duke@1: /* jjg@1326: * Copyright (c) 2001, 2012, Oracle and/or its affiliates. All rights reserved. duke@1: * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. duke@1: * duke@1: * This code is free software; you can redistribute it and/or modify it duke@1: * under the terms of the GNU General Public License version 2 only, as ohair@554: * published by the Free Software Foundation. Oracle designates this duke@1: * particular file as subject to the "Classpath" exception as provided ohair@554: * by Oracle in the LICENSE file that accompanied this code. duke@1: * duke@1: * This code is distributed in the hope that it will be useful, but WITHOUT duke@1: * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or duke@1: * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License duke@1: * version 2 for more details (a copy is included in the LICENSE file that duke@1: * accompanied this code). duke@1: * duke@1: * You should have received a copy of the GNU General Public License version duke@1: * 2 along with this work; if not, write to the Free Software Foundation, duke@1: * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. duke@1: * ohair@554: * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA ohair@554: * or visit www.oracle.com if you need additional information or have any ohair@554: * questions. duke@1: */ duke@1: duke@1: package com.sun.tools.javac.util; duke@1: duke@1: import java.util.*; duke@1: duke@1: /** duke@1: * Support for an abstract context, modelled loosely after ThreadLocal duke@1: * but using a user-provided context instead of the current thread. duke@1: * duke@1: *
Within the compiler, a single Context is used for each duke@1: * invocation of the compiler. The context is then used to ensure a duke@1: * single copy of each compiler phase exists per compiler invocation. duke@1: * duke@1: *
The context can be used to assist in extending the compiler by duke@1: * extending its components. To do that, the extended component must duke@1: * be registered before the base component. We break initialization duke@1: * cycles by (1) registering a factory for the component rather than duke@1: * the component itself, and (2) a convention for a pattern of usage duke@1: * in which each base component registers itself by calling an duke@1: * instance method that is overridden in extended components. A base duke@1: * phase supporting extension would look something like this: duke@1: * jjg@1358: *
{@code duke@1: * public class Phase { duke@1: * protected static final Context.Keyduke@1: * duke@1: *phaseKey = duke@1: * new Context.Key (); duke@1: * duke@1: * public static Phase instance(Context context) { duke@1: * Phase instance = context.get(phaseKey); duke@1: * if (instance == null) duke@1: * // the phase has not been overridden duke@1: * instance = new Phase(context); duke@1: * return instance; duke@1: * } duke@1: * duke@1: * protected Phase(Context context) { duke@1: * context.put(phaseKey, this); duke@1: * // other intitialization follows... duke@1: * } duke@1: * } jjg@1358: * }
In the compiler, we simply use Phase.instance(context) to get duke@1: * the reference to the phase. But in extensions of the compiler, we duke@1: * must register extensions of the phases to replace the base phase, duke@1: * and this must be done before any reference to the phase is accessed duke@1: * using Phase.instance(). An extended phase might be declared thus: duke@1: * jjg@1358: *
{@code duke@1: * public class NewPhase extends Phase { duke@1: * protected NewPhase(Context context) { duke@1: * super(context); duke@1: * } duke@1: * public static void preRegister(final Context context) { duke@1: * context.put(phaseKey, new Context.Factoryduke@1: * duke@1: *() { duke@1: * public Phase make() { duke@1: * return new NewPhase(context); duke@1: * } duke@1: * }); duke@1: * } duke@1: * } jjg@1358: * }
And is registered early in the extended compiler like this duke@1: * duke@1: *
duke@1: * NewPhase.preRegister(context); duke@1: *duke@1: * jjg@581: *
This is NOT part of any supported API.
jjg@581: * If you write code that depends on this, you do so at your own risk.
duke@1: * This code and its internal interfaces are subject to change or
duke@1: * deletion without notice.
duke@1: */
duke@1: public class Context {
duke@1: /** The client creates an instance of this class for each key.
duke@1: */
duke@1: public static class Key