From 91bafbbab45d115b53399acad5ebcb16011a78d2 Mon Sep 17 00:00:00 2001
From: Dainius Jocas <dainius.jocas@gmail.com>
Date: Tue, 9 Mar 2021 09:46:48 +0200
Subject: [PATCH] fix: javascript multithreaded exception

---
 src/polyglot/js.clj    | 11 +++++++++--
 test/polyglot_test.clj | 20 +++++++++++++++-----
 2 files changed, 24 insertions(+), 7 deletions(-)

diff --git a/src/polyglot/js.clj b/src/polyglot/js.clj
index 2f58791..797c9cb 100644
--- a/src/polyglot/js.clj
+++ b/src/polyglot/js.clj
@@ -29,7 +29,12 @@
   (let [^Context ctx (.build (Context/newBuilder (into-array String ["js"])))
         ^String wrapped-script (format "(query) => JSON.stringify((%s)(JSON.parse(query)))" script)
         ^Value f (.eval ctx "js" wrapped-script)]
-    (fn [^String value] (.asString (.execute f (object-array [value]))))))
+    (fn [^String value]
+      ; Turns out that can't be accesses by multiple threads
+      ; TODO: every thread should create its own Context
+      ; https://medium.com/graalvm/multi-threaded-java-javascript-language-interoperability-in-graalvm-2f19c1f9c37b
+      (locking ctx
+        (.asString (.execute f (object-array [value])))))))
 
 (defn script->transform-fn-vals
   "Given a JavaScript source code snippet creates a function that expects
@@ -39,7 +44,9 @@
   (let [^Context ctx (.build (Context/newBuilder (into-array String ["js"])))
         ^String wrapped-script (format "(...args) => { args[0] = JSON.parse(args[0]); return JSON.stringify((%s).apply(null, args));}" script)
         ^Value f (.eval ctx "js" wrapped-script)]
-    (fn [& vals] (.asString (.execute f (object-array vals))))))
+    (fn [& vals]
+      (locking ctx
+        (.asString (.execute f (object-array vals)))))))
 
 (comment
   (time
diff --git a/test/polyglot_test.clj b/test/polyglot_test.clj
index 08c2347..129f9d8 100644
--- a/test/polyglot_test.clj
+++ b/test/polyglot_test.clj
@@ -1,7 +1,8 @@
 (ns polyglot-test
   (:require [clojure.test :refer :all]
-            [polyglot.js :as js]
+            [core.async :as a]
             [core.json :as json]
+            [polyglot.js :as js]
             [polyglot :as polyglot]))
 
 (def empty-map {})
@@ -18,15 +19,24 @@
     (let [input-string (json/encode nested-map)]
       (is (= (json/encode (assoc-in nested-map [:foo :bar :quuz]  "corge"))
              (js/string->string input-string
-                                      "(s) => {
-                                        s['foo']['bar']['quuz'] = 'corge';
-                                        return s;
-                                      }")))))
+                                "(s) => {
+                                  s['foo']['bar']['quuz'] = 'corge';
+                                  return s;
+                                }")))))
 
   (testing "invalid script"
     (let [input-string (json/encode empty-map)]
       (is (thrown? Exception (= input-string (js/string->string input-string "(s) => function")))))))
 
+(deftest multithreaded-js
+  (let [data (json/encode {"foo" "bar"})
+        tf (polyglot.js/script->transform-fn
+             "(s) => {
+               s['foo'] = 'corge';
+               return s;
+             }")]
+    (is (= 100 (count (a/map-pipeline (fn [d] (tf d)) 10 (repeat 100 data)))))))
+
 (deftest polyglot-map-transformations
   (testing "simple cases"
     (let [m empty-map]