[SNMP4J] DefaultUdpTransportMapping class and ListenThread

[Frank Fock]

Hi,

Since Socket.receive blocks until a packet is received,
I do not see any advantage of the suggested code.

Best regards,
Frank

Vivi Zhang wrote:
> Hi,
> 
> I am looking at ways to tuning my application with embedded SNMP agent 
> with SNMP4J and SNMP4J-Agent.
> 
> I have two questions about the implementation of  inner class 
> ListernThread.
> Q1) Line 315 *   try {
>      socket.receive(packet);
>   }
>   catch (InterruptedIOException iiox) {
>         if (iiox.bytesTransferred <= 0) {
>         continue;
>   }*
>   If we see SocketTimeoutException since there is no packet to read, can 
> we put the thread to a small break before it goes for another 
> socket.receive() call?   The suggestion is intended to ease some 
> pressure on the CPU and network resource.  Do you see any potential 
> drawback from this change?
> 
> Q2) Line 307 *DatagramPacket packet = new DatagramPacket(buf, buf.length,
>                                             udpAddress.getInetAddress(),
>                                             udpAddress.getPort());**
>        *A DatagramPacket object is created repeatedly within the while 
> loop. What is the drawback if we move the stmt outiside while loop.  The 
> logic  behind this suggestion is avoiding object creating repeatedly 
> withing the loop.
> 
> Thanks.
> 
> Vivi
> 
> P.S.
> 
> I am using SNMP4J 1.9.3c.
> 
> Following is a section of code I cut from DefaultUdpTransportMapping.java.
> ============================================================================ 
> 
> 
> while (!stop) {
> *  DatagramPacket packet = new DatagramPacket(buf, buf.length,
>                                             udpAddress.getInetAddress(),
>                                             udpAddress.getPort());*
>  try {
>    try {
>      socket.receive(packet);
>    }
>    catch (InterruptedIOException iiox) {
>      if (iiox.bytesTransferred <= 0) {
>     *   continue;*
>      }
>    }
>    if (logger.isDebugEnabled()) {
>      logger.debug("Received message from "+packet.getAddress()+"/"+
>                   packet.getPort()+
>                   " with length "+packet.getLength()+": "+
>                   new OctetString(packet.getData(), 0,
>                                   packet.getLength()).toHexString());
>    }
>    ByteBuffer bis;
>    // If messages are processed asynchronously (i.e. multi-threaded)
>    // then we have to copy the buffer's content here!
>    if (isAsyncMsgProcessingSupported()) {
>      byte[] bytes = new byte[packet.getLength()];
>      System.arraycopy(packet.getData(), 0, bytes, 0, bytes.length);
>      bis = ByteBuffer.wrap(bytes);
>    }
>    else {
>      bis = ByteBuffer.wrap(packet.getData());
>    }
>    fireProcessMessage(new UdpAddress(packet.getAddress(),
>                                      packet.getPort()), bis);
>  }
>  catch (SocketTimeoutException stex) {
>    // ignore
>  }
>  catch (PortUnreachableException purex) {
>    synchronized (DefaultUdpTransportMapping.this) {
>      listener = null;
>    }
>    logger.error(purex);
>    if (logger.isDebugEnabled()) {
>      purex.printStackTrace();
>    }
>    if (SNMP4JSettings.isFowardRuntimeExceptions()) {
>      throw new RuntimeException(purex);
>    }
>    break;
>  }
>  catch (SocketException soex) {
>    logger.error("Socket for transport mapping "+toString()+
>                 " error: "+soex.getMessage(), soex);
>    stop = true;
>  }
>  catch (IOException iox) {
>    logger.warn(iox);
>    if (logger.isDebugEnabled()) {
>      iox.printStackTrace();
>    }
>    if (SNMP4JSettings.isFowardRuntimeExceptions()) {
>      throw new RuntimeException(iox);
>    }
>  }
> }
> synchronized (DefaultUdpTransportMapping.this) {
>  listener = null;
>  stop = true;
>  if (socket != null) {
>    socket.close();
>  }
> }
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