Re: Something is wrong with my threads

> On Apr 17, 2019, at 08:31, Andy Jones <[email protected]> wrote:
> 
> Would any of you smart folks like to tell me what stupid thing I am doing here?

SO MANY THINGS!

First off, you’re coding in a proportional font, and that always leads to bugs. :P

More seriously, I’ll comment inline and then provide my counter example:

> require “time"

You don’t need this require to use Time.now.

> def make_thread(idx)

I would avoid having a make_threads method. Methods are opaque, and often you create threads to do work from a queue. You can pass everything in to your make_threads method, or you can just use blocks.

>   Thread.new do
>     # Set things up and wait
>     Thread.current[:idx] = idx
>     Thread.stop

Why call Thread.stop, at all? What do you care? This smells of a control issue.

>     # do the work, then say we're done
>     Thread.current[:done] = true

I generally don’t store state in my threads. Threads are usually workers, not containers. They usually get data from some source, do work, and then put resultant data into another source.

>     Thread.stop

Ditto to #stop above. This thread would have been done if this line wasn’t here at all and it got to the end of it’s block. Control issues. Let go.

>   end
> end
>  
>  
> threads = []; 1.upto(200){|i| threads << make_thread(i) }

container = []; something.each { container << thing }

is the implementation for:

container = something.map { thing }

> starttm = Time.now
>  
> # Do the work
> threads.each{|t| t.run }

They would be running if you didn’t stop them.

> # Wait until all work is done or we time out
> sleep 0.1 until (threads.all?{|t| t[:done] } || Time.now >= starttm + 10)

I don’t get this. Leave them alone. Use Thread#join to let them finish their work and stop on their own.

> # If all work is not done, something has gone very wrong?
> fails = threads.reject{|t| t[:done] }
> if fails.size > 0
>   puts "FAIL"
>   fails.each{|e| puts "#{e[:idx]}: #{e.alive?}" }
> end

Don’t poke at your threads. It makes them angry.

-----

Here’s my counter:

t0 = Time.now

threads = 200.times.map { |i|
  Thread.new do
    Thread.current[:idx] = i # not necessary

    sleep 1                  # lots of "work"
  end
}

threads.each(&:join)         # finish working

p Time.now - t0

# => 1.013938


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