Make loading of libs thread safe, fixes babashka/babashka#1482

CHANGELOG.md

@@ -24,6 +24,7 @@ SCI is used in [babashka](https://github.com/babashka/babashka),
 - Improve top level macro expansion error location
 - Fix pprinting vars
 - Add `reader-conditional` to core vars
+- Fix [#babashka/1482](https://github.com/babashka/babashka/issues/1482): make loading of libs thread safe
 
 ## 0.6.37 (2022-12-20)
 

src/sci/impl/load.cljc

@@ -80,7 +80,7 @@
 (defn handle-require-libspec
   [ctx lib opts]
   (let [env* (:env ctx)
-        env @env* ;; NOTE: loading namespaces is not (yet) thread-safe
+        env @env*
         cnn (utils/current-ns-name)
         lib (get (:ns-aliases env) lib lib)]
     (if-let [as-alias (:as-alias opts)]
@@ -146,7 +146,7 @@
         (add-loaded-lib env* lib)
         nil))))
 
-(defn load-lib [ctx prefix lib & options]
+(defn load-lib* [ctx prefix lib options]
   (when (and prefix (pos? (.indexOf (name lib) #?(:clj (int \.)
                                                   :cljs \.))))
     (throw-error-with-location (str "Found lib name '" (name lib) "' containing period with prefix '"
@@ -156,6 +156,15 @@
         opts (apply hash-map options)]
     (handle-require-libspec ctx lib opts)))
 
+#?(:clj
+   (let [load-lock (Object.)]
+     (defn load-lib [ctx prefix lib & options]
+       (locking load-lock
+         (load-lib* ctx prefix lib options))))
+   :cljs
+   (defn load-lib [ctx prefix lib & options]
+     (load-lib* ctx prefix lib options)))
+
 (defn- prependss
   "Prepends a symbol or a seq to coll"
   [x coll]