SelectorImpl分析

Channel接口定义：http://donald-draper.iteye.com/blog/2369111
AbstractInterruptibleChannel接口定义：http://donald-draper.iteye.com/blog/2369238
SelectableChannel接口定义:http://donald-draper.iteye.com/blog/2369317
SelectionKey定义：http://donald-draper.iteye.com/blog/2369499
SelectorProvider定义：http://donald-draper.iteye.com/blog/2369615
AbstractSelectableChannel定义：http://donald-draper.iteye.com/blog/2369742
NetworkChannel接口定义：http://donald-draper.iteye.com/blog/2369773
ServerSocketChannel定义：http://donald-draper.iteye.com/blog/2369836
Selector定义：http://donald-draper.iteye.com/blog/2370015
AbstractSelector定义：http://donald-draper.iteye.com/blog/2370138
上一篇我们看了一下AbstractSelector，主要是维护取消key集合，和key的反注册。
取消的key放在一个set集合中，对集合进行添加操作时，必须同步取消key set集合。
反注册选择key完成的实际工作是，将key，从key对应的通道的选择key数组（这个我们在选择通道相关文章中有讲）中移除。
今天来看一下SelectorImpl

abstract class SelectorImpl extends AbstractSelector
{
    protected Set selectedKeys;//就绪key集合，即已经操作事件准备就绪的选择key
    protected HashSet keys;//与选择器关联的key集合
    private Set publicKeys;//外部访问key集合的代理
    private Set publicSelectedKeys;//外部访问就绪key集合代理
        protected SelectorImpl(SelectorProvider selectorprovider)
    {
        super(selectorprovider);
	//初始化就绪key集合和key集合
        keys = new HashSet();
        selectedKeys = new HashSet();
        if(Util.atBugLevel("1.4"))
        {
            publicKeys = keys;
            publicSelectedKeys = selectedKeys;
        } else
        {
	    //将当前key集合包装成不可修改的集合publicKes
            publicKeys = Collections.unmodifiableSet(keys);
	    //将就绪key集合包装成容量固定的集合
            publicSelectedKeys = Util.ungrowableSet(selectedKeys);
        }
    }
}

再来看构造的在bugLevel为1.4的情况下，就绪key和key集合的代理集合初始化分2步看：
1.BugLevel为1.4

if(Util.atBugLevel("1.4"))
    {
        publicKeys = keys;
        publicSelectedKeys = selectedKeys;
    }

2.BugLevel不为1.4

 else
        {
	    //将当前key集合包装成不可修改的集合publicKes
            publicKeys = Collections.unmodifiableSet(keys);
	    //将就绪key集合包装成容量固定的集合
            publicSelectedKeys = Util.ungrowableSet(selectedKeys);
        }

//Util,nio通道工具类，从定义来看应该是缓冲区工具

class Util
{
    private static ThreadLocal localSelector = new ThreadLocal();
    private static ThreadLocal localSelectorWrapper = new ThreadLocal();
    private static Unsafe unsafe = Unsafe.getUnsafe();
    private static int pageSize = -1;
    private static volatile Constructor directByteBufferConstructor = null;
    private static volatile Constructor directByteBufferRConstructor = null;
    private static volatile String bugLevel = null;
    private static boolean loaded = false;
    static final boolean $assertionsDisabled = !sun/nio/ch/Util.desiredAssertionStatus();
    static 
    {
        //通道IO工具
        TEMP_BUF_POOL_SIZE = IOUtil.IOV_MAX;
    }
}

