netty学习--netty源码中的部分util方法

• io.netty.buffer.AbstractByteBuf#calculateNewCapacity  申请内存空间

　　

private int calculateNewCapacity(int minNewCapacity) {
        final int maxCapacity = this.maxCapacity;
        // 1m = 1024kb = 1024*1024b
        final int threshold = 1048576 * 4; // 4 MiB page

        if (minNewCapacity == threshold) {
            return threshold;
        }

        // If over threshold, do not double but just increase by threshold.
    　　// 如果大于4M，假如是5M，那么
        if (minNewCapacity > threshold) {
            int newCapacity = minNewCapacity / threshold * threshold; // 5M/4M * 4M = 5M
            if (newCapacity > maxCapacity - threshold) { // if ( 5M > 8M(假设为8M) - 4M)
                newCapacity = maxCapacity; // 赋值为8M
            } else {
                newCapacity += threshold; // 赋值为5+4 = 9M
            }
            return newCapacity;
        }
　　　　
        // Not over threshold. Double up to 4 MiB, starting from 64.
        int newCapacity = 64;
        while (newCapacity < minNewCapacity) {// 假设传入的是100，那么因为要保证4字节对齐，一般申请的内存要是4的倍数，所以这边从64开始循环，128是满足的
            newCapacity <<= 1;
        }

        return Math.min(newCapacity, maxCapacity);
    }

• io.netty.util.concurrent.ThreadPerTaskExecutor  线程执行器

// jdk的类
public interface Executor {

    /**
     * Executes the given command at some time in the future.  The command
     * may execute in a new thread, in a pooled thread, or in the calling
     * thread, at the discretion of the {@code Executor} implementation.
     *
     * @param command the runnable task
     * @throws RejectedExecutionException if this task cannot be
     * accepted for execution
     * @throws NullPointerException if command is null
     */
    void execute(Runnable command);
}
//netty的实现类
public final class ThreadPerTaskExecutor implements Executor {
    private final ThreadFactory threadFactory;

    public ThreadPerTaskExecutor(ThreadFactory threadFactory) {
        if (threadFactory == null) {
            throw new NullPointerException("threadFactory");
        }
        this.threadFactory = threadFactory;
    }

    @Override
    public void execute(Runnable command) {
        threadFactory.newThread(command).start();
    }
}

线程工厂的调用：

        if (executor == null) {
            executor = new ThreadPerTaskExecutor(newDefaultThreadFactory());
        }

    protected ThreadFactory newDefaultThreadFactory() {
        return new DefaultThreadFactory(getClass());
    }

public class DefaultThreadFactory implements ThreadFactory {

    private static final AtomicInteger poolId = new AtomicInteger();

    private final AtomicInteger nextId = new AtomicInteger();
    private final String prefix;
    private final boolean daemon;
    private final int priority;

    public DefaultThreadFactory(Class<?> poolType, boolean daemon, int priority) {
        this(toPoolName(poolType), daemon, priority);
    }

    private static String toPoolName(Class<?> poolType) {
        if (poolType == null) {
            throw new NullPointerException("poolType");
        }
        String poolName;
        Package pkg = poolType.getPackage();
        if (pkg != null) {
            poolName = poolType.getName().substring(pkg.getName().length() + 1);
        } else {
            poolName = poolType.getName();
        }

        switch (poolName.length()) {
            case 0:
                return "unknown";
            case 1:
                return poolName.toLowerCase(Locale.US);
            default:
                if (Character.isUpperCase(poolName.charAt(0)) && Character.isLowerCase(poolName.charAt(1))) {
                    return Character.toLowerCase(poolName.charAt(0)) + poolName.substring(1);
                } else {
                    return poolName;
                }
        }
    }

    public DefaultThreadFactory(String poolName, boolean daemon, int priority) {
        if (poolName == null) {
            throw new NullPointerException("poolName");
        }
        if (priority < Thread.MIN_PRIORITY || priority > Thread.MAX_PRIORITY) {
            throw new IllegalArgumentException(
                    "priority: " + priority + " (expected: Thread.MIN_PRIORITY <= priority <= Thread.MAX_PRIORITY)");
        }

        prefix = poolName + '-' + poolId.incrementAndGet() + '-';
        this.daemon = daemon;
        this.priority = priority;
    }

    @Override
    public Thread newThread(Runnable r) {
        Thread t = new Thread(r, prefix + nextId.incrementAndGet());
        try {
            if (t.isDaemon()) {
                if (!daemon) {
                    t.setDaemon(false);
                }
            } else {
                if (daemon) {
                    t.setDaemon(true);
                }
            }

            if (t.getPriority() != priority) {
                t.setPriority(priority);
            }
        } catch (Exception ignored) {
            // Doesn't matter even if failed to set.
        }
        return t;
    }
}