package java.lang;
import java.lang.ref.*;

public class InheritableThreadLocal<T> extends ThreadLocal<T> {
  protected T childValue(T parentValue) {
    return parentValue;
  }

  ThreadLocalMap getMap(Thread t) {
    return t.inheritableThreadLocals;
  }

  void createMap(Thread t, T firstValue) {
    t.inheritableThreadLocals = new ThreadLocalMap(this, firstValue);
  }
}

package InheritableThreadLocal;

import java.util.Date;

public class InheritableThreadLocaExt extends InheritableThreadLocal{
  protected Object initialValue() {
    return new Date().getTime();

  }
  protected Object childValue(Object parentValue) {
    return parentValue+"对继承值进行修改";

  }

}

package InheritableThreadLocal;

public class tool {
  public static InheritableThreadLocaExt t=new InheritableThreadLocaExt();

}

package InheritableThreadLocal;

public class MyThread extends Thread{

  public void run() {
      try {
        for(int i=0;i<10;i++) {
          System.out.println("在线程A中："+tool.t.get());
        sleep(100);
        }
      } catch (InterruptedException e) {
        e.printStackTrace();
      }
    }  
}

package InheritableThreadLocal;

public class test {
  public static void main(String[] args) {
    try {
      for(int i=0;i<10;i++) {
        System.out.println("主线程中值："+tool.t.get());
        Thread.sleep(100);
      }
      Thread.sleep(5000);
      MyThread thread=new MyThread();
      thread.start();

    }catch(InterruptedException e){
      e.printStackTrace();
    }
  }
}

private void init(ThreadGroup g, Runnable target, String name,
           long stackSize, AccessControlContext acc,
           .
           .
           if (inheritThreadLocals && parent.inheritableThreadLocals != null)
      this.inheritableThreadLocals =
        ThreadLocal.createInheritedMap(parent.inheritableThreadLocals);

if (inheritThreadLocals && parent.inheritableThreadLocals != null)
      this.inheritableThreadLocals =
        ThreadLocal.createInheritedMap(parent.inheritableThreadLocals);

 static ThreadLocalMap createInheritedMap(ThreadLocalMap parentMap) {
    return new ThreadLocalMap(parentMap);
  }

private ThreadLocalMap(ThreadLocalMap parentMap) {
      Entry[] parentTable = parentMap.table;
      int len = parentTable.length;
      setThreshold(len);
      table = new Entry[len];

      for (int j = 0; j < len; j++) {
        Entry e = parentTable[j];
        if (e != null) {
          @SuppressWarnings("unchecked")
          ThreadLocal<Object> key = (ThreadLocal<Object>) e.get();
          if (key != null) {
            Object value = key.childValue(e.value);
            Entry c = new Entry(key, value);
            int h = key.threadLocalHashCode & (len - 1);
            while (table[h] != null)
              h = nextIndex(h, len);
            table[h] = c;
            size++;
          }
        }
      }
    }