文件通道解析一（读写操作，通道数据传输等）

Reference定义（PhantomReference，Cleaner）:[url]http://donald-draper.iteye.com/blog/2371661[/url]
FileChanne定义：[url]http://donald-draper.iteye.com/blog/2374149[/url]
文件读写方式简单综述:[url]http://donald-draper.iteye.com/blog/2374237[/url]
文件读写方式简单综述后续（文件，流构造）:[url]http://donald-draper.iteye.com/blog/2374294[/url]
文件通道创建方式综述：[url]http://donald-draper.iteye.com/blog/2374537[/url]
[size=medium][b]引言：[/b][/size]
获取区文件的通道一共有四种，第一种从FileOutputStream获取写模式文件通道，第二种从FileInputStream获取读模式文件通道，第三种从RandomAccessFile获取读写模式文件通道，第四种调用FileChannelImpl#open方法，这个过程首先从参数文件Path（WindowsPath）获取文件系统的提供者，实际为WindowsFileSystemProvider，委托给WindowsFileSystemProvider创建文件通道，WindowsFileSystemProvider根据WindowsPath和，文件属性WindowsSecurityDescriptor（FileAttribute[]），和打开选项集，将实际创建通道任务交给WindowsChannelFactory，WindowsChannelFactory首先将打开选项装换为内部的通道配置标志Flags（读写模式（read，writer），同步方式（sync，dsync），append等），然后根据Flags,和Path信息等信息创建文件，创建文件实际由WindowsNativeDispatcher完成。WindowsNativeDispatcher首先从线程本地缓存获取NativeBuffer，将Path信息放在NativeBuffer中，然后创建文件，创建后，将NativeBuffer释放，即放入线程本地缓存，以便重用。具体选择哪种方式，根据需要选择。
从今天开始，文件通道的具体实现FileChanneImpl

public class FileChannelImpl extends FileChannel
{
 private static final long allocationGranularity = initIDs();
    private final FileDispatcher nd;//文件分发器
    private final FileDescriptor fd;//文件描述
    private final boolean writable;//通道是否可写
    private final boolean readable;//通道是否可读
    private final boolean append;//通道写是否为追加模式
    private final Object parent;//创建通道的对象
    //下面这些属性，暂时不能确定是具体什么意思，只能先从字面上去理解，
    //这里我们先放在这里，后面用到在讲
    private final NativeThreadSet threads = new NativeThreadSet(2);
    private final Object positionLock = new Object();//文件读写是位置锁
    private static volatile boolean transferSupported = true;//是否支持通道传输
    private static volatile boolean pipeSupported = true;//是否支持管道
    private static volatile boolean fileSupported = true;//是否支持文件
    private static final long MAPPED_TRANSFER_SIZE = 8388608L;/
    private static final int TRANSFER_SIZE = 8192;
    private static final int MAP_RO = 0;
    private static final int MAP_RW = 1;
    private static final int MAP_PV = 2;
    private volatile FileLockTable fileLockTable;//存放文件锁的Table
    private static boolean isSharedFileLockTable;//文件锁table是否为共享
    private static volatile boolean propertyChecked;
    static final boolean $assertionsDisabled = !sun/nio/ch/FileChannelImpl.desiredAssertionStatus();

    static 
    {
        //加载nio，net资源库
        Util.load();
    }
     private static native long initIDs();
 }

来看构造

 public static FileChannel open(FileDescriptor filedescriptor, boolean flag, boolean flag1, Object obj)
    {
        return new FileChannelImpl(filedescriptor, flag, flag1, false, obj);
    }

    public static FileChannel open(FileDescriptor filedescriptor, boolean flag, boolean flag1, boolean flag2, Object obj)
    {
        return new FileChannelImpl(filedescriptor, flag, flag1, flag2, obj);
    }
    //创建FileChannelImpl
    private FileChannelImpl(FileDescriptor filedescriptor, boolean flag, boolean flag1, boolean flag2, Object obj)
    {
        fd = filedescriptor;
        readable = flag;
        writable = flag1;
        append = flag2;
        parent = obj;
        nd = new FileDispatcherImpl(flag2);
    }

