import groovyx.gpars.agent.Agent

/**
 * Conference stores number of registrations and allows parties to register and unregister.
 * It inherits from the Agent class and adds the register() and unregister() private methods,
 * which callers may use it the commands they submit to the Conference.
 */
class Conference extends Agent<Long> {
    def Conference() { super(0) }
    private def register(long num) { data += num }
    private def unregister(long num) { data -= num }
}

final Agent conference = new Conference()  //new Conference created

/**
 * Three external parties will try to register/unregister concurrently
 */

final Thread t1 = Thread.start {
    conference << {register(10L)}               //send a command to register 10 attendees
}

final Thread t2 = Thread.start {
    conference << {register(5L)}                //send a command to register 5 attendees
}

final Thread t3 = Thread.start {
    conference << {unregister(3L)}              //send a command to unregister 3 attendees
}

[t1, t2, t3]*.join()
assert 12L == conference.val