Cassandra 源码解析 2： 文件流传输 对象序列化

org.apache.cassandra.streaming

java文件流传输

发起端：读文件，写入socket：FileChannel.transferTo SocketChannel 

//FileStreamTaskSocketChannel channel = SocketChannel.open();// force local binding on correctly specified interface. channel.socket().bind(new InetSocketAddress(FBUtilities.getLocalAddress(), 0));// obey the unwritten law that all nodes on a cluster must use the same storage port.channel.connect(new InetSocketAddress(to, DatabaseDescriptor.getStoragePort()));//写入Comm header，标记stream socketByteBuffer buffer = MessagingService.constructStreamHeader(false);channel.write(buffer);RandomAccessFile raf = new RandomAccessFile(new File(file), "r");FileChannel fc = raf.getChannel();while (start < endPosition){ long bytesTransferred = fc.transferTo(start, CHUNK_SIZE, channel); start += bytesTransferred;} 

接收端：读socket,写入文件：FileChannel.transferFrom

//IncomingStreamReaderFileOutputStream fos = new FileOutputStream(pendingFile.getTargetFile(), true)FileChannel fc = fos.getChannel();long bytesRead = 0;while (bytesRead < pendingFile.getExpectedBytes()) {bytesRead += fc.transferFrom(socketChannel, bytesRead, FileStreamTask.CHUNK_SIZE);} 

 

控制流和数据流的分离

文件的大小和个数是由前一篇中介绍的Message来传输

• 首先由发起端发STREAM_INITIATE Message给接收端，通知要传输的每个文件名称和大小(startPosition, endPosition)

//StreamOut.transferSSTablesStreamOutManager.get(target).addFilesToStream(pendingFiles);StreamInitiateMessage biMessage = new StreamInitiateMessage(pendingFiles);Message message = StreamInitiateMessage.makeStreamInitiateMessage(biMessage);message.setHeader(StreamOut.TABLE_NAME, table.getBytes());MessagingService.instance.sendOneWay(message, target); 

• 接收端接到STREAM_INITIATE Message后，将待传送的File添加到Context中，并注册一个StreamCompletionHandler，然后回送STREAM_INITIATE_DONE Message

//StreamInitiateVerbHandlerStreamInManager.registerStreamCompletionHandler(message.getFrom(), new StreamCompletionHandler());Message doneMessage = new Message(FBUtilities.getLocalAddress(), "", StorageService.Verb.STREAM_INITIATE_DONE, new byte[0] );MessagingService.instance.sendOneWay(doneMessage, message.getFrom()); 

• 发送端接收到STREAM_INITIATE_DONE Message，开始第一个文件的传输(start本文刚开始的FileStreamTask)

// StreamInitiateDoneVerbHandlerStreamOutManager.get(message.getFrom()).startNext(); 

• 接收端开始接收文件(本文刚开始的IncomingStreamReader)，完毕后通过前面注册的StreamCompletionHandler发送Delete或者Stream的CompletedFileStatus(异常，重发)， STREAM_FINISHED Message

//IncomingStreamReaderhandleStreamCompletion(remoteAddress.getAddress());//handleStreamCompletionIStreamComplete streamComplete = StreamInManager.getStreamCompletionHandler(remoteHost); if (streamComplete != null) streamComplete.onStreamCompletion(remoteHost, pendingFile, streamStatus);//StreamCompletionHandlerMessagingService.instance.sendOneWay(streamStatus.makeStreamStatusMessage(), host); 

• 发送端收到STREAM_FINISHED Message，在StreamFinishedVerbHandler中处理，如果发送成功，则删除本地文件并开始下一文件，否则重新发送

switch (streamStatus.getAction()) { case DELETE: StreamOutManager.get(message.getFrom()).finishAndStartNext(streamStatus.getFile()); break; case STREAM: if (logger.isDebugEnabled()) logger.debug("Need to re-stream file " + streamStatus.getFile()); StreamOutManager.get(message.getFrom()).startNext(); break; default: break; } 

 

STREAM_REQUEST,  StreamRequestVerbHandler

STREAM_INITIATE, StreamInitiateVerbHandler

STREAM_INITIATE_DONE, StreamInitiateDoneVerbHandler

STREAM_FINISHED, StreamFinishedVerbHandler

java对象序列化

在java中序列化经常要进行byte[]和long, int, char, string基本类型之间的相互转换，一种简洁的方法是使用DataOutputStream + ByteArrayOutputStream

ByteArrayOutputStream bos = new ByteArrayOutputStream();DataOutputStream dos = new DataOutputStream(bos);dos.writeInt();dos.writeUTF();dos.writeLong();byte[] data = dos.toByteArray(); 

 

cassandra 中的做法是直接将两者耦合成一个新的对象

 

/** * An implementation of the DataOutputStream interface. This class is completely thread * unsafe. */public class DataOutputBuffer extends DataOutputStream{ private static class Buffer extends ByteArrayOutputStream { public byte[] getData() { return buf; } public int getLength() { return count; } public void reset() { count = 0; } public void write(DataInput in, int len) throws IOException { int newcount = count + len; if (newcount > buf.length) { byte newbuf[] = new byte[Math.max(buf.length << 1, newcount)]; System.arraycopy(buf, 0, newbuf, 0, count); buf = newbuf; } in.readFully(buf, count, len); count = newcount; } } private Buffer buffer; /** Constructs a new empty buffer. */ public DataOutputBuffer() { this(new Buffer()); } private DataOutputBuffer(Buffer buffer) { super(buffer); this.buffer = buffer; } /** * Returns the current contents of the buffer. Data is only valid to * {@link #getLength()}. */ public byte[] getData() { return buffer.getData(); } /** Returns the length of the valid data currently in the buffer. */ public int getLength() { return buffer.getLength(); } /** Resets the buffer to empty. */ public DataOutputBuffer reset() { this.written = 0; buffer.reset(); return this; } /** Writes bytes from a DataInput directly into the buffer. */ public void write(DataInput in, int length) throws IOException { buffer.write(in, length); } }