001/*
002 * Copyright (c) 2013, Oracle and/or its affiliates. All rights reserved.
003 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
004 *
005 * This code is free software; you can redistribute it and/or modify it
006 * under the terms of the GNU General Public License version 2 only, as
007 * published by the Free Software Foundation.
008 *
009 * This code is distributed in the hope that it will be useful, but WITHOUT
010 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
011 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
012 * version 2 for more details (a copy is included in the LICENSE file that
013 * accompanied this code).
014 *
015 * You should have received a copy of the GNU General Public License version
016 * 2 along with this work; if not, write to the Free Software Foundation,
017 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
018 *
019 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
020 * or visit www.oracle.com if you need additional information or have any
021 * questions.
022 */
023package jdk.internal.jvmci.options;
024
025/**
026 * An option that always returns the same {@linkplain #getValue() value}.
027 */
028public class StableOptionValue<T> extends OptionValue<T> {
029
030    /**
031     * Creates a stable option value.
032     */
033    public StableOptionValue(T value) {
034        super(value);
035    }
036
037    /**
038     * Used to assert the invariant for stability. Without using locks, this check is not safe
039     * against races and so it's only an assertion.
040     */
041    private boolean getValueCalled;
042
043    /**
044     * Creates an uninitialized stable option value for a subclass that initializes itself
045     * {@link #defaultValue() lazily}.
046     */
047    public StableOptionValue() {
048    }
049
050    /**
051     * Gets the value of this option.
052     */
053    @Override
054    public final T getValue() {
055        T result = super.getValue();
056        assert initGetValueCalled();
057        return result;
058    }
059
060    private boolean initGetValueCalled() {
061        getValueCalled = true;
062        return true;
063    }
064
065    /**
066     * {@inheritDoc}
067     * <p>
068     * This must only be called if {@link #getValue()} has never been called.
069     */
070    @Override
071    public final void setValue(Object v) {
072        assert !getValueCalled;
073        super.setValue(v);
074    }
075}