4833719: (bf) Views of MappedByteBuffers are not MappedByteBuffers, and cannot be forced

Reviewed-by: adinn

src/java.base/share/classes/java/nio/MappedByteBuffer.java

@@ -152,10 +152,20 @@ public abstract class MappedByteBuffer
      * @return true if the file was mapped using one of the sync map
      * modes, otherwise false.
      */
-    private boolean isSync() {
+    final boolean isSync() { // package-private
         return isSync;
     }
 
+    /**
+     * Returns the {@code FileDescriptor} associated with this
+     * {@code MappedByteBuffer}.
+     *
+     * @return the buffer's file descriptor; may be {@code null}
+     */
+    final FileDescriptor fileDescriptor() { // package-private
+        return fd;
+    }
+
     /**
      * Tells whether or not this buffer's content is resident in physical
      * memory.
@@ -205,7 +215,10 @@ public abstract class MappedByteBuffer
 
     /**
      * Forces any changes made to this buffer's content to be written to the
-     * storage device containing the mapped file.
+     * storage device containing the mapped file.  The region starts at index
+     * zero in this buffer and is {@code capacity()} bytes.  An invocation of
+     * this method behaves in exactly the same way as the invocation
+     * {@link force(int,int) force(0,capacity())}.
      *
      * <p> If the file mapped into this buffer resides on a local storage
      * device then when this method returns it is guaranteed that all changes
@@ -362,4 +375,41 @@ public abstract class MappedByteBuffer
         super.rewind();
         return this;
     }
+
+    /**
+     * {@inheritDoc}
+     *
+     * <p> Reading bytes into physical memory by invoking {@code load()} on the
+     * returned buffer, or writing bytes to the storage device by invoking
+     * {@code force()} on the returned buffer, will only act on the sub-range
+     * of this buffer that the returned buffer represents, namely
+     * {@code [position(),limit())}.
+     */
+    @Override
+    public abstract MappedByteBuffer slice();
+
+    /**
+     * {@inheritDoc}
+     *
+     * <p> Reading bytes into physical memory by invoking {@code load()} on the
+     * returned buffer, or writing bytes to the storage device by invoking
+     * {@code force()} on the returned buffer, will only act on the sub-range
+     * of this buffer that the returned buffer represents, namely
+     * {@code [index,index+length)}, where {@code index} and {@code length} are
+     * assumed to satisfy the preconditions.
+     */
+    @Override
+    public abstract MappedByteBuffer slice(int index, int length);
+
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    public abstract MappedByteBuffer duplicate();
+
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    public abstract MappedByteBuffer compact();
 }