Re: More info on sporadic OS/X crash

From: Steven Tamm <steventamm@mac.com>
Cc: Piet van Oostrum <piet@cs.uu.nl>, Eli Zaretskii <eliz@gnu.org>,
	emacs-devel@gnu.org
Subject: Re: More info on sporadic OS/X crash
Date: Thu, 29 Apr 2004 15:24:42 -0700	[thread overview]
Message-ID: <031ED742-9A2C-11D8-BE34-00039390AB82@mac.com> (raw)
In-Reply-To: <m3oepa218z.fsf@kfs-l.imdomain.dk>

 From the 10.2 and 10.3 select man pages.

      Select() should probably have been designed to return the time 
remaining
      from the original timeout, if any, by modifying the time value in 
place.
      However, it is unlikely this semantic will ever be implemented, as 
the
      change would cause source code compatibility problems.  In general 
it is
      unwise to assume that the timeout value will be unmodified by the
      select() call, and the caller should reinitialize it on each 
invocation.

However it appears that in the code for xnu-344/bsd/kern/sys_generic.c 
(which corresponds to 10.2), they actually implemented this change

So don't worry about the timeout changing.

-Steven

On Apr 29, 2004, at 9:32 AM, Kim F. Storm wrote:

> "Piet van Oostrum" <piet@cs.uu.nl> writes:
>
>>>>>>> "Eli Zaretskii" <eliz@gnu.org> (EZ) wrote:
>>
>>>> From: "Piet van Oostrum" <piet@cs.uu.nl>
>>>> Date: Wed, 28 Apr 2004 13:14:59 +0200
>>>>
>>>> (gdb) frame 1
>>>> #1  0x0012eeac in sys_select (n=126, rfds=0x38e7e4, wfds=0x0, 
>>>> efds=0x0, timeout=0xbfffc770) at mac.c:2787
>>>> 2787        return select(n, rfds, wfds, efds, timeout);
>>>> (gdb) print *timeout
>>>> $3 = {
>>>> tv_sec = 0,
>>>> tv_usec = 999996
>>>> }
>>>>
>>>> So this looks normal.
>>
>> EZ> Well, yes and no: how come it's 999996 microseconds instead of a 
>> full
>> EZ> second?  That is, why don't you see this instead?
>>
>> EZ>  $3 = {
>> EZ>    tv_sec = 1,
>> EZ>    tv_usec = 0
>> EZ>  }
>>
>> EZ> This higher frame in the backtrace:
>>
>>>> #2  0x00119948 in wait_reading_process_input (time_limit=1, 
>>>> microsecs=0, read_kbd=3506604, do_display=0) at process.c:4311
>>
>> EZ> seems to imply that wait_reading_process_input was called to wait 
>> for
>> EZ> 1 second and 0 microseconds, so where from did the small 
>> inaccuracy
>> EZ> creep in?
>>
>> There is some code just above the select that manipulates the usecs.
>> (The ADAPTIVE_READ_BUFFERING stuff). But I think it always makes it a
>> multiple of READ_OUTPUT_DELAY_INCREMENT, which this isn't.
>>
>> Then there's also timer_delay which gets calculated from something
>> with the current time in it, so maybe that's it.
>
> The Linux kernel adjusts the timeout value upon return from select to
> contain the amount of time "remaining to the specified timeout".  This
> is very useful in some situations.
>
> Maybe OS/X does that too.
>
> -- 
> Kim F. Storm <storm@cua.dk> http://www.cua.dk
>
>
>
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