Class FD_SOCK

java.lang.Object
org.jgroups.stack.Protocol
org.jgroups.protocols.FD_SOCK
All Implemented Interfaces:
Runnable

public class FD_SOCK extends Protocol implements Runnable
Failure detection protocol based on sockets. Failure detection is ring-based. Each member creates a server socket and announces its address together with the server socket's address in a multicast. A pinger thread will be started when the membership goes above 1 and will be stopped when it drops below 2. The pinger thread connects to its neighbor on the right and waits until the socket is closed. When the socket is closed by the monitored peer in an abnormal fashion (IOException), the neighbor will be suspected.

The main feature of this protocol is that no ping messages need to be exchanged between any 2 peers, and failure detection relies entirely on TCP sockets. The advantage is that no activity will take place between 2 peers as long as they are alive (i.e. have their server sockets open). The disadvantage is that hung servers or crashed routers will not cause sockets to be closed, therefore they won't be detected. The FD_SOCK protocol will work for groups where members are on different hosts

The costs involved are 2 additional threads: one that monitors the client side of the socket connection (to monitor a peer) and another one that manages the server socket. However, those threads will be idle as long as both peers are running.

Version:
$Id: FD_SOCK.java,v 1.83.2.7 2009/02/05 16:22:00 vlada Exp $
Author:
Bela Ban May 29 2001
  • Constructor Details

    • FD_SOCK

      public FD_SOCK()
  • Method Details

    • getName

      public String getName()
      Specified by:
      getName in class Protocol
    • getLocalAddress

      public String getLocalAddress()
    • getMembers

      public String getMembers()
    • getPingableMembers

      public String getPingableMembers()
    • getPingDest

      public String getPingDest()
    • getNumSuspectEventsGenerated

      public int getNumSuspectEventsGenerated()
    • printSuspectHistory

      public String printSuspectHistory()
    • setProperties

      public boolean setProperties(Properties props)
      Description copied from class: Protocol
      Configures the protocol initially. A configuration string consists of name=value items, separated by a ';' (semicolon), e.g.:
       "loopback=false;unicast_inport=4444"
       
      Overrides:
      setProperties in class Protocol
    • printCache

      public String printCache()
    • init

      public void init() throws Exception
      Description copied from class: Protocol
      Called after instance has been created (null constructor) and before protocol is started. Properties are already set. Other protocols are not yet connected and events cannot yet be sent.
      Overrides:
      init in class Protocol
      Throws:
      Exception - Thrown if protocol cannot be initialized successfully. This will cause the ProtocolStack to fail, so the channel constructor will throw an exception
    • start

      public void start() throws Exception
      Description copied from class: Protocol
      This method is called on a Channel.connect(String). Starts work. Protocols are connected and queues are ready to receive events. Will be called from bottom to top. This call will replace the START and START_OK events.
      Overrides:
      start in class Protocol
      Throws:
      Exception - Thrown if protocol cannot be started successfully. This will cause the ProtocolStack to fail, so Channel.connect(String) will throw an exception
    • stop

      public void stop()
      Description copied from class: Protocol
      This method is called on a Channel.disconnect(). Stops work (e.g. by closing multicast socket). Will be called from top to bottom. This means that at the time of the method invocation the neighbor protocol below is still working. This method will replace the STOP, STOP_OK, CLEANUP and CLEANUP_OK events. The ProtocolStack guarantees that when this method is called all messages in the down queue will have been flushed
      Overrides:
      stop in class Protocol
    • resetStats

      public void resetStats()
      Overrides:
      resetStats in class Protocol
    • up

      public Object up(Event evt)
      Description copied from class: Protocol
      An event was received from the layer below. Usually the current layer will want to examine the event type and - depending on its type - perform some computation (e.g. removing headers from a MSG event type, or updating the internal membership list when receiving a VIEW_CHANGE event). Finally the event is either a) discarded, or b) an event is sent down the stack using down_prot.down() or c) the event (or another event) is sent up the stack using up_prot.up().
      Overrides:
      up in class Protocol
    • down

      public Object down(Event evt)
      Description copied from class: Protocol
      An event is to be sent down the stack. The layer may want to examine its type and perform some action on it, depending on the event's type. If the event is a message MSG, then the layer may need to add a header to it (or do nothing at all) before sending it down the stack using down_prot.down(). In case of a GET_ADDRESS event (which tries to retrieve the stack's address from one of the bottom layers), the layer may need to send a new response event back up the stack using up_prot.up().
      Overrides:
      down in class Protocol
    • run

      public void run()
      Runs as long as there are 2 members and more. Determines the member to be monitored and fetches its server socket address (if n/a, sends a message to obtain it). The creates a client socket and listens on it until the connection breaks. If it breaks, emits a SUSPECT message. It the connection is closed regularly, nothing happens. In both cases, a new member to be monitored will be chosen and monitoring continues (unless there are fewer than 2 members).
      Specified by:
      run in interface Runnable