1 /*
   2  * Copyright (c) 2016, 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.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 package sun.java2d;
  26 
  27 import java.lang.ref.Reference;
  28 
  29 /**
  30 * This ReentrantContextProvider implementation uses a ThreadLocal to hold
  31  * the first ReentrantContext per thread and a ReentrantContextProviderCLQ to
  32  * store child ReentrantContext instances needed during recursion.
  33  *
  34  * Note: this implementation may keep up to one context in memory per thread.
  35  * Child contexts for recursive uses are stored in the queue using a WEAK
  36  * reference by default unless specified in the 2 argument constructor.
  37  *
  38  * @param <K> ReentrantContext subclass
  39  */
  40 public abstract class ReentrantContextProviderTL<K extends ReentrantContext>
  41     extends ReentrantContextProvider<K>
  42 {
  43     // Thread-local storage:
  44     private final ThreadLocal<Reference<K>> ctxTL
  45         = new ThreadLocal<Reference<K>>();
  46 
  47     // ReentrantContext CLQ provider for child contexts:
  48     private final ReentrantContextProviderCLQ<K> ctxProviderCLQ;
  49 
  50     /**
  51      * Create a new ReentrantContext provider using the given reference type
  52      * among hard, soft or weak.
  53      * It uses weak reference for the child contexts.
  54      *
  55      * @param refType reference type
  56      */
  57     public ReentrantContextProviderTL(final int refType) {
  58         this(refType, REF_WEAK);
  59     }
  60 
  61     /**
  62      * Create a new ReentrantContext provider using the given reference types
  63      * among hard, soft or weak
  64      *
  65      * @param refTypeTL reference type used by ThreadLocal
  66      * @param refTypeCLQ reference type used by ReentrantContextProviderCLQ
  67      */
  68     public ReentrantContextProviderTL(final int refTypeTL, final int refTypeCLQ)
  69     {
  70         super(refTypeTL);
  71 
  72         final ReentrantContextProviderTL<K> parent = this;
  73 
  74         this.ctxProviderCLQ = new ReentrantContextProviderCLQ<K>(refTypeCLQ) {
  75             @Override
  76             protected K newContext() {
  77                 return parent.newContext();
  78             }
  79         };
  80     }
  81 
  82     /**
  83      * Give a ReentrantContext instance for the current thread
  84      *
  85      * @return ReentrantContext instance
  86      */
  87     @Override
  88     public final K acquire() {
  89         K ctx = null;
  90         final Reference<K> ref = ctxTL.get();
  91         if (ref != null) {
  92             ctx = ref.get();
  93         }
  94         if (ctx == null) {
  95             // create a new ReentrantContext if none is available
  96             ctx = newContext();
  97             // update thread local reference:
  98             ctxTL.set(getOrCreateReference(ctx));
  99         }
 100         // Check reentrance:
 101         if (ctx.usage == USAGE_TL_INACTIVE) {
 102            ctx.usage = USAGE_TL_IN_USE;
 103         } else {
 104             // get or create another ReentrantContext from CLQ provider:
 105             ctx = ctxProviderCLQ.acquire();
 106         }
 107         return ctx;
 108     }
 109 
 110     /**
 111      * Restore the given ReentrantContext instance for reuse
 112      *
 113      * @param ctx ReentrantContext instance
 114      */
 115     @Override
 116     public final void release(final K ctx) {
 117         if (ctx.usage == USAGE_TL_IN_USE) {
 118            ctx.usage = USAGE_TL_INACTIVE;
 119         } else {
 120             ctxProviderCLQ.release(ctx);
 121         }
 122     }
 123 }