From: "Artūras Šlajus" <x11@...>
Date: 2009-09-10T05:37:54+09:00
Subject: EventMachine.defer and ActiveRecord connection pool?

Hello,

I'm writing a server with EM. I'm having some long-running tasks, so I'm
deferring those requests using EM.defer.

However, after 5 such deferred requests AR suddently stops working...
I'm using AR 2.3.4, so concurrency shouldn't be a problem. Gems
configuration:

REQUIRED_GEMS = [
  ['mysql', '>=2.7.0'],
  ['activerecord', '=2.3.4'],
  ['activesupport', '=2.3.4'],
  ['eventmachine', '=0.12.6'],
  ['json', '>=1.1.6'],
  "daemons"
]

Anyway, as you can see it happens after 5 requests (just simulated
action, one select query):

[2009-09-09 23:32:35|main|info ] Starting server...
[2009-09-09 23:32:36|main|info ] [Resources manager]
[Resources manager END] Time taken: 0.031 seconds
[2009-09-09 23:32:37|main|info ] [Resources manager]
[Resources manager END] Time taken: 0.016 seconds
[2009-09-09 23:32:38|main|info ] [Resources manager]
[Resources manager END] Time taken: 0.000 seconds
[2009-09-09 23:32:39|main|info ] [Resources manager]
[Resources manager END] Time taken: 0.016 seconds
[2009-09-09 23:32:40|main|info ] [Resources manager]
[Resources manager END] Time taken: 0.000 seconds
[2009-09-09 23:32:41|main|info ] [Resources manager]
[Resources manager END with EXCEPTION]
#<ActiveRecord::ConnectionTimeoutError: c
ould not obtain a database connection within 5 seconds.  The max pool
size is cu
rrently 5; consider increasing it.>

I'm running this code:
EventMachine::run {
  EventMachine::start_server "0.0.0.0", 843, FlashPolicyServer
  EventMachine::start_server "0.0.0.0", CONFIG['port'], GameServer

  # Resources manager
  EventMachine::PeriodicTimer.new(CONFIG['resources_manager.period']) do
    SingletonBlock.run("Resources manager", nil, nil, :defer => true) do
      "Time taken: %4.3f seconds" % Benchmark.realtime {
ResourcesEntry.tick }
    end
  end
}

Where SingletonBlock is:
# Class for running one block of same name at a time
class SingletonBlock
  @@running = {}
  @@lock = Mutex.new

  class << self
    def run(name, operation=nil, callback=nil, options={}, &block)
      unless running?(name)
        operation ||= block

        options.reverse_merge!(:defer => true)
        if options[:defer]
          EventMachine.defer(
            proc do
              SingletonBlock.started(name)
              LOGGER.block(name) { operation.call }
            end,
            proc do
              LOGGER.block("#{name} CALLBACK") { callback.call } if
callback
              SingletonBlock.finished(name)
            end
          )
        else
          SingletonBlock.started(name)
          LOGGER.block(name) { operation.call }
          LOGGER.block("#{name} CALLBACK") { callback.call } if callback
          SingletonBlock.finished(name)
        end
      end
    end

    def running?(name)
      @@lock.synchronize do
        ! @@running[name].nil?
      end
    end

    def started(name)
      @@lock.synchronize do
        @@running[name] = true
      end
    end

    def finished(name)
      @@lock.synchronize do
        @@running.delete(name)
      end
    end
  end
end

If I don't use EM.defer - everything works fine.

Googled - nothing found. Any ideas?
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