--- a/src/macosx/classes/sun/lwawt/macosx/CEmbeddedFrame.java	Tue Oct 11 16:57:34 2016 +0300
+++ b/src/macosx/classes/sun/lwawt/macosx/CEmbeddedFrame.java	Fri Oct 07 22:05:23 2016 +0400
@@ -91,7 +91,7 @@
         int x = (int)pluginX;
         int y = (int)pluginY;
 
-        responder.handleScrollEvent(x, y, modifierFlags, deltaX, deltaY);
+        responder.handleScrollEvent(x, y, modifierFlags, deltaX, deltaY, NSEvent.SCROLL_PHASE_UNSUPPORTED);
     }
 
     public void handleKeyEvent(int eventType, int modifierFlags, String characters,

--- a/src/macosx/classes/sun/lwawt/macosx/CPlatformResponder.java	Tue Oct 11 16:57:34 2016 +0300
+++ b/src/macosx/classes/sun/lwawt/macosx/CPlatformResponder.java	Fri Oct 07 22:05:23 2016 +0400
@@ -44,6 +44,8 @@
     private final PlatformEventNotifier eventNotifier;
     private final boolean isNpapiCallback;
     private int lastKeyPressCode = KeyEvent.VK_UNDEFINED;
+    private final DeltaAccumulator deltaAccumulatorX = new DeltaAccumulator();
+    private final DeltaAccumulator deltaAccumulatorY = new DeltaAccumulator();
 
     CPlatformResponder(final PlatformEventNotifier eventNotifier,
                        final boolean isNpapiCallback) {
@@ -90,37 +92,38 @@
      * Handles scroll events.
      */
     void handleScrollEvent(final int x, final int y, final int modifierFlags,
-                           final double deltaX, final double deltaY) {
+                           final double deltaX, final double deltaY,
+                           final int scrollPhase) {
         final int buttonNumber = CocoaConstants.kCGMouseButtonCenter;
         int jmodifiers = NSEvent.nsToJavaMouseModifiers(buttonNumber,
                                                         modifierFlags);
         final boolean isShift = (jmodifiers & InputEvent.SHIFT_DOWN_MASK) != 0;
 
+        int roundDeltaX = deltaAccumulatorX.getRoundedDelta(deltaX, scrollPhase);
+        int roundDeltaY = deltaAccumulatorY.getRoundedDelta(deltaY, scrollPhase);
+
         // Vertical scroll.
-        if (!isShift && deltaY != 0.0) {
-            dispatchScrollEvent(x, y, jmodifiers, deltaY);
+        if (!isShift && (deltaY != 0.0 || roundDeltaY != 0)) {
+            dispatchScrollEvent(x, y, jmodifiers, roundDeltaY, deltaY);
         }
         // Horizontal scroll or shirt+vertical scroll.
         final double delta = isShift && deltaY != 0.0 ? deltaY : deltaX;
-        if (delta != 0.0) {
+        final int roundDelta = isShift && roundDeltaY != 0 ? roundDeltaY : roundDeltaX;
+        if (delta != 0.0 || roundDelta != 0) {
             jmodifiers |= InputEvent.SHIFT_DOWN_MASK;
-            dispatchScrollEvent(x, y, jmodifiers, delta);
+            dispatchScrollEvent(x, y, jmodifiers, roundDelta, delta);
         }
     }
 
     private void dispatchScrollEvent(final int x, final int y,
-                                     final int modifiers, final double delta) {
+                                     final int modifiers,
+                                     final int roundDelta, final double delta) {
         final long when = System.currentTimeMillis();
         final int scrollType = MouseWheelEvent.WHEEL_UNIT_SCROLL;
         final int scrollAmount = 1;
-        int wheelRotation = (int) delta;
-        int signum = (int) Math.signum(delta);
-        if (signum * delta < 1) {
-            wheelRotation = signum;
-        }
         // invert the wheelRotation for the peer
         eventNotifier.notifyMouseWheelEvent(when, x, y, modifiers, scrollType,
-                scrollAmount, -wheelRotation, -delta, null);
+                scrollAmount, -roundDelta, -delta, null);
     }
 
