--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/java.net.http/share/classes/jdk/internal/net/http/WindowUpdateSender.java	Wed Feb 07 21:45:37 2018 +0000
@@ -0,0 +1,91 @@
+/*
+ * Copyright (c) 2015, 2018, 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.net.http;
+
+import java.lang.System.Logger.Level;
+import jdk.internal.net.http.frame.SettingsFrame;
+import jdk.internal.net.http.frame.WindowUpdateFrame;
+import jdk.internal.net.http.common.Utils;
+
+import java.util.concurrent.atomic.AtomicInteger;
+
+abstract class WindowUpdateSender {
+
+    final static boolean DEBUG = Utils.DEBUG;
+    final System.Logger debug =
+            Utils.getDebugLogger(this::dbgString, DEBUG);
+
+    final int limit;
+    final Http2Connection connection;
+    final AtomicInteger received = new AtomicInteger(0);
+
+    WindowUpdateSender(Http2Connection connection) {
+        this(connection, connection.clientSettings.getParameter(SettingsFrame.INITIAL_WINDOW_SIZE));
+    }
+
+    WindowUpdateSender(Http2Connection connection, int initWindowSize) {
+        this(connection, connection.getMaxReceiveFrameSize(), initWindowSize);
+    }
+
+    WindowUpdateSender(Http2Connection connection, int maxFrameSize, int initWindowSize) {
+        this.connection = connection;
+        int v0 = Math.max(0, initWindowSize - maxFrameSize);
+        int v1 = (initWindowSize + (maxFrameSize - 1)) / maxFrameSize;
+        v1 = v1 * maxFrameSize / 2;
+        // send WindowUpdate heuristic:
+        // - we got data near half of window size
+        //   or
+        // - remaining window size reached max frame size.
+        limit = Math.min(v0, v1);
+        debug.log(Level.DEBUG, "maxFrameSize=%d, initWindowSize=%d, limit=%d",
+                maxFrameSize, initWindowSize, limit);
+    }
+
+    abstract int getStreamId();
+
+    void update(int delta) {
+        debug.log(Level.DEBUG, "update: %d", delta);
+        if (received.addAndGet(delta) > limit) {
+            synchronized (this) {
+                int tosend = received.get();
+                if( tosend > limit) {
+                    received.getAndAdd(-tosend);
+                    sendWindowUpdate(tosend);
+                }
+            }
+        }
+    }
+
+    void sendWindowUpdate(int delta) {
+        debug.log(Level.DEBUG, "sending window update: %d", delta);
+        connection.sendUnorderedFrame(new WindowUpdateFrame(getStreamId(), delta));
+    }
+
+    String dbgString() {
+        return "WindowUpdateSender(stream: " + getStreamId() + ")";
+    }
+
+}