[brailleblaster] Re: utdml2brl.temp
- From: Keith Creasy <kcreasy@xxxxxxx>
- To: "brailleblaster@xxxxxxxxxxxxx" <brailleblaster@xxxxxxxxxxxxx>
- Date: Mon, 14 May 2012 08:39:50 -0400
Hi, just picked up on this thread.
My advice is to take the time to make the library thread-safe. I can't point to
any examples but do know some techniques that I used on our own braille
translator, which is thread safe and quite robust. Basically it boils down to
avoiding any global variables in the API and creating the API such that it just
creates an instance of the library object; i.e. a translator, and returns it as
a new object. Everything is encapsulated. The API is then used to destroy the
object on completion. Objects that do the work are not shared between processes
or threads.
A unique ID can be used to create directories for temp files if necessary.
It isn't really hard or complicated but converting a library that is not
thread-safe can obviously be error prone and should be introduced with care.
Keith
-----Original Message-----
From: brailleblaster-bounce@xxxxxxxxxxxxx
[mailto:brailleblaster-bounce@xxxxxxxxxxxxx] On Behalf Of John J. Boyer
Sent: Monday, May 14, 2012 8:15 AM
To: brailleblaster@xxxxxxxxxxxxx
Subject: [brailleblaster] Re: utdml2brl.temp
What is involved in making a library thread-safe? Is there a tutorial with
examples?
Thanks,
John
On Mon, May 14, 2012 at 12:12:52PM +0100, Michael Whapples wrote:
> Hello,
> Yes I agree with what you say about liblouisutdml not being thread
> safe and so the only real answer at the moment is to use it from
> synchronized blocks.
>
> If you don't intend to make it thread safe, then may be it would be
> worth making a note somewhere in the documentation explaining it is
> not thread safe and there are currently no plans to make it thread safe.
>
> As for what you suggest about using the file system of each machine in
> the cluster, this would not always work:
> * What about multi-core processors, there is only one file system in
> that case and so the available processing power is under utilised.
> * I don't know how the various cluster systems work, but I thought
> they are trying to work towards making the fact its running on a
> cluster more transparent and so there may be cases or the time might
> come where one could not do such a configuration as you describe.
>
> Whether its worth your time, I don't know, but as time goes on
> multi-threaded environments will become more and more improtant and so
> a thread safe option may be needed, is there one?
>
> Michael Whapples
> On 14/05/2012 11:44, John J. Boyer wrote:
> >I think the synchronized block is the only way to assure correct
> >performance. There are lots of shared variables. Making liblouisutdml
> >and liblouis thread-save would be a big unndertaking and there are
> >better ways to spend my time. Another solution would be to give each
> >machine in the cluster its own directories. The synchronized block
> >should not then exact much of a performance penalty.
> >
> >John
> >
> >On Mon, May 14, 2012 at 10:44:20AM +0100, Michael Whapples wrote:
> >>While synchronized blocks may prevent the issue showing, it might
> >>not be the real answer as it can lead to poor performance. In this
> >>case this probably is true.
> >>
> >>The reason is that synchronized means that other threads have to
> >>wait for the current thread to finish the synchronized block. In
> >>this case as there are multiple machines and really separate
> >>translations should be, well, separate, there should not really be a
> >>need to have to do translations sequentially. Sequential translation
> >>is not the most efficient/intended way to use a cluster environment.
> >>
> >>The original suggestion of having separate temp files for each
> >>translation is the correct and fastest way for this to work in a
> >>cluster environment. May be having it based on the file name is one
> >>solution, another would be to allow the calling application to set
> >>the temp file name for the current translation.
> >>
> >>Having said the above, even if the file name thing was seen to,
> >>there could very well be other bugs with using it in a
> >>multi-threaded environment (eg. there may be shared variables which
> >>multiple translations both may try to use, etc).
> >>
> >>So may be John's suggestion of using synchronized is the only way to
> >>do this in the immediate future, significant work could be needed to
> >>make liblouisutdml thread safe and so may simply not be the right
> >>choice for such a use.
> >>
> >>Michael Whapples
> >>On 14/05/2012 03:35, John J. Boyer wrote:
> >>>Hi Alex,
> >>>
> >>>If I remember right, you should do something like this
> >>>
> >>>synchronized {
> >>>file2brl (arguments);
> >>>}
> >>>
> >>>or you could call translateFile within the block.
> >>>
> >>>John
> >>>
> >>>On Sun, May 13, 2012 at 06:46:36PM -0700, Alex Jurgensen wrote:
> >>>>Hi John,
> >>>>
> >>>>My translation system consists of aprox 100 Thousand concurrent
> >>>>translations over a small cluster of machines. Do you have any
> >>>>advice for how I should implement the LibLouisUTDML interface in
> >>>>Java?
