OnlineAccountsV3: slightly rework Block.mint() so it doesn't need to filter so many online accounts

Slight optimization to BlockMinter by adding OnlineAccountsManager.hasOnlineAccounts():boolean instead of returning actual data, only to call isEmpty()!

src/main/java/org/qortal/block/Block.java

@@ -346,20 +346,24 @@ public class Block {
 		int version = parentBlock.getNextBlockVersion();
 		byte[] reference = parentBlockData.getSignature();
 
+		// Qortal: minter is always a reward-share, so find actual minter and get their effective minting level
+		int minterLevel = Account.getRewardShareEffectiveMintingLevel(repository, minter.getPublicKey());
+		if (minterLevel == 0) {
+			LOGGER.error("Minter effective level returned zero?");
+			return null;
+		}
+
+		long timestamp = calcTimestamp(parentBlockData, minter.getPublicKey(), minterLevel);
+
+		long onlineAccountsTimestamp = OnlineAccountsManager.toOnlineAccountTimestamp(timestamp);
+
 		// Fetch our list of online accounts
-		List<OnlineAccountData> onlineAccounts = OnlineAccountsManager.getInstance().getOnlineAccounts();
+		List<OnlineAccountData> onlineAccounts = OnlineAccountsManager.getInstance().getOnlineAccounts(onlineAccountsTimestamp);
 		if (onlineAccounts.isEmpty()) {
 			LOGGER.error("No online accounts - not even our own?");
 			return null;
 		}
 
-		// Find newest online accounts timestamp
-		long onlineAccountsTimestamp = 0;
-		for (OnlineAccountData onlineAccountData : onlineAccounts) {
-			if (onlineAccountData.getTimestamp() > onlineAccountsTimestamp)
-				onlineAccountsTimestamp = onlineAccountData.getTimestamp();
-		}
-
 		// Load sorted list of reward share public keys into memory, so that the indexes can be obtained.
 		// This is up to 100x faster than querying each index separately. For 4150 reward share keys, it
 		// was taking around 5000ms to query individually, vs 50ms using this approach.
@@ -368,10 +372,6 @@ public class Block {
 		// Map using index into sorted list of reward-shares as key
 		Map<Integer, OnlineAccountData> indexedOnlineAccounts = new HashMap<>();
 		for (OnlineAccountData onlineAccountData : onlineAccounts) {
-			// Disregard online accounts with different timestamps
-			if (onlineAccountData.getTimestamp() != onlineAccountsTimestamp)
-				continue;
-
 			Integer accountIndex = getRewardShareIndex(onlineAccountData.getPublicKey(), allRewardSharePublicKeys);
 			if (accountIndex == null)
 				// Online account (reward-share) with current timestamp but reward-share cancelled
@@ -399,15 +399,6 @@ public class Block {
 		byte[] minterSignature = minter.sign(BlockTransformer.getBytesForMinterSignature(parentBlockData,
 				minter.getPublicKey(), encodedOnlineAccounts));
 
-		// Qortal: minter is always a reward-share, so find actual minter and get their effective minting level
-		int minterLevel = Account.getRewardShareEffectiveMintingLevel(repository, minter.getPublicKey());
-		if (minterLevel == 0) {
-			LOGGER.error("Minter effective level returned zero?");
-			return null;
-		}
-
-		long timestamp = calcTimestamp(parentBlockData, minter.getPublicKey(), minterLevel);
-
 		int transactionCount = 0;
 		byte[] transactionsSignature = null;
 		int height = parentBlockData.getHeight() + 1;

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

@@ -114,8 +114,8 @@ public class BlockMinter extends Thread {
 				if (minLatestBlockTimestamp == null)
 					continue;
 
-				// No online accounts? (e.g. during startup)
-				if (OnlineAccountsManager.getInstance().getOnlineAccounts().isEmpty())
+				// No online accounts for current timestamp? (e.g. during startup)
+				if (!OnlineAccountsManager.getInstance().hasOnlineAccounts())
 					continue;
 
 				List<MintingAccountData> mintingAccountsData = repository.getAccountRepository().getMintingAccounts();

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

@@ -420,6 +420,20 @@ public class OnlineAccountsManager {
         LOGGER.debug("Broadcasted {} online account{} with timestamp {}", ourOnlineAccounts.size(), (ourOnlineAccounts.size() != 1 ? "s" : ""), onlineAccountsTimestamp);
     }
 
+    /**
+     * Returns whether online accounts manager has any online accounts with timestamp recent enough to be considered currently online.
+     */
+    // BlockMinter: only calls this to check whether returned list is empty or not, to determine whether minting is even possible or not
+    public boolean hasOnlineAccounts() {
+        final Long now = NTP.getTime();
+        if (now == null)
+            return false;
+
+        final long onlineTimestamp = toOnlineAccountTimestamp(now);
+
+        return this.currentOnlineAccounts.containsKey(onlineTimestamp);
+    }
+
     /**
      * Returns list of online accounts matching given timestamp.
      */
@@ -433,7 +447,6 @@ public class OnlineAccountsManager {
      * Returns list of online accounts with timestamp recent enough to be considered currently online.
      */
     // API: calls this to return list of online accounts - probably expects ALL timestamps - but going to get 'current' from now on
-    // BlockMinter: only calls this to check whether returned list is empty or not, to determine whether minting is even possible or not
     public List<OnlineAccountData> getOnlineAccounts() {
         final Long now = NTP.getTime();
         if (now == null)