JAVA-1392: Reduce lock contention in RPTokenFactory

Alexandre Dutra · Alexandre Dutra · commit 1faebac0ca4f · 2017-02-16T11:15:19.000+01:00
Motivation: RPTokenFactory.md5() is called for almost every query plan by TokenAwarePolicy. This method in turn calls MessageDigest.getInstance(String), which is known to create lock contentions (see https://bugs.openjdk.java.net/browse/JDK-7092821). Modification: Clone a prototype instance of MessageDigest instead of creating a new one from scratch, thus avoiding lock contention. See google/guava#1197. Result: RPTokenFactory.md5() has an improved performance as no more lock contentions arrive.
diff --git a/changelog/README.md b/changelog/README.md
@@ -10,6 +10,7 @@
 - [improvement] JAVA-1308: CodecRegistry performance improvements.
 - [improvement] JAVA-1241: Upgrade Netty to 4.1.x.
 - [improvement] JAVA-1287: Add CDC to TableOptionsMetadata and Schema Builder.
+- [improvement] JAVA-1392: Reduce lock contention in RPTokenFactory.
 
 Merged from 3.1.x branch:
 
diff --git a/driver-core/src/main/java/com/datastax/driver/core/Token.java b/driver-core/src/main/java/com/datastax/driver/core/Token.java
@@ -230,7 +230,6 @@ private long murmur(ByteBuffer data) {
                         k1 *= c2;
                         h1 ^= k1;
                 }
-                ;
 
                 //----------
                 // finalization
@@ -569,16 +568,45 @@ private static class RPTokenFactory extends Factory {
             private static final Token MIN_TOKEN = new RPToken(MIN_VALUE);
             private static final Token MAX_TOKEN = new RPToken(MAX_VALUE);
 
-            private BigInteger md5(ByteBuffer data) {
+            private final MessageDigest prototype;
+            private final boolean supportsClone;
+
+            private RPTokenFactory() {
+                prototype = createMessageDigest();
+                boolean supportsClone;
                 try {
-                    MessageDigest digest = MessageDigest.getInstance("MD5");
-                    digest.update(data.duplicate());
-                    return new BigInteger(digest.digest()).abs();
+                    prototype.clone();
+                    supportsClone = true;
+                } catch (CloneNotSupportedException e) {
+                    supportsClone = false;
+                }
+                this.supportsClone = supportsClone;
+            }
+
+            private static MessageDigest createMessageDigest() {
+                try {
+                    return MessageDigest.getInstance("MD5");
                 } catch (NoSuchAlgorithmException e) {
                     throw new RuntimeException("MD5 doesn't seem to be available on this JVM", e);
                 }
             }
 
+            private MessageDigest newMessageDigest() {
+                if (supportsClone) {
+                    try {
+                        return (MessageDigest) prototype.clone();
+                    } catch (CloneNotSupportedException ignored) {
+                    }
+                }
+                return createMessageDigest();
+            }
+
+            private BigInteger md5(ByteBuffer data) {
+                MessageDigest digest = newMessageDigest();
+                digest.update(data.duplicate());
+                return new BigInteger(digest.digest()).abs();
+            }
+
             @Override
             RPToken fromString(String tokenStr) {
                 return new RPToken(new BigInteger(tokenStr));
diff --git a/driver-core/src/test/java/com/datastax/driver/core/RPTokenFactoryTest.java b/driver-core/src/test/java/com/datastax/driver/core/RPTokenFactoryTest.java
@@ -15,15 +15,27 @@
  */
 package com.datastax.driver.core;
 
+import com.datastax.driver.core.utils.Bytes;
 import org.testng.annotations.Test;
 
+import java.nio.ByteBuffer;
 import java.util.List;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
 public class RPTokenFactoryTest {
     Token.Factory factory = Token.RPToken.FACTORY;
 
+    @Test(groups = "unit")
+    public void should_hash_consistently() {
+        ByteBuffer byteBuffer = Bytes.fromHexString("0xCAFEBABE");
+        Token tokenA = factory.hash(byteBuffer);
+        Token tokenB = factory.hash(byteBuffer);
+        assertThat(tokenA)
+                .isEqualTo(factory.fromString("59959303159920881837560881824507314222"))
+                .isEqualTo(tokenB);
+    }
+
     @Test(groups = "unit")
     public void should_split_range() {
         List<Token> splits = factory.split(factory.fromString("0"), factory.fromString("127605887595351923798765477786913079296"), 3);
