Added interface for manual switch to Short Sync

ethereumj-core/src/main/java/org/ethereum/facade/Ethereum.java

@@ -32,6 +32,7 @@
 import java.math.BigInteger;
 import java.net.InetAddress;
 import java.util.List;
+import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.Future;
 
 /**
@@ -216,5 +217,12 @@ ProgramResult callConstantFunction(String receiveAddress, ECKey senderPrivateKey
      */
     Integer getChainIdForNextBlock();
 
+    /**
+     * Manual switch to Short Sync mode
+     * Maybe useful in small private and detached networks when automatic detection fails
+     * @return Future, which completes when syncDone is turned to True in {@link org.ethereum.sync.SyncManager}
+     */
+    CompletableFuture<Void> switchToShortSync();
+
     void exitOn(long number);
 }

ethereumj-core/src/main/java/org/ethereum/facade/EthereumImpl.java

@@ -56,6 +56,7 @@
 import java.math.BigInteger;
 import java.net.InetAddress;
 import java.util.*;
+import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.Future;
 
@@ -380,6 +381,10 @@ public Integer getChainIdForNextBlock() {
         return nextBlockConfig.getChainId();
     }
 
+    public CompletableFuture<Void> switchToShortSync() {
+        return syncManager.switchToShortSync();
+    }
+
     @Override
     public void exitOn(long number) {
         worldManager.getBlockchain().setExitOn(number);

ethereumj-core/src/main/java/org/ethereum/sync/SyncManager.java

@@ -274,9 +274,7 @@ private void produceQueue() {
                             wrapper.getBlock().getTransactionsList().size(), ts);
 
                     if (wrapper.isNewBlock() && !syncDone) {
-                        syncDone = true;
-                        channelManager.onSyncDone(true);
-                        compositeEthereumListener.onSyncDone(syncDoneType);
+                        makeSyncDone();
                     }
                 }
 
@@ -311,6 +309,34 @@ private void produceQueue() {
         }
     }
 
+    private synchronized void makeSyncDone() {
+        if (syncDone) return;
+        syncDone = true;
+        channelManager.onSyncDone(true);
+        compositeEthereumListener.onSyncDone(syncDoneType);
+    }
+
+    public CompletableFuture<Void> switchToShortSync() {
+        final CompletableFuture<Void> syncDoneF = new CompletableFuture<>();
+        if(!syncDone) {
+            new Thread(() -> {
+                while(!blockQueue.isEmpty() && !syncDone) {
+                    try {
+                        Thread.sleep(100);
+                    } catch (InterruptedException e) {
+                        syncDoneF.completeExceptionally(e);
+                    }
+                }
+                makeSyncDone();
+                syncDoneF.complete(null);
+            }).start();
+        } else {
+            syncDoneF.complete(null);
+        }
+
+        return syncDoneF;
+    }
+
     /**
      * Adds NEW block to the queue
      *