从上面可以看出文件通道的构造，主要是初始化通道读写模式，追加模式append及文件分发器
FileDispatcherImpl。

public int write(ByteBuffer bytebuffer)
        throws IOException
    {
        ensureOpen();//确保通道打开
        if(!writable)//如果通道不可写，则抛出不可写异常
            throw new NonWritableChannelException();
        Object obj = positionLock;//获取position锁
        JVM INSTR monitorenter ;//进入同步
        int i;
        int j;
        i = 0;
        j = -1;
        int k;
        begin();
	...
        j = threads.add();
	//看到这里是不是很熟悉，在socketChannel和DatagramChannel都有讲过，这里不再讲
	//只不过nd为FileDispatcherImpl
        do
            i = IOUtil.write(fd, bytebuffer, -1L, nd, positionLock);
        while(i == -3 && isOpen());
	...
    }

    public long write(ByteBuffer abytebuffer[], int i, int j)
        throws IOException
    {
        if(i < 0 || j < 0 || i > abytebuffer.length - j)
            throw new IndexOutOfBoundsException();
        ensureOpen();
        if(!writable)
            throw new NonWritableChannelException();
        Object obj = positionLock;
        JVM INSTR monitorenter ;
        ...
	//看到这里是不是很熟悉，在socketChannel和DatagramChannel都有讲过，这里不再讲
	//只不过nd为FileDispatcherImpl
        do
            l = IOUtil.write(fd, abytebuffer, i, j, nd);
        while(l == -3L && isOpen());
	...
}
public int read(ByteBuffer bytebuffer)
        throws IOException
    {
        ensureOpen();
        if(!readable)
            throw new NonReadableChannelException();
        Object obj = positionLock;
        JVM INSTR monitorenter ;
        int i;
        int j;
        i = 0;
        j = -1;
        int k;
        ...
	//看到这里是不是很熟悉，在socketChannel和DatagramChannel都有讲过，这里不再讲
	//只不过nd为FileDispatcherImpl
        do
            i = IOUtil.read(fd, bytebuffer, -1L, nd, positionLock);
        while(i == -3 && isOpen());
	...
}
 public long read(ByteBuffer abytebuffer[], int i, int j)
        throws IOException
    {
        if(i < 0 || j < 0 || i > abytebuffer.length - j)
            throw new IndexOutOfBoundsException();
        ensureOpen();
        if(!readable)
            throw new NonReadableChannelException();
        Object obj = positionLock;
        JVM INSTR monitorenter ;
        ...
        do
            l = IOUtil.read(fd, abytebuffer, i, j, nd);
        while(l == -3L && isOpen());
       ...
    }

从上面可以看出文件通道的读写操作的实际操作都是由IOUtil协助FileDispatcherImpl完成完成，这一点和SocketChannel通道思路相似。

public long transferTo(long l, long l1, WritableByteChannel writablebytechannel)
        throws IOException
    {
        ensureOpen();//确保当前通道打开
        if(!writablebytechannel.isOpen())//如果目的通道，不可写则抛出ClosedChannelException
            throw new ClosedChannelException();
        if(!readable)//如果当前通道不可读，则抛出NonReadableChannelException
            throw new NonReadableChannelException();
	//如果目的通道为FileChannelImpl，且不可写，则抛出NonWritableChannelException
        if((writablebytechannel instanceof FileChannelImpl) && !((FileChannelImpl)writablebytechannel).writable)
            throw new NonWritableChannelException();
        if(l < 0L || l1 < 0L)//检查position和count参数
            throw new IllegalArgumentException();
	//获取当前文件通道size
        long l2 = size();
        if(l > l2)//如果position大于当前文件size，返回0
            return 0L;
        int i = (int)Math.min(l1, 2147483647L);//获取需要读取字节数，为count参数和2^31-1当中的最小的一个
        if(l2 - l < (long)i)
            i = (int)(l2 - l);//需要读取的字节数
        long l3;
        if((l3 = transferToDirectly(l, i, writablebytechannel)) >= 0L)
            return l3;
        if((l3 = transferToTrustedChannel(l, i, writablebytechannel)) >= 0L)
            return l3;
        else
            return transferToArbitraryChannel(l, i, writablebytechannel);
    }

