gistfile1.java

public final class InVar {
  private static final InheritableThreadLocal<String> S = new InheritableThreadLocal<String>() {
    @Override
    protected String childValue(String parentValue) {
      System.out.println("Child called");
      return parentValue + "b";
    }
  };

  public static void main(String[] args) throws Exception {
    S.set("A");

    final Runnable t2 = new Runnable() {
      @Override
      public void run() {
        System.out.println("T2:" + S.get());
      }
    };

    final Runnable t1 = new Runnable() {
      @Override
      public void run() {
        System.out.println("T1:" + S.get());
        S.set("C");

        Thread t = new Thread(t2);
        t.start();
        try { t.join(); } catch (Exception e) { /**/ }
      }
    };

    System.out.println("M:" + S.get());

    Thread t = new Thread(t1);
    t.start();
    t.join();
  }
}
/*
M:A
Child called
T1:Ab
Child called
T2:Cb
*/