apache mina:SimpleIoProcessorPool

本文介绍了SimpleIoProcessorPool的工作原理及实现细节,包括线程池的管理、IoSession与IoProcessor的关联机制以及如何通过Executor进行任务调度。

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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();
            }
        }
    }





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