Summary

TCP_KEEPIDLE, TCP_KEEPCOUNT, and TCP_KEEPINTERVAL are non-standard socket options supported on several platforms to provide fine control over the TCP/IP keep alive mechanism. It should be possible to set these socket options via the setOption method defined by java.net.Socket and java.nio.channels.SocketChannel.

Problem

When the SO_KEEPALIVE option is enabled, TCP probes a connection that has been idle for some amount of time. The default value for this idle period is 2 hours which is too long for most applications. The TCP_KEEPIDLE, TCP_KEEPCOUNT, TCP_KEEPINTERVAL option can be used to affect this value for a given socket.

Solution

Add a JDK-specific socket option that supports setting TCP_KEEPIDLE, TCP_KEEPCOUNT, TCP_KEEPINTERVAL, on platforms that support it. The option can be set/get through the existing set/getOption methods on Socket and NetworkChannel.

Specification

To jdk.net.ExtendedSocketOptions, add the following new socket options:

  
  /**
   * Keep-Alive idle time.
   *
   * The value of this socket option is an {@code Integer} that is the number
   * of seconds of idle time before keep-alive initiates a probe. The socket
   * option is specific to stream-oriented sockets using the TCP/IP protocol.
   * The exact semantics of this socket option are system dependent.
   *
   * When the {@link java.net.StandardSocketOptions#SO_KEEPALIVE
   * SO_KEEPALIVE} option is enabled, TCP probes a connection that has been
   * idle for some amount of time. The default value for this idle period is
   * system dependent, but is typically 2 hours. The {@code TCP_KEEPIDLE}
   * option can be used to affect this value for a given socket.
   */
  public static final SocketOption TCP_KEEPIDLE
          = new ExtSocketOption("TCP_KEEPIDLE", Integer.class);

  /**
   * Keep-Alive retransmission interval time.
   *
   * The value of this socket option is an {@code Integer} that is the number
   * of seconds to wait before retransmitting a keep-alive probe. The socket
   * option is specific to stream-oriented sockets using the TCP/IP protocol.
   * The exact semantics of this socket option are system dependent.
   *
   * When the {@link java.net.StandardSocketOptions#SO_KEEPALIVE
   * SO_KEEPALIVE} option is enabled, TCP probes a connection that has been
   * idle for some amount of time. If the remote system does not respond to a
   * keep-alive probe, TCP retransmits the probe after some amount of time.
   * The default value for this retransmission interval is system dependent,
   * but is typically 75 seconds. The {@code TCP_KEEPINTERVAL} option can be
   * used to affect this value for a given socket.
   */
  public static final SocketOption TCP_KEEPINTERVAL
          = new ExtSocketOption("TCP_KEEPINTERVAL", Integer.class);

  /**
   * Keep-Alive retransmission maximum limit.
   *
   * The value of this socket option is an {@code Integer} that is the maximum
   * number of keep-alive probes to be sent. The socket option is specific to
   * stream-oriented sockets using the TCP/IP protocol. The exact semantics of
   * this socket option are system dependent.
   *
   * When the {@link java.net.StandardSocketOptions#SO_KEEPALIVE
   * SO_KEEPALIVE} option is enabled, TCP probes a connection that has been
   * idle for some amount of time. If the remote system does not respond to a
   * keep-alive probe, TCP retransmits the probe a certain number of times
   * before a connection is considered to be broken. The default value for
   * this keep-alive probe retransmit limit is system dependent, but is
   * typically 8. The {@code TCP_KEEPCOUNT} option can be used to affect this
   * value for a given socket.
   */
  public static final SocketOption TCP_KEEPCOUNT
          = new ExtSocketOption("TCP_KEEPCOUNT", Integer.class);