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<font face="Times New Roman, Times, serif">I would be interested in
an implementation. I'm preparing a proposal to georeference the
complete cadastral map of the Netherlands in 1832 at a 10 cm/pixel
scale with Cloud facilities. Gdalwarp is the central piece of
software, and distributed processing capabilities would be very
important. Could you please think about the possibilities, and
what kind of funding would be required, so I can take that in
during the next few months?<br>
<br>
Jan<br>
<br>
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<div class="moz-cite-prefix">On 01/12/2013 04:35 PM, Even Rouault
wrote:<br>
</div>
<blockquote
cite="mid:201301121635.28975.even.rouault@mines-paris.org"
type="cite">
<blockquote type="cite">
<pre wrap="">ex. convert
multiple datasets to different output datasets in a parallel way.
</pre>
</blockquote>
<pre wrap="">
As Frank underlined, there's currently an issue with the global block cache
regarding write support.
Imagine that you have 2 threads A and B.
Thread A deal with dataset A, and thread B deal with dataset .
Thread A is in the middle of writing some tile/line of dataset A.
Thread B is trying to fill a new entry in the block cache (with new read data,
or new data to write). But the block cache is full. So the last recently used
entry must be discarded. If that entry is a dirty block of dataset A, then it
must be flushed to disk, in the context of thread B, but at that time thread A
is also writing data... Which might be an issue since drivers are re-entrant
(can be invoked by multiple threads, if each thread deal with different
datasets) not thread-safe.
This specific case here could be fixed in different ways :
A) Making drivers thread-safe (or accessing them through a thread-safe layer),
that is to say add a dataset level mutex
B) or having a per-dataset block cache instead of a global block cache
C) deal differently with dirty blocks. Only flush them if the operation that
need to discard the dirty block is initiated by an operation on the same
dataset as the dirty block.
</pre>
<blockquote type="cite">
<pre wrap="">Would
those parallel operations not be affected by GDAL caching for bot read and
write.Since the cache is set to a limit. Is Accessing the current used
cache value concurrent safeto increase it/decrease it ?
</pre>
</blockquote>
<pre wrap="">
Hum, I see that GDALGetCacheMax() and GDALSetCacheMax() are not thread safe
currently. We would need to protect them by the raster block mutex, with a
leading call to CPLMutexHolderD( &hRBMutex );
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</pre>
</blockquote>
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