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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * 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).
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 * 2 along with this work; if not, write to the Free Software Foundation,
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package org.graalvm.compiler.hotspot;

import static org.graalvm.compiler.hotspot.HotSpotGraalCompiler.fmt;
import static org.graalvm.compiler.hotspot.HotSpotGraalOptionValues.GRAAL_OPTION_PROPERTY_PREFIX;

import java.util.Arrays;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.atomic.AtomicInteger;

import org.graalvm.compiler.debug.TTY;
import org.graalvm.compiler.options.Option;
import org.graalvm.compiler.options.OptionKey;
import org.graalvm.compiler.options.OptionType;
import org.graalvm.compiler.options.OptionValues;

import jdk.vm.ci.code.CompilationRequest;

A watch dog that monitors the duration and compilation rate during a bootstrap. If time spent bootstrapping exceeds a specified timeout or the compilation rate falls below a given ratio of the maximum observed compilation rate (i.e., compilation slows down too much), the compiler will ignore all subsequent compilation requests, effectively draining the bootstrap completion queue and expediting completion of bootstrap. Note that the compilation rate is computed over the whole execution, not just the most recent measurement period. This means a sudden but temporary drop in any given measurement period won't cause bootstrapping to terminate early. This mechanism is based on past observations that a significantly falling bootstrap compilation rate implies a configuration where bootstrapping will take an unreasonably long time and it's better to drain the bootstrap compilation queue at some point that risk triggering timeouts in external harnesses such as integration tests. /**
 * A watch dog that monitors the duration and compilation rate during a
 * {@linkplain HotSpotGraalRuntimeProvider#isBootstrapping() bootstrap}. If time spent bootstrapping
 * exceeds a specified timeout or the compilation rate falls below a given ratio of the maximum
 * observed compilation rate (i.e., compilation slows down too much), the compiler will ignore all
 * subsequent compilation requests, effectively draining the bootstrap completion queue and
 * expediting completion of bootstrap. Note that the compilation rate is computed over the whole
 * execution, not just the most recent measurement period. This means a sudden but temporary drop in
 * any given measurement period won't cause bootstrapping to terminate early.
 *
 * This mechanism is based on past observations that a significantly falling bootstrap compilation
 * rate implies a configuration where bootstrapping will take an unreasonably long time and it's
 * better to drain the bootstrap compilation queue at some point that risk triggering timeouts in
 * external harnesses such as integration tests.
 */
final class BootstrapWatchDog extends Thread {

    public static class Options {
        // @formatter:off
        @Option(help = "Ratio of the maximum compilation rate below which the bootstrap compilation rate must not fall " +
                       "(0 or less disables monitoring).", type = OptionType.Debug)
        public static final OptionKey<Double> BootstrapWatchDogCriticalRateRatio = new OptionKey<>(0.25D);
        @Option(help = "Maximum time in minutes to spend bootstrapping (0 to disable this limit).", type = OptionType.Debug)
        public static final OptionKey<Double> BootstrapTimeout = new OptionKey<>(15D);
        // @formatter:on
    }

    
Count of completed compilations. This is updated by the compiler threads and read by the
watch dog thread.
/**
     * Count of completed compilations. This is updated by the compiler threads and read by the
     * watch dog thread.
     */
    private final AtomicInteger compilations = new AtomicInteger();

    
Set to true once the compilation rate drops too low or bootstrapping times out.
/**
     * Set to true once the compilation rate drops too low or bootstrapping times out.
     */
    private boolean hitCriticalRateOrTimeout;

    
The maximum compilation rate seen during execution.
/**
     * The maximum compilation rate seen during execution.
     */
    private double maxRate;

    private final HotSpotGraalRuntimeProvider graalRuntime;

    
Creates and returns a BootstrapWatchDog if Options.BootstrapWatchDogCriticalRateRatio is not set to 0 otherwise returns null. /**
     * Creates and returns a {@link BootstrapWatchDog} if
     * {@link Options#BootstrapWatchDogCriticalRateRatio} is not set to 0 otherwise returns
     * {@code null}.
     */
    static BootstrapWatchDog maybeCreate(HotSpotGraalRuntimeProvider graalRuntime) {
        OptionValues options = graalRuntime.getOptions();
        int timeout = (int) (Options.BootstrapTimeout.getValue(options) * 60);
        double maxRateDecrease = Options.BootstrapWatchDogCriticalRateRatio.getValue(options);
        return maxRateDecrease <= 0.0D && timeout == 0 ? null : new BootstrapWatchDog(graalRuntime, timeout, maxRateDecrease);
    }

    private BootstrapWatchDog(HotSpotGraalRuntimeProvider graalRuntime, int timeout, double maxRateDecrease) {
        this.setName(getClass().getSimpleName());
        this.start();
        this.graalRuntime = graalRuntime;
        this.timeout = timeout;
        this.maxRateDecrease = maxRateDecrease;
    }

    
Set to true to debug the watch dog.
/**
     * Set to true to debug the watch dog.
     */
    private static final boolean DEBUG = Boolean.getBoolean("debug.graal.BootstrapWatchDog");

    
Seconds to delay before starting to measure the compilation rate.
/**
     * Seconds to delay before starting to measure the compilation rate.
     */
    private static final int INITIAL_DELAY = 10;

    
Seconds between each compilation rate measurement.
/**
     * Seconds between each compilation rate measurement.
     */
    private static final long EPOCH = 5;

    
Time in seconds before stopping a bootstrap.
/**
     * Time in seconds before stopping a bootstrap.
     */
    private final int timeout;

