ActionCable, sometimes add_channel is not called.

[mmmpa]

Summary

One channel could not broadcast all messages. That was happened when one connected, after no one has a connection after someone disconnected.

In a case,

class OneChannel < ApplicationCable::Channel
  def subscribed
    stream_from 'one_stream'
  end

  def unsubscribed
     ActionCable.server.broadcast('one_stream', {type: 'leave'})
  end
end

Sometimes (about once every 7 times), SubscriberMap#broadcast is called after all channels are removed from @subscribers of SubscriberMap.

Then

@subscribers # => {one_stream: []}

Then next consumer comes, SubscriberMap#add_channel is not called, because new_channel = !@subscribers.key?(channel) is false.

SubscriberMap do not add channel for one_stream, until SubscriberMap#add_subscriber is called again after all channels are removed again.

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[maclover7]

Can you add a regression test?

[mmmpa]

I have no idea for the test.

[maclover7]

Hmm, maybe try adding a test where @subscribers is an empty Hash, then check out this new behavior with a call to broadcast?

[mmmpa]

Thank you. I tried.

[matthewd]

Backported as 81a16cb. Thanks!