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Truffle is a multi-language framework for executing dynamic languages
that achieves high performance when combined with Graal.
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package com.oracle.truffle.api.utilities;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
import com.oracle.truffle.api.Assumption;
import com.oracle.truffle.api.CompilerAsserts;
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.nodes.Node;
/**
* Holds an {@link Assumption}, and knows how to recreate it with the same properties on
* invalidation. Used as an Assumption factory that safely invalidates the previous Assumption and
* creates a new Assumption on invalidation.
*
* Note that you should be careful that repeated invalidations do not cause a deoptimization loop in
* that same way that you would with any other assumption.
*
* The Assumption instance should be obtained before doing the operation depending on it. In other
* words:
*
* - Obtain the current Assumption with {@link CyclicAssumption#getAssumption()}
* - Perform the operation/lookup which depends on the assumption
* - Cache the result and the Assumption
*
* On the fast-path, first check if the assumption is valid and in that case return the cached
* result. When invalidating, first write the new value, then invalidate the CyclicAssumption.
*
* {@codesnippet cyclicassumption}
*
* @since 0.8 or earlier
*/
public class CyclicAssumption {
private final String name;
private volatile Assumption assumption;
private static final AtomicReferenceFieldUpdater ASSUMPTION_UPDATER = AtomicReferenceFieldUpdater.newUpdater(CyclicAssumption.class, Assumption.class, "assumption");
/** @since 0.8 or earlier */
public CyclicAssumption(String name) {
this.name = name;
this.assumption = Truffle.getRuntime().createAssumption(name);
}
/** @since 0.8 or earlier */
@TruffleBoundary
public void invalidate() {
invalidate("");
}
/** @since 0.33 */
@TruffleBoundary
public void invalidate(String message) {
Assumption newAssumption = Truffle.getRuntime().createAssumption(name);
Assumption oldAssumption = ASSUMPTION_UPDATER.getAndSet(this, newAssumption);
oldAssumption.invalidate(message);
}
/** @since 0.8 or earlier */
public Assumption getAssumption() {
CompilerAsserts.neverPartOfCompilation("Cache the Assumption and do not call getAssumption() on the fast path");
return assumption;
}
}
class CyclicAssumptionSnippets {
// BEGIN: cyclicassumption
class MyContext {
CyclicAssumption symbolsRedefined = new CyclicAssumption("symbols");
Map symbols = new ConcurrentHashMap<>();
public void redefineSymbol(String symbol, Object value) {
symbols.put(symbol, value);
symbolsRedefined.invalidate();
}
}
class SymbolLookupNode extends Node {
final MyContext context;
final String symbol;
@CompilationFinal volatile LookupResult cachedLookup;
SymbolLookupNode(MyContext context, String symbol) {
this.context = context;
this.symbol = symbol;
}
public Object execute() {
LookupResult lookup = cachedLookup;
if (lookup == null || !lookup.assumption.isValid()) {
CompilerDirectives.transferToInterpreterAndInvalidate();
cachedLookup = doLookup(symbol);
}
return cachedLookup.value;
}
private LookupResult doLookup(String name) {
// First get the Assumption
CyclicAssumption symbolsRedefined = context.symbolsRedefined;
Assumption assumption = symbolsRedefined.getAssumption();
// Then lookup the value
Object value = context.symbols.get(name);
return new LookupResult(assumption, value);
}
}
class LookupResult {
final Assumption assumption;
final Object value;
LookupResult(Assumption assumption, Object value) {
this.assumption = assumption;
this.value = value;
}
}
// END: cyclicassumption
}