InheritableThreadLocal代碼
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);} }
測試代碼
import java.util.concurrent.atomic.AtomicInteger;/*** Created by hujunzheng on 2017/6/23.*/class ThreadCount {private static final AtomicInteger nextId = new AtomicInteger(0);private static final ThreadLocal<Integer> threadCount =ThreadLocal.withInitial(() -> nextId.getAndIncrement());//返回的是重寫了ThreadLocal initialValue()方法的ThreadLocal.SuppliedThreadLocal對象public static int get() {return threadCount.get();} }class ThreadSign {private static final AtomicInteger nextId = new AtomicInteger(0);private static final ThreadLocal<Integer> threadCount = new InheritableThreadLocal<Integer>() {@Overrideprotected Integer initialValue() {return nextId.getAndIncrement();}};public static int get() {return threadCount.get();} }public class ThreadLocalTest {public static void testThreadLocal() {for (int i = 0; i < 5; ++i) {int pi = i;new Thread(() -> {System.out.println(Thread.currentThread().getName() + " count->" + ThreadCount.get());for (int j = 0; j < 5; ++j) {new Thread(() -> System.out.println(" " + Thread.currentThread().getName() + " count->" + ThreadCount.get()), "cthread" + j + " pthread" + pi).start();}}, "pthread" + i).start();}}public static void testInheritableThreadLocal() {for(int i=0; i<5; ++i) {int pi = i;new Thread(() -> {System.out.println(Thread.currentThread().getName() + " sign->" + ThreadSign.get());for(int j=0; j<5; ++j) {new Thread(() -> System.out.println(" " + Thread.currentThread().getName() + " sign->" + ThreadSign.get()), "cthread" + j + " pthread" + pi).start();}}, "pthread" + i).start();}}public static void main(String[] args) { // testThreadLocal(); testInheritableThreadLocal();} }
測試結果
分別為testThreadLocal() 和?testInheritableThreadLocal() 測試結果。
比較后，看到ThreadLocal里的值，子線程里不能獲得；InheritableThreadLocal里的值，子線程可以獲得。
跟蹤一下代碼
參考
Java8增加功能--Effectively final 功能
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