transferTo方法有3点要关注
1

if((l3 = transferToDirectly(l, i, writablebytechannel)) >= 0L)
    return l3;

private long transferToDirectly(long l, int i, WritableByteChannel writablebytechannel)
        throws IOException
    {
        int j;
        int k;
        long l1;
        int i1;
        if(!transferSupported)//不支持通道传输，
            return -4L;
        FileDescriptor filedescriptor = null;
	//这一段的目的就是获取目的通道文件描述符
        if(writablebytechannel instanceof FileChannelImpl)
        {
            if(!fileSupported)//如果通道为文件通道，但不支持文件
                return -6L;
            filedescriptor = ((FileChannelImpl)writablebytechannel).fd;
        } else
        if(writablebytechannel instanceof SelChImpl)
        {
	    //如果目的通道为SinkChannelImpl，且不支持管道
            if((writablebytechannel instanceof SinkChannelImpl) && !pipeSupported)
                return -6L;
            filedescriptor = ((SelChImpl)writablebytechannel).getFD();
        }
        if(filedescriptor == null)
            return -4L;
        j = IOUtil.fdVal(fd);//获取当前文件通道文件描述符的值
        k = IOUtil.fdVal(filedescriptor);//获取目的通道文件描述符的值
        if(j == k)//当前通道与目的通道相同
            return -4L;
        ...
        do
            l1 = transferTo0(j, l, i, k);
        while(l1 == -3L && isOpen());
        ...
    }
    private native long transferTo0(int i, long l, long l1, int j);

2.

if((l3 = transferToTrustedChannel(l, i, writablebytechannel)) >= 0L)
    return l3;

private long transferToTrustedChannel(long l, long l1, WritableByteChannel writablebytechannel)
        throws IOException
    {
        boolean flag;
        long l2;
	//判断目的通道是否为可选择通道，及socketChannel或DatagramChannel，Pipe（sink，source）
        flag = writablebytechannel instanceof SelChImpl;
	//如果目的通道不是文件通道也不是可选择通道，则返回
        if(!(writablebytechannel instanceof FileChannelImpl) && !flag)
            return -4L;
        l2 = l1;
_L2:
        long l3;
        if(l2 <= 0L)
            break; /* Loop/switch isn't completed */
        l3 = Math.min(l2, 8388608L);//获取读取的size，为count和2^23中间小的一个
	//将当前文件通达映射到内存中
        MappedByteBuffer mappedbytebuffer = map(java.nio.channels.FileChannel.MapMode.READ_ONLY, l, l3);
        int i;
	//直接调用目的通道的write方法将映射文件内存写到通道中。
        i = writablebytechannel.write(mappedbytebuffer);
        if(!$assertionsDisabled && i < 0)
            throw new AssertionError();
        l2 -= i;
        if(flag)
        {
	    //如果目的通道非文件通道，则释放文件通道映射内存空间
            unmap(mappedbytebuffer);
            break; /* Loop/switch isn't completed */
        }
        ...
   }

再来看将通道数据映射到内存和释放映射内存空间

 //将通道数据映射到内存
     public MappedByteBuffer map(java.nio.channels.FileChannel.MapMode mapmode, long l, long l1)
        throws IOException
    {
     ...
      mappedbytebuffer = Util.newMappedByteBufferR(0, 0L, j, null);
      ...
    }
    //释放映射内存空间
     private static void unmap(MappedByteBuffer mappedbytebuffer)
    {
        Cleaner cleaner = ((DirectBuffer)mappedbytebuffer).cleaner();
        if(cleaner != null)
            cleaner.clean();
    }

3.