//通道IO工具

class IOUtil
{
    ...,这里省略一些方法，用到的时候再讲，主要是读写Socket
    static native boolean randomBytes(byte abyte0[]);
    static native long makePipe(boolean flag);
    static native boolean drain(int i)
        throws IOException;
    //配置阻塞模式
    static native void configureBlocking(FileDescriptor filedescriptor, boolean flag)
        throws IOException;
   //获取文件描述（Socket）的值
    static native int fdVal(FileDescriptor filedescriptor);
    //设置文件描述的值
    static native void setfdVal(FileDescriptor filedescriptor, int i);
    static native int iovMax();
    static native void initIDs();
    static final int IOV_MAX = iovMax();
    static final boolean $assertionsDisabled = !sun/nio/ch/IOUtil.desiredAssertionStatus();
    static 
    {
        Util.load();
    }
}

上面两个工具类我们在以后遇到的时候再讲，粗略地看一了，Util为nio的缓冲区工具，IOUtil为通道IO工具。
再回到就绪key和key集合的代理集合初始化的第一点：

if(Util.atBugLevel("1.4"))
    {
        publicKeys = keys;
        publicSelectedKeys = selectedKeys;
    } 

//Util

static boolean atBugLevel(String s)
    {
        if(bugLevel == null)
        {
            if(!VM.isBooted())
	        //如果虚拟器没启动，则返回false
                return false;
	    //在当前线程访问控制权限的环境下，获取系统属性sun.nio.ch.bugLevel
            String s1 = (String)AccessController.doPrivileged(new GetPropertyAction("sun.nio.ch.bugLevel"));
            bugLevel = s1 == null ? "" : s1;
        }
        return bugLevel.equals(s);
    }

关于bugLevel的相关连接：
Sun GlassFish Enterprise Server v3 Release Notes：
https://docs.oracle.com/cd/E19226-01/820-7688/6niu9p8i3/index.html
Use of the bug level variable  -Dsun.nio.ch.bugLevel=1.4：
https://community.oracle.com/thread/1240510
从上面来看bugLevel对应的是虚拟机启动的参数配置sun.nio.ch.bugLevel，
由于在nio包在1.4时加入，包中有一个bug问题，

"java.lang.NullPointerException
at sun.nio.ch.Util.atBugLevel(Util.java:326)
at sun.nio.ch.SelectorImpl.<init>(SelectorImpl.java:40)
at sun.nio.ch.WindowsSelectorImpl.<init>(WindowsSelectorImpl.java:104)
at sun.nio.ch.WindowsSelectorProvider.openSelector(WindowsSelectorProvider.java:26)
at java.nio.channels.Selector.open(Selector.java:209)

这个bug在jdk1.5中存在，直到jdk1.7才修复。
从上面的这些信息来看bugLevel应该是标记nio存在bug情况的jdk版本，
如果有不同的理解，可以给我留言。

atBugLevel方法有两点关注：
a.判断虚拟机是否启动
b.获取虚拟机参数sun.nio.ch.bugLevel
先看第一点
a.判断虚拟机是否启动

package sun.misc;
import java.util.Properties;

// Referenced classes of package sun.misc:
//            OSEnvironment, VMNotification

public class VM
{
    public VM()
    {
    }
    //下面这些变量，暂时不选关注，以后有时间，
    //我们在看，只需要看到的虚拟机是否启动booted
    private static boolean suspended = false;
    /**
     * @deprecated Field STATE_GREEN is deprecated
     */
    public static final int STATE_GREEN = 1;
    /**
     * @deprecated Field STATE_YELLOW is deprecated
     */
    public static final int STATE_YELLOW = 2;
    /**
     * @deprecated Field STATE_RED is deprecated
     */
    public static final int STATE_RED = 3;
    private static volatile boolean booted = false;
    private static long directMemory = 67108864L;/64M
    private static boolean pageAlignDirectMemory;
    private static boolean defaultAllowArraySyntax;
    private static boolean allowArraySyntax;
    private static final Properties savedProps = new Properties();
    private static volatile int finalRefCount = 0;
    private static volatile int peakFinalRefCount = 0;
    private static final int JVMTI_THREAD_STATE_ALIVE = 1;
    private static final int JVMTI_THREAD_STATE_TERMINATED = 2;
    private static final int JVMTI_THREAD_STATE_RUNNABLE = 4;
    private static final int JVMTI_THREAD_STATE_BLOCKED_ON_MONITOR_ENTER = 1024;
    private static final int JVMTI_THREAD_STATE_WAITING_INDEFINITELY = 16;
    private static final int JVMTI_THREAD_STATE_WAITING_WITH_TIMEOUT = 32;
    static 
    {
        defaultAllowArraySyntax = false;
        allowArraySyntax = defaultAllowArraySyntax;
        initialize();
    }
    private static native void initialize();
    public static void booted()
    {
        booted = true;
    }
    //VM是否启动
    public static boolean isBooted()
    {
        return booted;
    }
}

