Preload2: Add isSingleThreaded

Expose whether a UI is single-threaded to avoid spawning threads
in actions.

Bug: 31961946
Test: manual
Change-Id: I37c8daa6a00784e833bad53b8e83ab4417955df7

tools/preload2/src/com/android/preload/actions/AbstractThreadedAction.java

@@ -16,6 +16,7 @@
 
 package com.android.preload.actions;
 
+import com.android.preload.Main;
 import java.awt.event.ActionEvent;
 
 import javax.swing.AbstractAction;
@@ -28,7 +29,11 @@ public abstract class AbstractThreadedAction extends AbstractAction implements R
 
     @Override
     public void actionPerformed(ActionEvent e) {
+        if (Main.getUI().isSingleThreaded()) {
+            run();
+        } else {
             new Thread(this).start();
         }
+    }
 
 }

tools/preload2/src/com/android/preload/actions/RunMonkeyAction.java

@@ -58,7 +58,12 @@ public class RunMonkeyAction extends AbstractAction implements DeviceSpecific {
         if (packages.isEmpty()) {
             packages = DEFAULT_MONKEY_PACKAGES;
         }
-        new Thread(new RunMonkeyRunnable(packages)).start();
+        Runnable r = new RunMonkeyRunnable(packages);
+        if (Main.getUI().isSingleThreaded()) {
+            r.run();
+        } else {
+            new Thread(r).start();
+        }
     }
 
     private class RunMonkeyRunnable implements Runnable {

tools/preload2/src/com/android/preload/ui/IUI.java

@@ -18,6 +18,8 @@ public interface IUI {
 
     void ready();
 
+    boolean isSingleThreaded();
+
     Client getSelectedClient();
 
     int getSelectedDataTableRow();

tools/preload2/src/com/android/preload/ui/SwingUI.java

@@ -53,6 +53,11 @@ public class SwingUI extends JFrame implements IUI {
         super("Preloaded-classes computation");
     }
 
+    @Override
+    public boolean isSingleThreaded() {
+        return false;
+    }
+
     @Override
     public void prepare(ListModel<Client> clientListModel, TableModel dataTableModel,
             List<Action> actions) {