--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/jdk.dns.client/share/classes/jdk/dns/client/internal/util/ReloadTracker.java	Thu Oct 31 16:16:21 2019 +0000
@@ -0,0 +1,112 @@
+/*
+ * Copyright (c) 2019, 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
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package jdk.dns.client.internal.util;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.security.AccessController;
+import java.security.PrivilegedAction;
+import java.security.PrivilegedActionException;
+import java.security.PrivilegedExceptionAction;
+import java.util.concurrent.atomic.AtomicLong;
+
+public class ReloadTracker {
+
+    public static ReloadTracker newInstance(Path fileToTrack, long refreshTimeoutMillis) {
+        Path absolutePath = fileToTrack.toAbsolutePath();
+        return new ReloadTracker(absolutePath, refreshTimeoutMillis);
+    }
+
+    public static class ReloadStatus {
+        private final boolean isReloadNeeded;
+        private final long lastModificationTimestamp;
+        private final boolean fileExists;
+
+        ReloadStatus(boolean fileExists, boolean isReloadNeeded, long lastModificationTimestamp) {
+            this.isReloadNeeded = fileExists && isReloadNeeded;
+            this.lastModificationTimestamp = lastModificationTimestamp;
+            this.fileExists = fileExists;
+        }
+
+        public boolean isFileExists() {
+            return fileExists;
+        }
+
+        public boolean isReloadNeeded() {
+            return isReloadNeeded;
+        }
+
+        public long getLastModificationTimestamp() {
+            return lastModificationTimestamp;
+        }
+    }
+
+
+    private ReloadTracker(Path filePath, long refreshTimeoutMillis) {
+        this.filePath = filePath;
+        this.refreshTimeoutMillis = refreshTimeoutMillis;
+    }
+
+
+    public ReloadStatus getReloadStatus() {
+        boolean fileExists;
+        var pa = (PrivilegedAction<Boolean>) () -> filePath.toFile().isFile();
+        fileExists = System.getSecurityManager() == null ? pa.run() : AccessController.doPrivileged(pa);
+
+        long lastModificationTime = -1;
+        long lastReload = lastRefreshed.get();
+
+        // Do not update lastModification time if file doesn't exist
+        if (fileExists) {
+            try {
+                var pea = (PrivilegedExceptionAction<Long>) () -> Files.getLastModifiedTime(filePath).toMillis();
+                lastModificationTime = System.getSecurityManager() == null ? pea.run()
+                        : AccessController.doPrivileged(pea);
+            } catch (Exception e) {
+                // In case of Exception the tracked file will be reloaded, ie lastModificationTime == -1
+            }
+        }
+        return new ReloadStatus(fileExists,
+                (lastModificationTime != lastSeenChanged.get()) ||
+                        (System.currentTimeMillis() - lastReload > refreshTimeoutMillis),
+                lastModificationTime);
+    }
+
+    public void updateTimestamps(ReloadStatus rs) {
+        lastSeenChanged.set(rs.lastModificationTimestamp);
+        lastRefreshed.set(System.currentTimeMillis());
+    }
+
+    // Last timestamp when tracked file has been reloaded by consumer of this utility class
+    private final AtomicLong lastRefreshed = new AtomicLong(-1);
+    // Last processed FS last modified timestamp
+    private final AtomicLong lastSeenChanged = new AtomicLong(-1);
+    // Refresh timeout
+    private final long refreshTimeoutMillis;
+    // Path of the tracked file
+    private final Path filePath;
+}