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annotate graal/com.oracle.truffle.api/src/com/oracle/truffle/api/utilities/AssumedValue.java @ 13322:f28ea693056f

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New assumption utilities.
author Chris Seaton <chris.seaton@oracle.com>
date Fri, 13 Dec 2013 15:53:30 +0000
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children 0e7894989f37
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13322
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1 /*
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2 * Copyright (c) 2013, Oracle and/or its affiliates. All rights reserved.
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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4 *
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5 * This code is free software; you can redistribute it and/or modify it
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6 * under the terms of the GNU General Public License version 2 only, as
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7 * published by the Free Software Foundation. Oracle designates this
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8 * particular file as subject to the "Classpath" exception as provided
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9 * by Oracle in the LICENSE file that accompanied this code.
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10 *
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11 * This code is distributed in the hope that it will be useful, but WITHOUT
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12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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14 * version 2 for more details (a copy is included in the LICENSE file that
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15 * accompanied this code).
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16 *
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17 * You should have received a copy of the GNU General Public License version
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18 * 2 along with this work; if not, write to the Free Software Foundation,
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19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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20 *
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21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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22 * or visit www.oracle.com if you need additional information or have any
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23 * questions.
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24 */
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25 package com.oracle.truffle.api.utilities;
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26
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27 import com.oracle.truffle.api.*;
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28 import com.oracle.truffle.api.CompilerDirectives.CompilationFinal;
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29 import com.oracle.truffle.api.nodes.*;
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30
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31 /**
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32 * A {@link CompilationFinal} value combined with an {@link Assumption} to notify when it changes.
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33 * Note that you should be careful that modifications to this value do not cause deoptimization
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34 * loops. This could be by using a value that is monotonic.
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35 */
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36 public class AssumedValue<T> {
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37
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38 @CompilationFinal private T value;
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39 private final CyclicAssumption assumption;
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40
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41 public AssumedValue(String name, T initialValue) {
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42 assumption = new CyclicAssumption(name);
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43 value = initialValue;
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44 }
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45
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46 /**
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47 * Get the current value, updating it if it has been {@link #set}. The compiler may be able to
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48 * make this method return a constant value, but still accommodate mutation.
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49 */
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50 public T get() {
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51 try {
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52 assumption.getAssumption().check();
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53 } catch (InvalidAssumptionException e) {
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54 // No need to rewrite anything - just pick up the new value
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55 }
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56
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57 return value;
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58 }
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59
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60 /**
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61 * Set a new value, which will be picked up the next time {@link #get} is called.
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62 */
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63 public void set(T newValue) {
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64 value = newValue;
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65 assumption.invalidate();
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66 }
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67
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68 }