Use @ccall gc_safe=true for blocking calls #954

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1. giordano commented on Jul 13, 2026

   

   giordano

   on Jul 13, 2026

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   I presume you meant gc_safe=true for @ccall?
2. giordano commented on Jul 13, 2026

   

   giordano

   on Jul 13, 2026

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   Ooof, I suspect we can't use the @ccall form because we need to set the stdcall call convention on Windows:

   MPI.jl/src/api/api.jl

   Lines 102 to 108 in 9fc3490

   	# Microsoft MPI uses stdcall calling convention
   	# this only affects 32-bit Windows
   	# unfortunately we need to use ccall to call Get_library_version
   	# so check using library name instead
   	if use_stdcall
   	insert!(expr.args, 3, :stdcall)
   	end
3. giordano

   changed the title [-]Use `ccall=safe` for blocking calls[/-] [+]Use `@ccall gc_safe=true` for blocking calls[/+] on Jul 13, 2026
4. simonbyrne commented on Jul 19, 2026

   

   simonbyrne

   on Jul 19, 2026

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   stdcall is only different on 32-bit windows. Do we need to support that?
5. giordano commented on Jul 19, 2026

   

   giordano

   on Jul 19, 2026

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   I think we actually do it for 64-bit windows too:

   MPI.jl/src/api/api.jl

   Line 90 in 9fc3490

   const use_stdcall = startswith(basename(libmpi), "msmpi")

   In any case I already put a PR up to do this: #955
6. simonbyrne commented on Jul 19, 2026

   

   simonbyrne

   on Jul 19, 2026

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   What I meant is that on 64-bit Windows I think the calling conventions are all unified
7. giordano commented on Jul 21, 2026

   

   giordano

   on Jul 21, 2026

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   I'll open a PR to see if we can skip use_stdcall for 64-bit, but as much as I'd personally be happy with dropping support for 32-bit Windows I don't feel like pulling the plug now, we can perhaps do that in the next breaking release (by that time Julia upstream may drop support for 32-bit Windows entirely, making our decision easier)