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

@@ -22,10 +22,12 @@
  * or visit www.oracle.com if you need additional information or have any
  * questions.
  */
 
 package java.lang;
+import jdk.internal.misc.TerminatingThreadLocal;
+
 import java.lang.ref.*;
 import java.util.Objects;
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.function.Supplier;
 

@@ -169,10 +171,23 @@
         }
         return setInitialValue();
     }
 
     /**
+     * Returns {@code true} if there is a value in the current thread's copy of
+     * this thread-local variable, even if that values is {@code null}.
+     *
+     * @return {@code true} if current thread has associated value in this
+     *         thread-local variable; {@code false} if not
+     */
+    boolean isPresent() {
+        Thread t = Thread.currentThread();
+        ThreadLocalMap map = getMap(t);
+        return map != null && map.getEntry(this) != null;
+    }
+
+    /**
      * Variant of set() to establish initialValue. Used instead
      * of set() in case user has overridden the set() method.
      *
      * @return the initial value
      */

@@ -182,10 +197,11 @@
         ThreadLocalMap map = getMap(t);
         if (map != null)
             map.set(this, value);
         else
             createMap(t, value);
+        TerminatingThreadLocal.register(this);
         return value;
     }
 
     /**
      * Sets the current thread's copy of this thread-local variable