Rework meshopt_Allocator callback storage #896
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Using templated class static allowed us to avoid function calls even in unoptimized builds, but results in conflicts with Clang's C++20 module implementation when meshoptimizer.h is included in global module fragment. Instead, we now use a function static to store this state and require a function call to get access to it. The function static should, similarly to the previous code, be instantiated in translation units that use it and deduplicated by linker.
Before this change (and irrespectively of the previous change to callback storage), allocator callbacks were deduplicated by the linker within an individual module, but when meshoptimizer was compiled as a shared library, the library code and the calling code would get separate configuration. This meant that meshopt_setAllocator would only affect the allocation behavior of the library internals, but would not affect the temporary allocations done by meshopt_IndexAdapter. To fix that, we need to make sure the storage function can be implemented in allocator.cpp and exported.
This ensures that the allocator overrides work throughout the library usage both for inlined APIs via IndexAdapter and for internal library allocations, when shared library builds are used.
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Using templated class static allowed us to avoid function calls even in
unoptimized builds, but results in conflicts with Clang's C++20 module
implementation when meshoptimizer.h is included in global module
fragment. Instead, we now use a function static to store this state and
require a function call to get access to it.
Additionally, while allocator callbacks were deduplicated by the linker
within an individual module, when meshoptimizer was compiled as a
shared library the library code and the calling code would get
separate configuration, and allocator overrides would not affect temporary
allocations done by meshopt_IndexAdapter. To fix that, this PR introduces
a separate configuration option,
MESHOPTIMIZER_ALLOC_EXPORT,which can be used to declare the allocator storage function in the library
once.
Fixes #895.
This contribution is sponsored by Valve.