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<p class=MsoNormal><span style='color:#1F497D'>I think the reason is the fact
that the SDF provider keeps an update buffer for every table. All readers are
using the same cursor to avoid flushing the buffer everytime a query is executed.
Writing and reading at the same time is a common use case. <o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>Badreddine <o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<div>
<div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in'>
<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>
fdo-internals-bounces@lists.osgeo.org
[mailto:fdo-internals-bounces@lists.osgeo.org] <b>On Behalf Of </b>Haris
Kurtagic<br>
<b>Sent:</b> Wednesday, August 13, 2008 5:16 PM<br>
<b>To:</b> FDO Internals Mail List<br>
<b>Subject:</b> RE: [fdo-internals] RE: SDF feature reader <o:p></o:p></span></p>
</div>
</div>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><span style='color:#1F497D'>if i interpret code correctly
there was allready attempt to solve issue with multiple readers with
“Tag” in DbData and call to function RefreshData before every Get..
in feature reader.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>I would like to ask is why only
one sqlite cursor is used for one sqlite table for all readers. That looks like
potential source of problem ?<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>Create new sqlite cursor for
every reader ?<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>Haris<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<div>
<div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in'>
<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>
fdo-internals-bounces@lists.osgeo.org
[mailto:fdo-internals-bounces@lists.osgeo.org] <b>On Behalf Of </b>Badreddine
Karoui<br>
<b>Sent:</b> Wednesday, August 13, 2008 10:47 PM<br>
<b>To:</b> FDO Internals Mail List<br>
<b>Subject:</b> RE: [fdo-internals] RE: SDF feature reader <o:p></o:p></span></p>
</div>
</div>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><span style='color:#1F497D'>There is probably a way to fix
this issue and only make a copy if 2 readers are used. <o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>Badreddine<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<div>
<div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in'>
<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'> fdo-internals-bounces@lists.osgeo.org
[mailto:fdo-internals-bounces@lists.osgeo.org] <b>On Behalf Of </b>Traian
Stanev<br>
<b>Sent:</b> Wednesday, August 13, 2008 4:39 PM<br>
<b>To:</b> 'FDO Internals Mail List'<br>
<b>Subject:</b> RE: [fdo-internals] RE: SDF feature reader <o:p></o:p></span></p>
</div>
</div>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>Yes, this is an intentional
limitation, for the same reason (performance).<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>Traian<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<div style='border:none;border-left:solid blue 1.5pt;padding:0in 0in 0in 4.0pt'>
<div>
<div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in'>
<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>
fdo-internals-bounces@lists.osgeo.org
[mailto:fdo-internals-bounces@lists.osgeo.org] <b>On Behalf Of </b>Haris
Kurtagic<br>
<b>Sent:</b> Wednesday, August 13, 2008 4:53 PM<br>
<b>To:</b> FDO Internals Mail List<br>
<b>Subject:</b> RE: [fdo-internals] RE: SDF feature reader <o:p></o:p></span></p>
</div>
</div>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><span style='color:#1F497D'>Hm, but problem is not
thread related.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>Having 2 feature readers for
same SDF connection inside one thread will create invalid data.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>Haris<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<div>
<div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in'>
<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>
fdo-internals-bounces@lists.osgeo.org [mailto:fdo-internals-bounces@lists.osgeo.org]
<b>On Behalf Of </b>Traian Stanev<br>
<b>Sent:</b> Wednesday, August 13, 2008 10:32 PM<br>
<b>To:</b> FDO Internals Mail List<br>
<b>Subject:</b> RE: [fdo-internals] RE: SDF feature reader <o:p></o:p></span></p>
</div>
</div>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>This behavior is really a
tradeoff between performance and full thread safety. SDF is near the
performance end of the spectrum. I figure, if someone desires full <o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>thread safety, they can use a
real database.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>Traian<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<div style='border:none;border-left:solid blue 1.5pt;padding:0in 0in 0in 4.0pt'>
<div>
<div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in'>
<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>
fdo-internals-bounces@lists.osgeo.org
[mailto:fdo-internals-bounces@lists.osgeo.org] <b>On Behalf Of </b>Gavin Cramer<br>
<b>Sent:</b> Wednesday, August 13, 2008 4:27 PM<br>
<b>To:</b> FDO Internals Mail List<br>
<b>Subject:</b> RE: [fdo-internals] RE: SDF feature reader <o:p></o:p></span></p>
</div>
</div>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><span lang=EN-CA style='color:#1F497D'>GetGeometry (the one
returning an FdoByte *) has documentation that says the following:<o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-CA style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span lang=EN-CA style='color:#1F497D'>“The array's
memory area is only guaranteed to be valid until a call to ReadNext() or
Close(), or the disposal of this reader object.”<o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-CA style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span lang=EN-CA style='color:#1F497D'>So, the code is
behaving according to the specification. There should be a similar
statement for GetString, as well as any other accessor that returns a pointer
to non-reference-counted arrays, but I do not see one. Anyway, an FDO
client should expect the above behaviour from any FDO provider, even if it
actually does some internal copying.<o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-CA style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span lang=EN-CA style='color:#1F497D'>Regardless, it looks
like the behaviour that Haris sees is a defect. Different readers should
not be sharing an internal cursor.<o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-CA style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span lang=EN-CA style='color:#1F497D'>Gavin<o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-CA style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span lang=EN-CA style='color:#1F497D'><o:p> </o:p></span></p>
<div>
<div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in'>
<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>
fdo-internals-bounces@lists.osgeo.org
