import org.apache.hadoop.hdfs.protocol.proto.DataTransferProtos.ShortCircuitShmResponseProto; //导入依赖的package包/类
private void sendShmSuccessResponse(DomainSocket sock, NewShmInfo shmInfo)
    throws IOException {
  DataNodeFaultInjector.get().sendShortCircuitShmResponse();
  ShortCircuitShmResponseProto.newBuilder().setStatus(SUCCESS).
      setId(PBHelper.convert(shmInfo.shmId)).build().
      writeDelimitedTo(socketOut);
  // Send the file descriptor for the shared memory segment.
  byte buf[] = new byte[] { (byte)0 };
  FileDescriptor shmFdArray[] =
      new FileDescriptor[] { shmInfo.stream.getFD() };
  sock.sendFileDescriptors(shmFdArray, buf, 0, buf.length);
}
 

import org.apache.hadoop.hdfs.protocol.proto.DataTransferProtos.ShortCircuitShmResponseProto; //导入依赖的package包/类
private void sendShmSuccessResponse(DomainSocket sock, NewShmInfo shmInfo)
    throws IOException {
  DataNodeFaultInjector.get().sendShortCircuitShmResponse();
  ShortCircuitShmResponseProto.newBuilder().setStatus(SUCCESS).
      setId(PBHelperClient.convert(shmInfo.shmId)).build().
      writeDelimitedTo(socketOut);
  // Send the file descriptor for the shared memory segment.
  byte buf[] = new byte[] { (byte)0 };
  FileDescriptor shmFdArray[] =
      new FileDescriptor[] { shmInfo.stream.getFD() };
  sock.sendFileDescriptors(shmFdArray, buf, 0, buf.length);
}
 

import org.apache.hadoop.hdfs.protocol.proto.DataTransferProtos.ShortCircuitShmResponseProto; //导入依赖的package包/类
private void sendShmSuccessResponse(DomainSocket sock, NewShmInfo shmInfo)
    throws IOException {
  ShortCircuitShmResponseProto.newBuilder().setStatus(SUCCESS).
      setId(PBHelper.convert(shmInfo.shmId)).build().
      writeDelimitedTo(socketOut);
  // Send the file descriptor for the shared memory segment.
  byte buf[] = new byte[] { (byte)0 };
  FileDescriptor shmFdArray[] =
      new FileDescriptor[] { shmInfo.stream.getFD() };
  sock.sendFileDescriptors(shmFdArray, buf, 0, buf.length);
}
 

import org.apache.hadoop.hdfs.protocol.proto.DataTransferProtos.ShortCircuitShmResponseProto; //导入依赖的package包/类
/**
 * Ask the DataNode for a new shared memory segment.  This function must be
 * called with the manager lock held.  We will release the lock while
 * communicating with the DataNode.
 *
 * @param clientName    The current client name.
 * @param peer          The peer to use to talk to the DataNode.
 *
 * @return              Null if the DataNode does not support shared memory
 *                        segments, or experienced an error creating the
 *                        shm.  The shared memory segment itself on success.
 * @throws IOException  If there was an error communicating over the socket.
 *                        We will not throw an IOException unless the socket
 *                        itself (or the network) is the problem.
 */
private DfsClientShm requestNewShm(String clientName, DomainPeer peer)
    throws IOException {
  final DataOutputStream out = 
      new DataOutputStream(
          new BufferedOutputStream(peer.getOutputStream()));
  new Sender(out).requestShortCircuitShm(clientName);
  ShortCircuitShmResponseProto resp = 
      ShortCircuitShmResponseProto.parseFrom(
          PBHelper.vintPrefixed(peer.getInputStream()));
  String error = resp.hasError() ? resp.getError() : "(unknown)";
  switch (resp.getStatus()) {
  case SUCCESS:
    DomainSocket sock = peer.getDomainSocket();
    byte buf[] = new byte[1];
    FileInputStream fis[] = new FileInputStream[1];
    if (sock.recvFileInputStreams(fis, buf, 0, buf.length) < 0) {
      throw new EOFException("got EOF while trying to transfer the " +
          "file descriptor for the shared memory segment.");
    }
    if (fis[0] == null) {
      throw new IOException("the datanode " + datanode + " failed to " +
          "pass a file descriptor for the shared memory segment.");
    }
    try {
      DfsClientShm shm = 
          new DfsClientShm(PBHelper.convert(resp.getId()),
              fis[0], this, peer);
      if (LOG.isTraceEnabled()) {
        LOG.trace(this + ": createNewShm: created " + shm);
      }
      return shm;
    } finally {
      IOUtils.cleanup(LOG,  fis[0]);
    }
  case ERROR_UNSUPPORTED:
    // The DataNode just does not support short-circuit shared memory
    // access, and we should stop asking.
    LOG.info(this + ": datanode does not support short-circuit " +
        "shared memory access: " + error);
    disabled = true;
    return null;
  default:
    // The datanode experienced some kind of unexpected error when trying to
    // create the short-circuit shared memory segment.
    LOG.warn(this + ": error requesting short-circuit shared memory " +
        "access: " + error);
    return null;
  }
}
 

