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Truffle is a multi-language framework for executing dynamic languages
that achieves high performance when combined with Graal.
/*
* Copyright (c) 2020, 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
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* 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,
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*/
package com.oracle.truffle.api.nodes;
import java.lang.ref.WeakReference;
import com.oracle.truffle.api.CallTarget;
import com.oracle.truffle.api.CompilerDirectives;
import com.oracle.truffle.api.CompilerDirectives.CompilationFinal;
import com.oracle.truffle.api.CompilerDirectives.TruffleBoundary;
/**
* Thread local reference class to remember the current encapsulating node of an interpreter on the
* stack. The current encapsulating node is used whenever the code transitions from cached to
* uncached cases. This typically happens when the maximum limit for an inline cache was reached and
* the uncached version of a node will be used behind a {@link TruffleBoundary}. To correctly
* produce exception stack traces it is necessary to remember the node that transitioned to the
* uncached case. Uncached calls to {@link CallTarget} will automatically use the value of the
* encapsulating node. Truffle DSL produces such transitions automatically if Truffle libraries are
* used and they transition to uncached.
*
* Usage example for pushing and restoring the current node to the stack.
*
*
* EncapsulatingNodeReference encapsulating = EncapsulatingNodeReference.getCurrent();
* Node encapsulatingNode = encapsulating.set(currentNode);
* try {
* // follow uncached path
* } finally {
* encapsulating.set(encapsulatingNode);
* }
*
*
* The current encapsulating node can also be useful when constructing guest exceptions in
* slow-paths and the location of the error needs to be found out reliably. Usage example:
*
*
* final class LanguageException extends AbstractTruffleException {
*
* private LanguageException(Node locationNode) {
* super(locationNode);
* }
*
* static LanguageException create(Node locationNode) {
* CompilerAsserts.partialEvaluationConstant(locationNode);
* if (locationNode == null || !locationNode.isAdoptable()) {
* return new LanguageException(EncapsulatingNodeReference.getCurrent().get());
* } else {
* return new LanguageException(locationNode);
* }
* }
*
* // ...
* }
*
*
* Note that {@link Node#isAdoptable()} is a way to find out whether a node was used in an uncached
* scenario or not.
*
*
* @since 20.2
*/
public final class EncapsulatingNodeReference {
/*
* Fallback thread local used only if there is no current polyglot context entered.
*/
private static final ThreadLocal CURRENT = new ThreadLocal<>() {
@Override
protected EncapsulatingNodeReference initialValue() {
return new EncapsulatingNodeReference(Thread.currentThread());
}
};
@CompilationFinal private static volatile boolean seenNullContext;
private final WeakReference thread;
private Node reference;
EncapsulatingNodeReference(Thread t) {
this.thread = new WeakReference<>(t);
}
/**
* Sets the current encapsulating node for the current thread and returns its previous value.
* The passed node may be null. The set node must be {@link Node#isAdoptable()
* adoptable} and be adopted by a {@link RootNode} otherwise an {@link AssertionError} is
* thrown. This method must only be used from the thread it was {@link #getCurrent() requested}
* for. This method is safe to be called from compiled code paths.
*
* @since 20.2
*/
public Node set(Node node) {
assert node == null || node.isAdoptable() : "Node must be adoptable to be pushed as encapsulating node.";
assert node == null || node.getRootNode() != null : "Node must be adopted by a RootNode to be pushed as encapsulating node.";
assert Thread.currentThread() == this.thread.get();
Node old = this.reference;
this.reference = node;
return old;
}
/**
* Returns the current encapsulating node for the current thread. Returned node may be
* null. If the returned node is non-null then it is guaranteed to be
* {@link Node#isAdoptable() adoptable} and adopted by a {@link RootNode}. This method must only
* be used from the thread it was {@link #getCurrent() requested} for. This method is safe to be
* called from compiled code paths.
*
* @since 20.2
*/
public Node get() {
assert Thread.currentThread() == this.thread.get();
return reference;
}
/**
* Returns the encapsulating node reference of the {@link Thread#currentThread() current}
* thread. The returned value is never null. This method is safe to be called from
* compiled code paths.
*
* @since 20.2
*/
public static EncapsulatingNodeReference getCurrent() {
/*
* If we have never seen an out of context access (common-case) then we can deoptimize early
* when reading while not entered in a context. This flag has only an effect in compiled
* code paths, so we safe the read for the interpreter.
*/
boolean invalidateOnNull = CompilerDirectives.inCompiledCode() ? !seenNullContext : false;
EncapsulatingNodeReference ref = NodeAccessor.ENGINE.getEncapsulatingNodeReference(invalidateOnNull);
if (ref != null) {
// fast path inside contexts
return ref;
}
// use outside of a polyglot context
if (!seenNullContext) {
/*
* We deliberately do not use an assumption here, as an assumption would be too
* footprint heavy. Basically all compilation units that use encapsulating node
* references would be registered here. Non-eager deoptimization seems to be fine
* trade-off for this use-case as it is extremely unlikely that usages of this profile
* are compiled in cases where there is either a context and no context.
*/
CompilerDirectives.transferToInterpreterAndInvalidate();
seenNullContext = true;
}
return getThreadLocal();
}
@TruffleBoundary
private static EncapsulatingNodeReference getThreadLocal() {
return CURRENT.get();
}
}