| /* |
| * Copyright (c) 2016, 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 sun.java2d; |
| |
| import java.lang.ref.Reference; |
| import java.lang.ref.SoftReference; |
| import java.lang.ref.WeakReference; |
| |
| /** |
| * This abstract ReentrantContextProvider helper class manages the creation, |
| * storage, and retrieval of concrete ReentrantContext instances which can be |
| * subclassed to hold cached contextual data. |
| * |
| * It supports reentrancy as every call to acquire() provides a new unique context |
| * instance that must later be returned for reuse by a call to release(ctx) |
| * (typically in a try/finally block). |
| * |
| * It has a couple of abstract implementations which store references in a queue |
| * and/or thread-local storage. |
| * The Providers can be configured to hold ReentrantContext instances in memory |
| * using hard, soft or weak references. |
| * |
| * The acquire() and release() methods are used to retrieve and return the contexts. |
| * |
| * The {@code newContext()} method remains abstract in all implementations and |
| * must be provided by the module to create a new subclass of ReentrantContext |
| * with the appropriate contextual data in it. |
| * |
| * Sample Usage: |
| * - create a subclass ReentrantContextImpl to hold the thread state: |
| * |
| * static final class ReentrantContextImpl extends ReentrantContext { |
| * // specific cached data |
| * } |
| * |
| * - create the appropriate ReentrantContextProvider: |
| * |
| * private static final ReentrantContextProvider<ReentrantContextImpl> contextProvider = |
| * new ReentrantContextProviderTL<ReentrantContextImpl>(ReentrantContextProvider.REF_WEAK) |
| * { |
| * @Override |
| * protected ReentrantContextImpl newContext() { |
| * return new ReentrantContextImpl(); |
| * } |
| * }; |
| * ... |
| * void someMethod() { |
| * ReentrantContextImpl ctx = contextProvider.acquire(); |
| * try { |
| * // use the context |
| * } finally { |
| * contextProvider.release(ctx); |
| * } |
| * } |
| * |
| * @param <K> ReentrantContext subclass |
| * |
| * @see ReentrantContext |
| */ |
| public abstract class ReentrantContextProvider<K extends ReentrantContext> |
| { |
| // thread-local storage: inactive |
| static final byte USAGE_TL_INACTIVE = 0; |
| // thread-local storage: in use |
| static final byte USAGE_TL_IN_USE = 1; |
| // CLQ storage |
| static final byte USAGE_CLQ = 2; |
| |
| // hard reference |
| public static final int REF_HARD = 0; |
| // soft reference |
| public static final int REF_SOFT = 1; |
| // weak reference |
| public static final int REF_WEAK = 2; |
| |
| /* members */ |
| // internal reference type |
| private final int refType; |
| |
| /** |
| * Create a new ReentrantContext provider using the given reference type |
| * among hard, soft or weak |
| * |
| * @param refType reference type |
| */ |
| protected ReentrantContextProvider(final int refType) { |
| this.refType = refType; |
| } |
| |
| /** |
| * Create a new ReentrantContext instance |
| * |
| * @return new ReentrantContext instance |
| */ |
| protected abstract K newContext(); |
| |
| /** |
| * Give a ReentrantContext instance for the current thread |
| * |
| * @return ReentrantContext instance |
| */ |
| public abstract K acquire(); |
| |
| /** |
| * Restore the given ReentrantContext instance for reuse |
| * |
| * @param ctx ReentrantContext instance |
| */ |
| public abstract void release(K ctx); |
| |
| @SuppressWarnings("unchecked") |
| protected final Reference<K> getOrCreateReference(final K ctx) { |
| if (ctx.reference == null) { |
| // Create the reference: |
| switch (refType) { |
| case REF_HARD: |
| ctx.reference = new HardReference<K>(ctx); |
| break; |
| case REF_SOFT: |
| ctx.reference = new SoftReference<K>(ctx); |
| break; |
| default: |
| case REF_WEAK: |
| ctx.reference = new WeakReference<K>(ctx); |
| break; |
| } |
| } |
| return (Reference<K>) ctx.reference; |
| } |
| |
| /* Missing HardReference implementation */ |
| static final class HardReference<V> extends WeakReference<V> { |
| // kept strong reference: |
| private final V strongRef; |
| |
| HardReference(final V referent) { |
| // no referent needed for the parent WeakReference: |
| super(null); |
| this.strongRef = referent; |
| } |
| |
| @Override |
| public V get() { |
| return strongRef; |
| } |
| } |
| } |