b.获取虚拟机参数sun.nio.ch.bugLevel
//GetPropertyAction，获取系统属性Action

package sun.security.action;
import java.security.PrivilegedAction;
public class GetPropertyAction
    implements PrivilegedAction
{
    private String theProp;
    private String defaultVal;
    public GetPropertyAction(String s)
    {
        theProp = s;
    }
    public GetPropertyAction(String s, String s1)
    {
        theProp = s;
        defaultVal = s1;
    }
    //获取系统属性，为空返回默认属性值
    public String run()
    {
        String s = System.getProperty(theProp);
        return s != null ? s : defaultVal;
    }
    public volatile Object run()
    {
        return run();
    }
}

从上面一段分析可以看出，如果nio包的JDK版本存在bug问题，则就绪key和key集合的代理集合直接引用就绪key和key集合。
再回到就绪key和key集合的代理集合初始化的第二点：
2.BugLevel不为1.4

else
   {
      //将当前key集合包装成不可修改的集合publicKes
       publicKeys = Collections.unmodifiableSet(keys);
      //将就绪key集合包装成容量固定的集合
       publicSelectedKeys = Util.ungrowableSet(selectedKeys);
   }

将当前key集合包装成不可修改的集合publicKes，这个就不用说了，我们以前在java的集合综述篇中有说。我们主要将下一点将就绪key集合包装成容量固定的集合，
//Util

 static Set ungrowableSet(Set set)
    {
        return new Set(set) {
             final Set val$s;
            {
                s = set;
                super();
            }
            public int size()
            {
                return s.size();
            }
            public boolean isEmpty()
            {
                return s.isEmpty();
            }
            public boolean contains(Object obj)
            {
                return s.contains(obj);
            }
            ...
            public Iterator iterator()
            {
                return s.iterator();
            }
            ...
            public void clear()
            {
                s.clear();
            }

            public boolean remove(Object obj)
            {
                return s.remove(obj);
            }

            public boolean containsAll(Collection collection)
            {
                return s.containsAll(collection);
            }

            public boolean removeAll(Collection collection)
            {
                return s.removeAll(collection);
            }

            public boolean retainAll(Collection collection)
            {
                return s.retainAll(collection);
            }
	    //集合不可添加元素
            public boolean add(Object obj)
            {
                throw new UnsupportedOperationException();
            }
            public boolean addAll(Collection collection)
            {
                throw new UnsupportedOperationException();
            }
        };
    }

从上面来看
Util.ungrowableSet(Set set)方法，对集合Set进行简单的封装，移除迭代，比较等操作
直接委托给原始的Set集合，只是封装后的集合不允许添加元素，但可以移除，查询操作。
这段话是不是很熟悉，在Selector定义的文章，Java Doc有说就绪key集合SelectedKeys的
这些属性。
小节一下就绪key和key集合的初始化：
如果nio包的JDK版本存在bug问题，则就绪key和key集合的代理集合直接引用就绪key和key集合。否则将当前key集合包装成不可修改的代理集合publicKes，将就绪key集合包装成容量固定的集合publicSelectedKeys

