How to use Rails' exception handling mechanism in a background thread?


#1

I have some simple asynchronous processing that my app needs to do,
and I wanted something a bit lighter weight than any of the gems or
plugins I’ve run across that handle background processing. I decided
to roll my own, with the added benefit that I get to use native
threads rather than green threads since I’m using JRuby.

I’m unsure how to handle exceptions in the background thread. I’d like
to pass it to Rails’ exception handling mechanism so that it is dealt
with in the same way as exceptions that occur during the normal
request-response cycle (except for rendering the 500 page, of
course). Since I’ve got the exception notifier plugin installed, this
would email me, as well as log the exception to the log file.

Is there a way to let Rails handle the exception, where whatever
exception handling I have in my rails app would get used for
exceptions in the background thread?

In case it helps, I’ve included the code for my background thread
below.

Thanks,
Myron

class UserSubmissionProcessor
SLEEP_TIME = 30 unless defined? SLEEP_TIME
@@semaphore = Mutex.new
@@singleton_thread = nil unless defined? @@singleton_thread

def self.start_processor_if_necessary
@@semaphore.synchronize do
if @@singleton_thread.nil?
@@singleton_thread = Thread.new
{UserSubmissionProcessor.process}
end
end
end

private

def self.process
while true
begin
user_submission = UserSubmission.find(:first, :conditions =>
{:processing_completed => nil}, :order => ‘created_at’)

    if user_submission
      user_submission.process
    else
      sleep SLEEP_TIME
    end
  rescue Exception => ex
    #TODO: how to I propagate exceptions to rails' exception-

handling mechanism?
end
end
end
end