From owner-freebsd-bugs  Mon Dec 27 17:40: 6 1999
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Date: Mon, 27 Dec 1999 17:40:02 -0800 (PST)
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From: Mikhail Teterin <mi@kot.ne.mediaone.net>
Subject: Re: kern/13644
Reply-To: Mikhail Teterin <mi@kot.ne.mediaone.net>
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The following reply was made to PR kern/13644; it has been noted by GNATS.

From: Mikhail Teterin <mi@kot.ne.mediaone.net>
To: jasone@FreeBSD.org
Cc: freebsd-bugs@FreeBSD.org, FreeBSD-gnats-submit@FreeBSD.org,
	lawlopez@cisco.com, jseger@FreeBSD.org
Subject: Re: kern/13644
Date: Mon, 27 Dec 1999 20:38:58 -0500 (EST)

 jasone@FreeBSD.ORG once stated:
 
 =Synopsis: select(2) timer inaccurate, especially with -pthread
 =
 =State-Changed-From-To: open->closed
 =State-Changed-By: jasone
 =State-Changed-When: Mon Dec 27 12:39:03 PST 1999
 =State-Changed-Why: 
 =The kernel  implementation of  sleep() uses  tvtohz() to  calculate the
 =number of ticks  that tsleep() should sleep. tvtohz() adds  one tick to
 =allow  for the  possibility that  the current  tick is  almost expired.
 
 =select() guarantees that it will sleep  at least as long as the timeout
 =before returning an empty result (0).
 
 This is NOT what the man page states:
 
 	If timeout is a non-nil  pointer, it specifies a maximum
 	interval to wait for the selection to complete.
 
 =If the  number of ticks  passed to tsleep()  were reduced by  one, this
 =guarantee would no longer be possible.
 =
 =This is not a bug; it is  an artifact of correct implementation. If you
 =need higher resolution, use nanosleep().
 
 In  particular, TCL's  after(n)  implementation relies  on this  fact...
 People responsible for  the TCL port may need to  take a note... Because
 in TCL 8.x's  unix/tclUnixEvent.c there is a  function Tcl_Sleep(ms) and
 the comments in it say:
 
     /*
      * The only trick here is that select appears to return early
      * under some conditions, so we have to check to make sure that
      * the right amount of time really has elapsed.  If it's too
      * early, go back to sleep again.
      */
 
 
 Please, consider reviewing this again without the implementation details
 obstructing the view. :-)
 
 	-mi
 


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