[performance] faster ExecutionEnvironmentsPreferencePage.performOk()

Group touching the projects to a single async operation with workspace
rule. Totally get rid of UI Freeze. And ~9 sec faster for platform
workspace (~500 projects)

eclipse-jdt/eclipse.jdt.core#2884

Pattern taken from JavaCompilerPropertyPage.performOk()

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

@@ -18,6 +18,7 @@
 import java.util.Map;
 
 import org.eclipse.jdt.internal.debug.ui.IJavaDebugHelpContextIds;
+import org.eclipse.jdt.internal.ui.actions.WorkbenchRunnableAdapter;
 import org.eclipse.jdt.launching.IVMInstall;
 import org.eclipse.jdt.launching.JavaRuntime;
 import org.eclipse.jdt.launching.environments.IExecutionEnvironment;
@@ -257,22 +258,30 @@ public void checkStateChanged(CheckStateChangedEvent event) {
 	/* (non-Javadoc)
 	 * @see org.eclipse.jface.preference.IPreferencePage#performOk()
 	 */
+	@SuppressWarnings("restriction")
 	@Override
 	public boolean performOk() {
-		IExecutionEnvironmentsManager manager = JavaRuntime.getExecutionEnvironmentsManager();
-		IExecutionEnvironment[] environments = manager.getExecutionEnvironments();
-		for (int i = 0; i < environments.length; i++) {
-			IExecutionEnvironment environment = environments[i];
-			IVMInstall vm = (IVMInstall) fDefaults.get(environment);
-			// if the VM no longer exists - set to default to avoid illegal argument exception (bug 267914)
-			if (vm != null) {
-				if (vm.getVMInstallType().findVMInstall(vm.getId()) == null) {
-					vm = null;
+		WorkbenchRunnableAdapter op = new WorkbenchRunnableAdapter(monitor -> {
+			IExecutionEnvironmentsManager manager = JavaRuntime.getExecutionEnvironmentsManager();
+			IExecutionEnvironment[] environments = manager.getExecutionEnvironments();
+			monitor.beginTask(JREMessages.ExecutionEnvironmentsPreferencePage_performOk, environments.length);
+			for (int i = 0; i < environments.length; i++) {
+				IExecutionEnvironment environment = environments[i];
+				monitor.setTaskName(environment.getDescription());
+				IVMInstall vm = (IVMInstall) fDefaults.get(environment);
+				// if the VM no longer exists - set to default to avoid illegal argument exception (bug 267914)
+				if (vm != null) {
+					if (vm.getVMInstallType().findVMInstall(vm.getId()) == null) {
+						vm = null;
+					}
 				}
+				environment.setDefaultVM(vm);
+				monitor.worked(1);
 			}
-			environment.setDefaultVM(vm);
-		}
+		});
+		op.runAsUserJob(JREMessages.ExecutionEnvironmentsPreferencePage_performOk, null);
 		return super.performOk();
 	}
 
+
 }

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

@@ -138,6 +138,8 @@ public class JREMessages extends NLS {
 
 	public static String EEVMPage_7;
 
+	public static String ExecutionEnvironmentsPreferencePage_performOk;
+
 	public static String VMTypePage_0;
 
 	public static String VMTypePage_1;

org.eclipse.jdt.debug.ui/ui/org/eclipse/jdt/internal/debug/ui/jres/JREMessages.properties

@@ -133,6 +133,7 @@ EEVMPage_4=Enter definition file
 EEVMPage_5=Definition file does not exist
 EEVMPage_6=JRE Definition
 EEVMPage_7=Specify attributes for a JRE
+ExecutionEnvironmentsPreferencePage_performOk=Updating Execution Environments
 LibraryLabelProvider_0=Javadoc location: 
 VMTypePage_0=Select JRE Type
 VMTypePage_1=Select the type of JRE to add to the workspace.