--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/jdk.jshell/share/classes/jdk/jshell/execution/JdiExecutionControl.java	Tue Sep 12 19:03:39 2017 +0200
@@ -0,0 +1,125 @@
+/*
+ * Copyright (c) 2014, 2017, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package jdk.jshell.execution;
+
+import java.io.ObjectInput;
+import java.io.ObjectOutput;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.stream.Stream;
+import com.sun.jdi.ReferenceType;
+import com.sun.jdi.VirtualMachine;
+import jdk.jshell.spi.ExecutionControl;
+import static java.util.stream.Collectors.toMap;
+
+/**
+ * Abstract JDI implementation of {@link jdk.jshell.spi.ExecutionControl}.
+ *
+ * @since 9
+ */
+public abstract class JdiExecutionControl extends StreamingExecutionControl implements ExecutionControl {
+
+    /**
+     * Mapping from class names to JDI {@link ReferenceType}.
+     */
+    private final Map<String, ReferenceType> toReferenceType = new HashMap<>();
+
+    /**
+     * Create an instance.
+     * @param out the output from the remote agent
+     * @param in the input to the remote agent
+     */
+    protected JdiExecutionControl(ObjectOutput out, ObjectInput in) {
+        super(out, in);
+    }
+
+    /**
+     * Returns the JDI {@link VirtualMachine} instance.
+     *
+     * @return the virtual machine
+     * @throws EngineTerminationException if the VM is dead/disconnected
+     */
+    protected abstract VirtualMachine vm() throws EngineTerminationException;
+
+    /**
+     * Redefine the specified classes. Where 'redefine' is, as in JDI and JVMTI,
+     * an in-place replacement of the classes (preserving class identity) --
+     * that is, existing references to the class do not need to be recompiled.
+     * This implementation uses JDI
+     * {@link com.sun.jdi.VirtualMachine#redefineClasses(java.util.Map) }.
+     * It will be unsuccessful if
+     * the signature of the class has changed (see the JDI spec). The
+     * JShell-core is designed to adapt to unsuccessful redefine.
+     */
+    @Override
+    public void redefine(ClassBytecodes[] cbcs)
+            throws ClassInstallException, EngineTerminationException {
+        try {
+            // Convert to the JDI ReferenceType to class bytes map form needed
+            // by JDI.
+            VirtualMachine vm = vm();
+            Map<ReferenceType, byte[]> rmp = Stream.of(cbcs)
+                    .collect(toMap(
+                            cbc -> referenceType(vm, cbc.name()),
+                            cbc -> cbc.bytecodes()));
+            // Attempt redefine.  Throws exceptions on failure.
+            vm().redefineClasses(rmp);
+        } catch (EngineTerminationException ex) {
+            throw ex;
+        } catch (Exception ex) {
+            throw new ClassInstallException("redefine: " + ex.getMessage(), new boolean[cbcs.length]);
+        }
+        // forward the redefine to remote-end to register the redefined bytecode
+        try {
+            super.redefine(cbcs);
+        } catch (NotImplementedException ex) {
+            // this remote doesn't care about registering bytecode, so we don't either
+        }
+    }
+
+    /**
+     * Returns the JDI {@link ReferenceType} corresponding to the specified
+     * class name.
+     *
+     * @param vm the current JDI {@link VirtualMachine} as returned by
+     * {@code vm()}
+     * @param name the class name to look-up
+     * @return the corresponding {@link ReferenceType}
+     */
+    protected ReferenceType referenceType(VirtualMachine vm, String name) {
+        return toReferenceType.computeIfAbsent(name, n -> nameToRef(vm, n));
+    }
+
+    private static ReferenceType nameToRef(VirtualMachine vm, String name) {
+        List<ReferenceType> rtl = vm.classesByName(name);
+        if (rtl.size() != 1) {
+            return null;
+        }
+        return rtl.get(0);
+    }
+
+}