8384381: Remove AppContext from java.awt.EventQueue implementation

Reviewed-by: kizune, azvegint, serb

Author: prrace

src/java.desktop/share/classes/java/awt/EventQueue.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1996, 2025, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1996, 2026, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -40,6 +40,7 @@
 
 import java.util.concurrent.locks.Condition;
 import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReentrantLock;
 import java.util.concurrent.atomic.AtomicInteger;
 
 /**
@@ -112,11 +113,11 @@ public class EventQueue {
 
     /*
      * A single lock to synchronize the push()/pop() and related operations with
-     * all the EventQueues from the AppContext. Synchronization on any particular
+     * all the EventQueues. Synchronization on any particular
      * event queue(s) is not enough: we should lock the whole stack.
      */
-    private final Lock pushPopLock;
-    private final Condition pushPopCond;
+    private static final Lock pushPopLock = new ReentrantLock();
+    private static final Condition pushPopCond = pushPopLock.newCondition();
 
     /*
      * Dummy runnable to wake up EDT from getNextEvent() after
@@ -156,11 +157,6 @@ public void run() {
      */
     private volatile int waitForID;
 
-    /*
-     * AppContext corresponding to the queue.
-     */
-    private final AppContext appContext;
-
     private final String name = "AWT-EventQueue-" + threadInitNumber.getAndIncrement();
 
     private FwDispatcher fwDispatcher;
@@ -222,18 +218,6 @@ public EventQueue() {
         for (int i = 0; i < NUM_PRIORITIES; i++) {
             queues[i] = new Queue();
         }
-        /*
-         * NOTE: if you ever have to start the associated event dispatch
-         * thread at this point, be aware of the following problem:
-         * If this EventQueue instance is created in
-         * SunToolkit.createNewAppContext() the started dispatch thread
-         * may call AppContext.getAppContext() before createNewAppContext()
-         * completes thus causing mess in thread group to appcontext mapping.
-         */
-
-        appContext = AppContext.getAppContext();
-        pushPopLock = (Lock)appContext.get(AppContext.EVENT_QUEUE_LOCK_KEY);
-        pushPopCond = (Condition)appContext.get(AppContext.EVENT_QUEUE_COND_KEY);
     }
 
     /**
@@ -247,7 +231,7 @@ public EventQueue() {
      * @throws NullPointerException if {@code theEvent} is {@code null}
      */
     public void postEvent(AWTEvent theEvent) {
-        SunToolkit.flushPendingEvents(appContext);
+        SunToolkit.flushPendingEvents();
         postEventPrivate(theEvent);
     }
 
@@ -532,7 +516,7 @@ public AWTEvent getNextEvent() throws InterruptedException {
              * of the synchronized block to avoid deadlock when
              * event queues are nested with push()/pop().
              */
-            SunToolkit.flushPendingEvents(appContext);
+            SunToolkit.flushPendingEvents();
             pushPopLock.lock();
             try {
                 AWTEvent event = getNextEventPrivate();
@@ -572,7 +556,7 @@ AWTEvent getNextEvent(int id) throws InterruptedException {
              * of the synchronized block to avoid deadlock when
              * event queues are nested with push()/pop().
              */
-            SunToolkit.flushPendingEvents(appContext);
+            SunToolkit.flushPendingEvents();
             pushPopLock.lock();
             try {
                 for (int i = 0; i < NUM_PRIORITIES; i++) {
@@ -869,8 +853,8 @@ public void push(EventQueue newEventQueue) {
             newEventQueue.previousQueue = topQueue;
             topQueue.nextQueue = newEventQueue;
 
-            if (appContext.get(AppContext.EVENT_QUEUE_KEY) == topQueue) {
-                appContext.put(AppContext.EVENT_QUEUE_KEY, newEventQueue);
+            if (SunToolkit.currentEventQueue == topQueue) {
+                SunToolkit.currentEventQueue = newEventQueue;
             }
 
             pushPopCond.signalAll();
@@ -929,8 +913,8 @@ protected void pop() throws EmptyStackException {
                 topQueue.dispatchThread.setEventQueue(prevQueue);
             }
 
-            if (appContext.get(AppContext.EVENT_QUEUE_KEY) == this) {
-                appContext.put(AppContext.EVENT_QUEUE_KEY, prevQueue);
+            if (SunToolkit.currentEventQueue == this) {
+                SunToolkit.currentEventQueue = prevQueue;
             }
 
