RLP Import Error Reporting (#1753)

Exceptions encountered during the import of blocks is suppressed and the
importer can hang. Normally not a problem with perfect blocks but when
testing broken chains its a hinderance.

Signed-off-by: Danno Ferrin <danno.ferrin@gmail.com>

besu/src/main/java/org/hyperledger/besu/chainimport/RlpBlockImporter.java

@@ -41,6 +41,7 @@ import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 import java.util.concurrent.Semaphore;
 import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicReference;
 
 import com.google.common.base.MoreObjects;
 import com.google.common.base.Stopwatch;
@@ -98,6 +99,7 @@ public class RlpBlockImporter implements Closeable {
                     rlp, ScheduleBasedBlockHeaderFunctions.create(protocolSchedule)))) {
       BlockHeader previousHeader = null;
       CompletableFuture<Void> previousBlockFuture = null;
+      final AtomicReference<Throwable> threadedException = new AtomicReference<>();
       while (iterator.hasNext()) {
         final Block block = iterator.next();
         final BlockHeader header = block.getHeader();
@@ -132,7 +134,12 @@ public class RlpBlockImporter implements Closeable {
         }
 
         try {
-          blockBacklog.acquire();
+          do {
+            final Throwable t = (Exception) threadedException.get();
+            if (t != null) {
+              throw new RuntimeException("Error importing block", t);
+            }
+          } while (!blockBacklog.tryAcquire(1, SECONDS));
         } catch (final InterruptedException e) {
           LOG.error("Interrupted adding to backlog.", e);
           break;
@@ -142,6 +149,11 @@ public class RlpBlockImporter implements Closeable {
                 calculationFutures,
                 () -> evaluateBlock(context, block, header, protocolSpec, skipPowValidation),
                 importExecutor);
+        previousBlockFuture.exceptionally(
+            exception -> {
+              threadedException.set(exception);
+              return null;
+            });
 
         ++count;
         previousHeader = header;
@@ -251,6 +263,7 @@ public class RlpBlockImporter implements Closeable {
   public void close() {
     validationExecutor.shutdownNow();
     try {
+      //noinspection ResultOfMethodCallIgnored
       validationExecutor.awaitTermination(5, SECONDS);
     } catch (final Exception e) {
       LOG.error("Error shutting down validatorExecutor.", e);
@@ -258,6 +271,7 @@ public class RlpBlockImporter implements Closeable {
 
     importExecutor.shutdownNow();
     try {
+      //noinspection ResultOfMethodCallIgnored
       importExecutor.awaitTermination(5, SECONDS);
     } catch (final Exception e) {
       LOG.error("Error shutting down importExecutor", e);