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package com.pdd.pop.ext.glassfish.grizzly.strategies;

import java.io.IOException;
import java.util.concurrent.Executor;
import com.pdd.pop.ext.glassfish.grizzly.Connection;
import com.pdd.pop.ext.glassfish.grizzly.IOEvent;
import com.pdd.pop.ext.glassfish.grizzly.IOStrategy;
import com.pdd.pop.ext.glassfish.grizzly.Transport;
import com.pdd.pop.ext.glassfish.grizzly.nio.NIOConnection;
import com.pdd.pop.ext.glassfish.grizzly.nio.NIOTransport;
import com.pdd.pop.ext.glassfish.grizzly.threadpool.ThreadPoolConfig;

/**
 * Simple dynamic strategy, which switches I/O processing strategies, basing
 * on statistics. This implementation takes in consideration number of
 * {@link java.nio.channels.SelectionKey}s, which were selected last time by
 * {@link java.nio.channels.Selector}.
 *
 * SimpleDynamicIOStrategy is able to use 2 strategies underneath:
 * {@link SameThreadIOStrategy}, {@link WorkerThreadIOStrategy}.
 * And is able to switch between them basing on corresponding threshold
 * (threshold represents the number of selected
 * {@link java.nio.channels.SelectionKey}s).
 *
 * So the strategy is getting applied following way:
 *
 * {@link SameThreadIOStrategy} --(worker-thread threshold)--> {@link WorkerThreadIOStrategy}.
 *
 * @author Alexey Stashok
 */
public final class SimpleDynamicNIOStrategy implements IOStrategy {

    private static final SimpleDynamicNIOStrategy INSTANCE = new SimpleDynamicNIOStrategy();

    private final SameThreadIOStrategy sameThreadStrategy;
    private final WorkerThreadIOStrategy workerThreadStrategy;

    private static final int WORKER_THREAD_THRESHOLD = 1;


    // ------------------------------------------------------------ Constructors

    private SimpleDynamicNIOStrategy() {
        sameThreadStrategy = SameThreadIOStrategy.getInstance();
        workerThreadStrategy = WorkerThreadIOStrategy.getInstance();
    }


    // ---------------------------------------------------------- Public Methods


    public static SimpleDynamicNIOStrategy getInstance() {

        return INSTANCE;

    }

    @Override
    public boolean executeIoEvent(Connection connection, IOEvent ioEvent) throws IOException {
        return executeIoEvent(connection, ioEvent, true);
    }


    // ------------------------------------------------- Methods from IOStrategy


    @Override
    public Executor getThreadPoolFor(final Connection connection,
            final IOEvent ioEvent) {
        final int lastSelectedKeysCount = getLastSelectedKeysCount(connection);

        return lastSelectedKeysCount <= WORKER_THREAD_THRESHOLD ?
                     sameThreadStrategy.getThreadPoolFor(connection, ioEvent) :
                     workerThreadStrategy.getThreadPoolFor(connection, ioEvent);
    }

    @Override
    public boolean executeIoEvent(final Connection connection,
            final IOEvent ioEvent, final boolean isIoEventEnabled)
            throws IOException {
        
        final int lastSelectedKeysCount = getLastSelectedKeysCount(connection);

        return ((lastSelectedKeysCount <= WORKER_THREAD_THRESHOLD)
                     ? sameThreadStrategy.executeIoEvent(connection, ioEvent, isIoEventEnabled)
                     : workerThreadStrategy.executeIoEvent(connection, ioEvent, isIoEventEnabled));
    }

    @Override
    public ThreadPoolConfig createDefaultWorkerPoolConfig(final Transport transport) {

        final ThreadPoolConfig config = ThreadPoolConfig.defaultConfig().copy();
        final int selectorRunnerCount = ((NIOTransport) transport).getSelectorRunnersCount();
        config.setCorePoolSize(selectorRunnerCount * 2);
        config.setMaxPoolSize(selectorRunnerCount * 2);
        config.setMemoryManager(transport.getMemoryManager());
        return config;

    }


    // --------------------------------------------------------- Private Methods


    private static int getLastSelectedKeysCount(final Connection c) {
        return ((NIOConnection) c).getSelectorRunner().getLastSelectedKeysCount();
    }

}




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