再来看获取就绪key和key集合
//key集合

public Set keys()
 {
     if(!isOpen() && !Util.atBugLevel("1.4"))
         throw new ClosedSelectorException();
     else
         return publicKeys;
 }

//就绪key

 public Set selectedKeys()
 {
     if(!isOpen() && !Util.atBugLevel("1.4"))
         throw new ClosedSelectorException();
     else
         return publicSelectedKeys;
 }

从上面来看，其他线程获取选择器的就绪key和key集合，实际上返回的是
key集合的代理publicKeys和就绪key集合的代理publicSelectedKeys。

再来看几个选择操作：

 public int select()
        throws IOException
    {
        //委托给select(long l)
        return select(0L);
    }
 public int select(long l)
        throws IOException
    {
        if(l < 0L)
	    //负数抛出异常
            throw new IllegalArgumentException("Negative timeout");
        else
	    //委托给lockAndDoSelect(long l)
            return lockAndDoSelect(l != 0L ? l : -1L);
    }
 public int selectNow()
        throws IOException
    {
         //委托给lockAndDoSelect(long l)
        return lockAndDoSelect(0L);
    }

再来看lockAndDoSelect方法：

private int lockAndDoSelect(long l)
        throws IOException
    {
        SelectorImpl selectorimpl = this;
        JVM INSTR monitorenter ;
        if(!isOpen())
            throw new ClosedSelectorException();
	//取得key集合代理
        Set set = publicKeys;
        JVM INSTR monitorenter ;
	//取得就绪key代理
        Set set1 = publicSelectedKeys;
        JVM INSTR monitorenter ;
	//实际选择操作代理
        return doSelect(l);
        Exception exception;
        exception;
        throw exception;
        Exception exception1;
        exception1;
        throw exception1;
        Exception exception2;
        exception2;
        throw exception2;
    }

在上面的方法中有一些：

 JVM INSTR monitorenter ;
 ...
 Exception exception;
 exception;
 throw exception;

这个是什么意思，不是很理解，找了一下资料
JVM INSTR:
https://coderanch.com/t/385088/java/JVM-INSTR
JVM INSTR monitorenter and JVM INSTR monitorexit:
http://stackoverflow.com/questions/9547975/jvm-instr-monitorenter-and-jvm-instr-monitorexit
按照资料的说法，上述的这标记是JVM规范，实际相当与同步语句块（synchronized）；
JVM INSTR monitorenter进入同步，JVM INSTR monitorexit退出同步；

Exception exception;
exception;
throw exception;

相等于

catch(Exception exception)
{
    throw exception;
}

再来看实际选择操作
//实际选择操作

return doSelect(l);

//待父类扩展，我们在下一篇文章中再看

protected abstract int doSelect(long l)
        throws IOException;

select方法的3中操作形式，实际上委托给为lockAndDoSelect方法，方法实际上是同步的，
可安全访问，获取key集合代理publicKeys和就绪key代理集合publicSelectedKeys，然后交给
doSelect(long l)方法，这个方法为抽象方法，待子类扩展。
在AbstractSelector的close方法，最有调用了implCloseSelector；
下面来看关闭选择器的实际操作implCloseSelector

 public void implCloseSelector()
        throws IOException
    {
        wakeup();
        synchronized(this)
        {
            synchronized(publicKeys)
            {
                synchronized(publicSelectedKeys)
                {
                    implClose();
                }
            }
        }
    }

  

 //唤醒等待选择操作的线程，待子类扩展
    public abstract Selector wakeup();

   

//完成实际的关闭选择器工作
    protected abstract void implClose()
        throws IOException;

