1 /*
   2  * Copyright (c) 2013, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  */
  23 package jdk.vm.ci.options;
  24 
  25 /**
  26  * An option that always returns the same {@linkplain #getValue() value}.
  27  */
  28 public class StableOptionValue<T> extends OptionValue<T> {
  29 
  30     /**
  31      * Creates a stable option value.
  32      */
  33     public StableOptionValue(T value) {
  34         super(value);
  35     }
  36 
  37     /**
  38      * Used to assert the invariant for stability. Without using locks, this check is not safe
  39      * against races and so it's only an assertion.
  40      */
  41     private boolean getValueCalled;
  42 
  43     /**
  44      * Creates an uninitialized stable option value for a subclass that initializes itself
  45      * {@link #defaultValue() lazily}.
  46      */
  47     public StableOptionValue() {
  48     }
  49 
  50     /**
  51      * Gets the value of this option.
  52      */
  53     @Override
  54     public final T getValue() {
  55         T result = super.getValue();
  56         assert initGetValueCalled();
  57         return result;
  58     }
  59 
  60     private boolean initGetValueCalled() {
  61         getValueCalled = true;
  62         return true;
  63     }
  64 
  65     /**
  66      * {@inheritDoc}
  67      * <p>
  68      * This must only be called if {@link #getValue()} has never been called.
  69      */
  70     @Override
  71     public final void setValue(Object v) {
  72         assert !getValueCalled;
  73         super.setValue(v);
  74     }
  75 }