apacheGH-2787: Set flag before causing class initializations

jena-core/src/main/java/org/apache/jena/sys/JenaSystem.java

@@ -77,20 +77,22 @@ public static void logLifecycle(String fmt, Object ...args) {
     }
 
     public static void init() {
-        // Once jena is initialized, all calls are an immediate return.
         if ( initialized )
             return ;
-        // Overlapping attempts to perform initialization will block on the synchronized.
+        // Overlapping attempts to perform initialization will block on the synchronized
+        // but threads may have already have initialization locks.
         synchronized(JenaSystem.class) {
             if ( initialized )
                 return ;
+            // Set the flag before, before setup() takes any initialization locks
+            // that may deadlock with another thread.
+            // See https://github.com/apache/jena/issues/2787
+            initialized = true;
             setup();
             if ( DEBUG_INIT )
                 singleton.debug(DEBUG_INIT);
             singleton.initialize();
             singleton.debug(false);
-            // Last so overlapping initialization waits on the synchronized
-            initialized = true;
         }
     }