From: Tomas Pospisek's Mailing Lists <tpo2@...>
Date: 2007-03-02T06:16:26+09:00
Subject: Re: replacing the use of gettimeofday in the scheduler

On Fri, 2 Mar 2007, Avdi Grimm wrote:

> On 3/1/07, Eric Hodel <drbrain@segment7.net> wrote:
>> The Ruby thread scheduler uses setitimer(2) and select(2).  It
>> depends on the wall-clock for implementing features defined in terms
>> of the wall-clock (Kernel#sleep and Thread#join).
>
> <snip>
>
> Thanks for the explanation.  I'm probably missing something, I'm
> confused by why the functionality you describe in Kernel#sleep and
> Thread#join can't be implemented using only select(). Can you clarify?

It *is* implemented using select, but select is, per spec, allowed to 
return before the time's up. So rb_thread_wait_for(time) is (indirectly) 
using gettimeofday to find out how much time has gone by. And if

(diff = (gettimeofday_now - gettimeofday_before_we_called_select) > 0 )

then rb_thread_wait_for reiterates and sleeps (with select) again.

I can see the following solutions:

    * find a reliable time source that works cross-platform. uptime and
      ticks would be candidates, but I haven't found a way to have them
      cross-platform.
    * use thread_timer as a reliable time source
  *t

  --
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   Tomas Pospisek
   http://sourcepole.com -  Linux & Open Source Solutions
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