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break inference in Windows env caching to prevent a large set of invalidations from popular packages #52760

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break inference in Windows env caching to prevent a large set of invalidations from popular packages #52760

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8 changes: 7 additions & 1 deletion base/env.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -6,7 +6,7 @@ if Sys.iswindows()
const env_dict = IdDict{String, Vector{Cwchar_t}}()
const env_lock = ReentrantLock()

function memoized_env_lookup(str::AbstractString)
function _memoized_env_lookup(str::AbstractString)
# Windows environment variables have a different format from Linux / MacOS, and previously
# incurred allocations because we had to convert a String to a Vector{Cwchar_t} each time
# an environment variable was looked up. This function memoizes that lookup process, storing
Expand All @@ -20,6 +20,12 @@ if Sys.iswindows()
var
end

# The `@nospecialize`d `setindex!` in `iddict` called in `_memoized_env_lookup` unfortunately
# sets up a situation where adding a method `convert(::Type{Array}, ::SomeType)` invalidates
# the memoization method causing a cascade of upstream methods to be invalidated. Therefore,
# break the inference chain here with an `inferencebarrier`.
memoized_env_lookup(str::AbstractString) = inferencebarrier(_memoized_env_lookup(str))::Vector{Cwchar_t}

_getenvlen(var::Vector{UInt16}) = ccall(:GetEnvironmentVariableW,stdcall,UInt32,(Ptr{UInt16},Ptr{UInt16},UInt32),var,C_NULL,0)
_hasenv(s::Vector{UInt16}) = _getenvlen(s) != 0 || Libc.GetLastError() != ERROR_ENVVAR_NOT_FOUND
_hasenv(s::AbstractString) = _hasenv(memoized_env_lookup(s))
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