从implCloseSelector方法来看，首先唤醒等待选择操作的线程，唤醒方法wakeup待实现，
同步选择器，就绪key和key集合的代理publicKeys，publicSelectedKeys，调用implClose完成实际的关闭通道工作，待子类实现。
再来看注册通道到选择器：

 protected final SelectionKey register(AbstractSelectableChannel abstractselectablechannel, int i, Object obj)
    {
        if(!(abstractselectablechannel instanceof SelChImpl))
	    //如果可选择通道不是SelChImpl的实例，则抛出IllegalSelectorException
            throw new IllegalSelectorException();
	//更具可选择通道和选择器创建选择key
        SelectionKeyImpl selectionkeyimpl = new SelectionKeyImpl((SelChImpl)abstractselectablechannel, this);
        //设置key的附加物
	selectionkeyimpl.attach(obj);
	//同步key集合代理
        synchronized(publicKeys)
        {
	    //完成实际的注册工作
            implRegister(selectionkeyimpl);
        }
	//设置key的兴趣事件集
        selectionkeyimpl.interestOps(i);
        return selectionkeyimpl;
    }

  

 //待子类实现
    protected abstract void implRegister(SelectionKeyImpl selectionkeyimpl);

从可选通道注册方法来看，首先注册的通道必须是AbstractSelectableChannel类型，并且是SelChImpl实例。更具可选择通道和选择器构造选择key，设置选择key的附加物，同步key集合代理，调用implRegister方法完成实际的注册工作，implRegister方法待子类实现。
//再来看处理反注册队列，现在看，还不能完全理解此方法的意思，在后面的文章，
我们会继续说，现在不能能完全看到，只以目前的能力，阅读以下代码，理解多少是多少，
因为里面牵涉到JVM规范，不知道说的正不正确，我只以目前的能力来阅读代码。

 void processDeregisterQueue()
        throws IOException
    {
        Set set = cancelledKeys();//获取取消key集合
        Set set1 = set;
        JVM INSTR monitorenter ;//进入同步语句块
        Iterator iterator;
        if(set.isEmpty())
            break MISSING_BLOCK_LABEL_110;
        iterator = set.iterator();
_L2://遍历取消key集合
        SelectionKeyImpl selectionkeyimpl;
        if(!iterator.hasNext())
            break; /* Loop/switch isn't completed */
        selectionkeyimpl = (SelectionKeyImpl)iterator.next();
        try
        {
	    //完成实际取消选择key的反注册
            implDereg(selectionkeyimpl);
        }
        catch(SocketException socketexception)
        {
            IOException ioexception = new IOException("Error deregistering key");
            ioexception.initCause(socketexception);
            throw ioexception;
        }
	//从取消key集合中移除已经反注册的取消选择key
        iterator.remove();
        if(true) goto _L2; else goto _L1
_L1:
        break MISSING_BLOCK_LABEL_110;
        Exception exception;
        exception;
        iterator.remove();
        throw exception;
        Exception exception1;
        exception1;
        throw exception1;
    }

 

 //完成SelectionKey的实际反注册工作
    protected abstract void implDereg(SelectionKeyImpl selectionkeyimpl)
        throws IOException;

从processDeregisterQueue方法来看，主要是遍历取消key集合，反注册取消key，实际的
反注册工作由implDereg方法，implDereg方法待子类扩展。
成功，则从集合中移除。

