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 * Copyright (c) 2021, 2023, 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
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 * unmodified Software as contributed to or provided by such licensor, or (ii)
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 * (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
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package com.oracle.truffle.runtime;

import java.util.concurrent.BlockingQueue;
import java.util.concurrent.TimeUnit;

/**
 * See https://github.com/oracle/graal/blob/master/truffle/docs/TraversingCompilationQueue.md .
 */
final class DynamicThresholdsQueue extends TraversingBlockingQueue {

    private final int threads;
    private final double minScale;
    private final int minNormalLoad;
    private final int maxNormalLoad;
    private final double slope;

    DynamicThresholdsQueue(int threads, double minScale, int minNormalLoad, int maxNormalLoad, BlockingQueue entries) {
        super(entries);
        this.threads = threads;
        this.minScale = minScale;
        this.minNormalLoad = minNormalLoad;
        this.maxNormalLoad = maxNormalLoad;
        this.slope = (1 - minScale) / minNormalLoad;
    }

    private double load() {
        return (double) entries.size() / threads;
    }

    @Override
    public boolean add(Runnable e) {
        scaleThresholds();
        return super.add(e);
    }

    @Override
    public boolean offer(Runnable e) {
        scaleThresholds();
        return super.offer(e);
    }

    @Override
    public boolean offer(Runnable e, long timeout, TimeUnit unit) throws InterruptedException {
        scaleThresholds();
        return super.offer(e, timeout, unit);
    }

    @Override
    public Runnable poll(long timeout, TimeUnit unit) throws InterruptedException {
        scaleThresholds();
        return super.poll(timeout, unit);
    }

    @Override
    public Runnable poll() {
        scaleThresholds();
        return super.poll();
    }

    private void scaleThresholds() {
        OptimizedTruffleRuntime.getRuntime().setCompilationThresholdScale(FixedPointMath.toFixedPoint(scale()));
    }

    /**
     * @return f(x) where x is the load of the queue and f is a function that
     *
     *         - Grows linearly between coordinates (0, minScale) and (minNormalLoad, 1)
     *
     *         - Equals 1 for all x between minNormalLoad and maxNormalLoad (inclusively)
     *
     *         - For all x > maxNormalLoad - grows at the same rate as for x < minNormalLoad, but
     *         starting at coordinate (maxNormalLoad, 1)
     */
    private double scale() {
        double x = load();
        if (minNormalLoad <= x && x <= maxNormalLoad) {
            return 1;
        }
        if (x < minNormalLoad) {
            return slope * x + minScale;
        }
        return slope * x + (1 - slope * maxNormalLoad);
    }
}