8372048: Performance improvement on Linux remote desktop

Backport-of: 0b3df489e9d3b6d876a67793e082b930c17ade3e

Author: GoeLin

src/java.desktop/unix/classes/sun/awt/screencast/ScreencastHelper.java

@@ -66,9 +66,11 @@ public class ScreencastHelper {
     private static final int DELAY_BEFORE_SESSION_CLOSE = 2000;
 
     private static volatile TimerTask timerTask = null;
-    private static final Timer timerCloseSession
-            = new Timer("auto-close screencast session", true);
 
+    private static class TimerHolder {
+        private static final Timer timerCloseSession =
+                new Timer("auto-close screencast session", true);
+    }
 
     private ScreencastHelper() {}
 
@@ -152,7 +154,7 @@ public void run() {
             }
         };
 
-        timerCloseSession.schedule(timerTask, DELAY_BEFORE_SESSION_CLOSE);
+        TimerHolder.timerCloseSession.schedule(timerTask, DELAY_BEFORE_SESSION_CLOSE);
     }
 
     public static synchronized void getRGBPixels(

src/java.desktop/unix/classes/sun/awt/screencast/TokenStorage.java

@@ -252,6 +252,7 @@ public void run() {
     }
 
     private static WatchService watchService;
+    private static volatile boolean isWatcherThreadStarted = false;
 
     private static void setupWatch() {
         doPrivilegedRunnable(() -> {
@@ -273,10 +274,6 @@ private static void setupWatch() {
                 }
             }
         });
-
-        if (watchService != null) {
-            new WatcherThread(watchService).start();
-        }
     }
 
     // called from native
@@ -353,7 +350,27 @@ private static boolean readTokens(Path path) {
         return true;
     }
 
+    private static void startWatcherThreadIfNeeded() {
+        if (!isWatcherThreadStarted) {
+            // not sure if the double-checked locking is actually needed here
+            // the getTokens is only called from ScreencastHelper#getRGBPixels
+            // and ScreencastHelper#remoteDesktop* methods (which are synchronized),
+            // but it may change later.
+            synchronized (TokenStorage.class) {
+                if (!isWatcherThreadStarted) {
+                    readTokens(PROPS_PATH);
+                    if (watchService != null) {
+                        new WatcherThread(watchService).start();
+                    }
+                    isWatcherThreadStarted = true;
+                }
+            }
+        }
+    }
+
     static Set<TokenItem> getTokens(List<Rectangle> affectedScreenBounds) {
+        startWatcherThreadIfNeeded();
+
         // We need an ordered set to store tokens
         // with exact matches at the beginning.
         LinkedHashSet<TokenItem> result = new LinkedHashSet<>();