Package org.jgroups.protocols

Class Discovery

  • Direct Known Subclasses:
    PING, TCPGOSSIP, TCPPING
    public abstract class Discovery
extends Protocol
    The Discovery protocol layer retrieves the initial membership (used by the GMS when started by sending event FIND_INITIAL_MBRS down the stack). We do this by specific subclasses, e.g. by mcasting PING requests to an IP MCAST address or, if gossiping is enabled, by contacting the GossipRouter. The responses should allow us to determine the coordinator whom we have to contact, e.g. in case we want to join the group. When we are a server (after having received the BECOME_SERVER event), we'll respond to PING requests with a PING response.

    The FIND_INITIAL_MBRS event will eventually be answered with a FIND_INITIAL_MBRS_OK event up the stack. The following properties are available

    • timeout - the timeout (ms) to wait for the initial members, default is 3000=3 secs
    • num_initial_members - the minimum number of initial members for a FIND_INITAL_MBRS, default is 2
    • num_ping_requests - the number of GET_MBRS_REQ messages to be sent (min=1), distributed over timeout ms
    Version:
    $Id: Discovery.java,v 1.32.2.6 2008/09/19 10:56:43 belaban Exp $
    Author:
    Bela Ban

    • Constructor Detail

      • Discovery

        public Discovery()

    • Method Detail

      • init

        public void init()
          throws java.lang.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:
        java.lang.Exception - Thrown if protocol cannot be initialized successfully. This will cause the ProtocolStack to fail, so the channel constructor will throw an exception

      • localAddressSet

        public void localAddressSet​(Address addr)
        Called after local_addr was set

      • sendGetMembersRequest

        public abstract void sendGetMembersRequest()

      • handleDisconnect

        public void handleDisconnect()

      • handleConnect

        public void handleConnect()

      • getTimeout

        public long getTimeout()

      • setTimeout

        public void setTimeout​(long timeout)

      • getNumInitialMembers

        public int getNumInitialMembers()

      • setNumInitialMembers

        public void setNumInitialMembers​(int num_initial_members)

      • getNumPingRequests

        public int getNumPingRequests()

      • setNumPingRequests

        public void setNumPingRequests​(int num_ping_requests)

      • getNumberOfDiscoveryRequestsSent

        public int getNumberOfDiscoveryRequestsSent()

      • providedUpServices

        public java.util.Vector<java.lang.Integer> providedUpServices()
        Description copied from class: Protocol
        List of events that are provided to layers above (they will be handled when sent down from above).
        Overrides:
        providedUpServices in class Protocol
        Returns:
        Vector (of Integers)

      • setProperties

        public boolean setProperties​(java.util.Properties props)
        sets the properties of the PING protocol. The following properties are available property: timeout - the timeout (ms) to wait for the initial members, default is 3000=3 secs property: num_initial_members - the minimum number of initial members for a FIND_INITAL_MBRS, default is 2
        Overrides:
        setProperties in class Protocol
        Parameters:
        props - - a property set
        Returns:
        returns true if all properties were parsed properly returns false if there are unrecnogized properties in the property set

      • start

        public void start()
           throws java.lang.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:
        java.lang.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

      • findInitialMembers

        public java.util.List<PingRsp> findInitialMembers​(Promise<JoinRsp> promise)
        Finds the initial membership: sends a GET_MBRS_REQ to all members, waits 'timeout' ms or until 'num_initial_members' have been retrieved
        Returns:
        List

      • findInitialMembersAsString

        public java.lang.String findInitialMembersAsString()

      • up

        public java.lang.Object up​(Event evt)
        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 PassDown or c) the event (or another event) is sent up the stack using PassUp.

        For the PING protocol, the Up operation does the following things. 1. If the event is a Event.MSG then PING will inspect the message header. If the header is null, PING simply passes up the event If the header is PingHeader.GET_MBRS_REQ then the PING protocol will PassDown a PingRequest message If the header is PingHeader.GET_MBRS_RSP we will add the message to the initial members vector and wake up any waiting threads. 2. If the event is Event.SET_LOCAL_ADDR we will simple set the local address of this protocol 3. For all other messages we simple pass it up to the protocol above

        Overrides:
        up in class Protocol
        Parameters:
        evt - - the event that has been sent from the layer below

      • down

        public java.lang.Object down​(Event evt)
        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 PassDown. 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(). The PING protocol is interested in several different down events, Event.FIND_INITIAL_MBRS - sent by the GMS layer and expecting a GET_MBRS_OK Event.TMP_VIEW and Event.VIEW_CHANGE - a view change event Event.BECOME_SERVER - called after client has joined and is fully working group member Event.CONNECT, Event.DISCONNECT.
        Overrides:
        down in class Protocol

      • makeView

        protected final View makeView​(java.util.Vector mbrs)