From: Michael Baker <michaeltbaker@...>
Date: 2010-12-18T16:03:09+09:00
Subject: Re: background threads

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I'm not sure that I understand your question, but there are few things I see
that might be problematic. One problem is that you pass the variable that
you want to change, aFlag, to the Thread constructor. This creates a local
copy of aFlag for the thread. When you change aFlag to true inside of
setSignal, it's not changing the copy of aFlag used by your thread. If you
want to access the same aFlag that you set to false at the top of your run
method, you would do it as follows:

self.aFlag = false

Thread.new() { |arg|
while !self.aFlag
  # do something
end
}

If you do this, you'll need to be sure to prevent your two threads from
accessing the aFlag variable at the same time with a mutex lock.

Inside of setSignal you say c.aFlag = true. I'm assuming you mean self.aFlag
= true.

In display you call sleep without a parameter. This will cause your main
thread to sleep forever after you start the second thread, meaning that your
program will stop there.

I hope this helps!

On Fri, Dec 17, 2010 at 7:56 PM, Venkat Akkineni <
venkatram.akkineni@gmail.com> wrote:

> Hello
>
> Here is a class when run starts printing numbers to the console in a new
> thread. The   c.setSignal(true) starts the infinite loop. The loop keeps
> printing to the console. But the program never goes beyond that
> statement and understandably so, therefore "I am here" never gets
> printed.
>
> I am trying to start a thread and let it run in the background until I
> call a method and set the aFlag to false. I am unable to visualize this
> using semaphores and threads. Could somebody help me.
>
> class Example
>
>  attr_accessor :aFlag , :tr
>
>
>
>  def run
>    self.aFlag = false
>    i = 0
>
>    self.tr=Thread.new(self.aFlag) { |aFlag|
>      while !aFlag
>        puts i
>
>        i=i+1
>        sleep 1
>      end
>    }
>  end
>
>  def display
>    self.run
>    sleep
>  end
>
>  def setSignal(signal)
>    if signal == true
>      display
>    else
>      c.aFlag=true
>    end
>  end
>
> end
>
>
>  c = Example.new
>  c.setSignal(true)
>
>
> puts "I am here"
>
> --
> Posted via http://www.ruby-forum.com/.
>
>

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