     /**
@@ -256,4 +259,46 @@
     void handleWindowFocusEvent(boolean gained, LWWindowPeer opposite) {
         eventNotifier.notifyActivation(gained, opposite);
     }
+
+    static class DeltaAccumulator {
+
+        static final double MIN_THRESHOLD = 0.1;
+        static final double MAX_THRESHOLD = 0.5;
+        double accumulatedDelta;
+
+        int getRoundedDelta(double delta, int scrollPhase) {
+
+            int roundDelta = (int) Math.round(delta);
+
+            if (scrollPhase == NSEvent.SCROLL_PHASE_UNSUPPORTED) { // mouse wheel
+                if (roundDelta == 0 && delta != 0) {
+                    roundDelta = delta > 0 ? 1 : -1;
+                }
+            } else { // trackpad
+                boolean begin = scrollPhase == NSEvent.SCROLL_PHASE_BEGAN;
+                boolean end = scrollPhase == NSEvent.SCROLL_MASK_PHASE_ENDED
+                        || scrollPhase == NSEvent.SCROLL_MASK_PHASE_CANCELLED;
+
+                if (begin) {
+                    accumulatedDelta = 0;
+                }
+
+                accumulatedDelta += delta;
+
+                double absAccumulatedDelta = Math.abs(accumulatedDelta);
+                if (absAccumulatedDelta > MAX_THRESHOLD) {
+                    roundDelta = (int) Math.round(accumulatedDelta);
+                    accumulatedDelta -= roundDelta;
+                }
+
+                if (end) {
+                    if (roundDelta == 0 && absAccumulatedDelta > MIN_THRESHOLD) {
+                        roundDelta = accumulatedDelta > 0 ? 1 : -1;
+                    }
+                }
+            }
+
+            return roundDelta;
+        }
+    }
 }

--- a/src/macosx/classes/sun/lwawt/macosx/CPlatformView.java	Tue Oct 11 16:57:34 2016 +0300
+++ b/src/macosx/classes/sun/lwawt/macosx/CPlatformView.java	Fri Oct 07 22:05:23 2016 +0400
@@ -192,7 +192,8 @@
 
         if (event.getType() == CocoaConstants.NSScrollWheel) {
             responder.handleScrollEvent(x, y, event.getModifierFlags(),
-                                        event.getScrollDeltaX(), event.getScrollDeltaY());
+                                        event.getScrollDeltaX(), event.getScrollDeltaY(),
+                                        event.getScrollPhase());
         } else {
             responder.handleMouseEvent(event.getType(), event.getModifierFlags(), event.getButtonNumber(),
                                        event.getClickCount(), x, y, event.getAbsX(), event.getAbsY());

--- a/src/macosx/classes/sun/lwawt/macosx/NSEvent.java	Tue Oct 11 16:57:34 2016 +0300
+++ b/src/macosx/classes/sun/lwawt/macosx/NSEvent.java	Fri Oct 07 22:05:23 2016 +0400
@@ -32,6 +32,13 @@
  * JDK functionality.
  */
 final class NSEvent {
+
+    static final int SCROLL_PHASE_UNSUPPORTED = 1;
+    static final int SCROLL_PHASE_BEGAN = 2;
+    static final int SCROLL_PHASE_CONTINUED = 3;
+    static final int SCROLL_MASK_PHASE_CANCELLED = 4;
+    static final int SCROLL_MASK_PHASE_ENDED = 5;
+
     private int type;
     private int modifierFlags;
 
@@ -42,6 +49,7 @@
     private int y;
     private double scrollDeltaY;
     private double scrollDeltaX;
+    private int scrollPhase;
     private int absX;
     private int absY;
 
