NewBlockHeaders performance improvement (#230)

* NewBlockHeaders performance improvement

When sending out new block headers to the websocket subscribers we
serialized the block once per each subscriber.  This had some crypto
calls for each serialization and was CPU bound with redundant
calculations.

We can memoize the result and only serialize it once per block.

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

ethereum/api/src/main/java/org/hyperledger/besu/ethereum/api/jsonrpc/websocket/subscription/blockheaders/NewBlockHeadersSubscriptionService.java

@@ -24,6 +24,10 @@ import org.hyperledger.besu.ethereum.chain.BlockAddedObserver;
 import org.hyperledger.besu.ethereum.chain.Blockchain;
 import org.hyperledger.besu.ethereum.core.Hash;
 
+import java.util.function.Supplier;
+
+import com.google.common.base.Suppliers;
+
 public class NewBlockHeadersSubscriptionService implements BlockAddedObserver {
 
   private final SubscriptionManager subscriptionManager;
@@ -45,11 +49,15 @@ public class NewBlockHeadersSubscriptionService implements BlockAddedObserver {
           subscribers -> {
             final Hash newBlockHash = event.getBlock().getHash();
 
+            // memoize
+            final Supplier<BlockResult> blockWithTx =
+                Suppliers.memoize(() -> blockWithCompleteTransaction(newBlockHash));
+            final Supplier<BlockResult> blockWithoutTx =
+                Suppliers.memoize(() -> blockWithTransactionHash(newBlockHash));
+
             for (final NewBlockHeadersSubscription subscription : subscribers) {
               final BlockResult newBlock =
-                  subscription.getIncludeTransactions()
-                      ? blockWithCompleteTransaction(newBlockHash)
-                      : blockWithTransactionHash(newBlockHash);
+                  subscription.getIncludeTransactions() ? blockWithTx.get() : blockWithoutTx.get();
 
               subscriptionManager.sendMessage(subscription.getSubscriptionId(), newBlock);
             }

ethereum/api/src/test/java/org/hyperledger/besu/ethereum/api/jsonrpc/websocket/subscription/blockheaders/NewBlockHeadersSubscriptionServiceTest.java

@@ -149,6 +149,29 @@ public class NewBlockHeadersSubscriptionServiceTest {
     verify(blockchainQueries, times(1)).blockByHash(any());
   }
 
+  @Test
+  public void shouldOnlyCreateResponsesOnce() {
+    final NewBlockHeadersSubscription subscription1 = createSubscription(true);
+    final NewBlockHeadersSubscription subscription2 = createSubscription(false);
+    final NewBlockHeadersSubscription subscription3 = createSubscription(true);
+    final NewBlockHeadersSubscription subscription4 = createSubscription(false);
+    mockSubscriptionManagerNotifyMethod(subscription1, subscription2, subscription3, subscription4);
+
+    simulateAddingBlockOnCanonicalChain();
+
+    verify(subscriptionManager, times(4))
+        .sendMessage(subscriptionIdCaptor.capture(), responseCaptor.capture());
+    assertThat(subscriptionIdCaptor.getAllValues())
+        .containsExactly(
+            subscription1.getSubscriptionId(),
+            subscription2.getSubscriptionId(),
+            subscription3.getSubscriptionId(),
+            subscription4.getSubscriptionId());
+
+    verify(blockchainQueries, times(1)).blockByHashWithTxHashes(any());
+    verify(blockchainQueries, times(1)).blockByHash(any());
+  }
+
   private BlockResult expectedBlockWithTransactions(final List<Hash> objects) {
     final BlockWithMetadata<Hash, Hash> testBlockWithMetadata =
         new BlockWithMetadata<>(blockHeader, objects, Collections.emptyList(), UInt256.ONE, 1);
@@ -159,11 +182,12 @@ public class NewBlockHeadersSubscriptionServiceTest {
     return expectedNewBlock;
   }
 
-  private void mockSubscriptionManagerNotifyMethod(final NewBlockHeadersSubscription subscription) {
+  private void mockSubscriptionManagerNotifyMethod(
+      final NewBlockHeadersSubscription... subscriptions) {
     doAnswer(
             invocation -> {
               Consumer<List<NewBlockHeadersSubscription>> consumer = invocation.getArgument(2);
-              consumer.accept(Collections.singletonList(subscription));
+              consumer.accept(List.of(subscriptions));
               return null;
             })
         .when(subscriptionManager)