else
    return transferToArbitraryChannel(l, i, writablebytechannel);

private long transferToArbitraryChannel(long l, int i, WritableByteChannel writablebytechannel)
        throws IOException
    {
        ByteBuffer bytebuffer;
        long l1;
        long l2;
        int j = Math.min(i, 8192);
	//从线程缓存获取临时DirectByteBuffer
        bytebuffer = Util.getTemporaryDirectBuffer(j);
        l1 = 0L;
        l2 = l;
        long l3;
        Util.erase(bytebuffer);
        do
        {
            if(l1 >= (long)i)
                break;
            bytebuffer.limit(Math.min((int)((long)i - l1), 8192));
            int k = read(bytebuffer, l2);
            if(k <= 0)
                break;
            bytebuffer.flip();
	    //调用目的通道的写操作，直接写临时DirectByteBuffer
            int i1 = writablebytechannel.write(bytebuffer);
            l1 += i1;
            if(i1 != k)
                break;
            l2 += i1;
            bytebuffer.clear();
        } while(true);
        l3 = l1;
        Util.releaseTemporaryDirectBuffer(bytebuffer);
        return l3;
        ...
    }

从上面可以看出文件通道传输方法transferTo，首先确保当前文件通道是否打开，是否可读，然后检查目的通道是否关闭，是否可写；然后先调用文件通道本地方法传输通道的数据到目的通道，如果失败，则将文件通道数据，映射到内存MappedByteBuffer，然后调用目的通道的写操作（MappedByteBuffer），如果再失败，则将通道数据，写到DirectByteBuffer中，然后在调用目的通道的写操作（DirectByteBuffer）。
再看文件通道传输方法transferFrom

 public long transferFrom(ReadableByteChannel readablebytechannel, long l, long l1)
        throws IOException
    {
        ensureOpen();//确保当前通道打开
        if(!readablebytechannel.isOpen())//确保源通道打开
            throw new ClosedChannelException();
        if(!writable)//如果当前通道不可写
            throw new NonWritableChannelException();
        if(l < 0L || l1 < 0L)//检查postion和count参数
            throw new IllegalArgumentException();
        if(l > size())//位置大于当前文件size，则直接返回
            return 0L;
	 //如果源通道为文件通道
        if(readablebytechannel instanceof FileChannelImpl)
            return transferFromFileChannel((FileChannelImpl)readablebytechannel, l, l1);
	//其他可读通道
        else
            return transferFromArbitraryChannel(readablebytechannel, l, l1);
    }

这个方法我们需要关注2点
1.

//如果源通道为文件通道
  if(readablebytechannel instanceof FileChannelImpl)
      return transferFromFileChannel((FileChannelImpl)readablebytechannel, l, l1);

private long transferFromFileChannel(FileChannelImpl filechannelimpl, long l, long l1)
        throws IOException
    {
        if(!filechannelimpl.readable)
            throw new NonReadableChannelException();
        Object obj = filechannelimpl.positionLock;
        JVM INSTR monitorenter ;
        long l2;
        long l3;
        long l4;
        long l5;
        l2 = filechannelimpl.position();
        l3 = Math.min(l1, filechannelimpl.size() - l2);
        l4 = l3;
        l5 = l2;
_L2:
        MappedByteBuffer mappedbytebuffer;
        if(l4 <= 0L)
            break; /* Loop/switch isn't completed */
        long l6 = Math.min(l4, 8388608L);
	//将源通道数据映射到内存
        mappedbytebuffer = filechannelimpl.map(java.nio.channels.FileChannel.MapMode.READ_ONLY, l5, l6);
	//委托writer方法
        long l8 = write(mappedbytebuffer, l);
        if(!$assertionsDisabled && l8 <= 0L)
            throw new AssertionError();
        l5 += l8;
        l += l8;
        l4 -= l8;
        unmap(mappedbytebuffer);
        if(true) goto _L2; else goto _L1
        IOException ioexception;
        ioexception;
        if(l4 == l3)
            throw ioexception;
	//读完，则释放通道映射内存
        unmap(mappedbytebuffer);
          goto _L1
        Exception exception;
        exception;
        unmap(mappedbytebuffer);
        throw exception;
_L1:
        long l7;
        l7 = l3 - l4;
	//未读完移动源通道的position
        filechannelimpl.position(l2 + l7);
        return l7;
        Exception exception1;
        exception1;
        throw exception1;
    }

