Make some global variables constant

src/Sandbox.jl

@@ -51,7 +51,7 @@ include("Docker.jl")
 # Load the UserNamespace executor
 include("UserNamespaces.jl")
 
-all_executors = Type{<:SandboxExecutor}[
+const all_executors = Type{<:SandboxExecutor}[
     # We always prefer the UserNamespaces executor, if we can use it,
     # and the unprivileged one most of all.  Only after that do we try `docker`.
     UnprivilegedUserNamespacesExecutor,
@@ -89,16 +89,15 @@ function select_executor(verbose::Bool)
     error("Could not find any available executors for $(triplet(HostPlatform()))!")
 end
 
-_preferred_executor = nothing
+const _preferred_executor = Ref{Union{Nothing, (x->Type{x}).(all_executors)...}}(nothing)
 const _preferred_executor_lock = ReentrantLock()
 function preferred_executor(;verbose::Bool = false)
     lock(_preferred_executor_lock) do
         # If we've already asked this question, return the old answer
-        global _preferred_executor
-        if _preferred_executor === nothing
-            _preferred_executor = select_executor(verbose)
+        if _preferred_executor[] === nothing
+            _preferred_executor[] = select_executor(verbose)
         end
-        return _preferred_executor
+        return _preferred_executor[]
     end
 end
 

src/utils.jl

@@ -198,27 +198,26 @@ Wrapper around libc's `getuid()` function
 """
 getgid() = ccall(:getgid, Cint, ())
 
-_sudo_cmd = nothing
+const _sudo_cmd = Ref{Union{Vector{String}, Nothing}}(nothing)
 function sudo_cmd()
-    global _sudo_cmd
 
     # Use cached value if we've already run this
-    if _sudo_cmd !== nothing
-        return _sudo_cmd
+    if _sudo_cmd[] !== nothing
+        return _sudo_cmd[]
     end
 
-    if getuid() == 0
+    _sudo_cmd[] = if getuid() == 0
         # If we're already root, don't use any kind of sudo program
-        _sudo_cmd = String[]
+        String[]
     elseif Sys.which("sudo") !== nothing success(`sudo -V`)
         # If `sudo` is available, use that
-        _sudo_cmd = ["sudo"]
+        ["sudo"]
     elseif Sys.which("su") !== nothing
         # Fall back to `su` if all else fails
-        _sudo_cmd = ["su", "root", "-c"]
+        ["su", "root", "-c"]
     else
         @warn("No known sudo-like wrappers!")
-        _sudo_cmd = String[]
+        String[]
     end
-    return _sudo_cmd
+    return _sudo_cmd[]
 end