GDALDataset::RasterIO() / GDALDatasetRasterIO[Ex](): accept a const int* panBandList, instead of a int*, and related changes #9961
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…nt* panBandList, instead of a int* But no changes to the IRasterIO() virtual method as the moment, assuming that all implementations do not alter the passed array
rouault
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do you mean this would be an API break for third party drivers?
I can't think of a better one. |
elpaso
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May 20, 2024
| CPL_IGNORE_RET_VAL(psJob->poMEMDS->RasterIO( | ||
| GF_Read, psJob->nXOff, psJob->nYOff, psJob->nXSize, psJob->nYSize, | ||
| psJob->pBuffer, psJob->nBufXSize, psJob->nBufYSize, psJob->eDT, | ||
| psJob->nBandCount, nullptr, 0, 0, psJob->nBandSpace, &sExtraArg)); | ||
| psJob->nBandCount, anBands.data(), 0, 0, psJob->nBandSpace, |
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how it this (and previous) change related to the const correctness?
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The issue is that this code abuses mutlithreading. It does multithreaded read on the same dataset. Before when passing panBandMap==nullptr a temporary array was allocated by GDALDataset::RasterIO(). I changed the later to rather use a member variable to hold the temporary array. And thus there was suddently a concurrent modification of that temporary array causing chaos.
…const int* panBandList For now we use a #define ``` // This macro can be defined to check that GDALDataset::IRasterIO() // implementations do not alter the passed panBandList. It is not defined // by default (and should not!), hence int* is used. \#if defined(GDAL_BANDMAP_TYPE_CONST_SAFE) \#define BANDMAP_TYPE const int * \#else \#define BANDMAP_TYPE int * \#endif ```
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elpaso
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May 21, 2024
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Currently GDALDataset::RasterIO() / GDALDatasetRasterIOEx take a "int* panBandList", whereas its semantics is really "const int*".
To do the changes fully one should also change the virtual method GDALDataset::IRasterIO() in a similar way, but that would affect out-of-tree drivers, so I've used a compromise where I changed in-tree code to use a BANDMAP_TYPE define that evaluates to "int *" for backward compatibility, but with an easy way to check it is const ready, with the below
I'm not totally sure this a good idea/approach