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Fix FFTW threading conflict that made FFTs 100x slower after loading FastTransforms #270

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Fix FFTW threading conflict that made FFTs 100x slower after loading FastTransforms #270

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Copilot Jul 10, 2026
f898b65
Use Threads.nthreads() instead of Sys.CPU_THREADS/2 to set FFTW threa…
Copilot Jul 10, 2026
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2 changes: 1 addition & 1 deletion src/libfasttransforms.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -13,7 +13,7 @@ ft_set_num_threads(n::Integer) = ccall((:ft_set_num_threads, libfasttransforms),
ft_fftw_plan_with_nthreads(n::Integer) = ccall((:ft_fftw_plan_with_nthreads, libfasttransforms), Cvoid, (Cint, ), n)

function __init__()
n = ceil(Int, Sys.CPU_THREADS/2)
n = Threads.nthreads()
ft_set_num_threads(n)
ccall((:ft_fftw_init_threads, libfasttransforms), Cint, ())
ft_fftw_plan_with_nthreads(n)
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2 changes: 1 addition & 1 deletion test/libfasttransformstests.jl
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Original file line number Diff line number Diff line change
@@ -1,6 +1,6 @@
using FastTransforms, Test

FastTransforms.ft_set_num_threads(ceil(Int, Base.Sys.CPU_THREADS/2))
FastTransforms.ft_set_num_threads(Threads.nthreads())

@ranocha ranocha Jul 10, 2026

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Shouldnt this be done in __init__ anyway?


@testset "libfasttransforms" begin
n = 64
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