Use `@ccall gc_safe=true` for blocking calls

[vchuravy]

We should use https://github.com/JuliaGPU/GPUToolbox.jl/blob/f971bcdeb2cd8096333549e6563cf03a76459ae2/src/ccalls.jl#L110 for Wait and allreduce

[giordano]

I presume you meant gc_safe=true for @ccall?

[giordano]

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

[simonbyrne]

stdcall is only different on 32-bit windows. Do we need to support that?

[giordano]

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

[simonbyrne]

What I meant is that on 64-bit Windows I think the calling conventions are all unified

[giordano]

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)