fixup! JBR-5980: Pasting from clipboard not working reliably in Windows.

(also fixes JBR-6267: Image retreived from the Clipboard is not the same image that was set to the Clipboard)

- Sets the system property awt.windows.clipboard.cache.disabled to false by default ;
- Adds memory barriers around the native flag AwtClipboard::isOwner ;
- Allows back WM_ACTIVATEAPP messages to reach ::DefWindowProc .

src/java.desktop/windows/classes/sun/awt/windows/WClipboard.java

@@ -160,8 +160,9 @@ final class WClipboard extends SunClipboard {
         // ====================== JBR-5980 Pasting from clipboard not working reliably in Windows ======================
         boolean flagInitializer = false; // let's fall back in the default behavior
         try {
+            // is "false" by default due to JBR-6267
             flagInitializer =
-                "true".equalsIgnoreCase(System.getProperty("awt.windows.clipboard.cache.disabled", "true"));
+                "true".equalsIgnoreCase(System.getProperty("awt.windows.clipboard.cache.disabled", "false"));
         } catch (Throwable ignored) {
         }
         isContentsCacheDisabled = flagInitializer;

src/java.desktop/windows/native/libawt/windows/awt_Clipboard.cpp

@@ -49,7 +49,7 @@ volatile BOOL AwtClipboard::isClipboardViewerRegistered = FALSE;
  */
 
 void AwtClipboard::LostOwnership(JNIEnv *env) {
-    isOwner = FALSE;
+    (void)::InterlockedExchange(&AwtClipboard::isOwner, FALSE); // isOwner = FALSE;
 
     if (theCurrentClipboard != NULL) {
         env->CallVoidMethod(theCurrentClipboard, lostSelectionOwnershipMID);
@@ -96,7 +96,7 @@ void AwtClipboard::UnregisterClipboardViewer(JNIEnv *env) {
 
 // ======================== JBR-5980 Pasting from clipboard not working reliably in Windows ===========================
 volatile BOOL AwtClipboard::areOwnershipExtraChecksEnabled = FALSE;
-volatile BOOL AwtClipboard::isOwner = FALSE;
+volatile LONG /* BOOL */ AwtClipboard::isOwner = FALSE;
 jmethodID AwtClipboard::ensureNoOwnedDataMID = nullptr;
 
 void AwtClipboard::SetOwnershipExtraChecksEnabled(BOOL enabled) {
@@ -113,7 +113,10 @@ void AwtClipboard::ExtraCheckOfOwnership() {
         return;
     }
 
-    if (isOwner == TRUE) {
+    const bool isOwner =
+        // Checks the actual value of AwtClipboard::isOwner without altering it
+        (::InterlockedCompareExchange(&AwtClipboard::isOwner, TRUE, TRUE) != LONG{FALSE});
+    if (isOwner) {
         const HWND toolkitHwnd = AwtToolkit::GetInstance().GetHWnd();
 
         if (::OpenClipboard(toolkitHwnd) == 0) {

src/java.desktop/windows/native/libawt/windows/awt_Clipboard.h

@@ -54,7 +54,7 @@ public:
         (void)::InterlockedExchange(&isGettingOwnership, TRUE);  // isGettingOwnership = TRUE
         VERIFY(EmptyClipboard());
         (void)::InterlockedExchange(&isGettingOwnership, FALSE); // isGettingOwnership = FALSE
-        AwtClipboard::isOwner = TRUE;
+        (void)::InterlockedExchange(&isOwner, TRUE);             // isOwner = TRUE;
     }
 
     INLINE static BOOL IsGettingOwnership() {
@@ -78,7 +78,12 @@ public:
 
 private:
     static volatile BOOL areOwnershipExtraChecksEnabled;
-    static volatile BOOL isOwner;
+    // Although the variable's type is LONG, it's supposed to be treated as BOOL,
+    //     with the only possible values TRUE and FALSE.
+    // Also, all accesses to the variable (both reading and writing) MUST be performed using
+    //     Windows Interlocked Variable Access API.
+    // LONG is only used to make sure it's safe to pass the variable to ::Interlocked*** functions.
+    static volatile LONG /* BOOL */ isOwner;
     // ================================================================================================================
 };
 

src/java.desktop/windows/native/libawt/windows/awt_Component.cpp

@@ -1609,7 +1609,6 @@ LRESULT AwtComponent::WindowProc(UINT message, WPARAM wParam, LPARAM lParam)
               // the window is being activated, let's check if we still own the clipboard
               AwtClipboard::ExtraCheckOfOwnership();
           }
-          mr = mrConsume;
           break;
       case WM_MOUSEACTIVATE: {
           AwtWindow *window = GetContainer();