import org.apache.hadoop.hdfs.protocol.proto.DataTransferProtos.ShortCircuitShmResponseProto; //导入依赖的package包/类
private void sendShmErrorResponse(Status status, String error)
    throws IOException {
  ShortCircuitShmResponseProto.newBuilder().setStatus(status).
      setError(error).build().writeDelimitedTo(socketOut);
}
 

import org.apache.hadoop.hdfs.protocol.proto.DataTransferProtos.ShortCircuitShmResponseProto; //导入依赖的package包/类
/**
 * Ask the DataNode for a new shared memory segment.  This function must be
 * called with the manager lock held.  We will release the lock while
 * communicating with the DataNode.
 *
 * @param clientName    The current client name.
 * @param peer          The peer to use to talk to the DataNode.
 *
 * @return              Null if the DataNode does not support shared memory
 *                        segments, or experienced an error creating the
 *                        shm.  The shared memory segment itself on success.
 * @throws IOException  If there was an error communicating over the socket.
 *                        We will not throw an IOException unless the socket
 *                        itself (or the network) is the problem.
 */
private DfsClientShm requestNewShm(String clientName, DomainPeer peer)
    throws IOException {
  final DataOutputStream out =
      new DataOutputStream(
          new BufferedOutputStream(peer.getOutputStream()));
  new Sender(out).requestShortCircuitShm(clientName);
  ShortCircuitShmResponseProto resp =
      ShortCircuitShmResponseProto.parseFrom(
        PBHelperClient.vintPrefixed(peer.getInputStream()));
  String error = resp.hasError() ? resp.getError() : "(unknown)";
  switch (resp.getStatus()) {
  case SUCCESS:
    DomainSocket sock = peer.getDomainSocket();
    byte buf[] = new byte[1];
    FileInputStream fis[] = new FileInputStream[1];
    if (sock.recvFileInputStreams(fis, buf, 0, buf.length) < 0) {
      throw new EOFException("got EOF while trying to transfer the " +
          "file descriptor for the shared memory segment.");
    }
    if (fis[0] == null) {
      throw new IOException("the datanode " + datanode + " failed to " +
          "pass a file descriptor for the shared memory segment.");
    }
    try {
      DfsClientShm shm =
          new DfsClientShm(PBHelperClient.convert(resp.getId()),
              fis[0], this, peer);
      LOG.trace("{}: createNewShm: created {}", this, shm);
      return shm;
    } finally {
      try {
        fis[0].close();
      } catch (Throwable e) {
        LOG.debug("Exception in closing " + fis[0], e);
      }
    }
  case ERROR_UNSUPPORTED:
    // The DataNode just does not support short-circuit shared memory
    // access, and we should stop asking.
    LOG.info(this + ": datanode does not support short-circuit " +
        "shared memory access: " + error);
    disabled = true;
    return null;
  default:
    // The datanode experienced some kind of unexpected error when trying to
    // create the short-circuit shared memory segment.
    LOG.warn(this + ": error requesting short-circuit shared memory " +
        "access: " + error);
    return null;
  }
}