@@ -62,7 +70,7 @@
     // Called from native
     NSEvent(int type, int modifierFlags, int clickCount, int buttonNumber,
                    int x, int y, int absX, int absY,
-                   double scrollDeltaY, double scrollDeltaX) {
+                   double scrollDeltaY, double scrollDeltaX, int scrollPhase) {
         this.type = type;
         this.modifierFlags = modifierFlags;
         this.clickCount = clickCount;
@@ -73,6 +81,7 @@
         this.absY = absY;
         this.scrollDeltaY = scrollDeltaY;
         this.scrollDeltaX = scrollDeltaX;
+        this.scrollPhase = scrollPhase;
     }
 
     int getType() {
@@ -107,6 +116,10 @@
         return scrollDeltaX;
     }
 
+    int getScrollPhase() {
+        return scrollPhase;
+    }
+
     int getAbsX() {
         return absX;
     }

--- a/src/macosx/native/sun/awt/AWTView.m	Tue Oct 11 16:57:34 2016 +0300
+++ b/src/macosx/native/sun/awt/AWTView.m	Fri Oct 07 22:05:23 2016 +0400
@@ -386,7 +386,7 @@
     }
 
     static JNF_CLASS_CACHE(jc_NSEvent, "sun/lwawt/macosx/NSEvent");
-    static JNF_CTOR_CACHE(jctor_NSEvent, jc_NSEvent, "(IIIIIIIIDD)V");
+    static JNF_CTOR_CACHE(jctor_NSEvent, jc_NSEvent, "(IIIIIIIIDDI)V");
     jobject jEvent = JNFNewObject(env, jctor_NSEvent,
                                   [event type],
                                   [event modifierFlags],
@@ -395,7 +395,8 @@
                                   (jint)localPoint.x, (jint)localPoint.y,
                                   (jint)absP.x, (jint)absP.y,
                                   [event deltaY],
-                                  [event deltaX]);
+                                  [event deltaX],
+                                  [AWTToolkit scrollStateWithEvent: event]);
     if (jEvent == nil) {
         // Unable to create event by some reason.
         return;

--- a/src/macosx/native/sun/awt/CTrayIcon.m	Tue Oct 11 16:57:34 2016 +0300
+++ b/src/macosx/native/sun/awt/CTrayIcon.m	Fri Oct 07 22:05:23 2016 +0400
@@ -136,7 +136,7 @@
     clickCount = [event clickCount];
 
     static JNF_CLASS_CACHE(jc_NSEvent, "sun/lwawt/macosx/NSEvent");
-    static JNF_CTOR_CACHE(jctor_NSEvent, jc_NSEvent, "(IIIIIIIIDD)V");
+    static JNF_CTOR_CACHE(jctor_NSEvent, jc_NSEvent, "(IIIIIIIIDDI)V");
     jobject jEvent = JNFNewObject(env, jctor_NSEvent,
                                   [event type],
                                   [event modifierFlags],
@@ -145,7 +145,8 @@
                                   (jint)localPoint.x, (jint)localPoint.y,
                                   (jint)absP.x, (jint)absP.y,
                                   [event deltaY],
-                                  [event deltaX]);
+                                  [event deltaX],
+                                  [AWTToolkit scrollStateWithEvent: event]);
     if (jEvent == nil) {
         // Unable to create event by some reason.
         return;

--- a/src/macosx/native/sun/awt/LWCToolkit.h	Tue Oct 11 16:57:34 2016 +0300
+++ b/src/macosx/native/sun/awt/LWCToolkit.h	Fri Oct 07 22:05:23 2016 +0400
@@ -40,6 +40,7 @@
 @interface AWTToolkit : NSObject { }
 + (long) getEventCount;
 + (void) eventCountPlusPlus;
++ (jint) scrollStateWithEvent: (NSEvent*) event;
 @end
 