这个方法，待子类实现，我们以后再看

void putEventOps(SelectionKeyImpl selectionkeyimpl, int i)
{
   }

总结：
     SelectorImpl有4个集合分别为就绪key集合，key集合，key集合的代理publicKeys及就绪key集合的代理publicSelectedKeys；实际是两个集合就绪key集合和key集合，publicSelectedKeys和publicKeys是其他线程访问上述两个集合的代理。
     SelectorImpl构造的时候，初始化选择器提供者SelectorProvider，创建就绪key集合和key集合，然后初始化就绪key和key集合的代理，初始化过程为，如果nio包的JDK版本存在bug问题，则就绪key和key集合的代理集合直接引用就绪key和key集合。否则将当前key集合包装成不可修改的代理集合publicKes，将就绪key集合包装成容量固定的集合publicSelectedKeys。
其他线程获取选择器的就绪key和key集合，实际上返回的是key集合的代理publicKeys和就绪key集合的代理publicSelectedKeys。
     select方法的3中操作形式，实际上委托给为lockAndDoSelect方法，方法实际上是同步的，可安全访问，获取key集合代理publicKeys和就绪key代理集合publicSelectedKeys，然后交给doSelect(long l)方法，这个方法为抽象方法，待子类扩展。实际的关闭选择器操作implCloseSelector方法，首先唤醒等待选择操作的线程，唤醒方法wakeup待实现，同步选择器，就绪key和key集合的代理publicKeys，publicSelectedKeys，调用implClose完成实际的关闭通道工作，待子类实现。
     可选通道注册方法，首先注册的通道必须是AbstractSelectableChannel类型，并且是SelChImpl实例。更具可选择通道和选择器构造选择key，设置选择key的附加物，同步key集合代理，调用implRegister方法完成实际的注册工作，implRegister方法待子类实现。
     processDeregisterQueue方法，主要是遍历取消key集合，反注册取消key，实际的反注册工作由implDereg方法，implDereg方法待子类扩展。成功，则从集合中移除。


附：这部分只作为扩展，没有特别的解析，设计，只是贴出代码，有兴趣可以看一下
//VM

package sun.misc;

import java.util.Properties;

// Referenced classes of package sun.misc:
//            OSEnvironment, VMNotification

public class VM
{ 
     private static boolean suspended = false;
    /**
     * @deprecated Field STATE_GREEN is deprecated
     */
    public static final int STATE_GREEN = 1;
    /**
     * @deprecated Field STATE_YELLOW is deprecated
     */
    public static final int STATE_YELLOW = 2;
    /**
     * @deprecated Field STATE_RED is deprecated
     */
    public static final int STATE_RED = 3;
    private static volatile boolean booted = false;
    private static long directMemory = 67108864L;
    private static boolean pageAlignDirectMemory;
    private static boolean defaultAllowArraySyntax;
    private static boolean allowArraySyntax;
    private static final Properties savedProps = new Properties();
    private static volatile int finalRefCount = 0;
    private static volatile int peakFinalRefCount = 0;
    private static final int JVMTI_THREAD_STATE_ALIVE = 1;
    private static final int JVMTI_THREAD_STATE_TERMINATED = 2;
    private static final int JVMTI_THREAD_STATE_RUNNABLE = 4;
    private static final int JVMTI_THREAD_STATE_BLOCKED_ON_MONITOR_ENTER = 1024;
    private static final int JVMTI_THREAD_STATE_WAITING_INDEFINITELY = 16;
    private static final int JVMTI_THREAD_STATE_WAITING_WITH_TIMEOUT = 32;
    static 
    {
        defaultAllowArraySyntax = false;
        allowArraySyntax = defaultAllowArraySyntax;
        initialize();
    }
    public VM()
    {
    } 
    private static native void initialize();
     public static void booted()
    {
        booted = true;
    }
    public static boolean isBooted()
    {
        return booted;
    }
    public static long maxDirectMemory()
    {
        return directMemory;
    }
    public static boolean isDirectMemoryPageAligned()
    {
        return pageAlignDirectMemory;
    }
     public static void initializeOSEnvironment()
    {
        if(!booted)
            OSEnvironment.initialize();
    }
    public static int getFinalRefCount()
    {
        return finalRefCount;
    }
    public static int getPeakFinalRefCount()
    {
        return peakFinalRefCount;
    }
    public static void addFinalRefCount(int i)
    {
        finalRefCount += i;
        if(finalRefCount > peakFinalRefCount)
            peakFinalRefCount = finalRefCount;
    }
    public static Thread.State toThreadState(int i)
    {
        if((i & 4) != 0)
            return Thread.State.RUNNABLE;
        if((i & 1024) != 0)
            return Thread.State.BLOCKED;
        if((i & 16) != 0)
            return Thread.State.WAITING;
        if((i & 32) != 0)
            return Thread.State.TIMED_WAITING;
        if((i & 2) != 0)
            return Thread.State.TERMINATED;
        if((i & 1) == 0)
            return Thread.State.NEW;
        else
            return Thread.State.RUNNABLE;
    }
    public static boolean allowArraySyntax()
    {
        return allowArraySyntax;
    }
    /**
     * @deprecated Method threadsSuspended is deprecated
     */
    public static boolean threadsSuspended()
    {
        return suspended;
    }
    public static boolean allowThreadSuspension(ThreadGroup threadgroup, boolean flag)
    {
        return threadgroup.allowThreadSuspension(flag);
    }
    /**
     * @deprecated Method suspendThreads is deprecated
     */
    public static boolean suspendThreads()
    {
        suspended = true;
        return true;
    }
    /**
     * @deprecated Method unsuspendThreads is deprecated
     */
    public static void unsuspendThreads()
    {
        suspended = false;
    }
    /**
     * @deprecated Method unsuspendSomeThreads is deprecated
     */
    public static void unsuspendSomeThreads()
    {
    }
    /**
     * @deprecated Method getState is deprecated
     */
    public static final int getState()
    {
        return 1;
    }
    /**
     * @deprecated Method registerVMNotification is deprecated
     */
    public static void registerVMNotification(VMNotification vmnotification)
    {
    
