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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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/*
 * Copyright (c) 2017, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * 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
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */
package com.oracle.truffle.api.vm;

import static com.oracle.truffle.api.vm.VMAccessor.LANGUAGE;

import java.lang.ref.ReferenceQueue;
import java.lang.ref.WeakReference;
import java.util.Arrays;
import java.util.concurrent.ConcurrentHashMap;

import com.oracle.truffle.api.CallTarget;
import com.oracle.truffle.api.source.Source;

final class PolyglotSourceCache {

    private final ConcurrentHashMap sourceCache;
    private final ReferenceQueue deadSources = new ReferenceQueue<>();

    PolyglotSourceCache() {
        this.sourceCache = new ConcurrentHashMap<>();
    }

    CallTarget parseCached(PolyglotLanguageContext context, Source source, String[] argumentNames) {
        cleanupStaleEntries();

        CallTarget target;
        if (source.isCached()) {
            Object sourceId = VMAccessor.SOURCE.getSourceIdentifier(source);
            WeakSourceKey ref = new WeakSourceKey(sourceId, source, argumentNames, deadSources);
            target = sourceCache.get(ref);
            if (target == null) {
                target = parseImpl(context, argumentNames, VMAccessor.SOURCE.copySource(source));
                CallTarget prev = sourceCache.putIfAbsent(ref, target);
                if (prev != null) {
                    /*
                     * Parsed twice -> discard the one not in the cache.
                     */
                    target = prev;
                }
            }
        } else {
            target = parseImpl(context, argumentNames, source);
        }
        return target;
    }

    private static CallTarget parseImpl(PolyglotLanguageContext context, String[] argumentNames, Source source) {
        CallTarget parsedTarget = LANGUAGE.parse(context.requireEnv(), source, null, argumentNames);
        if (parsedTarget == null) {
            throw new IllegalStateException(String.format("Parsing resulted in a null CallTarget for %s.", source));
        }
        return parsedTarget;
    }

    private void cleanupStaleEntries() {
        WeakSourceKey sourceRef = null;
        while ((sourceRef = (WeakSourceKey) deadSources.poll()) != null) {
            sourceCache.remove(sourceRef);
        }
    }

    private static final class WeakSourceKey extends WeakReference {

        final Object key;
        private final String[] arguments;

        WeakSourceKey(Object key, Source value, String[] arguments, ReferenceQueue q) {
            super(value, q);
            this.key = key;
            this.arguments = arguments != null && arguments.length == 0 ? null : arguments;
        }

        @Override
        public int hashCode() {
            final int prime = 31;
            int result = 1;
            result = prime * result + key.hashCode();
            result = prime * result + Arrays.hashCode(arguments);
            return result;
        }

        @Override
        public boolean equals(Object obj) {
            if (obj instanceof WeakSourceKey) {
                WeakSourceKey other = (WeakSourceKey) obj;
                return key.equals(other.key) && Arrays.equals(arguments, other.arguments);
            } else {
                return false;
            }
        }
    }

}