 /*

--- a/src/macosx/native/sun/awt/LWCToolkit.m	Tue Oct 11 16:57:34 2016 +0300
+++ b/src/macosx/native/sun/awt/LWCToolkit.m	Fri Oct 07 22:05:23 2016 +0400
@@ -39,6 +39,13 @@
 
 #import "sizecalc.h"
 
+// SCROLL PHASE STATE
+#define SCROLL_PHASE_UNSUPPORTED 1
+#define SCROLL_PHASE_BEGAN 2
+#define SCROLL_PHASE_CONTINUED 3
+#define SCROLL_PHASE_CANCELLED 4
+#define SCROLL_PHASE_ENDED 5
+
 int gNumberOfButtons;
 jint* gButtonDownMasks;
 
@@ -54,6 +61,23 @@
     eventCount++;
 }
 
++ (jint) scrollStateWithEvent: (NSEvent*) event {
+
+    if ([event type] != NSScrollWheel) {
+        return 0;
+    }
+
+    NSEventPhase phase = [event phase];
+    NSEventPhase momentumPhase = [event momentumPhase];
+
+    if (!phase && !momentumPhase) return SCROLL_PHASE_UNSUPPORTED;
+    switch (phase) {
+        case NSEventPhaseBegan: return SCROLL_PHASE_BEGAN;
+        case NSEventPhaseCancelled: return SCROLL_PHASE_CANCELLED;
+        case NSEventPhaseEnded: return SCROLL_PHASE_ENDED;
+    }
+    return SCROLL_PHASE_CONTINUED;
+}
 @end
 
 

