Don't fail deferrables when callbacks raise exceptions

[thoughtless]

With the current implementation, any exception raised by an EM callback will be rescue by Mysql2::EM::Client::Watcher, and the deferrable will be failed. While I'm certainly not the most qualified person to make this judgement, I don't think that is very idiomatic. I do know that this has made my life rather difficult in trying to work with these deferrables.

Here is an example:

EM.run do
  client = Mysql2::EM::Client.new
  defer = client.query "INSERT INTO `messages` (`content`) VALUES ('what up?')"
  defer.callback do |result|
    publish_to_queue
  end
  defer.errback do |err|
    LOGGER.error "Problem inserting into database: #{err.inspect}"
  end
end

But what if publish_to_queue fails because my queue server is down? With the current implementation, I'll also see an error in my log file saying that there was a problem inserting into the database; however, the database INSERT worked just fine.

With this patch, the above will not write a message to the log when publish_to_queue raises an exception.

[qqshfox]

igrigorik/em-synchrony#71

I have already fixed this in production environment for over 6 months.

PS

0.3.8 (November 9th, 2011)

remove fiber support from mysql2, the code has moved to the em-synchrony gem.

[thoughtless]

@qqshfox Are you saying that this shouldn't be part of the mysql2 gem? I would think that one shouldn't be required to use em-synchrony to have this behavior.

Also, thanks for the link. It exposed a bug in my implementation (now fixed).

[qqshfox]

@thoughtless You are right. This has nothing to do with fiber (em-synchonry).

But I never use it w/o fiber... So I just thouht you were playing it with fiber...

[qqshfox]

@thoughtless I think that I should have sent that patch here.

[brianmario]

thanks!