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annotate truffle/com.oracle.truffle.api/src/com/oracle/truffle/api/utilities/AssumedValue.java @ 21951:9c8c0937da41

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Moving all sources into truffle subdirectory
author Jaroslav Tulach <jaroslav.tulach@oracle.com>
date Wed, 17 Jun 2015 10:58:08 +0200
parents graal/com.oracle.truffle.api/src/com/oracle/truffle/api/utilities/AssumedValue.java@935de03661c1
children dc83cc1f94f2
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1 /*
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2 * Copyright (c) 2013, 2014, 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 value that the compiler can assume is constant, but can be changed by invalidation.
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33 * <p>
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34 * Compiled code that uses the value will be invalidated each time the value changes, so you should
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35 * take care to only change values infrequently, or to monitor the number of times the value has
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36 * changed and at some point to replace the value with something more generic so that it does not
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37 * have to be changed and code does not have to keep being recompiled.
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38 */
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39 public class AssumedValue<T> {
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40
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41 private final String name;
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42
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43 @CompilationFinal private T value;
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44 @CompilationFinal private Assumption assumption;
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45
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46 public AssumedValue(T initialValue) {
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47 this(null, initialValue);
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48 }
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49
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50 public AssumedValue(String name, T initialValue) {
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51 this.name = name;
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52 value = initialValue;
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53 assumption = Truffle.getRuntime().createAssumption(name);
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54 }
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55
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56 /**
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57 * Get the current value, updating it if it has been {@link #set}. The compiler may be able to
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58 * make this method return a constant value, but still accommodate mutation.
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59 */
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60 public T get() {
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61 try {
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62 assumption.check();
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63 } catch (InvalidAssumptionException e) {
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64 // No need to rewrite anything - just pick up the new values
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65 }
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66
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67 return value;
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68 }
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69
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70 /**
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71 * Set a new value, which will be picked up the next time {@link #get} is called.
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72 */
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73 public void set(T newValue) {
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74 CompilerDirectives.transferToInterpreter();
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75
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76 value = newValue;
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77 final Assumption oldAssumption = assumption;
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78 assumption = Truffle.getRuntime().createAssumption(name);
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79 oldAssumption.invalidate();
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80 }
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81
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82 }