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/*
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * The Universal Permissive License (UPL), Version 1.0
 *
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 * 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
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 * 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
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 * (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),
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 * Software and the Larger Work(s), and to sublicense the foregoing rights on
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package com.oracle.truffle.js.runtime.objects;

import java.lang.invoke.MethodHandles;
import java.lang.invoke.VarHandle;

import com.oracle.truffle.api.Assumption;
import com.oracle.truffle.js.runtime.Errors;
import com.oracle.truffle.js.runtime.JSContext;
import com.oracle.truffle.js.runtime.util.DebugCounter;

/**
 * @see JSShape
 */
public final class JSSharedData {
    private final JSContext context;
    private final JSDynamicObject proto;
    private volatile Assumption prototypeAssumption;

    private static final VarHandle PROTOTYPE_ASSUMPTION_VAR_HANDLE;
    static {
        MethodHandles.Lookup lookup = MethodHandles.lookup();
        try {
            PROTOTYPE_ASSUMPTION_VAR_HANDLE = lookup.findVarHandle(JSSharedData.class, "prototypeAssumption", Assumption.class);
        } catch (NoSuchFieldException | IllegalAccessException e) {
            throw Errors.shouldNotReachHere(e);
        }
    }

    private static final DebugCounter prototypeAssumptionsCreated = DebugCounter.create("Prototype assumptions created");
    private static final DebugCounter prototypeAssumptionsRemoved = DebugCounter.create("Prototype assumptions removed");

    public JSSharedData(JSContext context, JSDynamicObject prototype) {
        this.context = context;
        this.proto = prototype;
    }

    JSContext getContext() {
        return context;
    }

    public JSDynamicObject getPrototype() {
        return proto;
    }

    Assumption getPrototypeAssumption() {
        Assumption assumption = prototypeAssumption;
        if (assumption != null) {
            return assumption;
        }
        assumption = Assumption.create("stable prototype");
        if (!PROTOTYPE_ASSUMPTION_VAR_HANDLE.compareAndSet(this, (Assumption) null, assumption)) {
            assumption = prototypeAssumption;
        } else {
            prototypeAssumptionsCreated.inc();
        }
        return assumption;
    }

    void invalidatePrototypeAssumption() {
        Assumption assumption = prototypeAssumption;
        if (assumption == null || assumption == Assumption.NEVER_VALID) {
            return;
        }
        assumption.invalidate();
        if (!PROTOTYPE_ASSUMPTION_VAR_HANDLE.compareAndSet(this, assumption, Assumption.NEVER_VALID)) {
            assert prototypeAssumption == Assumption.NEVER_VALID;
        } else {
            prototypeAssumptionsRemoved.inc();
        }
    }
}