Motion passed with +1 from PSC members KurtS, JukkaR, JavierJS and me.
Le 11/09/2024 à 21:26, Even Rouault via gdal-dev a écrit :
Hi,
I move to approve RFC 101 "Raster dataset read-only thread-safety":
https://github.com/OSGeo/gdal/pull/10676
Starting with my +1,
The candidate implementation is available in
https://github.com/OSGeo/gdal/pull/10746. While fine tuning it, I
realized there were subtleties, related to the fact we use
thread-local datasets under the hood, for methods returning a
non-"primitive" type, such as a "const char*" whose lifetime is tied
to a dataset/band. If we'd get it from a thread-local dataset, and
that one would be later evicted from the cache (not very common, but
could happen if one would open tons of thread-safe datasets at the
same time), then you could have use-after-free issues. For such
methods (GetMetadata(), GetMetadataItem(), GetProjectionRef(), etc. as
well as GetColorTable() which returns a GDALColorTable pointer, or
GetSpatialRef() which returns a OGRSpatialReference*), I've preferred
to protect their access with a mutex around the "prototype" dataset
passed when constructing GDALMultiThreadedDataset, whose lifetime is
at least as long as GDALMultiThreadedDataset (cf commit
https://github.com/OSGeo/gdal/pull/10746/commits/849e9cea711efd30c47fd90a7a6b71a75611c1a5#diff-687008dd6e3d5ac8ad05568272746ed75b84de50bde508f78f2d79a6842825c7L428)
. Normally such methods aren't called in user code repeatedly, so
there should be any noticeable lock contention in practice. The main
objective of the RFC which is to be able to issue RasterIO() requests
in parallel isn't affected by that. Ah, and one thing I realized is
that OGRSpatialReference isn't thread-safe, so I've also added an
optional SetThreadSafe() on it, to also use a per-instance mutex in
multi-threaded scenarios (cf commit
https://github.com/OSGeo/gdal/pull/10746/commits/c7e1862273dd018e58a01f25b21fdff6dbfdd1cd).
Multi-threading is hard...
Even
--
http://www.spatialys.com
My software is free, but my time generally not.
_______________________________________________
gdal-dev mailing list
gdal-dev@lists.osgeo.org
https://lists.osgeo.org/mailman/listinfo/gdal-dev
