Class DistributedQueue

java.lang.Object
org.jgroups.blocks.DistributedQueue
All Implemented Interfaces:
Cloneable, MembershipListener, MessageListener
public class DistributedQueue extends Object implements MessageListener, MembershipListener, Cloneable
Provides the abstraction of a java.util.LinkedList that is replicated at several locations. Any change to the list (reset, add, remove, etc.) will transparently be propagated to all replicas in the group. All read-only methods will always access the local replica.

Both keys and values added to the list must be serializable, the reason being that they will be sent across the network to all replicas of the group. An instance of this class will contact an existing member of the group to fetch its initial state. Beware to use a total protocol on initialization or elements would not be in same order on all replicas.

Author:
Romuald du Song

  • Field Details

    • logger

      protected org.apache.commons.logging.Log logger

    • mutex

      protected final Object mutex

    • stopped

      protected boolean stopped

    • internalQueue

      protected LinkedList internalQueue

    • channel

      protected Channel channel

    • disp

      protected RpcDispatcher disp

    • groupname

      protected String groupname

    • notifs

      protected Vector notifs

    • members

      protected Vector members

  • Constructor Details

    • DistributedQueue

      public DistributedQueue(String groupname, ChannelFactory factory, String properties, long state_timeout) throws ChannelException
      Creates a DistributedQueue
      Parameters:
      groupname - The name of the group to join
      factory - The ChannelFactory which will be used to create a channel
      properties - The property string to be used to define the channel
      state_timeout - The time to wait until state is retrieved in milliseconds. A value of 0 means wait forever.
      Throws:
      ChannelException

    • DistributedQueue

      public DistributedQueue(JChannel channel)

    • DistributedQueue

      public DistributedQueue(PullPushAdapter adapter, Serializable id)
      Uses a user-provided PullPushAdapter to create the dispatcher rather than a Channel. If id is non-null, it will be used to register under that id. This is typically used when another building block is already using PullPushAdapter, and we want to add this building block in addition. The id is the used to discriminate between messages for the various blocks on top of PullPushAdapter. If null, we will assume we are the first block created on PullPushAdapter. The caller needs to call start(), before using the this block. It gives the opportunity for the caller to register as a lessoner for Notifications events.
      Parameters:
      adapter - The PullPushAdapter which to use as underlying transport
      id - A serializable object (e.g. an Integer) used to discriminate (multiplex/demultiplex) between requests/responses for different building blocks on top of PullPushAdapter.

  • Method Details

    • init

      protected final void init()

    • start

      public final void start(long state_timeout) throws ChannelClosedException, ChannelNotConnectedException
      Throws:
      ChannelClosedException
      ChannelNotConnectedException

    • getLocalAddress

      public Address getLocalAddress()

    • getChannel

      public Channel getChannel()

    • addNotifier

      public void addNotifier(DistributedQueue.Notification n)

    • removeNotifier

      public void removeNotifier(DistributedQueue.Notification n)

    • stop

      public void stop()

    • add

      public void add(Object value)
      Add the speficied element at the bottom of the queue
      Parameters:
      value -

    • addAtHead

      public void addAtHead(Object value)
      Add the speficied element at the top of the queue
      Parameters:
      value -

    • addAll

      public void addAll(Collection values)
      Add the speficied collection to the top of the queue. Elements are added in the order that they are returned by the specified collection's iterator.
      Parameters:
      values -

    • getContents

      public Vector getContents()

    • size

      public int size()

    • peek

      public Object peek()
      returns the first object on the queue, without removing it. If the queue is empty this object blocks until the first queue object has been added
      Returns:
      the first object on the queue

    • reset

      public void reset()

    • checkResult

      protected void checkResult(RspList rsp, Object retval)

    • remove

      public Object remove()
      Try to return the first objet in the queue.It does not wait for an object.
      Returns:
      the first object in the queue or null if none were found.

    • remove

      public Object remove(long timeout)
      Parameters:
      timeout - The time to wait until an entry is retrieved in milliseconds. A value of 0 means wait forever.
      Returns:
      the first object in the queue or null if none were found

    • toString

      public String toString()
      Overrides:
      toString in class Object

    • _add

      public void _add(Object value)

    • _addAtHead

      public void _addAtHead(Object value)

    • _reset

      public void _reset()

    • _private_reset

      protected void _private_reset()

    • _remove

      public Object _remove()

    • _addAll

      public void _addAll(Collection c)

    • receive

      public void receive(Message msg)
      Description copied from interface: MessageListener
      Called when a message is received.
      Specified by:
      receive in interface MessageListener
      Parameters:
      msg -

    • getState

      public byte[] getState()
      Description copied from interface: MessageListener
      Answers the group state; e.g., when joining.
      Specified by:
      getState in interface MessageListener
      Returns:
      byte[]

    • setState

      public void setState(byte[] new_state)
      Description copied from interface: MessageListener
      Sets the group state; e.g., when joining.
      Specified by:
      setState in interface MessageListener
      Parameters:
      new_state -

    • viewAccepted

      public void viewAccepted(View new_view)
      Description copied from interface: MembershipListener
      Called when a change in membership has occurred. No long running actions or sending of messages should be done in this callback. If some long running action needs to be performed, it should be done in a separate thread.

      Note that on reception of the first view (a new member just joined), the channel will not yet be in the connected state. This only happens when Channel.connect(String) returns.

      Specified by:
      viewAccepted in interface MembershipListener

    • suspect

      public void suspect(Address suspected_mbr)
      Called when a member is suspected
      Specified by:
      suspect in interface MembershipListener

    • block

      public void block()
      Block sending and receiving of messages until ViewAccepted is called
      Specified by:
      block in interface MembershipListener

    • main

      public static void main(String[] args)