Started work to compute a PoW nonce in the online accounts manager.

This isn't used for anything yet, but it's enough to measure the performance implications of continually computing a nonce.

src/main/java/org/qortal/controller/Controller.java

@@ -469,6 +469,10 @@ public class Controller extends Thread {
 		// LOGGER.info("Starting arbitrary-transaction data manager");
 		// ArbitraryDataManager.getInstance().start();
 
+		// Online accounts manager
+		LOGGER.info("Starting online accounts manager");
+		OnlineAccountsManager.getInstance().start();
+
 		// Auto-update service?
 		if (Settings.getInstance().isAutoUpdateEnabled()) {
 			LOGGER.info("Starting auto-update");
@@ -1028,6 +1032,10 @@ public class Controller extends Thread {
 				// LOGGER.info("Shutting down arbitrary-transaction data manager");
 				// ArbitraryDataManager.getInstance().shutdown();
 
+				// Online accounts manager
+				 LOGGER.info("Shutting down online accounts manager");
+				 OnlineAccountsManager.getInstance().shutdown();
+
 				if (blockMinter != null) {
 					LOGGER.info("Shutting down block minter");
 					blockMinter.shutdown();

src/main/java/org/qortal/controller/OnlineAccountsManager.java

@@ -7,6 +7,7 @@ import org.qortal.account.Account;
 import org.qortal.account.PrivateKeyAccount;
 import org.qortal.account.PublicKeyAccount;
 import org.qortal.block.BlockChain;
+import org.qortal.crypto.MemoryPoW;
 import org.qortal.data.account.MintingAccountData;
 import org.qortal.data.account.RewardShareData;
 import org.qortal.data.network.OnlineAccountData;
@@ -24,12 +25,14 @@ import org.qortal.utils.NTP;
 import java.util.*;
 import java.util.stream.Collectors;
 
-public class OnlineAccountsManager {
+public class OnlineAccountsManager extends Thread {
 
     private static final Logger LOGGER = LogManager.getLogger(OnlineAccountsManager.class);
 
     private static OnlineAccountsManager instance;
 
+    private volatile boolean isStopping = false;
+
     // To do with online accounts list
     private static final long ONLINE_ACCOUNTS_TASKS_INTERVAL = 10 * 1000L; // ms
     private static final long ONLINE_ACCOUNTS_BROADCAST_INTERVAL = 1 * 60 * 1000L; // ms
@@ -38,6 +41,8 @@ public class OnlineAccountsManager {
     /** How many (latest) blocks' worth of online accounts we cache */
     private static final int MAX_BLOCKS_CACHED_ONLINE_ACCOUNTS = 2;
 
+    public static final int POW_BUFFER_SIZE = 8 * 1024 * 1024; // bytes
+
     private long onlineAccountsTasksTimestamp = Controller.startTime + ONLINE_ACCOUNTS_TASKS_INTERVAL; // ms
 
     /** Cache of current 'online accounts' */
@@ -57,6 +62,36 @@ public class OnlineAccountsManager {
         return instance;
     }
 
+    @Override
+    public void run() {
+        Thread.currentThread().setName("Online Accounts Manager");
+
+        try {
+            while (!isStopping) {
+                Thread.sleep(2000);
+
+                int difficulty = 15;
+                long timestamp = System.currentTimeMillis();
+
+                LOGGER.info("Computing nonce at difficulty {} for timestamp {}...", difficulty, timestamp);
+
+                byte[] bytes = Longs.toByteArray(timestamp);
+                Integer nonce = MemoryPoW.compute2(bytes, POW_BUFFER_SIZE, difficulty);
+
+                LOGGER.info("Computed nonce: {}. Time taken: {} ms", nonce, (System.currentTimeMillis() - timestamp));
+            }
+
+        } catch (InterruptedException e) {
+            // Fall-through to exit thread...
+        }
+    }
+
+    public void shutdown() {
+        isStopping = true;
+        this.interrupt();
+    }
+
+
 
     public void checkOnlineAccountsTasks(long now) {
         // Perform tasks to do with managing online accounts list

src/main/java/org/qortal/crypto/MemoryPoW.java

@@ -1,5 +1,7 @@
 package org.qortal.crypto;
 
+import org.qortal.controller.Controller;
+
 import java.nio.ByteBuffer;
 
 public class MemoryPoW {
@@ -33,6 +35,10 @@ public class MemoryPoW {
 			if (Thread.currentThread().isInterrupted())
 				return -1;
 
+			// Or, if the Controller is stopping, do the same
+			if (Controller.isStopping())
+				return -1;
+
 			seed *= seedMultiplier; // per nonce
 
 			state[0] = longHash[0] ^ seed;