src/java.base/share/classes/java/lang/Thread.java

@@ -1224,11 +1224,12 @@
             throw new NullPointerException("name cannot be null");
         }
 
         this.name = name;
         if (threadStatus != 0) {
-            setNativeName(name);
+            // Don't modify JNI-attached threads
+            setNativeName(name, false);
         }
     }
 
     /**
      * Returns this thread's name.

@@ -2140,7 +2141,10 @@
     private native void setPriority0(int newPriority);
     private native void stop0(Object o);
     private native void suspend0();
     private native void resume0();
     private native void interrupt0();
-    private native void setNativeName(String name);
+
+    // May be called directly via JNI or reflection (when permitted) to
+    // allow JNI-attached threads to set their native name
+    private native void setNativeName(String name, boolean allowAttachedThread);
 }