This is a simple threaded pool worker system that can process tasks in the order they are received.


pool =

pool.perform do
  # ... Action to be enqueued here

The worker pool has some sensible defaults as to how many workers will be created, zero when there's no work, up to twenty when there's enough work to be performed. These settings can be customized.

Constructor options:

  • :worker_class - What kind of worker to spawn. Should be a Worker subclass.
  • :workers_min - The minimum number of workers to have running.
  • :workers_max - The maximum number of workers to have running.
  • :count_per_worker - The ratio of tasks to workers.

The default EnThpool::Worker class should suffice for most tasks. If necessary, this can be subclassed. This would be useful if the worker needs to perform some kind of resource initialization before it's able to complete any tasks, such as establishing a database connection.

There is a method after_initialize that will execute on the worker thread immediately after the worker is created. This is useful for performing post-initialization functions that would otherwise block the main thread:

class ExampleDatabaseWorker < Thpool::Worker
  def after_initialize
     # Create a database handle.
     @db =

     # Pass in the database handle as the arguments to the blocks being
     # processed.
     @args = [ @db ]

It's also possible to re-write the perform method to pass in additional arguments.

If you need to do something immediately before or after processing of a block, two methods are available. As an example this can be used to record the amount of time it took to complete a task:

class ExampleDatabaseWorker < Thpool::Worker
  def before_perform(block)
    @start_time =

  def after_perform(block)
    puts "Took %ds" % ( - @start_time)

If exceptions are generated within the worker thread either because of processing a task or otherwise, these are passed back to the Thpool object via the handle_exception method. The default behavior is to re-raise these, but it's also possible to perform some additional handling here to rescue from or ignore them:

class ExampleDatabasePool < Thpool
  def handle_exception(worker, exception, block = nil)
    # Pass through to a custom exception logger


Copyright (c) 2013 Scott Tadman, The Working Group Inc. See LICENSE.txt for further details.