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1   /*
2    * Copyright (c) 2005, 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  
26  package sun.java2d.pipe;
27  
28  import java.util.HashSet;
29  import java.util.Set;
30  import sun.awt.SunToolkit;
31  
32  /**
33   * The RenderQueue class encapsulates a RenderBuffer on which rendering
34   * operations are enqueued.  Note that the RenderQueue lock must be acquired
35   * before performing any operations on the queue (e.g. enqueuing an operation
36   * or flushing the queue).  A sample usage scenario follows:
37   *
38   *     public void drawSomething(...) {
39   *         rq.lock();
40   *         try {
41   *             ctx.validate(...);
42   *             rq.ensureCapacity(4);
43   *             rq.getBuffer().putInt(DRAW_SOMETHING);
44   *             ...
45   *         } finally {
46   *             rq.unlock();
47   *         }
48   *     }
49   *
50   * If you are enqueuing an operation that involves 8-byte parameters (i.e.
51   * long or double values), it is imperative that you ensure proper
52   * alignment of the underlying RenderBuffer.  This can be accomplished
53   * simply by providing an offset to the first 8-byte parameter in your
54   * operation to the ensureCapacityAndAlignment() method.  For example:
55   *
56   *     public void drawStuff(...) {
57   *         rq.lock();
58   *         try {
59   *             RenderBuffer buf = rq.getBuffer();
60   *             ctx.validate(...);
61   *             // 28 total bytes in the operation, 12 bytes to the first long
62   *             rq.ensureCapacityAndAlignment(28, 12);
63   *             buf.putInt(DRAW_STUFF);
64   *             buf.putInt(x).putInt(y);
65   *             buf.putLong(addr1);
66   *             buf.putLong(addr2);
67   *         } finally {
68   *             rq.unlock();
69   *         }
70   *     }
71   */
72  public abstract class RenderQueue {
73  
74      /** The size of the underlying buffer, in bytes. */
75      private static final int BUFFER_SIZE = 32000;
76  
77      /** The underlying buffer for this queue. */
78      protected RenderBuffer buf;
79  
80      /**
81       * A Set containing hard references to Objects that must stay alive until
82       * the queue has been completely flushed.
83       */
84      protected Set refSet;
85  
86      protected RenderQueue() {
87          refSet = new HashSet();
88          buf = RenderBuffer.allocate(BUFFER_SIZE);
89      }
90  
91      /**
92       * Locks the queue for read/write access.
93       */
94      public final void lock() {
95          /*
96           * Implementation note: In theory we should have two separate locks:
97           * one lock to synchronize access to the RenderQueue, and then a
98           * separate lock (the AWT lock) that only needs to be acquired when
99           * we are about to flush the queue (using native windowing system
100          * operations).  In practice it has been difficult to enforce the
101          * correct lock ordering; sometimes AWT will have already acquired
102          * the AWT lock before grabbing the RQ lock (see 6253009), while the
103          * expected order should be RQ lock and then AWT lock.  Due to this
104          * issue, using two separate locks is prone to deadlocks.  Therefore,
105          * to solve this issue we have decided to eliminate the separate RQ
106          * lock and instead just acquire the AWT lock here.  (Someday it might
107          * be nice to go back to the old two-lock system, but that would
108          * require potentially risky changes to AWT to ensure that it never
109          * acquires the AWT lock before calling into 2D code that wants to
110          * acquire the RQ lock.)
111          */
112         SunToolkit.awtLock();
113     }
114 
115     /**
116      * Attempts to lock the queue.  If successful, this method returns true,
117      * indicating that the caller is responsible for calling
118      * <code>unlock</code>; otherwise this method returns false.
119      */
120     public final boolean tryLock() {
121         return SunToolkit.awtTryLock();
122     }
123 
124     /**
125      * Unlocks the queue.
126      */
127     public final void unlock() {
128         SunToolkit.awtUnlock();
129     }
130 
131     /**
132      * Adds the given Object to the set of hard references, which will
133      * prevent that Object from being disposed until the queue has been
134      * flushed completely.  This is useful in cases where some enqueued
135      * data could become invalid if the reference Object were garbage
136      * collected before the queue could be processed.  (For example, keeping
137      * a hard reference to a FontStrike will prevent any enqueued glyph
138      * images associated with that strike from becoming invalid before the
139      * queue is flushed.)  The reference set will be cleared immediately
140      * after the queue is flushed each time.
141      */
142     public final void addReference(Object ref) {
143         refSet.add(ref);
144     }
145 
146     /**
147      * Returns the encapsulated RenderBuffer object.
148      */
149     public final RenderBuffer getBuffer() {
150         return buf;
151     }
152 
153     /**
154      * Ensures that there will be enough room on the underlying buffer
155      * for the following operation.  If the operation will not fit given
156      * the remaining space, the buffer will be flushed immediately, leaving
157      * an empty buffer for the impending operation.
158      *
159      * @param opsize size (in bytes) of the following operation
160      */
161     public final void ensureCapacity(int opsize) {
162         if (buf.remaining() < opsize) {
163             flushNow();
164         }
165     }
166 
167     /**
168      * Convenience method that is equivalent to calling ensureCapacity()
169      * followed by ensureAlignment().  The ensureCapacity() call allows for an
170      * extra 4 bytes of space in case the ensureAlignment() method needs to
171      * insert a NOOP token on the buffer.
172      *
173      * @param opsize size (in bytes) of the following operation
174      * @param first8ByteValueOffset offset (in bytes) from the current
175      * position to the first 8-byte value used in the following operation
176      */
177     public final void ensureCapacityAndAlignment(int opsize,
178                                                  int first8ByteValueOffset)
179     {
180         ensureCapacity(opsize + 4);
181         ensureAlignment(first8ByteValueOffset);
182     }
183 
184     /**
185      * Inserts a 4-byte NOOP token when necessary to ensure that all 8-byte
186      * parameters for the following operation are added to the underlying
187      * buffer with an 8-byte memory alignment.
188      *
189      * @param first8ByteValueOffset offset (in bytes) from the current
190      * position to the first 8-byte value used in the following operation
191      */
192     public final void ensureAlignment(int first8ByteValueOffset) {
193         int first8ByteValuePosition = buf.position() + first8ByteValueOffset;
194         if ((first8ByteValuePosition & 7) != 0) {
195             buf.putInt(BufferedOpCodes.NOOP);
196         }
197     }
198 
199     /**
200      * Immediately processes each operation currently pending on the buffer.
201      * This method will block until the entire buffer has been flushed.  The
202      * queue lock must be acquired before calling this method.
203      */
204     public abstract void flushNow();
205 
206     /**
207      * Immediately processes each operation currently pending on the buffer,
208      * and then invokes the provided task.  This method will block until the
209      * entire buffer has been flushed and the provided task has been executed.
210      * The queue lock must be acquired before calling this method.
211      */
212     public abstract void flushAndInvokeNow(Runnable task);
213 
214     /**
215      * Updates the current position of the underlying buffer, and then
216      * flushes the queue immediately.  This method is useful when native code
217      * has added data to the queue and needs to flush immediately.
218      */
219     public void flushNow(int position) {
220         buf.position(position);
221         flushNow();
222     }
223 }