JBR-9865 Wayland: More granular locking in clipboard

This patch removes holding a clipboard-global lock when receiving data
by reading from a pipe, since that has the potential to cause deadlocks
under specific circumstances.

To synchronize destroying the offer objects on the Java side, they are
now refcounted.

Author: tsarn

src/java.desktop/unix/classes/sun/awt/wl/WLClipboard.java

@@ -224,19 +224,29 @@ protected long[] getClipboardFormats() {
     protected byte[] getClipboardData(long format) throws IOException {
         final WLDataTransferer wlDataTransferer = (WLDataTransferer) DataTransferer.getInstance();
         final long utf8StringFormat = wlDataTransferer.getFormatForNativeAsLong(utf8String);
-        synchronized (dataLock) {
+        WLDataOffer offer = null;
+
+        try {
+            synchronized (dataLock) {
+                offer = clipboardDataOfferedToUs.ref();
+            }
+
             // Iterate over all mime types, since the mapping between mime types and java formats might not be 1:1
             // Also treat text/plain;charset=utf-8 as UTF8_STRING
-            for (var mime : clipboardDataOfferedToUs.getMimes()) {
+            for (var mime : offer.getMimes()) {
                 long curFormat = wlDataTransferer.getFormatForNativeAsLong(mime);
-                if (curFormat == format) {
-                    return clipboardDataOfferedToUs.receiveData(mime);
-                } else if (mime.equalsIgnoreCase(plainTextUtf8) && utf8StringFormat == format) {
-                    return clipboardDataOfferedToUs.receiveData(mime);
+                boolean isUtf8String = mime.equalsIgnoreCase(plainTextUtf8) && utf8StringFormat == format;
+                if (curFormat == format || isUtf8String) {
+                    return offer.receiveData(mime);
                 }
             }
+
+            throw new IOException("No appropriate mime type found for WLClipboard.getClipboardData with format = " + format);
+        } finally {
+            if (offer != null) {
+                offer.unref();
+            }
         }
-        throw new IOException("No appropriate mime type found for WLClipboard.getClipboardData with format = " + format);
     }
 
     @Override
@@ -267,7 +277,7 @@ void handleClipboardOffer(WLDataOffer offer /* nullable */) {
             }
 
             if (clipboardDataOfferedToUs != null) {
-                clipboardDataOfferedToUs.destroy();
+                clipboardDataOfferedToUs.unref();
             }
             clipboardDataOfferedToUs = offer;
         }

src/java.desktop/unix/classes/sun/awt/wl/WLDataOffer.java

@@ -42,6 +42,7 @@ public interface EventListener {
     private int sourceActions = 0;
     private int selectedAction = 0;
     private EventListener listener;
+    private int refcount = 1;
 
     private static native void destroyImpl(long nativePtr);
 
@@ -60,14 +61,21 @@ private WLDataOffer(long nativePtr) {
         this.nativePtr = nativePtr;
     }
 
-    // after calling destroy(), this object enters an invalid state and needs to be deleted
-    public synchronized void destroy() {
-        if (nativePtr != 0) {
-            destroyImpl(nativePtr);
-            nativePtr = 0;
+    public synchronized void unref() {
+        if (nativePtr != 0 && refcount > 0) {
+            --refcount;
+            if (refcount == 0) {
+                destroyImpl(nativePtr);
+                nativePtr = 0;
+            }
         }
     }
 
+    public synchronized WLDataOffer ref() {
+        ++refcount;
+        return this;
+    }
+
     public synchronized byte[] receiveData(String mime) throws IOException  {
         int fd;
 

src/java.desktop/unix/classes/sun/awt/wl/WLDropTargetContextPeer.java

@@ -137,7 +137,7 @@ private synchronized void updateActions() {
 
     private synchronized void reset() {
         if (currentOffer != null) {
-            currentOffer.destroy();
+            currentOffer.unref();
         }
 
         currentOffer = null;