From: Tom Ricks <carrottop123@...>
Date: 2009-05-26T07:40:38+09:00
Subject: Re: Running code at a certain time?

Caleb Clausen wrote:
> On 5/25/09, Tom Ricks <carrottop123@gmail.com> wrote:
>> Hello all,
>>    I am new to ruby and I am attempting to run some code at a certain
>> time. The Ruby Time class is very interesting, you can add time, and do
>> all of these amazing things but i cannot find a way to run code at a
>> certain time. I feel like I'm missing something. So far all I have is:
>>
>> sleep(1) while Time.now < ("Time")
>>
>> How would I link some code to be run to this? Or is there an easier way?
>> 
> The proper answer depends on the context where this code will be used.
> Do you want your whole program to stop until some target time?
> But if this code runs within the context of
> some larger system, which cannot afford to have the whole program be
> unable to respond to events for many seconds in a row (rails, for
> example), then sleep is a bad idea.

Well, I'm not really sure. The intent is to have a repetitive code ran 
at quite a few different times with changing variables. The sleep option 
doesn't really seem reliable and realistic, although its the only thing 
so far. The code I can come up with is this:

class TestClass
  def testtime(timetorun)
    timetorun = @timetorun
    sleep(1) while Time.now.strftime("%I:%M:%S %p") < ("#{@timetorun}")
    #Somewhere code to run when Time.now = timetorun
  end
end
test = TestClass.new
test.testtime("11:04:40 AM")

The problems are #1. I don't know how to link the time code to the code 
to be run when the time code is fulfilled. #2. If I have a list of times 
to be run, and one time is out of order, it will just sleep past the out 
of order time. #3. While the code is waiting for a certain time, with 
sleep, it cannot do anything else. Is there a way that I can run code 
that will watch for a time to be fulfilled on many levels instead of 
just waiting until a time, moving on and waiting for the next? Is it 
possible to do something like this:

when test.testtime is true/finished?
 run some code
end

> In some cases, you might be able
> to put your sleep and code_to_be_delayed in another thread, but then
> you run into the problem of thread synchronization.

How would I do this?

Your example of

sleep(target_time-Time.now)
code_to_be_delayed

seems to work better, although it still shuts the whole code down for a 
while.
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