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Truffle is a multi-language framework for executing dynamic languages
that achieves high performance when combined with Graal.
/*
* Copyright (c) 2021, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* The Universal Permissive License (UPL), Version 1.0
*
* Subject to the condition set forth below, permission is hereby granted to any
* person obtaining a copy of this software, associated documentation and/or
* data (collectively the "Software"), free of charge and under any and all
* copyright rights in the Software, and any and all patent rights owned or
* freely licensable by each licensor hereunder covering either (i) the
* unmodified Software as contributed to or provided by such licensor, or (ii)
* the Larger Works (as defined below), to deal in both
*
* (a) the Software, and
*
* (b) any piece of software and/or hardware listed in the lrgrwrks.txt file if
* one is included with the Software each a "Larger Work" to which the Software
* is contributed by such licensors),
*
* without restriction, including without limitation the rights to copy, create
* derivative works of, display, perform, and distribute the Software and make,
* use, sell, offer for sale, import, export, have made, and have sold the
* Software and the Larger Work(s), and to sublicense the foregoing rights on
* either these or other terms.
*
* This license is subject to the following condition:
*
* The above copyright notice and either this complete permission notice or at a
* minimum a reference to the UPL must be included in all copies or substantial
* portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* SOFTWARE.
*/
package com.oracle.truffle.polyglot;
import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
import com.oracle.truffle.api.Assumption;
import com.oracle.truffle.api.CompilerDirectives;
import com.oracle.truffle.api.CompilerDirectives.CompilationFinal;
import com.oracle.truffle.api.CompilerDirectives.TruffleBoundary;
import com.oracle.truffle.api.Truffle;
import com.oracle.truffle.api.utilities.TruffleWeakReference;
/*
* Note: this type may be a good candidate for being standarized in the Truffle utilities package in the future.
*/
@SuppressWarnings("rawtypes")
final class WeakAssumedValue {
private static final AtomicReferenceFieldUpdater PROFILE_UPDATER = AtomicReferenceFieldUpdater.newUpdater(WeakAssumedValue.class,
Profile.class, "profile");
private static final Assumption INVALID_ASSUMPTION;
static {
Assumption assumption = Truffle.getRuntime().createAssumption();
assumption.invalidate();
INVALID_ASSUMPTION = assumption;
}
@CompilationFinal private volatile Profile profile;
private final String name;
WeakAssumedValue(String name) {
this.name = name;
}
public void invalidate() {
invalidateImpl(this.profile);
}
private void invalidateImpl(Profile currentProfile) {
if (currentProfile != null) {
currentProfile.assumption.invalidate();
}
Profile previous = PROFILE_UPDATER.getAndSet(this, Profile.INVALID);
assert previous == currentProfile || previous == Profile.INVALID;
}
/**
* Returns true if this assumed value contains a valid constant value, else
* false.
*/
public boolean isValid() {
Profile p = this.profile;
if (p == null) {
return false;
}
return p.assumption.isValid();
}
/**
* Resets the weak assumed value. Do not use this repeatedly to avoid deoptimization loops.
*/
public void reset() {
invalidateImpl(this.profile);
this.profile = null;
}
/**
* Return the contained value as a constant if it can be resolved or null if it
* cannot be resolved to a constant. In {@link CompilerDirectives#inInterpreter() interpreted}
* mode this method always returns null.
*/
public T getConstant() {
if (!CompilerDirectives.inCompiledCode() || !CompilerDirectives.isPartialEvaluationConstant(this)) {
/*
* This is only relevant if we are in compiled code as in interpreted mode the value is
* never constant.
*/
return null;
}
Profile p = this.profile;
if (p != null) {
if (p.assumption.isValid()) {
return p.get();
} else {
return null;
}
}
return null;
}
/**
* Updates the internal value and invalidates the profile if a new value is set.
*/
@SuppressWarnings("unchecked")
@TruffleBoundary
public void update(T newValue) {
assert newValue != null;
Profile currentProfile = this.profile;
if (currentProfile == Profile.INVALID) {
// already invalid -> nothing to speculate on
return;
}
Profile newProfile;
if (currentProfile == null) {
// fresh profile set the profile
newProfile = new Profile<>(newValue, name);
if (!PROFILE_UPDATER.compareAndSet(this, currentProfile, newProfile)) {
update(newValue);
}
} else if (currentProfile.get() == newValue) {
// value is the same. No reason to invalidate.
return;
} else {
invalidateImpl(currentProfile);
}
}
static final class Profile {
private static final Profile INVALID = new Profile<>();
// Invariant to simplify conditions: type is non-null if assumption is valid
final Assumption assumption;
final TruffleWeakReference reference;
private Profile() {
this.assumption = INVALID_ASSUMPTION;
this.reference = null;
}
private Profile(V value, String name) {
assert value != null;
this.assumption = Truffle.getRuntime().createAssumption(name);
this.reference = new TruffleWeakReference<>(value);
}
V get() {
TruffleWeakReference ref = reference;
if (ref == null) {
return null;
}
return ref.get();
}
}
}