apache mina:SimpleIoProcessorPool

An IoProcessor pool that distributes IoSessions into one or more IoProcessors.
Most current transport implementations use this pool internally to perform better in a multi-core environment.
and therefore, you won't need to use this pool directly unless you are running multiple IoServices in the same JVM.

SimpleIoProcessorPool 主要处理IO输入输出线程池的管理。主要功能为创建线程池,把IoSession与IoProcessor线程相关联,管理IoProcessor线程。

其中,IoProcessor线程与IoSession相关联的代码如下,这就意味着一个线程同时处理多个IoSession的输入输出操作。

    /**     * 根据IoSession ID和线程池的顺序把线程和IoSession相关联在一起     * Find the processor associated to a session. If it hasen't be stored into     * the session's attributes, pick a new processor and stores it.     */    @SuppressWarnings("unchecked")    private IoProcessor<S> getProcessor(S session) {        IoProcessor<S> processor = (IoProcessor<S>) session.getAttribute(PROCESSOR);        if (processor == null) {            if (disposed || disposing) {                throw new IllegalStateException("A disposed processor cannot be accessed.");            }            processor = pool[Math.abs((int) session.getId()) % pool.length];            if (processor == null) {                throw new IllegalStateException("A disposed processor cannot be accessed.");            }            session.setAttributeIfAbsent(PROCESSOR, processor);        }        return processor;    }

当IoSession和IoProcessor相关联后,IoProcessor的生命周期交由Executor来管理。

    /**     *  在把IoSession和IoProcessor相关联后,调用startupProcessor()方法,把IoProcessor交由Executor关联     */    public final void add(S session) {        getProcessor(session).add(session);    }

    public final void add(S session) {        if (disposed || disposing) {            throw new IllegalStateException("Already disposed.");        }        // Adds the session to the newSession queue and starts the worker        newSessions.add(session);        startupProcessor();    }

    /**     * Starts the inner Processor, asking the executor to pick a thread in its     * pool. The Runnable will be renamed     */    private void startupProcessor() {        Processor processor = processorRef.get();        if (processor == null) {            processor = new Processor();            if (processorRef.compareAndSet(null, processor)) {                executor.execute(new NamePreservingRunnable(processor, threadName));            }        }        // Just stop the select() and start it again, so that the processor        // can be activated immediately.        wakeup();    }

SimpleIoProcessorPool的成员字段如下：

public class SimpleIoProcessorPool<S extends AbstractIoSession> implements IoProcessor<S> {    /** A logger for this class */    private final static Logger LOGGER = LoggerFactory.getLogger(SimpleIoProcessorPool.class);    /** The default pool size, when no size is provided. */    //创建默认线程的数量    private static final int DEFAULT_SIZE = Runtime.getRuntime().availableProcessors() + 1;    /** A key used to store the processor pool in the session's Attributes */    //在IoSession持有IoProcessor的标记    private static final AttributeKey PROCESSOR = new AttributeKey(SimpleIoProcessorPool.class, "processor");    /** The pool table */    //线程池    private final IoProcessor<S>[] pool;    /** The contained  which is passed to the IoProcessor when they are created */    private final Executor executor;    /** A flag set to true if we had to create an executor */    private final boolean createdExecutor;    /** A lock to protect the disposal against concurrent calls */    private final Object disposalLock = new Object();    /** A flg set to true if the IoProcessor in the pool are being disposed */    private volatile boolean disposing;    /** A flag set to true if all the IoProcessor contained in the pool have been disposed */    private volatile boolean disposed;}

其中,默认创建IoProcessor线程的数量为CPU+1;

    private static final int DEFAULT_SIZE = Runtime.getRuntime().availableProcessors() + 1;

线程也都是预先创建好,等待IO操作产生时,减少线程创建的时间。

    /**     * Creates a new instance of SimpleIoProcessorPool with an executor     *     * @param processorType The type of IoProcessor to use     * @param executor The {@link Executor}     * @param size The number of IoProcessor in the pool     */    @SuppressWarnings("unchecked")    public SimpleIoProcessorPool(Class<? extends IoProcessor<S>> processorType, Executor executor, int size, SelectorProvider selectorProvider) {        if (processorType == null) {            throw new IllegalArgumentException("processorType");        }        if (size <= 0) {            throw new IllegalArgumentException("size: " + size + " (expected: positive integer)");        }        // Create the executor if none is provided        createdExecutor = (executor == null);        if (createdExecutor) {            this.executor = Executors.newCachedThreadPool();            // Set a default reject handler            ((ThreadPoolExecutor) this.executor).setRejectedExecutionHandler(new ThreadPoolExecutor.CallerRunsPolicy());        } else {            this.executor = executor;        }        pool = new IoProcessor[size];        boolean success = false;        Constructor<? extends IoProcessor<S>> processorConstructor = null;        boolean usesExecutorArg = true;        try {            // We create at least one processor            try {                try {                    processorConstructor = processorType.getConstructor(ExecutorService.class);                    pool[0] = processorConstructor.newInstance(this.executor);                } catch (NoSuchMethodException e1) {                    // To the next step...                    try {                        if(selectorProvider==null) {                            processorConstructor = processorType.getConstructor(Executor.class);                            pool[0] = processorConstructor.newInstance(this.executor);                        } else {                            processorConstructor = processorType.getConstructor(Executor.class, SelectorProvider.class);                            pool[0] = processorConstructor.newInstance(this.executor,selectorProvider);                        }                    } catch (NoSuchMethodException e2) {                        // To the next step...                        try {                            processorConstructor = processorType.getConstructor();                            usesExecutorArg = false;                            pool[0] = processorConstructor.newInstance();                        } catch (NoSuchMethodException e3) {                            // To the next step...                        }                    }                }            } catch (RuntimeException re) {                LOGGER.error("Cannot create an IoProcessor :{}", re.getMessage());                throw re;            } catch (Exception e) {                String msg = "Failed to create a new instance of " + processorType.getName() + ":" + e.getMessage();                LOGGER.error(msg, e);                throw new RuntimeIoException(msg, e);            }            if (processorConstructor == null) {                // Raise an exception if no proper constructor is found.                String msg = String.valueOf(processorType) + " must have a public constructor with one "                        + ExecutorService.class.getSimpleName() + " parameter, a public constructor with one "                        + Executor.class.getSimpleName() + " parameter or a public default constructor.";                LOGGER.error(msg);                throw new IllegalArgumentException(msg);            }            // Constructor found now use it for all subsequent instantiations            for (int i = 1; i < pool.length; i++) {                try {                    if (usesExecutorArg) {                        if(selectorProvider==null) {                            pool[i] = processorConstructor.newInstance(this.executor);                        } else {                            pool[i] = processorConstructor.newInstance(this.executor, selectorProvider);                        }                    } else {                        pool[i] = processorConstructor.newInstance();                    }                } catch (Exception e) {                    // Won't happen because it has been done previously                }            }            success = true;        } finally {            if (!success) {                dispose();            }        }    }