Fix TaggedLogging to allow loggers to be instantiated multiple times without having to share the stack of tags

[atombender]

This is accomplished by using a unique key for the thread-local tag list. Fixes #9064.

[jeremy]

Looks good. Having a thread-local formatter might feel nicer, but it's a hassle to implement. /cc @tenderlove

[carlosantoniodasilva]

Don't we have Thread local configs now, that could be used for it?

[atombender]

@carlosantoniodasilva: The tagged logger already uses a thread-local. The problem is that it acts as if there can only be a single tagged logger instance.

Here's my example from the previous issue (sorry about the dupe, didn't know Github listed pull requests in the issue tracker):

my_logger = ActiveSupport::TaggedLogging.new(Rails.logger)
my_logger.push_tags "my_tag"
my_logger.info "test"  # outputs "[my_tag] [my_tag] test"
Rails.logger.info "test"  # outputs "[my_tag] test"

It's also not safe to wrap a unique logger (ie., one that does not delegate to a logger shared around in the app, like Rails.logger):

my_logger = ActiveSupport::TaggedLogging.new(Logger.new($stdout))
my_logger.push_tags "my_tag"
Rails.logger.info "test"  # outputs "[my_tag] test"
Rails.logger.tagged("other_tag") do
  my_logger.info "test"  # outputs "[my_tag] [other_tag]"
end

In other words, TaggedLogging is effectively a singleton within a single thread.

The fix uses a unique key to store the thread-local tag list. (The only weakness is that the thread-local key will never be garbage collected until the thread dies, but it seems unrealistic that anyone would create a huge number of loggers.)

[ches]

👍

I wanted this behavior and expected it to just work. Particularly because current_tags is undocumented and was private in 3.2, one had to go to the source to see why it doesn't. I smacked my head when I got there.

[stephankaag]

@rafaelfranca Was this change ever released? Looks like it's not included in ActiveSupport 4.2.

https://github.com/rails/rails/blob/4-2-stable/activesupport/lib/active_support/tagged_logging.rb#L46

[atombender]

@stephankaag: No, for some reason it's still only on master, even though it was merged more than 10 months ago. Not sure how the release process works, but I'm assuming it will end up in 4.3 (or 5.0).