    /**
     * @deprecated Method asChange is deprecated
     */
    public static void asChange(int i, int j)
    {
    }
    /**
     * @deprecated Method asChange_otherthread is deprecated
     */
    public static void asChange_otherthread(int i, int j)
    {
    }
    public static String getSavedProperty(String s)
    {
        if(savedProps.isEmpty())
            throw new IllegalStateException("Should be non-empty if initialized");
        else
            return savedProps.getProperty(s);
    }
    public static void saveAndRemoveProperties(Properties properties)
    {
        if(booted)
            throw new IllegalStateException("System initialization has completed");
        savedProps.putAll(properties);
        String s = (String)properties.remove("sun.nio.MaxDirectMemorySize");
        if(s != null)
            if(s.equals("-1"))
            {
                directMemory = Runtime.getRuntime().maxMemory();
            } else
            {
                long l = Long.parseLong(s);
                if(l > -1L)
                    directMemory = l;
            }
        s = (String)properties.remove("sun.nio.PageAlignDirectMemory");
        if("true".equals(s))
            pageAlignDirectMemory = true;
        s = properties.getProperty("sun.lang.ClassLoader.allowArraySyntax");
        allowArraySyntax = s != null ? Boolean.parseBoolean(s) : defaultAllowArraySyntax;
        properties.remove("java.lang.Integer.IntegerCache.high");
        properties.remove("sun.zip.disableMemoryMapping");
        properties.remove("sun.java.launcher.diag");
    }
}

在代码中经常看到这个语句JVM INSTR monitorenter ;来看一下JVM：
只贴出源码，暂时放在这以后再啃。

class JVM
{
    JVM()
    {
    }
    static long activate(String s, DTraceProvider adtraceprovider[])
    {
        return activate0(s, adtraceprovider);
    }
    static void dispose(long l)
    {
        dispose0(l);
    }
    static boolean isEnabled(Method method)
    {
        return isEnabled0(method);
    }
    static boolean isSupported()
    {
        return isSupported0();
    }
    static Class defineClass(ClassLoader classloader, String s, byte abyte0[], int i, int j)
    {
        return defineClass0(classloader, s, abyte0, i, j);
    }
    private static native long activate0(String s, DTraceProvider adtraceprovider[]);
    private static native void dispose0(long l);
    private static native boolean isEnabled0(Method method);
    private static native boolean isSupported0();
    private static native Class defineClass0(ClassLoader classloader, String s, byte abyte0[], int i, int j);
    static 
    {
        AccessController.doPrivileged(new LoadLibraryAction("jsdt"));
    }
}

