HADOOP-10829. Iteration on CredentialProviderFactory.serviceLoader is thread-unsafe. Contributed by Benoy Antony and Rakesh R.

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/security/alias/CredentialProviderFactory.java

@@ -22,6 +22,7 @@ import java.io.IOException;
 import java.net.URI;
 import java.net.URISyntaxException;
 import java.util.ArrayList;
+import java.util.Iterator;
 import java.util.List;
 import java.util.ServiceLoader;
 
@@ -49,6 +50,15 @@ public abstract class CredentialProviderFactory {
       ServiceLoader.load(CredentialProviderFactory.class,
           CredentialProviderFactory.class.getClassLoader());
 
+  // Iterate through the serviceLoader to avoid lazy loading.
+  // Lazy loading would require synchronization in concurrent use cases.
+  static {
+    Iterator<CredentialProviderFactory> iterServices = serviceLoader.iterator();
+    while (iterServices.hasNext()) {
+      iterServices.next();
+    }
+  }
+
   public static List<CredentialProvider> getProviders(Configuration conf
                                                ) throws IOException {
     List<CredentialProvider> result = new ArrayList<CredentialProvider>();