             // Wake up EDT waiting in getNextEvent(), so it can
@@ -1053,7 +1037,7 @@ final boolean isDispatchThreadImpl() {
     final void initDispatchThread() {
         pushPopLock.lock();
         try {
-            if (dispatchThread == null && !threadGroup.isDestroyed() && !appContext.isDisposed()) {
+            if (dispatchThread == null && !threadGroup.isDestroyed()) {
                 EventDispatchThread t = new EventDispatchThread(threadGroup, name, EventQueue.this);
                 t.setContextClassLoader(classLoader);
                 t.setPriority(Thread.NORM_PRIORITY + 1);
@@ -1071,7 +1055,7 @@ final void detachDispatchThread(EventDispatchThread edt) {
         /*
          * Minimize discard possibility for non-posted events
          */
-        SunToolkit.flushPendingEvents(appContext);
+        SunToolkit.flushPendingEvents();
         /*
          * This synchronized block is to secure that the event dispatch
          * thread won't die in the middle of posting a new event to the
@@ -1129,7 +1113,7 @@ final EventDispatchThread getDispatchThread() {
      * {@code removeNotify} method.
      */
     final void removeSourceEvents(Object source, boolean removeAllEvents) {
-        SunToolkit.flushPendingEvents(appContext);
+        SunToolkit.flushPendingEvents();
         pushPopLock.lock();
         try {
             for (int i = 0; i < NUM_PRIORITIES; i++) {

src/java.desktop/share/classes/sun/awt/AppContext.java

@@ -43,9 +43,6 @@
 import java.lang.ref.SoftReference;
 
 import sun.util.logging.PlatformLogger;
-import java.util.concurrent.locks.Condition;
-import java.util.concurrent.locks.Lock;
-import java.util.concurrent.locks.ReentrantLock;
 import java.util.concurrent.atomic.AtomicInteger;
 
 /**
@@ -121,17 +118,6 @@ public final class AppContext {
     /* Since the contents of an AppContext are unique to each Java
      * session, this class should never be serialized. */
 
-    /*
-     * The key to put()/get() the Java EventQueue into/from the AppContext.
-     */
-    public static final Object EVENT_QUEUE_KEY = new StringBuffer("EventQueue");
-
-    /*
-     * The keys to store EventQueue push/pop lock and condition.
-     */
-    public static final Object EVENT_QUEUE_LOCK_KEY = new StringBuilder("EventQueue.Lock");
-    public static final Object EVENT_QUEUE_COND_KEY = new StringBuilder("EventQueue.Condition");
-
     /* A map of AppContexts, referenced by ThreadGroup.
      */
     private static final Map<ThreadGroup, AppContext> threadGroup2appContext =
@@ -225,12 +211,6 @@ public boolean isDisposed() {
         threadGroup2appContext.put(threadGroup, this);
 
         this.contextClassLoader = Thread.currentThread().getContextClassLoader();
-        // Initialize push/pop lock and its condition to be used by all the
-        // EventQueues within this AppContext
-        Lock eventQueuePushPopLock = new ReentrantLock();
-        put(EVENT_QUEUE_LOCK_KEY, eventQueuePushPopLock);
-        Condition eventQueuePushPopCond = eventQueuePushPopLock.newCondition();
-        put(EVENT_QUEUE_COND_KEY, eventQueuePushPopCond);
     }
 
     private static final ThreadLocal<AppContext> threadAppContext =

src/java.desktop/share/classes/sun/awt/SunToolkit.java

@@ -133,10 +133,6 @@ private static void initStatic() {
      */
     public static final int GRAB_EVENT_MASK = 0x80000000;
 
-    /* The key to put()/get() the PostEventQueue into/from the AppContext.
-     */
-    private static final String POST_EVENT_QUEUE_KEY = "PostEventQueue";
-
     /**
      * Number of buttons.
      * By default it's taken from the system. If system value does not
@@ -156,20 +152,17 @@ private static void initStatic() {
      */
     public static final int MAX_BUTTONS_SUPPORTED = 20;
 
