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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) 2014, 2016, 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 java.util.Arrays;

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;

final class ContextStore {
    final Object vm;

    @CompilationFinal(dimensions = 1) private Object[] store;
    @CompilationFinal private Assumption storeStable;

    ContextStore(Object vm, int capacity) {
        this.vm = vm;
        this.store = new Object[capacity < 4 ? 4 : capacity];
        this.storeStable = Truffle.getRuntime().createAssumption("context store stable");
    }

    Object getContext(int index) {
        if (!storeStable.isValid()) {
            CompilerDirectives.transferToInterpreterAndInvalidate();
            storeStable = Truffle.getRuntime().createAssumption();
        }
        return index < store.length ? store[index] : null;
    }

    void setContext(int languageId, Object context) {
        if (languageId >= store.length) {
            store = Arrays.copyOf(store, store.length << 1);
        }
        store[languageId] = context;
        storeStable.invalidate();
    }

}