[GitHub] [incubator-livy] wypoon commented on a change in pull request #275: [LIVY-745] Ensure that a single RSCClientFactory gets loaded.

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wypoon commented on a change in pull request #275: [LIVY-745] Ensure that a single RSCClientFactory gets loaded.
URL: https://github.com/apache/incubator-livy/pull/275#discussion_r374945260
 
 

 ##########
 File path: api/src/main/java/org/apache/livy/LivyClientBuilder.java
 ##########
 @@ -118,27 +121,29 @@ public LivyClient build() {
     }
 
     LivyClient client = null;
-    ServiceLoader<LivyClientFactory> loader = ServiceLoader.load(LivyClientFactory.class,
-      classLoader());
-    if (!loader.iterator().hasNext()) {
-      throw new IllegalStateException("No LivyClientFactory implementation was found.");
-    }
-
-    Exception error = null;
-    for (LivyClientFactory factory : loader) {
-      try {
-        client = factory.createClient(uri, config);
-      } catch (Exception e) {
-        if (!(e instanceof RuntimeException)) {
-          e = new RuntimeException(e);
+    boolean loaded = false;
+    // ServiceLoader instances are not safe for use by multiple concurrent threads.
+    // Ensure that the ServiceLoader's iterator is called by only one thread at a time.
+    synchronized (CLIENT_FACTORY_LOADER) {
 
 Review comment:
   What I decided to do is to load the service providers into a static List that has a thread-safe iterator. Then LivyClientBuilder#build can iterate through the client factories in this List.

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