digital-fabric / affect Goto Github PK

Affect.capture doesn't seem thread-safe because it mutates the current context (@@current) class variable and Affect is shared across threads.

For example:

t1 = Thread.new  {
  Affect.capture(log: -> (message) { puts "logging 1: #{message}" }) do
    Affect.perform(:log, "foo")
  end
}

t2 = Thread.new {
  Affect.capture(log: -> (message) { puts "logging 2: #{message}" }) do
    Affect.perform(:log, "bar")
  end
}
t1.join
t2.join

might end up printing "logging 2: foo\nlogging 2: bar\n" instead of "logging 1: foo\nlogging 2: bar\n".

This specific issue can be fixed by using Thread.current[:current_ctx] to attach the current context to the current thread (do you want me to open a PR?). However: I think this will lead to other issues when using Threads in user-land [1].

So I looked into using the fiber implementation which doesn't mutate global state, so the above code works fine. I believe it has the same problem when using Thread.new around perform as the Thread.current solution, though. Fibers don't seem to play nicely with threads.

Do you have any experience using your affect library in a multi-threaded environment? Maybe it's best to simply ban threads from user-land?

[1] The part of a code base which only cares about perform, not about how to handle the effects.