Careful microoptimisations for 2x performance improvement

src/corefunctionality.jl

@@ -1,22 +1,29 @@
-
 const pool = WeakKeyDict{String, Void}()
 
-function intern!(wkd::WeakKeyDict{K}, key)::K where K
-    kk = convert(K, key)
-    kwr = WeakRef(kk)
-    lock(wkd) do
-        found_key = getkey(wkd.ht, kwr, Base.secret_table_token)
-        found = !(found_key === Base.secret_table_token)
-
-        if found
-            return found_key.value
-        else
-            # Not found, so add it,
-            # and mark it as a reference we track to delete!
-            finalizer(kk, wkd.finalizer)
-            wkd.ht[kwr]=nothing
-            return kk
-        end
+# This forces the type to be inferred (I don't know that the @noinline is reqired or even good)
+@noinline getvalue(::Type{K}, wk) where K = wk.value::K
+
+
+# NOTE: This code is carefully optimised. Do not tweak it (for readability or otherwise) without benchmarking
+@inline function intern!(wkd::WeakKeyDict{K}, key)::K where K
+    kk::K = convert(K, key)
+
+    lock(wkd.lock)
+        # hand positioning the locks and unlocks (rather than do block or try finally, seems to be faster)
+    index = Base.ht_keyindex2(wkd.ht, kk) # returns index if present, or -index if not
+    # note hash of weakref is equal to the hash of value, so avoid constructing it if not required
+    if index > 0
+        # found it
+        @inbounds found_key = wkd.ht.keys[index]
+        unlock(wkd.lock)
+        return getvalue(K, found_key) # return the strong ref
+    else
+        # Not found, so add it,
+        # and mark it as a reference we track to delete!
+        finalizer(kk, wkd.finalizer) # finalizer is set on the strong ref
+        @inbounds Base._setindex!(wkd.ht, nothing, WeakRef(kk), -index)
+        unlock(wkd.lock)
+        return kk # Return the strong ref
     end
 end