再来看

//委托writer方法
long l8 = write(mappedbytebuffer, l);

public int write(ByteBuffer bytebuffer, long l)
        throws IOException
    {
        ...
	//这段代码又来了，不过此处的nd，为FileDispatcherImpl，与SocketDispatcher没有太多的区别
	只不过多了几个turncate和force等方法而已
        do
            i = IOUtil.write(fd, bytebuffer, l, nd, positionLock);
        while(i == -3 && isOpen());
       ...
    }

//IOUtil

 static int write(FileDescriptor filedescriptor, ByteBuffer bytebuffer, long l, NativeDispatcher nativedispatcher, Object obj)
        throws IOException
    {
        ...
        int i1 = writeFromNativeBuffer(filedescriptor, bytebuffer1, l, nativedispatcher, obj);
        ...
    }

    private static int writeFromNativeBuffer(FileDescriptor filedescriptor, ByteBuffer bytebuffer, long l, NativeDispatcher nativedispatcher, Object obj)
        throws IOException
    {
       ...
        if(l != -1L)
            i1 = nativedispatcher.pwrite(filedescriptor, ((DirectBuffer)bytebuffer).address() + (long)i, k, l, obj);
        else
            i1 = nativedispatcher.write(filedescriptor, ((DirectBuffer)bytebuffer).address() + (long)i, k);
        if(i1 > 0)
            bytebuffer.position(i + i1);
        return i1;
    }

//FileDispatcherImpl

class FileDispatcherImpl extends FileDispatcher
{
   ...
    //这一部分，没有什么好说的，看看就行
  int write(FileDescriptor filedescriptor, long l, int i)
        throws IOException
    {
        return write0(filedescriptor, l, i, append);
    }
     static native int write0(FileDescriptor filedescriptor, long l, int i, boolean flag)
        throws IOException;

    int pwrite(FileDescriptor filedescriptor, long l, int i, long l1, Object obj)
        throws IOException
    {
        Object obj1 = obj;
        JVM INSTR monitorenter ;
        return pwrite0(filedescriptor, l, i, l1);
        Exception exception;
        exception;
        throw exception;
    }
    static native int pwrite0(FileDescriptor filedescriptor, long l, int i, long l1)
        throws IOException;
   ...
}

2.其他可读通道

 else
      return transferFromArbitraryChannel(readablebytechannel, l, l1);

private long transferFromArbitraryChannel(ReadableByteChannel readablebytechannel, long l, long l1)
        throws IOException
    {
        ByteBuffer bytebuffer;
        long l2;
        long l3;
        int i = (int)Math.min(l1, 8192L);
        bytebuffer = Util.getTemporaryDirectBuffer(i);
        l2 = 0L;
        l3 = l;
        long l4;
        Util.erase(bytebuffer);
        do
        {
            if(l2 >= l1)
                break;
            bytebuffer.limit((int)Math.min(l1 - l2, 8192L));
	    //从源通道读取数据到临时DirectByteBuffer
            int j = readablebytechannel.read(bytebuffer);
            if(j <= 0)
                break;
            bytebuffer.flip();
	    //委托write，写DirectByteBuffer，即由IOUtil协助FileDispatcherImpl完成
            int k = write(bytebuffer, l3);
            l2 += k;
            if(k != j)
                break;
            l3 += k;
            bytebuffer.clear();
        } while(true);
        l4 = l2;
        Util.releaseTemporaryDirectBuffer(bytebuffer);
        ...
    }

从上面可以看出文件通道传输方法transferFrom，确保当前通道可写，打开，源通道可读打开，如果源通道为文件通道，将源通道数据映射的内存MappedByteBuffer，然后由IOUtil协助FileDispatcherImpl，将MappedByteBuffer写入当前通道，如果源通道非文件通道，则先调用源通道的读操作，从源通道读取数据，写到临时DirectByteBuffer，委托write，写DirectByteBuffer到当前通道，即由IOUtil协助FileDispatcherImpl，将DirectByteBuffer
写入当前通道。
再来看force操作：

public void force(boolean flag)
        throws IOException
    {
       ...
        do
            i = nd.force(fd, flag);
        while(i == -3 && isOpen());
       ...
    }

