8058870: Mac: JFXPanel deadlocks in jnlp mode

Reviewed-by: serb, alexsch

src/share/classes/javax/swing/JComponent.java

@@ -56,6 +56,7 @@ import java.io.ObjectInputStream;
 import java.io.IOException;
 import java.io.ObjectInputValidation;
 import java.io.InvalidObjectException;
+import java.util.concurrent.atomic.AtomicBoolean;
 
 import javax.swing.border.*;
 import javax.swing.event.*;
@@ -352,7 +353,8 @@ public abstract class JComponent extends Container implements Serializable,
     private static final int AUTOSCROLLS_SET                          = 25;
     private static final int FOCUS_TRAVERSAL_KEYS_FORWARD_SET         = 26;
     private static final int FOCUS_TRAVERSAL_KEYS_BACKWARD_SET        = 27;
-    private static final int REVALIDATE_RUNNABLE_SCHEDULED            = 28;
+
+    private transient AtomicBoolean revalidateRunnableScheduled = new AtomicBoolean(false);
 
     /**
      * Temporary rectangles.
@@ -4859,16 +4861,11 @@ public abstract class JComponent extends Container implements Serializable,
             // To avoid a flood of Runnables when constructing GUIs off
             // the EDT, a flag is maintained as to whether or not
             // a Runnable has been scheduled.
-            synchronized(this) {
-                if (getFlag(REVALIDATE_RUNNABLE_SCHEDULED)) {
-                    return;
-                }
-                setFlag(REVALIDATE_RUNNABLE_SCHEDULED, true);
+            if (revalidateRunnableScheduled.getAndSet(true)) {
+                return;
             }
             SunToolkit.executeOnEventHandlerThread(this, () -> {
-                synchronized(JComponent.this) {
-                    setFlag(REVALIDATE_RUNNABLE_SCHEDULED, false);
-                }
+                revalidateRunnableScheduled.set(false);
                 revalidate();
             });
         }
@@ -5508,6 +5505,7 @@ public abstract class JComponent extends Container implements Serializable,
             ToolTipManager.sharedInstance().registerComponent(this);
         }
         setWriteObjCounter(this, (byte)0);
+        revalidateRunnableScheduled = new AtomicBoolean(false);
     }