[mailto:fdo-internals-bounces@lists.osgeo.org] <b>On Behalf Of </b>Badreddine
Karoui<br>
<b>Sent:</b> Wednesday, August 13, 2008 4:14 PM<br>
<b>To:</b> FDO Internals Mail List<br>
<b>Subject:</b> RE: [fdo-internals] RE: SDF feature reader <o:p></o:p></span></p>
</div>
</div>
<p class=MsoNormal><span lang=EN-CA><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>The free threaded provider would
use FdoThreadCapability_MultiThreaded defined in <a
href="https://svn.osgeo.org/fdo/trunk/Fdo/Unmanaged/Inc/Fdo/Connections/Capabilities/ThreadCapability.h">https://svn.osgeo.org/fdo/trunk/Fdo/Unmanaged/Inc/Fdo/Connections/Capabilities/ThreadCapability.h</a><o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>The SDF provider is returning
FdoThreadCapability_PerConnectionThreaded. <o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>I had a quick look and I can see
that the SDFSimpleFeatureReader::GetGeometry(FdoString*, FdoInt32*) is returing
the pointer from the internal buffer. This may have been done to avoid paying
the penalty of copying the geometry. The second oveload,
GetGeometry(FdoString*) is returing a copy and should not have the same issue. <o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>We may have to be extra carefull
in case we decide to fix this issue to make sure the reader performance is not
impacted. <o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>Badreddine<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<div>
<div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in'>
<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>
fdo-internals-bounces@lists.osgeo.org
[mailto:fdo-internals-bounces@lists.osgeo.org] <b>On Behalf Of </b>Haris
Kurtagic<br>
<b>Sent:</b> Wednesday, August 13, 2008 3:12 PM<br>
<b>To:</b> FDO Internals Mail List<br>
<b>Subject:</b> RE: [fdo-internals] RE: SDF feature reader <o:p></o:p></span></p>
</div>
</div>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><span style='color:#1F497D'>it looks that feature readers
are sharing same sqlite cursor with one data buffer. (BTW: Application
is sending this readers to be used by another app so it is not able to create
new buffers)<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>Hm, you have lost me in this
threading namings :)<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>Same SDF connection can’t
be shared across threads, right ? ( I thought that as thread safe )<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>I would like to understand
reasons for that behavior and if there are rooms for improvements.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>Sqlite connection can be shared
between threads.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>Thank you,<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>Haris<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<div>
<div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in'>
<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>
fdo-internals-bounces@lists.osgeo.org
[mailto:fdo-internals-bounces@lists.osgeo.org] <b>On Behalf Of </b>Badreddine
Karoui<br>
<b>Sent:</b> Wednesday, August 13, 2008 8:36 PM<br>
<b>To:</b> FDO Internals Mail List<br>
<b>Subject:</b> RE: [fdo-internals] RE: SDF feature reader <o:p></o:p></span></p>
</div>
</div>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><span style='color:#1F497D'>It was not obvious that the
readers were on the same thread. In that case it’s a defect. Make sure to
copy the geometry before ReadNext is called. It’s possible the second
reader(ReadNext) is invalidating the geometry.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>The SDF provider is thread safe
but not free threaded, it’s per-connection threaded.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>Badreddine<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<div>
<div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in'>
<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>
fdo-internals-bounces@lists.osgeo.org
[mailto:fdo-internals-bounces@lists.osgeo.org] <b>On Behalf Of </b>Haris
Kurtagic<br>
<b>Sent:</b> Wednesday, August 13, 2008 2:39 PM<br>
<b>To:</b> FDO Internals Mail List<br>
<b>Subject:</b> RE: [fdo-internals] RE: SDF feature reader <o:p></o:p></span></p>
</div>
</div>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><span style='color:#1F497D'>I was saying for two
feature readers inside same thread will result in error.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>Also, i would like to understand
why SDF provider is not thread safe.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>Haris<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'> <o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
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<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>
fdo-internals-bounces@lists.osgeo.org
[mailto:fdo-internals-bounces@lists.osgeo.org] <b>On Behalf Of </b>Badreddine
Karoui<br>
<b>Sent:</b> Wednesday, August 13, 2008 8:18 PM<br>
<b>To:</b> FDO Internals Mail List<br>
<b>Subject:</b> [fdo-internals] RE: SDF feature reader <o:p></o:p></span></p>
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<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><span style='color:#1F497D'>The SDF provider is per
connection threaded which means only one thread can access a reader at a time. You
can have many threads using their own connections/readers at the same time.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>Badreddine<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
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<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>
fdo-internals-bounces@lists.osgeo.org
[mailto:fdo-internals-bounces@lists.osgeo.org] <b>On Behalf Of </b>Haris
Kurtagic<br>
<b>Sent:</b> Wednesday, August 13, 2008 2:29 PM<br>
<b>To:</b> FDO Internals Mail List<br>
<b>Subject:</b> [fdo-internals] SDF feature reader <o:p></o:p></span></p>
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<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Hi,<o:p></o:p></p>
<p class=MsoNormal>I have issue when when more than one feature reader is
created against same SDF connection<o:p></o:p></p>
<p class=MsoNormal>It looks like same buffer ( created by sqlite cursor ) is
shared betwean feature readers.<o:p></o:p></p>
<p class=MsoNormal>This will cause that data returned from feature reader with
function GetGeometry will be corrupted when another reader is used.<o:p></o:p></p>
<p class=MsoNormal>Is this a bug or I am not looking into it correctly ?<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>I would like to be able to use multi thread access to sqlite
database.<o:p></o:p></p>
<p class=MsoNormal>If I am right, SDF provider is not “thread safe”
? if so, what are main reasons for it ?<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Thank you,<o:p></o:p></p>
<p class=MsoNormal>Haris<o:p></o:p></p>
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