Chaining.java

/*
 *      Copyright (C) 2012, 2016  higherfrequencytrading.com
 *      Copyright (C) 2016 Roman Leventov
 *
 *      This program is free software: you can redistribute it and/or modify
 *      it under the terms of the GNU Lesser General Public License as published by
 *      the Free Software Foundation, either version 3 of the License.
 *
 *      This program 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 Lesser General Public License for more details.
 *
 *      You should have received a copy of the GNU Lesser General Public License
 *      along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

package net.openhft.chronicle.hash.impl.stage.hash;

import net.openhft.chronicle.map.VanillaChronicleMap;
import net.openhft.sg.Stage;
import net.openhft.sg.Staged;

import java.util.ArrayList;
import java.util.List;
import java.util.function.BiFunction;

@Staged
public abstract class Chaining extends ChainingInterface {

    public final List<ChainingInterface> contextChain;
    public final int indexInContextChain;
    /**
     * First context, ever created in this thread. rootContextInThisThread === contextChain.get(0).
     */
    public final ChainingInterface rootContextInThisThread;

    public Chaining(VanillaChronicleMap map) {
        contextChain = new ArrayList<>();
        contextChain.add(this);
        indexInContextChain = 0;
        rootContextInThisThread = this;
        initMap(map);
    }
    
    public Chaining(ChainingInterface rootContextInThisThread, VanillaChronicleMap map) {
        contextChain = rootContextInThisThread.getContextChain();
        indexInContextChain = contextChain.size();
        contextChain.add(this);
        this.rootContextInThisThread = rootContextInThisThread;
        initMap(map);
    }

    @Override
    public List<ChainingInterface> getContextChain() {
        return contextChain;
    }

    public <T> T contextAtIndexInChain(int index) {
        //noinspection unchecked
        return (T) contextChain.get(index);
    }

    /**
     * This method stores a reference to the context's owner ChronicleMap into a field of the
     * context in the beginning of each usage of the context. Previously, this field was final and
     * set only once during context creation. It was preventing ChronicleMap objects from becoming
     * dead and collected by the GC, while any thread, from which the ChronicleMap was accessed
     * (hence a thread local context created), is alive.
     *
     * <p>The chain of strong references:
     * 1) Thread ->
     * 2) ThreadLocalMap ->
     * 3) Entry with ThreadLocal {@link net.openhft.chronicle.map.VanillaChronicleMap#cxt} as weak
     * referent and a context (e. g. {@link net.openhft.chronicle.map.impl.CompiledMapQueryContext})
     * as value (a simple field, not a weak reference!) ->
     * 4) final reference to the owner {@link VanillaChronicleMap} ->
     * 5) ThreadLocal {@link net.openhft.chronicle.map.VanillaChronicleMap#cxt} (a strong reference
     * this time! note that this ThreadLocal is an instance field of VanillaChronicleMap)
     *
     * <p>So in order to break this chain at step 4), contexts store references to their owner
     * ChronicleMaps only when contexts are used.
     */
    public abstract void initMap(VanillaChronicleMap map);

    @Stage("Used") public boolean used;
    @Stage("Used") private boolean firstContextLockedInThisThread;

    @Override
    public boolean usedInit() {
        return used;
    }

    /**
     * Init method parameterized to avoid automatic initialization. {@code used} argument should
     * always be {@code true}.
     */
    @Override
    public void initUsed(boolean used, VanillaChronicleMap map) {
        assert used;
        firstContextLockedInThisThread = rootContextInThisThread.lockContextLocally(map);
        initMap(map);
        this.used = true;
    }

    @SuppressWarnings("unused")
    void closeUsed() {
        used = false;
        if (firstContextLockedInThisThread)
            rootContextInThisThread.unlockContextLocally();
    }

    @Override
    public <T extends ChainingInterface> T getContext(
            Class<? extends T> contextClass, BiFunction<ChainingInterface,
            VanillaChronicleMap, T> createChaining,
            VanillaChronicleMap map) {
        for (ChainingInterface context : contextChain) {
            if (context.getClass() == contextClass && !context.usedInit()) {
                return initUsedAndReturn(map, context);
            }
        }
        int maxNestedContexts = 1 << 10;
        if (contextChain.size() > maxNestedContexts) {
            throw new IllegalStateException(map.toIdentityString() +
                    ": More than " + maxNestedContexts + " nested ChronicleHash contexts\n" +
                    "are not supported. Very probable that you simply forgot to close context\n" +
                    "somewhere (recommended to use try-with-resources statement).\n" +
                    "Otherwise this is a bug, please report with this\n" +
                    "stack trace on https://github.com/OpenHFT/Chronicle-Map/issues");
        }
        //noinspection unchecked
        T context = createChaining.apply(this, map);
        return initUsedAndReturn(map, context);
    }

    private static <T extends ChainingInterface> T initUsedAndReturn(
            VanillaChronicleMap map, ChainingInterface context) {
        try {
            context.initUsed(true, map);
            //noinspection unchecked
            return (T) context;
        } catch (Throwable throwable) {
            try {
                ((AutoCloseable) context).close();
            } catch (Throwable t) {
                throwable.addSuppressed(t);
            }
            throw throwable;
        }
    }
}