = new Display();
	Shell shell = new Shell(display);
	shell.setText("Snippet 395 - ToolBar computeSize with WRAP");
	shell.setLayout(new GridLayout(1, false));

	// Create a toolbar WITHOUT SWT.WRAP
	ToolBar toolBarNoWrap = new ToolBar(shell, SWT.FLAT | SWT.RIGHT);
	addItems(toolBarNoWrap);

	// Create a toolbar WITH SWT.WRAP
	ToolBar toolBarWrap = new ToolBar(shell, SWT.FLAT | SWT.RIGHT | SWT.WRAP);
	addItems(toolBarWrap);

	// Compute sizes
	Point sizeNoWrap = toolBarNoWrap.computeSize(SWT.DEFAULT, SWT.DEFAULT);
	Point sizeWrap = toolBarWrap.computeSize(SWT.DEFAULT, SWT.DEFAULT);

	// Display results
	Label resultLabel = new Label(shell, SWT.WRAP);
	resultLabel.setLayoutData(new GridData(SWT.FILL, SWT.CENTER, true, false));
	StringBuilder sb = new StringBuilder();
	sb.append("ToolBar without WRAP: " + sizeNoWrap.x + " x " + sizeNoWrap.y + "\n");
	sb.append("ToolBar with    WRAP: " + sizeWrap.x + " x " + sizeWrap.y + "\n\n");

	int widthDiff = Math.abs(sizeNoWrap.x - sizeWrap.x);
	if (widthDiff > sizeNoWrap.x / 2) {
		sb.append("RESULT: Large width difference (" + widthDiff + "px). "
			+ "The GTK sizing bug may still be present.\n"
			+ "The WRAP toolbar is likely reporting only the arrow width.");
	} else {
		sb.append("RESULT: Widths are similar (diff=" + widthDiff + "px). "
			+ "The GTK sizing bug appears to be fixed.");
	}
	resultLabel.setText(sb.toString());

	// Also print to console
	System.out.println(sb);

	shell.pack();
	shell.open();
	while (!shell.isDisposed()) {
		if (!display.readAndDispatch()) display.sleep();
	}
	display.dispose();
}

private static void addItems(ToolBar toolBar) {
	for (int i = 0; i < 5; i++) {
		ToolItem item = new ToolItem(toolBar, SWT.PUSH);
		item.setText("Action " + (i + 1));
	}
}

}

[akurtakov]

Changes in GTK3.java should have caused changes in gtk3.c and gtk3_stats.h

[github-actions]

Test Results (linux)

   94 files  ±0     94 suites  ±0   14m 12s ⏱️ -9s
4 575 tests ±0  4 354 ✅ ±0  221 💤 ±0  0 ❌ ±0 
3 329 runs  ±0  3 257 ✅ ±0   72 💤 ±0  0 ❌ ±0 

Results for commit 07a989d. ± Comparison against base commit dbac219.

♻️ This comment has been updated with latest results.

[vogella]

Changes in GTK3.java should have caused changes in gtk3.c and gtk3_stats.h

I do not see how. The gtk-dev-guide.md mentions that "SWT Tools also generates JNI bindings (i.e. os.c, os_stat.c, etc.) for you automatically." but my SDK build does not have the SWT Tools installled. And mvn clean install '-Dnative=gtk.linux.x86_64' -DskipTests does also not do this.

Manually updated gtk3.c. The stats files (gtk3_stats.c/gtk3_stats.h) didn't seemt to have an entry for this function.

[akurtakov]

SWT tools work only as eclipse plugin and do their work on save of java file as regular builder. The entry in gtk3_stats is gtk_1toolbar_1set_1show_1arrow_FUNC but I would prefer to see the changes done by the builder manually to reduce extra changes in other PRs where swt tools do the work.

[vogella]

SWT tools work only as eclipse plugin and do their work on save of java file as regular builder. The entry in gtk3_stats is gtk_1toolbar_1set_1show_1arrow_FUNC but I would prefer to see the changes done by the builder manually to reduce extra changes in other PRs where swt tools do the work.

As discussed via chat the tools usage is not document nor part of the SDK build. I will suggest to @HannesWell to document the usage in his pending #3212 for documention improvements

[vogella]

Coooool. After installing the swt.tools the c files get updated. Very nice feature. Would be nice if that would also be baked into the command line build.

@akurtakov PR updated as requested.

[akurtakov]

I'm updating jnigen in eclipse-platform/www.eclipse.org-eclipse#535 - outdated version available at https://eclipse.dev/eclipse/swt/jnigen.html

[vogella]

Any further concerns about this PR @akurtakov ?