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The Netty project is an effort to provide an asynchronous event-driven network application framework and tools for rapid development of maintainable high performance and high scalability protocol servers and clients. In other words, Netty is a NIO client server framework which enables quick and easy development of network applications such as protocol servers and clients. It greatly simplifies and streamlines network programming such as TCP and UDP socket server.

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/*
 * Copyright 2012 The Netty Project
 *
 * The Netty Project licenses this file to you under the Apache License,
 * version 2.0 (the "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at:
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 */
package org.jboss.netty.channel.socket.nio;

import java.io.IOException;
import java.nio.channels.CancelledKeyException;
import java.nio.channels.Selector;
import java.util.concurrent.TimeUnit;

import org.jboss.netty.logging.InternalLogger;
import org.jboss.netty.logging.InternalLoggerFactory;
import org.jboss.netty.util.internal.SystemPropertyUtil;

final class SelectorUtil {
    private static final InternalLogger logger =
        InternalLoggerFactory.getInstance(SelectorUtil.class);

    static final int DEFAULT_IO_THREADS = Runtime.getRuntime().availableProcessors() * 2;
    static final long DEFAULT_SELECT_TIMEOUT = 500;
    static final long SELECT_TIMEOUT =
            SystemPropertyUtil.getLong("org.jboss.netty.selectTimeout", DEFAULT_SELECT_TIMEOUT);
    static final long SELECT_TIMEOUT_NANOS = TimeUnit.MILLISECONDS.toNanos(SELECT_TIMEOUT);
    static final boolean EPOLL_BUG_WORKAROUND =
            SystemPropertyUtil.getBoolean("org.jboss.netty.epollBugWorkaround", false);

    // Workaround for JDK NIO bug.
    //
    // See:
    // - http://bugs.sun.com/view_bug.do?bug_id=6427854
    // - https://github.com/netty/netty/issues/203
    static {
        String key = "sun.nio.ch.bugLevel";
        try {
            String buglevel = System.getProperty(key);
            if (buglevel == null) {
                System.setProperty(key, "");
            }
        } catch (SecurityException e) {
            if (logger.isDebugEnabled()) {
                logger.debug("Unable to get/set System Property '" + key + '\'', e);
            }
        }
        if (logger.isDebugEnabled()) {
            logger.debug("Using select timeout of " + SELECT_TIMEOUT);
            logger.debug("Epoll-bug workaround enabled = " + EPOLL_BUG_WORKAROUND);
        }
    }

    static int select(Selector selector) throws IOException {
        try {
            return selector.select(SELECT_TIMEOUT);
        } catch (CancelledKeyException e) {
            if (logger.isDebugEnabled()) {
                logger.debug(
                        CancelledKeyException.class.getSimpleName() +
                        " raised by a Selector - JDK bug?", e);
            }
            // Harmless exception - log anyway
        }
        return -1;
    }

    private SelectorUtil() {
        // Unused
    }
}