diff -r 1c96344ecd49 -r 65ec6de1d6b4 langtools/src/jdk.jshell/share/classes/jdk/internal/jshell/tool/StopDetectingInputStream.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/langtools/src/jdk.jshell/share/classes/jdk/internal/jshell/tool/StopDetectingInputStream.java	Mon Oct 19 19:15:16 2015 +0200
@@ -0,0 +1,168 @@
+/*
+ * Copyright (c) 2015, 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.internal.jshell.tool;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.util.function.Consumer;
+
+public final class StopDetectingInputStream extends InputStream {
+    public static final int INITIAL_SIZE = 128;
+
+    private final Runnable stop;
+    private final Consumer<Exception> errorHandler;
+
+    private boolean initialized;
+    private int[] buffer = new int[INITIAL_SIZE];
+    private int start;
+    private int end;
+    private State state = State.WAIT;
+
+    public StopDetectingInputStream(Runnable stop, Consumer<Exception> errorHandler) {
+        this.stop = stop;
+        this.errorHandler = errorHandler;
+    }
+
+    public synchronized InputStream setInputStream(InputStream input) {
+        if (initialized)
+            throw new IllegalStateException("Already initialized.");
+        initialized = true;
+
+        Thread reader = new Thread() {
+            @Override
+            public void run() {
+                try {
+                    int read;
+                    while (true) {
+                        //to support external terminal editors, the "cmdin.read" must not run when
+                        //an external editor is running. At the same time, it needs to run while the
+                        //user's code is running (so Ctrl-C is detected). Hence waiting here until
+                        //there is a confirmed need for input.
+                        waitInputNeeded();
+                        if ((read = input.read()) == (-1)) {
+                            break;
+                        }
+                        if (read == 3 && state == StopDetectingInputStream.State.BUFFER) {
+                            stop.run();
+                        } else {
+                            write(read);
+                        }
+                    }
+                } catch (IOException ex) {
+                    errorHandler.accept(ex);
+                } finally {
+                    state = StopDetectingInputStream.State.CLOSED;
+                }
+            }
+        };
+        reader.setDaemon(true);
+        reader.start();
+
+        return this;
+    }
+
+    @Override
+    public synchronized int read() {
+        while (start == end) {
+            if (state == State.CLOSED) {
+                return -1;
+            }
+            if (state == State.WAIT) {
+                state = State.READ;
+            }
+            notifyAll();
+            try {
+                wait();
+            } catch (InterruptedException ex) {
+                //ignore
+            }
+        }
+        try {
+            return buffer[start];
+        } finally {
+            start = (start + 1) % buffer.length;
+        }
+    }
+
+    public synchronized void write(int b) {
+        if (state != State.BUFFER) {
+            state = State.WAIT;
+        }
+        int newEnd = (end + 1) % buffer.length;
+        if (newEnd == start) {
+            //overflow:
+            int[] newBuffer = new int[buffer.length * 2];
+            int rightPart = (end > start ? end : buffer.length) - start;
+            int leftPart = end > start ? 0 : start - 1;
+            System.arraycopy(buffer, start, newBuffer, 0, rightPart);
+            System.arraycopy(buffer, 0, newBuffer, rightPart, leftPart);
+            buffer = newBuffer;
+            start = 0;
+            end = rightPart + leftPart;
+            newEnd = end + 1;
+        }
+        buffer[end] = b;
+        end = newEnd;
+        notifyAll();
+    }
+
+    public synchronized void setState(State state) {
+        this.state = state;
+        notifyAll();
+    }
+
+    private synchronized void waitInputNeeded() {
+        while (state == State.WAIT) {
+            try {
+                wait();
+            } catch (InterruptedException ex) {
+                //ignore
+            }
+        }
+    }
+
+    public enum State {
+        /* No reading from the input should happen. This is the default state. The StopDetectingInput
+         * must be in this state when an external editor is being run, so that the external editor
+         * can read from the input.
+         */
+        WAIT,
+        /* A single input character should be read. Reading from the StopDetectingInput will move it
+         * into this state, and the state will be automatically changed back to WAIT when a single
+         * input character is obtained. This state is typically used while the user is editing the
+         * input line.
+         */
+        READ,
+        /* Continuously read from the input. Forward Ctrl-C ((int) 3) to the "stop" Runnable, buffer
+         * all other input. This state is typically used while the user's code is running, to provide
+         * the ability to detect Ctrl-C in order to stop the execution.
+         */
+        BUFFER,
+        /* The input is closed.
+        */
+        CLOSED
+    }
+
+}