+    public static volatile EventQueue currentEventQueue;
+    private static volatile PostEventQueue postEventQueue;
+
     /**
-     * Creates and initializes EventQueue instance for the specified
-     * AppContext.
-     * Note that event queue must be created from createNewAppContext()
-     * only in order to ensure that EventQueue constructor obtains
-     * the correct AppContext.
-     * @param appContext AppContext to associate with the event queue
+     * Creates and initializes EventQueue instance.
      */
-    private static void initEQ(AppContext appContext) {
-        EventQueue eventQueue = new EventQueue();
-        appContext.put(AppContext.EVENT_QUEUE_KEY, eventQueue);
-
-        PostEventQueue postEventQueue = new PostEventQueue(eventQueue);
-        appContext.put(POST_EVENT_QUEUE_KEY, postEventQueue);
+    private static synchronized void initEQ() {
+        if (currentEventQueue == null) {
+            currentEventQueue = new EventQueue();
+            postEventQueue = new PostEventQueue(currentEventQueue);
+        }
     }
 
     public SunToolkit() {
@@ -279,8 +272,7 @@ static final AppContext createNewAppContext(ThreadGroup threadGroup) {
         // the calls to AppContext.getAppContext() from EventQueue ctor
         // return correct values
         AppContext appContext = new AppContext(threadGroup);
-        initEQ(appContext);
-
+        initEQ();
         return appContext;
     }
 
@@ -468,12 +460,6 @@ public static void postEvent(AppContext appContext, AWTEvent event) {
         // otherwise have to be modified to precisely identify
         // system-generated events.
         setSystemGenerated(event);
-        AppContext eventContext = targetToAppContext(event.getSource());
-        if (eventContext != null && !eventContext.equals(appContext)) {
-            throw new RuntimeException("Event posted on wrong app context : " + event);
-        }
-        PostEventQueue postEventQueue =
-            (PostEventQueue)appContext.get(POST_EVENT_QUEUE_KEY);
         if (postEventQueue != null) {
             postEventQueue.postEvent(event);
         }
@@ -498,18 +484,6 @@ public void run() {
      * EventQueue yet.
      */
     public static void flushPendingEvents()  {
-        AppContext appContext = AppContext.getAppContext();
-        flushPendingEvents(appContext);
-    }
-
-    /*
-     * Flush the PostEventQueue for the right AppContext.
-     * The default flushPendingEvents only flushes the thread-local context,
-     * which is not always correct, c.f. 3746956
-     */
-    public static void flushPendingEvents(AppContext appContext) {
-        PostEventQueue postEventQueue =
-                (PostEventQueue)appContext.get(POST_EVENT_QUEUE_KEY);
         if (postEventQueue != null) {
             postEventQueue.flush();
         }
@@ -600,20 +574,6 @@ class AWTInvocationLock {}
         }
     }
 
-    /*
-     * Returns true if the calling thread is the event dispatch thread
-     * contained within AppContext which associated with the given target.
-     * Use this call to ensure that a given task is being executed
-     * (or not being) on the event dispatch thread for the given target.
-     */
-    public static boolean isDispatchThreadForAppContext(Object target) {
-        AppContext appContext = targetToAppContext(target);
-        EventQueue eq = (EventQueue)appContext.get(AppContext.EVENT_QUEUE_KEY);
-
-        AWTAccessor.EventQueueAccessor accessor = AWTAccessor.getEventQueueAccessor();
-        return accessor.isDispatchThreadImpl(eq);
-    }
-
     @Override
     public Dimension getScreenSize() {
         return GraphicsEnvironment.getLocalGraphicsEnvironment()
@@ -1035,13 +995,8 @@ protected EventQueue getSystemEventQueueImpl() {
     }
 
     public static EventQueue getSystemEventQueueImplPP() {
-        return getSystemEventQueueImplPP(AppContext.getAppContext());
-    }
-
-    public static EventQueue getSystemEventQueueImplPP(AppContext appContext) {
-        EventQueue theEventQueue =
-            (EventQueue)appContext.get(AppContext.EVENT_QUEUE_KEY);
-        return theEventQueue;
+        initEQ();
+        return currentEventQueue;
     }
 
     /**
@@ -2021,7 +1976,7 @@ public static boolean isSystemGenerated(AWTEvent e) {
 
 
 /*
- * PostEventQueue is a Thread that runs in the same AppContext as the
+ * PostEventQueue is a Thread tied to the
  * Java EventQueue.  It is a queue of AWTEvents to be posted to the
  * Java EventQueue.  The toolkit Thread (AWT-Windows/AWT-Motif) posts
  * events to this queue, which then calls EventQueue.postEvent().