来看这一句：

 static 
    {
        AccessController.doPrivileged(new LoadLibraryAction("jsdt"));
    }

jsdt:JavaScript Development Tools (JSDT)：
http://www.eclipse.org/webtools/jsdt/
//LoadLibraryAction

package sun.security.action;
import java.security.PrivilegedAction;
public class LoadLibraryAction
    implements PrivilegedAction
{

    public LoadLibraryAction(String s)
    {
        theLib = s;
    }

    public Void run()
    {

       //系统加载lib库
        System.loadLibrary(theLib);
        return null;
    }

    public volatile Object run()
    {
        return run();
    }

    private String theLib;
}

//System

/**
     * Loads the system library specified by the <code>libname</code>
     * argument. The manner in which a library name is mapped to the
     * actual system library is system dependent.
     * <p>
     * The call <code>System.loadLibrary(name)</code> is effectively
     * equivalent to the call
     * <blockquote><pre>
     * Runtime.getRuntime().loadLibrary(name)
     * </pre></blockquote>
     *
     * @param      libname   the name of the library.
     * @exception  SecurityException  if a security manager exists and its
     *             <code>checkLink</code> method doesn't allow
     *             loading of the specified dynamic library
     * @exception  UnsatisfiedLinkError  if the library does not exist.
     * @exception  NullPointerException if <code>libname</code> is
     *             <code>null</code>
     * @see        java.lang.Runtime#loadLibrary(java.lang.String)
     * @see        java.lang.SecurityManager#checkLink(java.lang.String)
     */
    public static void loadLibrary(String libname) {
        Runtime.getRuntime().loadLibrary0(getCallerClass(), libname);
    }

//Runtime

synchronized void loadLibrary0(Class fromClass, String libname) {
        SecurityManager security = System.getSecurityManager();
        if (security != null) {
            security.checkLink(libname);
        }
        if (libname.indexOf((int)File.separatorChar) != -1) {
            throw new UnsatisfiedLinkError(
    "Directory separator should not appear in library name: " + libname);
        }
        ClassLoader.loadLibrary(fromClass, libname, false);
    }

//ClassLoader

// Invoked in the java.lang.Runtime class to implement load and loadLibrary.
    static void loadLibrary(Class fromClass, String name,
                            boolean isAbsolute) {
        ClassLoader loader =
            (fromClass == null) ? null : fromClass.getClassLoader();
        if (sys_paths == null) {
            usr_paths = initializePath("java.library.path");
            sys_paths = initializePath("sun.boot.library.path");
        }
        if (isAbsolute) {
            if (loadLibrary0(fromClass, new File(name))) {
                return;
            }
            throw new UnsatisfiedLinkError("Can't load library: " + name);
        }
        if (loader != null) {
            String libfilename = loader.findLibrary(name);
            if (libfilename != null) {
                File libfile = new File(libfilename);
                if (!libfile.isAbsolute()) {
                    throw new UnsatisfiedLinkError(
    "ClassLoader.findLibrary failed to return an absolute path: " + libfilename);
                }
                if (loadLibrary0(fromClass, libfile)) {
                    return;
                }
                throw new UnsatisfiedLinkError("Can't load " + libfilename);
            }
        }
        for (int i = 0 ; i < sys_paths.length ; i++) {
            File libfile = new File(sys_paths[i], System.mapLibraryName(name));
            if (loadLibrary0(fromClass, libfile)) {
                return;
            }
        }
        if (loader != null) {
            for (int i = 0 ; i < usr_paths.length ; i++) {
                File libfile = new File(usr_paths[i],
                                        System.mapLibraryName(name));
                if (loadLibrary0(fromClass, libfile)) {
                    return;
                }
            }
        }
        // Oops, it failed
        throw new UnsatisfiedLinkError("no " + name + " in java.library.path");
    }