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/test/javax/swing/plaf/basic/BasicScrollPaneUI/8166591/TooMuchWheelRotationEventsTest.java	Fri Oct 07 22:05:23 2016 +0400
@@ -0,0 +1,188 @@
+/*
+ * Copyright (c) 2016, 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.
+ *
+ * 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.
+ */
+
+import java.awt.Color;
+import java.awt.GridBagConstraints;
+import java.awt.GridBagLayout;
+import java.awt.event.ActionEvent;
+import java.awt.event.ActionListener;
+import java.awt.event.WindowAdapter;
+import java.awt.event.WindowEvent;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
+import javax.swing.BoxLayout;
+import javax.swing.JButton;
+import javax.swing.JFrame;
+import javax.swing.JPanel;
+import javax.swing.JScrollPane;
+import javax.swing.JTextArea;
+import javax.swing.SwingUtilities;
+
+/*
+ * @test
+ * @bug 8166591
+ * @summary [macos 10.12] Trackpad scrolling of text on OS X 10.12 Sierra
+ *    is very fast (Trackpad, Retina only)
+ * @run main/manual/othervm TooMuchWheelRotationEventsTest
+ */
+public class TooMuchWheelRotationEventsTest {
+
+    private static volatile boolean testResult = false;
+    private static volatile CountDownLatch countDownLatch;
+    private static final String INSTRUCTIONS = "INSTRUCTIONS:\n"
+            + "Try to check the issue on Mac OS X 10.12 Sierra with trackpad"
+            + " on Retina display.\n"
+            + "\n"
+            + "If the trackpad is not supported, press PASS\n"
+            + "\n"
+            + "Use the trackpad to slightly scroll the JTextArea horizontally and vertically.\n"
+            + "If the text area is scrolled too fast press FAIL, else press PASS.";
+
+    public static void main(String args[]) throws Exception {
+        countDownLatch = new CountDownLatch(1);
+
+        SwingUtilities.invokeLater(TooMuchWheelRotationEventsTest::createUI);
+        countDownLatch.await(15, TimeUnit.MINUTES);
+
+        if (!testResult) {
+            throw new RuntimeException("Test fails!");
+        }
+    }
+
+    private static void createUI() {
+
+        final JFrame mainFrame = new JFrame("Trackpad scrolling test");
+        GridBagLayout layout = new GridBagLayout();
+        JPanel mainControlPanel = new JPanel(layout);
+        JPanel resultButtonPanel = new JPanel(layout);
+
+        GridBagConstraints gbc = new GridBagConstraints();
+
+        JPanel testPanel = createTestPanel();
+
+        gbc.gridx = 0;
+        gbc.gridy = 0;
+        gbc.fill = GridBagConstraints.HORIZONTAL;
+        mainControlPanel.add(testPanel, gbc);
+
+        JTextArea instructionTextArea = new JTextArea();
+        instructionTextArea.setText(INSTRUCTIONS);
+        instructionTextArea.setEditable(false);
+        instructionTextArea.setBackground(Color.white);
+
+        gbc.gridx = 0;
+        gbc.gridy = 1;
+        gbc.fill = GridBagConstraints.HORIZONTAL;
+        mainControlPanel.add(instructionTextArea, gbc);
+
+        JButton passButton = new JButton("Pass");
+        passButton.setActionCommand("Pass");
+        passButton.addActionListener((ActionEvent e) -> {
+            testResult = true;
+            mainFrame.dispose();
+            countDownLatch.countDown();
+
+        });
+
+        JButton failButton = new JButton("Fail");
+        failButton.setActionCommand("Fail");
+        failButton.addActionListener(new ActionListener() {
+            @Override
+            public void actionPerformed(ActionEvent e) {
+                mainFrame.dispose();
+                countDownLatch.countDown();
+            }
+        });
+
+        gbc.gridx = 0;
+        gbc.gridy = 0;
+        resultButtonPanel.add(passButton, gbc);
+
+        gbc.gridx = 1;
+        gbc.gridy = 0;
+        resultButtonPanel.add(failButton, gbc);
+
+        gbc.gridx = 0;
+        gbc.gridy = 2;
+        mainControlPanel.add(resultButtonPanel, gbc);
+
+        mainFrame.add(mainControlPanel);
+        mainFrame.pack();
+
+        mainFrame.addWindowListener(new WindowAdapter() {
+
+            @Override
+            public void windowClosing(WindowEvent e) {
+                mainFrame.dispose();
+                countDownLatch.countDown();
+            }
+        });
+        mainFrame.setVisible(true);
+    }
+
+    private static JPanel createTestPanel() {
+        JPanel panel = new JPanel();
+        panel.setLayout(new BoxLayout(panel, BoxLayout.Y_AXIS));
+        JTextArea textArea = new JTextArea(20, 20);
+        textArea.setText(getLongString());
+        JScrollPane scrollPane = new JScrollPane(textArea);
+        panel.add(scrollPane);
+        return panel;
+    }
+
+    private static String getLongString() {
+
+        String lowCaseString = getLongString('a', 'z');
+        String upperCaseString = getLongString('A', 'Z');
+        String digitsString = getLongString('0', '9');
+
+        int repeat = 30;
+        StringBuilder lowCaseBuilder = new StringBuilder();
+        StringBuilder upperCaseBuilder = new StringBuilder();
+        StringBuilder digitsBuilder = new StringBuilder();
+
+        for (int i = 0; i < repeat; i++) {
+            lowCaseBuilder.append(lowCaseString).append(' ');
+            upperCaseBuilder.append(upperCaseString).append(' ');
+            digitsBuilder.append(digitsString).append(' ');
+        }
+
+        StringBuilder builder = new StringBuilder();
+        for (int i = 0; i < 200; i++) {
+            builder.append(upperCaseBuilder).append('\n')
+                    .append(lowCaseBuilder).append('\n')
+                    .append(digitsBuilder).append("\n\n\n");
+        }
+
+        return builder.toString();
+    }
+
+    private static String getLongString(char c1, char c2) {
+
+        char[] chars = new char[c2 - c1 + 1];
+        for (char i = c1; i <= c2; i++) {
+            chars[i - c1] = i;
+        }
+        return new String(chars);
+    }
+}