incorporate comments

Author: carstenbauer

src/MKL.jl

@@ -15,23 +15,26 @@ if lowercase(mkl_path) == "mkl_jll"
     # Only load MKL_jll if we are suppoed to use it as the MKL source
     # to avoid an unnecessary download of the (lazy) artifact.
     import MKL_jll
-    const libmkl_rt = MKL_jll.libmkl_rt
+    const mkl_found = MKL_jll.is_available()
+    const libmkl_rt = mkl_found ? MKL_jll.libmkl_rt : nothing
 elseif lowercase(mkl_path) == "system"
     # We expect the "system" MKL to already be loaded,
     # or be on our linker search path.
     libname = string("libmkl_rt", ".", Libdl.dlext)
     const libmkl_rt = find_library(libname, [""])
-    libmkl_rt == "" && error("Couldn't find $libname. Try to specify the path to `libmkl_rt` explicitly.")
+    const mkl_found = libmkl_rt != ""
+    mkl_found || @warn("Couldn't find $libname. Try to specify the path to `libmkl_rt` explicitly.")
 else
     # mkl_path should be a valid path to libmkl_rt.
     const libmkl_rt = mkl_path
-    isfile(libmkl_rt) || error("Couldn't find MKL library at $libmkl_rt.")
+    const mkl_found = isfile(libmkl_rt)
+    mkl_found || @warn("Couldn't find MKL library at $libmkl_rt.")
 end
 
 # Changing the MKL provider/path preference
 function set_mkl_path(path)
-    if lowercase(path) ∉ ("mkl_jll", "system")
-        isfile(path) || error("The provided argument $path doesn't seem to be a valid path to libmkl_rt.")
+    if lowercase(path) ∉ ("mkl_jll", "system") && !isfile(path)
+        error("The provided argument $path neither seems to be a valid path to libmkl_rt nor \"mkl_jll\" or \"system\".")
     end
     @set_preferences!("mkl_path" => path)
     @info("New MKL preference set; please restart Julia to see this take effect", path)
@@ -71,23 +74,30 @@ function set_interface_layer(interface::Interface = INTERFACE_LP64)
     return nothing
 end
 
+function lbt_mkl_forwarding()
+    if Sys.isapple()
+        set_threading_layer(THREADING_SEQUENTIAL)
+    end
+    # MKL 2022 and onwards have 64_ for ILP64 suffixes. The LP64 interface
+    # includes LP64 APIs for the non-suffixed symbols and ILP64 API for the
+    # 64_ suffixed symbols. LBT4 in Julia is necessary for this to work.
+    set_interface_layer(INTERFACE_LP64)
+    if Base.USE_BLAS64
+        # Load ILP64 forwards
+        BLAS.lbt_forward(libmkl_rt; clear=true, suffix_hint="64")
+        # Load LP64 forward
+        BLAS.lbt_forward(libmkl_rt; suffix_hint="")
+    else
+        BLAS.lbt_forward(libmkl_rt; clear=true, suffix_hint="")
+    end
+    return nothing
+end
+
 function __init__()
-    if !(mkl_path == "mkl_jll" && !MKL_jll.is_available())
-        if Sys.isapple()
-            set_threading_layer(THREADING_SEQUENTIAL)
-        end
-        # MKL 2022 and onwards have 64_ for ILP64 suffixes. The LP64 interface
-        # includes LP64 APIs for the non-suffixed symbols and ILP64 API for the
-        # 64_ suffixed symbols. LBT4 in Julia is necessary for this to work.
-        set_interface_layer(INTERFACE_LP64)
-        if Base.USE_BLAS64
-            # Load ILP64 forwards
-            BLAS.lbt_forward(libmkl_rt; clear=true, suffix_hint="64")
-            # Load LP64 forward
-            BLAS.lbt_forward(libmkl_rt; suffix_hint="")
-        else
-            BLAS.lbt_forward(libmkl_rt; clear=true, suffix_hint="")
-        end
+    if mkl_found
+        lbt_mkl_forwarding()
+    else
+        @warn("MKL library couldn't be found. Please make sure to set the `mkl_path` preference correctly (e.g. via `MKL.set_mkl_path`).")
     end
 end