[fdo-internals] RE: SDF feature reader

[Haris Kurtagic]

Ok, I read that  .h many times :)

 

I would appreciate if you can help me to understand and discuss why sdf
provider is not FdoThreadCapability_PerCommandThreaded.

 

Thank you,

Haris

 

From: fdo-internals-bounces at lists.osgeo.org
[mailto:fdo-internals-bounces at lists.osgeo.org] On Behalf Of Badreddine
Karoui
Sent: Wednesday, August 13, 2008 10:14 PM
To: FDO Internals Mail List
Subject: RE: [fdo-internals] RE: SDF feature reader 

 

The free threaded provider would use FdoThreadCapability_MultiThreaded
defined in
https://svn.osgeo.org/fdo/trunk/Fdo/Unmanaged/Inc/Fdo/Connections/Capabi
lities/ThreadCapability.h

 

The SDF provider is returning FdoThreadCapability_PerConnectionThreaded.


 

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. 

We may have to be extra carefull in case we decide to fix this issue to
make sure the reader performance is not impacted. 

 

Badreddine

 

From: fdo-internals-bounces at lists.osgeo.org
[mailto:fdo-internals-bounces at lists.osgeo.org] On Behalf Of Haris
Kurtagic
Sent: Wednesday, August 13, 2008 3:12 PM
To: FDO Internals Mail List
Subject: RE: [fdo-internals] RE: SDF feature reader 

 

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)

 

Hm, you have lost me in this threading namings :)

 

Same SDF connection can't be shared across threads, right ? ( I thought
that as thread safe )

I would like to understand reasons for that behavior and if there are
rooms for improvements.

Sqlite connection can be shared between threads.

 

Thank you,

Haris

 

From: fdo-internals-bounces at lists.osgeo.org
[mailto:fdo-internals-bounces at lists.osgeo.org] On Behalf Of Badreddine
Karoui
Sent: Wednesday, August 13, 2008 8:36 PM
To: FDO Internals Mail List
Subject: RE: [fdo-internals] RE: SDF feature reader 

 

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.

 

The SDF provider is thread safe but not free threaded, it's
per-connection threaded.

 

Badreddine

 

From: fdo-internals-bounces at lists.osgeo.org
[mailto:fdo-internals-bounces at lists.osgeo.org] On Behalf Of Haris
Kurtagic
Sent: Wednesday, August 13, 2008 2:39 PM
To: FDO Internals Mail List
Subject: RE: [fdo-internals] RE: SDF feature reader 

 

I was saying  for  two feature readers inside same thread will result in
error.

 

Also, i would like to understand why SDF provider is not thread safe.

 

Haris

 

 

 

 

From: fdo-internals-bounces at lists.osgeo.org
[mailto:fdo-internals-bounces at lists.osgeo.org] On Behalf Of Badreddine
Karoui
Sent: Wednesday, August 13, 2008 8:18 PM
To: FDO Internals Mail List
Subject: [fdo-internals] RE: SDF feature reader 

 

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.

 

Badreddine

 

From: fdo-internals-bounces at lists.osgeo.org
[mailto:fdo-internals-bounces at lists.osgeo.org] On Behalf Of Haris
Kurtagic
Sent: Wednesday, August 13, 2008 2:29 PM
To: FDO Internals Mail List
Subject: [fdo-internals] SDF feature reader 

 

Hi,

I have issue when when more than one feature reader is created against
same SDF connection

It looks like same buffer ( created by sqlite cursor ) is shared betwean
feature readers.

This will cause that data returned from feature reader with function
GetGeometry will be corrupted when another reader is used.

Is this a bug or I am not looking into it correctly ?

 

I would like to be able to use multi thread access to sqlite database.

If I am right, SDF provider is not "thread safe" ? if so, what are main
reasons for  it ?

 

Thank you,

Haris

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