    
The watch dog hits a critical compilation rate if the current compilation rate falls below this ratio of the maximum compilation rate. /**
     * The watch dog {@link #hitCriticalCompilationRateOrTimeout() hits} a critical compilation rate
     * if the current compilation rate falls below this ratio of the maximum compilation rate.
     */
    private final double maxRateDecrease;

    @Override
    public void run() {
        if (DEBUG) {
            TTY.printf("%nStarted %s%n", this);
        }
        long start = System.currentTimeMillis();
        Map<Thread, Watch> requestsAtTimeout = null;
        Map<Thread, StackTraceElement[]> stacksAtTimeout = null;
        try {
            Thread.sleep(INITIAL_DELAY * 1000);
            while (true) {
                int currentCompilations = compilations.get();
                long elapsed = System.currentTimeMillis() - start;
                double rate = currentCompilations / seconds(elapsed);
                if (DEBUG) {
                    TTY.printf("%.2f: compilation rate is %.2f/sec%n", seconds(elapsed), rate);
                }
                if (rate > maxRate) {
                    maxRate = rate;
                } else if (rate < (maxRate * maxRateDecrease)) {
                    TTY.printf("%nAfter %.2f seconds bootstrapping, compilation rate is %.2f compilations per second " +
                                    "which is below %.2f times the max compilation rate of %.2f%n", seconds(elapsed), rate, maxRateDecrease, maxRate);
                    TTY.printf("To enable monitoring of long running individual compilations, re-run with -D%s%s=%.2f%n",
                                    GRAAL_OPTION_PROPERTY_PREFIX, CompilationWatchDog.Options.CompilationWatchDogStartDelay.getName(),
                                    seconds(elapsed) - 5);
                    hitCriticalRateOrTimeout = true;
                    return;
                }
                if (elapsed > timeout * 1000) {
                    if (requestsAtTimeout == null) {
                        requestsAtTimeout = snapshotRequests();
                        stacksAtTimeout = new HashMap<>();
                        for (Thread t : requestsAtTimeout.keySet()) {
                            stacksAtTimeout.put(t, t.getStackTrace());
                        }
                    } else {
                        TTY.printf("%nHit bootstrapping timeout after %.2f seconds%n", seconds(elapsed));
                        Map<Thread, Watch> requestsNow = snapshotRequests();
                        for (Map.Entry<Thread, Watch> e : requestsAtTimeout.entrySet()) {
                            Thread t = e.getKey();
                            CompilationRequest request1 = requestsAtTimeout.get(t).request;
                            CompilationRequest request2 = requestsNow.get(t).request;
                            if (request1 != null && request1 == request2) {
                                StackTraceElement[] stackTraceNow = t.getStackTrace();
                                TTY.printf("Printing stack trace for current compilation of %s lasting more than %d seconds:%n%s",
                                                fmt(request1.getMethod()), EPOCH, fmt(stackTraceNow));
                                if (Arrays.equals(stacksAtTimeout.get(t), stackTraceNow)) {
                                    TTY.printf("\t** Identical stack trace %d seconds ago, implying a hung compilation **%n",
                                                    EPOCH);
                                }
                            } else {
                                if (DEBUG) {
                                    TTY.printf("%s was compiling %s%n", t, fmt(request1.getMethod()));
                                }
                            }
                        }
                        hitCriticalRateOrTimeout = true;
                        return;
                    }
                }
                if (!graalRuntime.isBootstrapping()) {
                    return;
                }

                Thread.sleep(EPOCH * 1000);
            }
        } catch (InterruptedException e) {
            e.printStackTrace(TTY.out);
        }
    }

    private Map<Thread, Watch> snapshotRequests() {
        synchronized (requests) {
            return new HashMap<>(requests);
        }
    }

    private static double seconds(long ms) {
        return (double) ms / 1000;
    }

    
Queries whether a critically low compilation rate or timeout occurred. /**
     * Queries whether a critically low compilation rate or {@link #timeout} occurred.
     */
    boolean hitCriticalCompilationRateOrTimeout() {
        return hitCriticalRateOrTimeout;
    }

    private final Map<Thread, Watch> requests = new HashMap<>();
    private final ThreadLocal<Watch> requestForThread = new ThreadLocal<>();

    
Opens a scope for watching the compilation of a given method.
Params:
request – a compilation request about to be processed
Returns:
null if the compilation watch dog is disabled otherwise this object. The returned value should be used in a try-with-resources statement whose scope is the whole compilation so that leaving the scope will cause Watch.close() to be called./**
     * Opens a scope for watching the compilation of a given method.
     *
     * @param request a compilation request about to be processed
     * @return {@code null} if the compilation watch dog is disabled otherwise this object. The
     *         returned value should be used in a {@code try}-with-resources statement whose scope
     *         is the whole compilation so that leaving the scope will cause {@link Watch#close()}
     *         to be called.
     */
    Watch watch(CompilationRequest request) {
        Watch watch = requestForThread.get();
        if (watch == null) {
            watch = new Watch();
            synchronized (requests) {
                requests.put(Thread.currentThread(), watch);
            }
        }
        watch.open(request);
        return watch;
    }

    
Object for watching the compilations requests of a single compiler thread.
/**
     * Object for watching the compilations requests of a single compiler thread.
     */
    class Watch implements AutoCloseable {
        CompilationRequest request;

        void open(CompilationRequest r) {
            assert this.request == null;
            this.request = r;
        }

        @Override
        public void close() {
            compilations.incrementAndGet();
            request = null;
        }
    }
}