class Rinda::RingFinger

RingFinger is used by RingServer clients to discover the RingServer’s TupleSpace. Typically, all a client needs to do is call RingFinger.primary to retrieve the remote TupleSpace, which it can then begin using.

To find the first available remote TupleSpace:

Rinda::RingFinger.primary

To create a RingFinger that broadcasts to a custom list:

rf = Rinda::RingFinger.new  ['localhost', '192.0.2.1']
rf.primary

Rinda::RingFinger also understands multicast addresses and sets them up properly. This allows you to run multiple RingServers on the same host:

rf = Rinda::RingFinger.new ['239.0.0.1']
rf.primary

You can set the hop count (or TTL) for multicast searches using multicast_hops.

If you use IPv6 multicast you may need to set both an address and the outbound interface index:

rf = Rinda::RingFinger.new ['ff02::1']
rf.multicast_interface = 1
rf.primary

At this time there is no easy way to get an interface index by name.

Attributes

broadcast_list [RW]

The list of addresses where RingFinger will send query packets.

multicast_hops [RW]

Maximum number of hops for sent multicast packets (if using a multicast address in the broadcast list). The default is 1 (same as UDP broadcast).

multicast_interface [RW]

The interface index to send IPv6 multicast packets from.

port [RW]

The port that RingFinger will send query packets to.

primary [RW]

Contain the first advertised TupleSpace after lookup_ring_any is called.

Public Class Methods

finger ()

Creates a singleton RingFinger and looks for a RingServer. Returns the created RingFinger.

# File lib/rinda/ring.rb, line 288
def self.finger
  unless @@finger
    @@finger = self.new
    @@finger.lookup_ring_any
  end
  @@finger
end

new (broadcast_list=@@broadcast_list, port=Ring_PORT)

Creates a new RingFinger that will look for RingServers at port on the addresses in broadcast_list.

If broadcast_list contains a multicast address then multicast queries will be made using the given multicast_hops and multicast_interface.

# File lib/rinda/ring.rb, line 344
def initialize(broadcast_list=@@broadcast_list, port=Ring_PORT)
  @broadcast_list = broadcast_list || ['localhost']
  @port = port
  @primary = nil
  @rings = []

  @multicast_hops = 1
  @multicast_interface = 0
end

primary ()

Returns the first advertised TupleSpace.

# File lib/rinda/ring.rb, line 299
def self.primary
  finger.primary
end

to_a ()

Contains all discovered TupleSpaces except for the primary.

# File lib/rinda/ring.rb, line 306
def self.to_a
  finger.to_a
end

Public Instance Methods

each () { |primary| ... }

Iterates over all discovered TupleSpaces starting with the primary.

# File lib/rinda/ring.rb, line 364
def each
  lookup_ring_any unless @primary
  return unless @primary
  yield(@primary)
  @rings.each { |x| yield(x) }
end

lookup_ring (timeout=5, &block)

Looks up RingServers waiting timeout seconds. RingServers will be given block as a callback, which will be called with the remote TupleSpace.

# File lib/rinda/ring.rb, line 376
def lookup_ring(timeout=5, &block)
  return lookup_ring_any(timeout) unless block_given?

  msg = Marshal.dump([[:lookup_ring, DRbObject.new(block)], timeout])
  @broadcast_list.each do |it|
    send_message(it, msg)
  end
  sleep(timeout)
end

lookup_ring_any (timeout=5)

Returns the first found remote TupleSpace. Any further recovered TupleSpaces can be found by calling to_a.

# File lib/rinda/ring.rb, line 390
def lookup_ring_any(timeout=5)
  queue = Thread::Queue.new

  Thread.new do
    self.lookup_ring(timeout) do |ts|
      queue.push(ts)
    end
    queue.push(nil)
  end

  @primary = queue.pop
  raise('RingNotFound') if @primary.nil?

  Thread.new do
    while it = queue.pop
      @rings.push(it)
    end
  end

  @primary
end

to_a ()

Contains all discovered TupleSpaces except for the primary.

# File lib/rinda/ring.rb, line 357
def to_a
  @rings
end