--- /dev/null	2014-06-09 15:34:15.646999981 +0100
+++ new/src/java.base/share/classes/jdk/internal/jimage/concurrent/ConcurrentPReader.java	2014-11-20 16:04:06.201374538 +0000
@@ -0,0 +1,149 @@
+/*
+ * Copyright (c) 2014, 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.jimage.concurrent;
+
+import java.io.FileDescriptor;
+import java.io.FileInputStream;
+import java.io.IOException;
+
+import jdk.internal.jimage.PReader;
+
+import sun.misc.Unsafe;
+
+/**
+ * A PReader implementation that supports concurrent pread operations.
+ */
+public class ConcurrentPReader extends PReader {
+
+    private static final Unsafe UNSAFE = Unsafe.getUnsafe();
+    private static final long BA_OFFSET = (long) UNSAFE.arrayBaseOffset(byte[].class);
+
+    /**
+     * A temporary buffer that is cached on a per-thread basis.
+     */
+    private static class TemporaryBuffer {
+        static final ThreadLocal<TemporaryBuffer> CACHED_BUFFER =
+             new ThreadLocal<TemporaryBuffer>() {
+                @Override
+                protected TemporaryBuffer initialValue() { return null; }
+             };
+
+        static final TemporaryBuffer NOT_AVAILABLE = new TemporaryBuffer(0L, 0);
+
+        final long address;
+        final int size;
+
+        TemporaryBuffer(long address, int size) {
+            this.address = address;
+            this.size = size;
+        }
+
+        long address() { return address; }
+        int size() { return size; }
+
+        /**
+         * Returns the {@code TemporaryBuffer} for the current thread. The buffer
+         * is guaranteed to be of at least the given size. Returns {@code null}
+         * if a buffer cannot be cached for this thread.
+         */
+        static TemporaryBuffer get(int len) {
+            TemporaryBuffer buffer = CACHED_BUFFER.get();
+
+            // cached buffer large enough?
+            if (buffer != null && buffer.size() >= len) {
+                return buffer;
+            }
+
+            // if this is an InnocuousThread then don't return anything
+            if (buffer == NOT_AVAILABLE)
+                return null;
+
+            if (buffer != null) {
+                // replace buffer in cache with a larger buffer
+                long originalAddress = buffer.address();
+                long address = UNSAFE.allocateMemory(len);
+                buffer = new TemporaryBuffer(address, len);
+                CACHED_BUFFER.set(buffer);
+                UNSAFE.freeMemory(originalAddress);
+            } else {
+                // first usage.
+                if (Thread.currentThread() instanceof sun.misc.InnocuousThread) {
+                    buffer = NOT_AVAILABLE;
+                } else {
+                    long address = UNSAFE.allocateMemory(len);
+                    buffer = new TemporaryBuffer(address, len);
+                }
+                CACHED_BUFFER.set(buffer);
+            }
+            return buffer;
+        }
+    }
+
+    private final FileDescriptor fd;
+
+    private ConcurrentPReader(FileInputStream fis) throws IOException {
+        super(fis.getChannel());
+        this.fd = fis.getFD();
+    }
+
+    public ConcurrentPReader(String file) throws IOException {
+        this(new FileInputStream(file));
+    }
+
+    @Override
+    public byte[] read(int len, long position) throws IOException {
+        // need a temporary area of memory to read into
+        TemporaryBuffer buffer = TemporaryBuffer.get(len);
+        long address;
+        if (buffer == null) {
+            address = UNSAFE.allocateMemory(len);
+        } else {
+            address = buffer.address();
+        }
+        try {
+            int n = pread(fd, address, len, position);
+            if (n != len)
+                throw new InternalError("short read, not handled yet");
+            byte[] result = new byte[n];
+            UNSAFE.copyMemory(null, address, result, BA_OFFSET, len);
+            return result;
+        } finally {
+            if (buffer == null) {
+                UNSAFE.freeMemory(address);
+            }
+        }
+    }
+
+    private static native int pread(FileDescriptor fd, long address, int len, long pos)
+        throws IOException;
+
+    private static native void initIDs();
+
+    static {
+        System.loadLibrary("java");
+        initIDs();
+    }
+}