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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
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 *
 * 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).
 *
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 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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package com.oracle.svm.core.genscavenge;

import static com.oracle.svm.core.genscavenge.CollectionPolicy.Options.PercentTimeInIncrementalCollection;
import static com.oracle.svm.core.genscavenge.HeapPolicy.getMaximumHeapSize;
import static com.oracle.svm.core.genscavenge.HeapPolicy.getMinimumHeapSize;

import org.graalvm.compiler.options.Option;
import org.graalvm.nativeimage.Platform;
import org.graalvm.nativeimage.Platforms;
import org.graalvm.nativeimage.hosted.Feature.FeatureAccess;
import org.graalvm.word.UnsignedWord;

import com.oracle.svm.core.log.Log;
import com.oracle.svm.core.option.HostedOptionKey;
import com.oracle.svm.core.option.RuntimeOptionKey;
import com.oracle.svm.core.util.TimeUtils;
import com.oracle.svm.core.util.UserError;

A collection policy decides when to collect incrementally or completely. /** A collection policy decides when to collect incrementally or completely. */
public abstract class CollectionPolicy {
    public static class Options {
        @Option(help = "The initial garbage collection policy, as a fully-qualified class name (might require quotes or escaping).")//
        public static final HostedOptionKey<String> InitialCollectionPolicy = new HostedOptionKey<>(BySpaceAndTime.class.getName());

        @Option(help = "Percentage of total collection time that should be spent on young generation collections.")//
        public static final RuntimeOptionKey<Integer> PercentTimeInIncrementalCollection = new RuntimeOptionKey<>(50);
    }

    @Platforms(Platform.HOSTED_ONLY.class)
    static CollectionPolicy getInitialPolicy(FeatureAccess access) {
        return instantiatePolicy(access, CollectionPolicy.class, Options.InitialCollectionPolicy.getValue());
    }

    @Platforms(Platform.HOSTED_ONLY.class)
    private static <T> T instantiatePolicy(FeatureAccess access, Class<T> policyClass, String className) {
        Class<?> policy = access.findClassByName(className);
        if (policy == null) {
            throw UserError.abort("Policy %s does not exist. It must be a fully qualified class name.", className);
        }
        Object result;
        try {
            result = policy.getDeclaredConstructor().newInstance();
        } catch (Exception ex) {
            throw UserError.abort("Policy %s cannot be instantiated.", className);
        }
        if (!policyClass.isInstance(result)) {
            throw UserError.abort("Policy %s does not extend %s.", className, policyClass.getTypeName());
        }
        return policyClass.cast(result);
    }

    
Return true if the current collection should entail an incremental collection. /** Return {@code true} if the current collection should entail an incremental collection. */
    public abstract boolean collectIncrementally();

    
Return true if the current collection should entail a complete collection. /** Return {@code true} if the current collection should entail a complete collection. */
    public abstract boolean collectCompletely();

    CollectionPolicy() {
    }

    public abstract void nameToLog(Log log);

    public abstract String getName();

    static GCAccounting getAccounting() {
        return GCImpl.getGCImpl().getAccounting();
    }

    public static class OnlyIncrementally extends CollectionPolicy {

        @Override
        public boolean collectIncrementally() {
            return true;
        }

        @Override
        public boolean collectCompletely() {
            return false;
        }

        @Override
        public void nameToLog(Log log) {
            log.string(getName());
        }

        @Override
        public String getName() {
            return "only incrementally";
        }
    }

    public static class OnlyCompletely extends CollectionPolicy {

        @Override
        public boolean collectIncrementally() {
            return false;
        }

        @Override
        public boolean collectCompletely() {
            return true;
        }

        @Override
        public void nameToLog(Log log) {
            log.string(getName());
        }

        @Override
        public String getName() {
            return "only completely";
        }
    }

    public static class NeverCollect extends CollectionPolicy {

        @Override
        public boolean collectIncrementally() {
            return false;
        }

        @Override
        public boolean collectCompletely() {
            return false;
        }

        @Override
        public void nameToLog(Log log) {
            log.string(getName());
        }

        @Override
        public String getName() {
            return "never collect";
        }
    }

    
A collection policy that delays complete collections until the heap has at least `-Xms` space
in it, and then tries to balance time in incremental and complete collections.
/**
     * A collection policy that delays complete collections until the heap has at least `-Xms` space
     * in it, and then tries to balance time in incremental and complete collections.
     */
    public static class BySpaceAndTime extends CollectionPolicy {
        @Override
        public boolean collectIncrementally() {
            return true;
        }

        @Override
        public boolean collectCompletely() {
            return estimateUsedHeapAtNextIncrementalCollection().aboveThan(getMaximumHeapSize()) ||
                            GCImpl.getChunkBytes().aboveThan(getMinimumHeapSize()) && enoughTimeSpentOnIncrementalGCs();
        }

        
Estimates the heap size at the next incremental collection assuming that the whole
current young generation gets promoted.
/**
         * Estimates the heap size at the next incremental collection assuming that the whole
         * current young generation gets promoted.
         */
        private static UnsignedWord estimateUsedHeapAtNextIncrementalCollection() {
            UnsignedWord currentYoungBytes = HeapImpl.getHeapImpl().getYoungGeneration().getChunkBytes();
            UnsignedWord maxYoungBytes = HeapPolicy.getMaximumYoungGenerationSize();
            UnsignedWord oldBytes = getAccounting().getOldGenerationAfterChunkBytes();
            return currentYoungBytes.add(maxYoungBytes).add(oldBytes);
        }

        private static boolean enoughTimeSpentOnIncrementalGCs() {
            int incrementalWeight = PercentTimeInIncrementalCollection.getValue();
            assert incrementalWeight >= 0 && incrementalWeight <= 100 : "BySpaceAndTimePercentTimeInIncrementalCollection should be in the range [0..100].";

            long actualIncrementalNanos = getAccounting().getIncrementalCollectionTotalNanos();
            long completeNanos = getAccounting().getCompleteCollectionTotalNanos();
            long totalNanos = actualIncrementalNanos + completeNanos;
            long expectedIncrementalNanos = TimeUtils.weightedNanos(incrementalWeight, totalNanos);
            return TimeUtils.nanoTimeLessThan(expectedIncrementalNanos, actualIncrementalNanos);
        }

        @Override
        public void nameToLog(Log log) {
            log.string(getName()).string(": ").signed(Options.PercentTimeInIncrementalCollection.getValue()).string("% in incremental collections");
        }

        @Override
        public String getName() {
            return "by space and time";
        }
    }
}