> >>>>
> >>>>Regards,
> >>>>Alex,
> >>>>
> >>>>
> >>>>
> >>>>
> >>>>Alex Jurgensen,
> >>>>Community Coordinator,
> >>>>The Camp Bowen Society for the Visually Impaired,
> >>>>
> >>>>Explore Camp Bowen online at: http://www.campbowen.ca/
> >>>>
> >>>>Phone: 778-908-0521
> >>>>E-mail: ASquared21@xxxxxxxxx
> >>>>
> >>>>
> >>>>
> >>>>
> >>>>On 2012-05-13, at 6:37 PM, John J. Boyer wrote:
> >>>>
> >>>>>Hi Alex,
> >>>>>
> >>>>>If you are using Java it would be best to use a synchronized
> >>>>>block. If a translation is started while another is in progress
> >>>>>they will interfere with each other, even if you use a method
> >>>>>that does not generate file2brl.temp. Each translation takes only
> >>>>>a few seconds, so your users should not notice much delay.
> >>>>>
> >>>>>John
> >>>>>
> >>>>>On Sat, May 12, 2012 at 06:13:50PM -0700, Alex Jurgensen wrote:
> >>>>>>Hi John,
> >>>>>>
> >>>>>>To add to my previous question, I was wondering if such a
> >>>>>>feature could work as follows:
> >>>>>>
> >>>>>>/usr/bin/file2brl --tempfile /tmp/myfile.temp
> >>>>>>/home/Alex/myfile.xml /home/Alex/myfile.brl
> >>>>>>
> >>>>>>Regards,
> >>>>>>Alex,
> >>>>>>
> >>>>>>
> >>>>>>Alex Jurgensen,
> >>>>>>Community Coordinator,
> >>>>>>The Camp Bowen Society for the Visually Impaired,
> >>>>>>
> >>>>>>Explore Camp Bowen online at: http://www.campbowen.ca/
> >>>>>>
> >>>>>>Phone: 778-908-0521
> >>>>>>E-mail: ASquared21@xxxxxxxxx
> >>>>>>
> >>>>>>
> >>>>>>
> >>>>>>
> >>>>>>On 2012-05-12, at 5:23 PM, John J. Boyer wrote:
> >>>>>>
> >>>>>>>Hi Alex,
> >>>>>>>
> >>>>>>>I assume you are referring to file2brl.temp This file is
> >>>>>>>overwritten each time the file2brl command-line program or the
> >>>>>>>file2brl method in the Java bindings is run. It is not intended
> >>>>>>>for any permanent use, but may be useful for debuging. What are
> >>>>>>>your reasons for wanting a file name that reflects the source
> >>>>>>>file?
> >>>>>>>
> >>>>>>>Thanks,
> >>>>>>>John
> >>>>>>>
> >>>>>>>On Sat, May 12, 2012 at 01:06:56PM -0700, Alex Jurgensen wrote:
> >>>>>>>>Hi John,
> >>>>>>>>
> >>>>>>>>Is it possible to have LibLouisUTDML create a temporary file
> >>>>>>>>that is not named utdml2brl.temp, but rather, uses the name of
> >>>>>>>>the source document one is translating? For example,
> >>>>>>>>"file1.temp" or "file2.temp"
> >>>>>>>>
> >>>>>>>>Regards,
> >>>>>>>>Alex,
> >>>>>>>>
> >>>>>>>>Alex Jurgensen,
> >>>>>>>>Software Engineer,
> >>>>>>>>ASInnovations,
> >>>>>>>>
> >>>>>>>>"We might be blind, but we have a vision."
> >>>>>>>>
> >>>>>>>>Phone: 778-908-0521
> >>>>>>>>E-mail: VoiceOverTrainer@xxxxxx
> >>>>>>>>
> >>>>>>>--
> >>>>>>>John J. Boyer; President, Chief Software Developer
> >>>>>>>Abilitiessoft, Inc.
> >>>>>>>http://www.abilitiessoft.com
> >>>>>>>Madison, Wisconsin USA
> >>>>>>>Developing software for people with disabilities
> >>>>>>>
> >>>>>>>
> >>>>>--
> >>>>>John J. Boyer; President, Chief Software Developer Abilitiessoft,
> >>>>>Inc.
> >>>>>http://www.abilitiessoft.com
> >>>>>Madison, Wisconsin USA
> >>>>>Developing software for people with disabilities
> >>>>>
> >>>>>
>
--
John J. Boyer; President, Chief Software Developer Abilitiessoft, Inc.
http://www.abilitiessoft.com
Madison, Wisconsin USA
Developing software for people with disabilities
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