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Re: Suggested note to Checkpoint 5.5 on timeliness

From: Ian Jacobs <ij@w3.org>
Date: Wed, 08 Mar 2000 11:20:34 -0500
Message-ID: <38C67DD2.41516867@w3.org>
To: Hans Riesebos <HRiesebos@alva-bv.nl>
CC: schwer@us.ibm.com, "<" <w3c-wai-ua@w3.org>
Hans Riesebos wrote:

Rich, Hans, and others,

If there are known security issues for these techniques, that at
least deserves a mention in the Techniques document. Please suggest
wording.

 - Ian
 
> Rich,
> 
> our outSPOKEN makes happily use of in-process CPU-time and other priveleges that come with it to build our OSM. We couldn't very well do it without. The point is that going in-process in our case is a kind of security-hole in the MS windows system (certainly for NT). Microsoft is discouraging this way of working en looks for ways to solve this security-hole. The main reason is that MS software (including the OS) crashes because of this kind of practice. MS is left to proof that they did not crash but some other program caused this and they are simply disbeliieved.
> 
> When MS software needed in process execution in MS software, that would be entirely another case (as would Screen Reader software in OS/2).
> 
> I am totally aware that what we are asking from UA's is to voluntarily execute (of course only bits of) AT-code in-process. If it is the consensus of this working group that we mention this as a useful technique (in the techniques document), than that is oke with me. For myself, I would like a secure solution. If that means a bit less performance now, so be it. I still think that there are more ways to improve performance.
> 
> I may be wrong, but I do not think that the process-switches (even with bursts of a hunderd per second) and data copying (even several Kb per second) account for most of the performance "losses" currently experienced in interprocess communication.
> 
> Hans
> 
> >>> <schwer@us.ibm.com> 03/07/00 10:41PM >>>
> 
> Hans,
> 
> First, you don't architect your solution to have the entire AT software
> package run in process with the application. You have only the portions
> necessary to improve performance run in process with the application. We
> did this very successfully in Screen Reader/2 when supporting Windows. If
> you were to use the Java access bridge or the SVK to help support Java
> appications you are successful also. Much of what you need can run in
> process and if the Java app dies you only lose the part of the AT dealing
> with that application which is dead anyway.
> 
> Also, if the main AT goes down the the part running in the UA should not go
> down.
> 
> Given current technologies, in particular OSM it is extremely easy to not
> only bring the application down but the entire system. Since ultimately the
> OSM will run in process for all applications by virtue of the fact that it
> is a DLL linked in the graphics call chain of the application. So, there is
> nothing new that in-proces introduces that is not already an issue today
> for other AT mechanisms for getting at information.
> 
> Your downside concerns are not warranted.
> 
> Rich
> 
> Rich Schwerdtfeger
> Lead Architect, IBM Special Needs Systems
> EMail/web: schwer@us.ibm.com http://www.austin.ibm.com/sns/rich.htm
> 
> "Two roads diverged in a wood, and I -
> I took the one less traveled by, and that has made all the difference.",
> Frost
> 
> "Hans Riesebos" <HRiesebos@alva-bv.nl> on 03/07/2000 11:21:05 AM
> 
> To:   jongund@ux1.cso.uiuc.edu
> cc:   "<" <w3c-wai-ua@w3.org>
> Subject:  Re: Suggested note to Checkpoint 5.5 on timeliness
> 
> Rich wrote:
> 
> <PROPOSEDRICH>
> >This checkpoint is designed to reduce delays that an assistive
> >technology user might experience due to communication overhead when
> >accessing
> >parts of your application such as your DOM.
> >Timely exchange is import for preventing loss of information,
> >a risk when changes in content occur faster than the
> >exchange with the assistive technology. One effective technique
> >for providing timely access is to allow assistive technologies to run
> >in the same process space as the user agent, thus eliminating
> >inter-application communication delays.
> ></PROPOSEDRICH>
> >
> 
> I'm really sorry that I only bring this "in process" argument to attention
> now. I understood that the mention of "in process" would never make it to
