--- a/jdk/src/java.base/share/classes/sun/nio/ch/FileChannelImpl.java	Wed Dec 07 15:32:31 2016 -0500
+++ b/jdk/src/java.base/share/classes/sun/nio/ch/FileChannelImpl.java	Fri Dec 02 13:22:16 2016 -0800
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2000, 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
@@ -898,57 +898,62 @@
             if (!isOpen())
                 return null;
 
-            long filesize;
-            do {
-                filesize = nd.size(fd);
-            } while ((filesize == IOStatus.INTERRUPTED) && isOpen());
-            if (!isOpen())
-                return null;
-
-            if (filesize < position + size) { // Extend file size
-                if (!writable) {
-                    throw new IOException("Channel not open for writing " +
-                        "- cannot extend file to required size");
-                }
-                int rv;
+            long mapSize;
+            int pagePosition;
+            synchronized (positionLock) {
+                long filesize;
                 do {
-                    rv = nd.truncate(fd, position + size);
-                } while ((rv == IOStatus.INTERRUPTED) && isOpen());
+                    filesize = nd.size(fd);
+                } while ((filesize == IOStatus.INTERRUPTED) && isOpen());
                 if (!isOpen())
                     return null;
-            }
-            if (size == 0) {
-                addr = 0;
-                // a valid file descriptor is not required
-                FileDescriptor dummy = new FileDescriptor();
-                if ((!writable) || (imode == MAP_RO))
-                    return Util.newMappedByteBufferR(0, 0, dummy, null);
-                else
-                    return Util.newMappedByteBuffer(0, 0, dummy, null);
-            }
+
+                if (filesize < position + size) { // Extend file size
+                    if (!writable) {
+                        throw new IOException("Channel not open for writing " +
+                            "- cannot extend file to required size");
+                    }
+                    int rv;
+                    do {
+                        rv = nd.allocate(fd, position + size);
+                    } while ((rv == IOStatus.INTERRUPTED) && isOpen());
+                    if (!isOpen())
+                        return null;
+                }
+
+                if (size == 0) {
+                    addr = 0;
+                    // a valid file descriptor is not required
+                    FileDescriptor dummy = new FileDescriptor();
+                    if ((!writable) || (imode == MAP_RO))
+                        return Util.newMappedByteBufferR(0, 0, dummy, null);
+                    else
+                        return Util.newMappedByteBuffer(0, 0, dummy, null);
+                }
 
-            int pagePosition = (int)(position % allocationGranularity);
-            long mapPosition = position - pagePosition;
-            long mapSize = size + pagePosition;
-            try {
-                // If no exception was thrown from map0, the address is valid
-                addr = map0(imode, mapPosition, mapSize);
-            } catch (OutOfMemoryError x) {
-                // An OutOfMemoryError may indicate that we've exhausted memory
-                // so force gc and re-attempt map
-                System.gc();
+                pagePosition = (int)(position % allocationGranularity);
+                long mapPosition = position - pagePosition;
+                mapSize = size + pagePosition;
                 try {
-                    Thread.sleep(100);
-                } catch (InterruptedException y) {
-                    Thread.currentThread().interrupt();
-                }
-                try {
+                    // If map0 did not throw an exception, the address is valid
                     addr = map0(imode, mapPosition, mapSize);
-                } catch (OutOfMemoryError y) {
-                    // After a second OOME, fail
-                    throw new IOException("Map failed", y);
+                } catch (OutOfMemoryError x) {
+                    // An OutOfMemoryError may indicate that we've exhausted
+                    // memory so force gc and re-attempt map
+                    System.gc();
+                    try {
+                        Thread.sleep(100);
+                    } catch (InterruptedException y) {
+                        Thread.currentThread().interrupt();
+                    }
+                    try {
+                        addr = map0(imode, mapPosition, mapSize);
+                    } catch (OutOfMemoryError y) {
+                        // After a second OOME, fail
+                        throw new IOException("Map failed", y);
+                    }
                 }
-            }
+            } // synchronized
 
             // On Windows, and potentially other platforms, we need an open
             // file descriptor for some mapping operations.