stan_test.rb

require 'stan/client'
require 'monitor'
require 'thread'

class MinimalTest

  def initialize
    @queue = Queue.new
    @subscriptions = []
  end

  def subscribe_to_stan(durable)
    @subscriptions << stan.subscribe('test.nats', queue: 'goldstar', durable_name: durable) do |payload|
      STDOUT.puts("got test.nats #{payload} #{durable}")
    end
  end

  def publish_to_stan
    @count ||= 0
    @count += 1
    STDOUT.puts("publishing")
    stan.publish('test.nats', @count.to_s)
  end

  def unsubscriber
    STDOUT.puts("setting up unsubscriber")
    stan.nats.subscribe("unsubscribe_all.goldstar") do
      STDOUT.puts("unsubscribing")
      @queue.push(@subscription)
    end
  end

  def execute
    loop do
      publish_to_stan
      sleep 2
    end
  end

  def unsubscribe_thread
    STDOUT.puts('running thread')
    Thread.new do
      subscription = @queue.pop
      subscription.close
    end
  end

  def stan
    return @stan if @stan

    @stan = STAN::Client.new.tap do |client|
      client.connect('gse_cluster', 'stan_test', nats: {
        servers: ['nats://0.0.0.0:4222']
      })

      client.nats.on_error do |e|
        STDOUT.puts("NATS ERROR #{e}")
        STDOUT.puts(e.backtrace)
      end

      at_exit do
        client.close
      end
    end
  end
end

MinimalTest.new.tap do |m|
  m.unsubscriber
  m.unsubscribe_thread
  m.subscribe_to_stan('durable1')
  m.execute
end

doesn't actually event require two subscriptions - a single subscription is enough to demonstrate the issue.

Turns out the trick is to unsubscribe from a different thread. You can communicate which subscriptions objects should be unsubscribed over a Queue.

@stephenprater Thanks for sharing, fixing the issue in the client now here: nats-io/nats-pure.rb#27