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/*
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
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* 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
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*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
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package com.oracle.truffle.api.utilities;
import com.oracle.truffle.api.Assumption;
import com.oracle.truffle.api.CompilerDirectives;
import com.oracle.truffle.api.CompilerDirectives.CompilationFinal;
import com.oracle.truffle.api.Truffle;
import com.oracle.truffle.api.nodes.InvalidAssumptionException;
/**
* A value that the compiler can assume is constant, but can be changed by invalidation.
*
* Compiled code that uses the value will be invalidated each time the value changes, so you should
* take care to only change values infrequently, or to monitor the number of times the value has
* changed and at some point to replace the value with something more generic so that it does not
* have to be changed and code does not have to keep being recompiled.
*
* @since 0.8 or earlier
*/
public class AssumedValue {
private final String name;
@CompilationFinal private T value;
@CompilationFinal private Assumption assumption;
/** @since 0.8 or earlier */
public AssumedValue(T initialValue) {
this(null, initialValue);
}
/** @since 0.8 or earlier */
public AssumedValue(String name, T initialValue) {
this.name = name;
value = initialValue;
assumption = Truffle.getRuntime().createAssumption(name);
}
/**
* Get the current value, updating it if it has been {@link #set}. The compiler may be able to
* make this method return a constant value, but still accommodate mutation.
*
* @since 0.8 or earlier
*/
public T get() {
try {
assumption.check();
} catch (InvalidAssumptionException e) {
// No need to rewrite anything - just pick up the new values
}
return value;
}
/**
* Set a new value, which will be picked up the next time {@link #get} is called.
*
* @since 0.8 or earlier
*/
public void set(T newValue) {
CompilerDirectives.transferToInterpreter();
value = newValue;
final Assumption oldAssumption = assumption;
assumption = Truffle.getRuntime().createAssumption(name);
oldAssumption.invalidate();
}
}