[performance] faster ExecutionEnvironmentsPreferencePage.performOk()

Group touching the projects to a single WorkspaceOperation
Reduces UI freeze by ~9 sec for platform workspace (~500 projects)

eclipse-jdt/eclipse.jdt.core#2884

org.eclipse.jdt.debug.ui/ui/org/eclipse/jdt/internal/debug/ui/jres/ExecutionEnvironmentsPreferencePage.java

@@ -17,6 +17,8 @@
 import java.util.HashMap;
 import java.util.Map;
 
+import org.eclipse.core.resources.ResourcesPlugin;
+import org.eclipse.core.runtime.CoreException;
 import org.eclipse.jdt.internal.debug.ui.IJavaDebugHelpContextIds;
 import org.eclipse.jdt.launching.IVMInstall;
 import org.eclipse.jdt.launching.JavaRuntime;
@@ -259,6 +261,15 @@ public void checkStateChanged(CheckStateChangedEvent event) {
 	 */
 	@Override
 	public boolean performOk() {
+		try {
+			ResourcesPlugin.getWorkspace().run(p -> updateAllEnvironments(), null);
+		} catch (CoreException e) {
+			throw new RuntimeException(e);
+		}
+		return super.performOk();
+	}
+
+	public void updateAllEnvironments() {
 		IExecutionEnvironmentsManager manager = JavaRuntime.getExecutionEnvironmentsManager();
 		IExecutionEnvironment[] environments = manager.getExecutionEnvironments();
 		for (int i = 0; i < environments.length; i++) {
@@ -272,7 +283,6 @@ public boolean performOk() {
 			}
 			environment.setDefaultVM(vm);
 		}
-		return super.performOk();
 	}
 
 }