Made keys immutability configurable

src/main/java/net/openhft/chronicle/map/ChronicleMapBuilder.java

@@ -622,6 +622,22 @@ public class ChronicleMapBuilder<K, V> implements Cloneable {
         return this;
     }
 
+    /**
+     * Specifies that key objects, queried with the maps created by this builder, are inherently
+     * immutable. Keys in {@code ChronicleMap} are not required to be immutable, as in ordinary
+     * {@link Map} implementations, because they are serialized off-heap. However,
+     * {@code ChronicleMap} implementations can benefit from the knowledge that keys are not mutated
+     * between queries. By default, {@code ChronicleMapBuilder} detects immutability automatically
+     * only for very few standard JDK types (for example, for {@link String}), it is not recommended
+     * to rely on {@code ChronicleMapBuilder} to be smart enough about this.
+     *
+     * @return this builder back
+     */
+    public ChronicleMapBuilder<K, V> immutableKeys() {
+        keyBuilder.instancesAreMutable(false);
+        return this;
+    }
+
     public ChronicleMapBuilder<K, V> valueMarshallerAndFactory(
             @NotNull BytesMarshaller<V> valueMarshaller, @NotNull ObjectFactory<V> valueFactory) {
         valueBuilder.marshaller(valueMarshaller, valueFactory);

src/main/java/net/openhft/chronicle/map/SerializationBuilder.java

@@ -45,11 +45,16 @@ final class SerializationBuilder<E> implements Cloneable {
                 Externalizable.class.isAssignableFrom(c);
     }
 
+    private static boolean instancesAreMutable(Class c) {
+        return c != String.class;
+    }
+
     enum Role {KEY, VALUE}
     private enum CopyingInterop {FROM_MARSHALLER, FROM_WRITER}
 
     private final Serializable bufferIdentity;
     final Class<E> eClass;
+    private boolean instancesAreMutable;
     private SizeMarshaller sizeMarshaller = stopBit();
     private BytesReader<E> reader;
     private Object interop;
@@ -62,6 +67,7 @@ final class SerializationBuilder<E> implements Cloneable {
     SerializationBuilder(Class<E> eClass, Role role) {
         this.bufferIdentity = role;
         this.eClass = eClass;
+        instancesAreMutable = instancesAreMutable(eClass);
 
         ObjectFactory<E> factory = null;
         if (role == Role.VALUE) {
@@ -144,13 +150,13 @@ final class SerializationBuilder<E> implements Cloneable {
     }
 
     public SerializationBuilder<E> maxSize(long maxSize) {
-        boolean mutable = eClass != String.class; // for example
         if (copyingInterop == CopyingInterop.FROM_MARSHALLER) {
             metaInteropProvider(CopyingMetaBytesInterop
-                    .<E, BytesMarshaller<E>>providerForBytesMarshaller(mutable, maxSize));
+                    .<E, BytesMarshaller<E>>providerForBytesMarshaller(
+                            instancesAreMutable, maxSize));
         } else if (copyingInterop == CopyingInterop.FROM_WRITER) {
             metaInteropProvider(CopyingMetaBytesInterop
-                    .<E, BytesWriter<E>>providerForBytesWriter(mutable, maxSize));
+                    .<E, BytesWriter<E>>providerForBytesWriter(instancesAreMutable, maxSize));
         }
         return this;
     }
@@ -165,6 +171,11 @@ final class SerializationBuilder<E> implements Cloneable {
         return this;
     }
 
+    public SerializationBuilder<E> instancesAreMutable(boolean mutable) {
+        this.instancesAreMutable = mutable;
+        return this;
+    }
+
     public SizeMarshaller sizeMarshaller() {
         return sizeMarshaller;
     }