Class: Cod::WorkQueue

Inherits:
Object
  • Object
show all
Defined in:
lib/cod/work_queue.rb

Overview

Describes a queue that stores work items given through #schedule and works through those items in order if #predicate is true.

Synopsis:

queue = WorkQueue.new
queue.predicate { true }
queue.schedule { 
  # some work
}

# Will try to work through items right now. 
queue.try_work

# Will cleanly shutdown background threads, but not finish work. 
queue.shutdown

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize ⇒ WorkQueue

:nodoc:



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# File 'lib/cod/work_queue.rb', line 21

def initialize
  # NOTE: This is an array that is protected by careful coding, rather
  # than a mutex. Queue would be right, but Rubys GIL will interfere with
  # that producing more deadlocks than I would like.
  @queue = Array.new
  
  @try_work_exclusive_section = ExclusiveSection.new

  @thread = Thread.start(&method(:thread_main))
  @thread.priority = Thread.current.priority - 10
end

Instance Attribute Details

#thread ⇒ Object (readonly)

The internal thread that is used to work on scheduled items in the background.



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# File 'lib/cod/work_queue.rb', line 35

def thread
  @thread
end

Instance Method Details

#clear_thread_semaphore ⇒ Object 



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# File 'lib/cod/work_queue.rb', line 99

def clear_thread_semaphore
  @one_turn = false
end

#exclusive ⇒ Object

Allows to perform other work mutually exclusive with the work performed in the queue. (see ExclusiveSection)



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# File 'lib/cod/work_queue.rb', line 51

def exclusive
  @try_work_exclusive_section.enter { yield }
end

#predicate(&predicate) ⇒ Object

Before any kind of work is attempted, this predicate must evaluate to true. It is tested repeatedly.

Example:

work_queue.predicate { connection.established? }



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# File 'lib/cod/work_queue.rb', line 67

def predicate(&predicate)
  @predicate = predicate
end

#predicate? ⇒ Boolean

Evaluates the predicate. If the predicate is not set, this returns nil.

Returns:

  • (Boolean) 


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# File 'lib/cod/work_queue.rb', line 57

def predicate?
  @predicate && @predicate.call
end

#schedule(&work) ⇒ Object

Schedules a piece of work. Example:

work_queue.schedule { a_piece_of_work }



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# File 'lib/cod/work_queue.rb', line 75

def schedule(&work)
  exclusive {
    @queue << work
  }
end

#shutdown ⇒ Object

Shuts down the queue properly, without waiting for work to be completed.



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# File 'lib/cod/work_queue.rb', line 83

def shutdown
  return unless @thread
  
  @shutdown_requested = true
  @thread.join
  @thread = nil
end

#size ⇒ Object

Returns the size of the queue.



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# File 'lib/cod/work_queue.rb', line 93

def size
  exclusive {
    @queue.size
  }
end

#thread_semaphore_set? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/cod/work_queue.rb', line 102

def thread_semaphore_set?
  @one_turn
end

#try_work ⇒ Object 



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# File 'lib/cod/work_queue.rb', line 37

def try_work
  exclusive {
    # NOTE if predicate is nil or not set, no work will be accomplished. 
    # This is the way I need it. 
    while !@queue.empty? && predicate?
      wi = @queue.shift
      wi.call
    end
  }
end