From: Aldric Giacomoni <aldric@...>
Date: 2009-12-16T23:14:55+09:00
Subject: Re: Using threads to show progress

Brian Candler wrote:
> Piyush Ranjan wrote:
>> In the enumerate thread keep pushing id to queue whenever there is a new
>> object being worked on.
>> 
>>  dictated_exams.each do |exam|
>>        queue.push exam.id
>>  end
> 
> That's a really good suggestion: the consumer will block when it tries 
> to pop from the queue, so you don't need to spin.
> 
The idea of the queue is very good.

I now have this code going for me :

require 'thread'
queue = Queue.new

dictated_exams = (1..1_000_000)
backspaces = 8 # Max of dictated_exams string size
worker_thread = Thread.new do
  dictated_exams.each do |exam|
    queue << exam
  end
end
consumer_thread = Thread.new do
  while true
    id = queue.pop
    print "\b" * backspaces
    print id
  end
end
worker_thread.join
consumer_thread.kill

As someone noticed, I am new to threads (I didn't think it was written 
on my forehead, but I guess it must be next to the "Kick me" sign on my 
back). I'm looking for a way to have an idea of what long rake tasks are 
doing. I wrote a long and convoluted task to find and delete rows which 
contain duplicate data. While I am working on it and polishing it up, 
I'd like to be able to keep track of what it does. It has a couple of 
'each' statements, so I will probably end up needing to call a 
'printing' thread a few times, once for each step -- that is why I can't 
just use the main thread to print..
And this also gave me the idea of trying my hand at writing a simple gem 
or plugin to indicate progress (I know it's been done before, but it may 
be good practice for me).

David said that threads aren't elegant. I somewhat agree, I don't really 
like working with them, they seem clunky right now, but it seems to be a 
pretty good way to separate the "showing progress" code and the "getting 
work done" code. Are there better ways to do this?
My original reason for wanting this, which may be misguided, was the 
cost in time for doing a "print" - I remember my early days with Ruby, 
working on Project Euler and trying to keep track of how fast my 
brute-force solutions were going.. And they went MUCH faster without a 
"put" in the loop.
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