Proper Mutex usage / Good coding style? - ruby

Question

Within the following code, the producer periodically_fill_page_queue might add a page to the queue that is currently being consumed (read: in the consumer before the status being_processed is set).
class Example
def initialize
#threads = ThreadGroup.new
#page_queue = Queue.new
Thread.abort_on_exception = true
end
def start
periodically_fill_page_queue
periodically_process_page_queue
end
def periodically_fill_page_queue
#threads.add(Thread.new do
loop do
if #page_queue.empty?
Page.with_state(:waiting).each do |p|
p.queued!
#page_queue << f
end
end
sleep 2
end
end)
end
def periodically_process_page_queue
loop do
until file = #page_queue.pop
sleep 2
end
page.being_processed
process(page)
end
end
def process(page)
sleep 120
page.processed
end
end
class Page < ActiveRecord::Base
state_machine :state, :initial => :waiting do
event :queued do
transition :waiting => :queued
end
event :being_processed do
transition :queued => :being_processed
end
event :processed do
transition :being_processed => :processed
end
end
end
To avoid this, i'd use a Mutex object:
def initialize
...
#mutex = Mutex.new
end
def periodically_process_page_queue
loop do
until file = #page_queue.pop
sleep 2
end
#mutex.synchronize { page.being_processed }
process(page)
end
end
Is this "good" coding style, or are there any more elegant approaches?
Thanks!

Answer 1

Not with this design. Some alternative designs might do one of the below, but naturally have their own can of worms.
"Fork"
For each job you start a new thread or process, giving it the job
Delegation
Delegate the task to a queue in each thread. Each thread pulls from its own unique queue.
Stride
You have a circular buffer and each thread checks at a different interval. E.G. Num_threads + thread.id
This probably isn't for your situation.
Range
A thread is responsible for a range of jobs. num_threads * thread.id
This probably isn't for your situation.