//FileDispatcherImpl

int force(FileDescriptor filedescriptor, boolean flag)
        throws IOException
    {
        return force0(filedescriptor, flag);
    }
static native int force0(FileDescriptor filedescriptor, boolean flag)
        throws IOException;

再来看truncate方法

 public FileChannel truncate(long l)
        throws IOException
    {
        ...
        do
            i = nd.truncate(fd, l);
        while(i == -3 && isOpen());
        ...
    }

//FileDispatcherImpl

int truncate(FileDescriptor filedescriptor, long l)
        throws IOException
    {
        return truncate0(filedescriptor, l);
    }
static native int truncate0(FileDescriptor filedescriptor, long l)
        throws IOException;

再来看其他函数

//返回通道当前位置
 public long position()
        throws IOException
    {
        ...
	//append模式，则为文件尾，否则为文件头
        do
            l = append ? nd.size(fd) : position0(fd, -1L);
        while(l == -3L && isOpen());
        ...
    }
 //定位postion到位置l
 public FileChannel position(long l)
        throws IOException
    {
       ...
        do
            l1 = position0(fd, l);
        while(l1 == -3L && isOpen());
        ...
    }

private native long position0(FileDescriptor filedescriptor, long l);

//获取通道当前size
public long size()
        throws IOException
    {
        ...
        do
            l = nd.size(fd);
        while(l == -3L && isOpen());
       ...
    }

//FileDispatcherImpl

long size(FileDescriptor filedescriptor)
        throws IOException
    {
        return size0(filedescriptor);
    }
static native long size0(FileDescriptor filedescriptor)
        throws IOException;

[size=medium][b]总结：[/b][/size]
[color=blue] 文件通道的构造，主要是初始化通道读写模式，追加模式append及文件分发器，FileDispatcherImpl。
文件通道的读写操作的实际操作都是由IOUtil协助FileDispatcherImpl完成，这一点和SocketChannel通道读写思路基本相同。
文件通道传输方法transferTo，首先确保当前文件通道是否打开，是否可读，然后检查目的通道是否关闭，是否可写；然后先调用文件通道本地方法传输通道的数据到目的通道，如果失败，则将文件通道数据，映射到内存MappedByteBuffer，然后调用目的通道的写操作（MappedByteBuffer），如果再失败，则将通道数据，写到DirectByteBuffer中，然后在调用目的通道的写操作（DirectByteBuffer）。
文件通道传输方法transferFrom，确保当前通道可写，打开，源通道可读打开，如果源通道为文件通道，将源通道数据映射的内存MappedByteBuffer，然后由IOUtil协助FileDispatcherImpl，将MappedByteBuffer
写入当前通道，如果源通道非文件通道，则先调用源通道的读操作，从源通道读取数据，写到临时DirectByteBuffer，委托write，写DirectByteBuffer到当前通道，即由IOUtil协助FileDispatcherImpl，将DirectByteBuffer写入当前通道。[/color]
文件通道解析二（文件锁，关闭通道）：[url]http://donald-draper.iteye.com/blog/2374736[/url]
附：
//FileDispatcher

abstract class FileDispatcher extends NativeDispatcher
{
    FileDispatcher()
    {
    }
    abstract int force(FileDescriptor filedescriptor, boolean flag)
        throws IOException;
    abstract int truncate(FileDescriptor filedescriptor, long l)
        throws IOException;
    abstract long size(FileDescriptor filedescriptor)
        throws IOException;
    abstract int lock(FileDescriptor filedescriptor, boolean flag, long l, long l1, boolean flag1)
        throws IOException;
    abstract void release(FileDescriptor filedescriptor, long l, long l1)
        throws IOException;
    abstract FileDescriptor duplicateForMapping(FileDescriptor filedescriptor)
        throws IOException;
    public static final int NO_LOCK = -1;
    public static final int LOCKED = 0;
    public static final int RET_EX_LOCK = 1;
    public static final int INTERRUPTED = 2;
}