> the checkpoint-text (or notes with it).
> 
> Shouldn't we have techniques in the techniques document?
> 
> The argument:
> 
> "In process"  IS an effective technique. It has an important downside. If
> the AT crashes "in process" it crashes the UA. The AT can also have the UA
> crash by (inadvertently?) corrupt internal data of the UA. I am (almost)
> sure this is not what a UA is willing to do.
> 
> A way to a solution?
> 
> The "in process" technique leads to three performance improvements:
> 1) No process switching needed
> 2) No waiting until the next process switch is needed
> 3) No copying of data needed (reaching other process's memory is not
> possible on Win32 platforms. I am not sure but I believe it is possible on
> the Macintosh)
> 
> Point 3 can be solved by using shared memory (is a technique). I am aware
> that shared memory can be corrupted when it is writable.
> 
> Point 2 can be solved by giving higher (or equal?) priority to the
> AT-process-threads or explicitly allowing a switch by the UA. I am aware
> that the AT could starve the UA.
> 
> Point 1 can ONLY be solved by going "in process". It has the disadvantages
> of data corruption AND the AT taking all the CPU time AND corruption of
> internal UA-data.
> 
> Bottom-line.
> In process is a technique that has great efficiency and a big downside. I
> personally think the downside is too big to even recommend this technique.
> It still is a technique and should (if mentioned) be mentioned in the
> techniques document.
> 
> sincerely, Hans Riesebos
> ALVA, The Netherlands
> HRiesebos@alva-bv.nl
> 
> >>> Jon Gunderson <jongund@ux1.cso.uiuc.edu> 03/06/00 06:22PM >>>
> Hans,
> 
> 1. Would a clause that said:
> 
> "One effective technique in operating sytems that use separate process
> spaces for providing timely access is to allow assistive technologies to
> run in the same process space as the user agent, thus eliminating
> inter-application communication delays"
> 
> 2. Do you have any examples of what techniques would be useful on a
> Macintosh operating system to support inter-process communication?
> 
> Thanks,
> Jon
> 
> At 05:35 PM 3/6/00 +0100, Hans Riesebos wrote:
> >I think that the "In process" must not be mentioned or at best be
> mentioned
> >in the techniques document (not in the guidelines).
> >Letting an AT in process is a potential security hole! Also, for the
> >Macintosh, there are no seperate process-spaces and therefore is in
> process
> >less meaningful.
> >
> >>>> Jon Gunderson <jongund@ux1.cso.uiuc.edu> 03/03/00 04:44PM >>>
> >Note to checkpoint 5.5: This checkpoint is designed to promote the use of
> >APIs which provide efficient exchange of information between user agents
> >and assistive technologies.  Notably in multi-tasking operating systems
> >this requires the ability to access the DOM and other Accessibility APIs
> in
> >process.  In process communication eliminates the time delays which occur
> >with out-of-process communication between applications.  The time delays
> >can result in slower response to user actions or potentially the user
> >missing important information.
> >
> >Jon
> >
> >Jon Gunderson, Ph.D., ATP
> >Coordinator of Assistive Communication and Information Technology
> >Chair, W3C WAI User Agent Working Group
> >Division of Rehabilitation - Education Services
> >College of Applied Life Studies
> >University of Illinois at Urbana/Champaign
> >1207 S. Oak Street, Champaign, IL  61820
> >
> >Voice: (217) 244-5870
> >Fax: (217) 333-0248
> >
> >E-mail: jongund@uiuc.edu
> >
> >WWW: http://www.staff.uiuc.edu/~jongund
> >WWW: http://www.w3.org/wai/ua
> >
> >
> 
> Jon Gunderson, Ph.D., ATP
> Coordinator of Assistive Communication and Information Technology
> Chair, W3C WAI User Agent Working Group
> Division of Rehabilitation - Education Services
> College of Applied Life Studies
> University of Illinois at Urbana/Champaign
> 1207 S. Oak Street, Champaign, IL  61820
> 
> Voice: (217) 244-5870
> Fax: (217) 333-0248
> 
> E-mail: jongund@uiuc.edu
> 
> WWW: http://www.staff.uiuc.edu/~jongund
> WWW: http://www.w3.org/wai/ua

-- 
Ian Jacobs (jacobs@w3.org)   http://www.w3.org/People/Jacobs
Cell:                        +1 917 450-8783
Received on Wednesday, 8 March 2000 11:21:59 GMT

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