Bug 546274: [GTK] vm crash when scrolling StyledText

The method scrollInPixels() doesn't seem to be needed. I've reverted the
fix from commit 64ae338b9c279c9bbcc158165aa451193a503c0a to preserve
stability on GTK3, but on GTK4 this method is never called.

Tested with the snippet attached, as well as the Canvas tab on
ControlExample (GTK3 and GTK4).

Change-Id: If907bf6c4c805c24eb021b687d5affbbc2e8bc3f
Signed-off-by: Eric Williams <ericwill@redhat.com>

1 files changed, 102 insertions, 0 deletions

diff --git a/tests/org.eclipse.swt.tests.gtk/ManualTests/org/eclipse/swt/tests/gtk/snippets/Bug546274_StyledTextVMCrash.java b/tests/org.eclipse.swt.tests.gtk/ManualTests/org/eclipse/swt/tests/gtk/snippets/Bug546274_StyledTextVMCrash.java
new file mode 100644
index 0000000000..878da10e23
--- /dev/null
+++ b/tests/org.eclipse.swt.tests.gtk/ManualTests/org/eclipse/swt/tests/gtk/snippets/Bug546274_StyledTextVMCrash.java
@@ -0,0 +1,102 @@
+/*******************************************************************************
+ * Copyright (c) 2019 Syntevo 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:
+ *     Syntevo - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.swt.tests.gtk.snippets;
+
+import org.eclipse.swt.SWT;
+import org.eclipse.swt.custom.StyledText;
+import org.eclipse.swt.graphics.GC;
+import org.eclipse.swt.graphics.Image;
+import org.eclipse.swt.layout.FillLayout;
+import org.eclipse.swt.widgets.Composite;
+import org.eclipse.swt.widgets.Display;
+import org.eclipse.swt.widgets.Shell;
+
+public class Bug546274_StyledTextVMCrash {
+	private static class MyStyledText extends StyledText {
+		int 	cairoCacheSize = 16;	// see MAX_FREED_POOL_SIZE in cairo
+		Image 	tempImages[] = new Image[cairoCacheSize];
+		GC 		tempGCs[] = new GC[cairoCacheSize];
+
+		public MyStyledText(Composite parent, int style) {
+			super(parent, style);
+			allocTempGCs();
+		}
+
+		void allocTempGCs() {
+			for (int i = 0; i < cairoCacheSize; i++) {
+				tempImages[i] = new Image(this.getDisplay(), 1, 1);
+				tempGCs[i] = new GC(tempImages[i]);
+			}
+		}
+
+		@Override
+		public void scroll(int destX, int destY, int x, int y, int width, int height, boolean all) {
+			// Evaluate with debugger: (cachedCairo.handle == this.cachedCairo);
+			// This already shows that 'this.cachedCairo' can't be used.
+			Image tempImage = new Image(this.getDisplay(), 1, 1);
+			GC cachedCairo = new GC(tempImage);
+
+			// Evict 'cachedCairo' from Cairo's cache 'context_pool' by
+			// 1) Populating cache with free objects
+			// 2) Releasing 'cachedCairo' and it will be truly deleted
+			{
+				if (tempGCs != null) {
+					for (int i = 0; i < tempGCs.length; i++) {
+						tempGCs[i].dispose();
+						tempImages[i].dispose();
+					}
+				}
+
+				cachedCairo.dispose();
+				tempImage.dispose();
+			}
+
+			// Make sure the same malloc() block can't be used again
+			for (int i = 1; i < 1024; i++) {
+				// Intentional leak
+				org.eclipse.swt.internal.gtk.GTK.malloc(i);
+			}
+
+			super.scroll(destX, destY, x, y, width, height, all);
+
+			// Drain Cairo's cache 'context_pool' to force the next cairo to use malloc()
+			allocTempGCs();
+		}
+	}
+
+	public static void main(String[] args) {
+		final Display display = new Display();
+
+		final Shell shell = new Shell(display, SWT.SHELL_TRIM);
+		shell.setLayout(new FillLayout(SWT.VERTICAL));
+		shell.setSize(300, 200);
+
+		String hintText = "Try to horz scroll this StyledText\n" +
+						"\n" +
+						"Horz scrollbar is forced by this long line of text xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx";
+
+		final StyledText text = new MyStyledText(shell, SWT.BORDER | SWT.H_SCROLL);
+		text.setText(hintText);
+
+		shell.open();
+
+		while (!shell.isDisposed()) {
+			if (!display.readAndDispatch()) {
+				display.sleep();
+			}
+		}
+
+		display.dispose();
+	}
+}