+
+ class QueueRing
+ # A QueueRing is implemented as an array with elements in the form
+ # [chan, [message1, message2, ...]
+ # Note that the channel +chan+ has no actual bearing with the channels
+ # to which messages will be sent
+
+ def initialize
+ @storage = Array.new
+ @last_idx = -1
+ end
+
+ def clear
+ @storage.clear
+ @last_idx = -1
+ end
+
+ def length
+ len = 0
+ @storage.each {|c|
+ len += c[1].size
+ }
+ return len
+ end
+ alias :size :length
+
+ def empty?
+ @storage.empty?
+ end
+
+ def push(mess, chan)
+ cmess = @storage.assoc(chan)
+ if cmess
+ idx = @storage.index(cmess)
+ cmess[1] << mess
+ @storage[idx] = cmess
+ else
+ @storage << [chan, [mess]]
+ end
+ end
+
+ def next
+ if empty?
+ warning "trying to access empty ring"
+ return nil
+ end
+ save_idx = @last_idx
+ @last_idx = (@last_idx + 1) % @storage.size
+ mess = @storage[@last_idx][1].first
+ @last_idx = save_idx
+ return mess
+ end
+
+ def shift
+ if empty?
+ warning "trying to access empty ring"
+ return nil
+ end
+ @last_idx = (@last_idx + 1) % @storage.size
+ mess = @storage[@last_idx][1].shift
+ @storage.delete(@storage[@last_idx]) if @storage[@last_idx][1] == []
+ return mess
+ end
+
+ end
+
+ class MessageQueue
+
+ def initialize
+ # a MessageQueue is an array of QueueRings
+ # rings have decreasing priority, so messages in ring 0
+ # are more important than messages in ring 1, and so on
+ @rings = Array.new(3) { |i|
+ if i > 0
+ QueueRing.new
+ else
+ # ring 0 is special in that if it's not empty, it will
+ # be popped. IOW, ring 0 can starve the other rings
+ # ring 0 is strictly FIFO and is therefore implemented
+ # as an array
+ Array.new
+ end
+ }
+ # the other rings are satisfied round-robin
+ @last_ring = 0
+ self.extend(MonitorMixin)
+ @non_empty = self.new_cond
+ end
+
+ def clear
+ self.synchronize do
+ @rings.each { |r| r.clear }
+ @last_ring = 0
+ end
+ end
+
+ def push(mess, chan=nil, cring=0)
+ ring = cring
+ self.synchronize do
+ if ring == 0
+ warning "message #{mess} at ring 0 has channel #{chan}: channel will be ignored" if !chan.nil?
+ @rings[0] << mess
+ else
+ error "message #{mess} at ring #{ring} must have a channel" if chan.nil?
+ @rings[ring].push mess, chan
+ end
+ @non_empty.signal
+ end
+ end
+
+ def shift(tmout = nil)
+ self.synchronize do
+ @non_empty.wait(tmout) if self.empty?
+ return unsafe_shift
+ end
+ end
+
+ protected
+
+ def empty?
+ !@rings.find { |r| !r.empty? }
+ end
+
+ def length
+ @rings.inject(0) { |s, r| s + r.size }
+ end
+ alias :size :length
+
+ def unsafe_shift
+ if !@rings[0].empty?
+ return @rings[0].shift
+ end
+ (@rings.size - 1).times do
+ @last_ring = (@last_ring % (@rings.size - 1)) + 1
+ return @rings[@last_ring].shift unless @rings[@last_ring].empty?
+ end
+ warning "trying to access an empty message queue"
+ return nil
+ end
+
+ end