InheritableThreadLocal使用与源码分析
InheritableThreadLocal使用
子线程需要获取父线程中的ThreadLocal中的值的时候，使用InheritableThreadLocal
public class TestInheritableThreadLocal {
public static final SecureRandom random = new SecureRandom();
public static ThreadLocal<Integer> threadLocal = new ThreadLocal<>();
public static void main(String[] args) {
threadLocal.set(random.nextInt());
GetValThread thread = new GetValThread();
thread.start();
System.out.println("main----" + threadLocal.get());
}
static class GetValThread extends Thread {
@Override
public void run() {
System.out.println("local thread ----" + threadLocal.get());
}
}
}
运行结果如下：
main-----1845871892
local thread ----null
代码
public static ThreadLocal<Integer> threadLocal = new ThreadLocal<>();
修改为：
public static ThreadLocal<Integer> threadLocal = new InheritableThreadLocal<>();
1
运行结果如下：
main-----610914016
local thread -----610914016
InheritableThreadLocal源码分析
InheritableThreadLocal源码很简单，重写了ThreadLocal中“
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);
}
}
InheritableThreadLocal获取值的过程如下，从自己的ThreadLocalMap中取值。
public T get() {
Thread t = Thread.currentThread();
ThreadLocalMap map = getMap(t);
if (map != null) {
ThreadLocalMap.Entry e = map.getEntry(this);
if (e != null) {
@SuppressWarnings("unchecked")
T result = (T)e.value;
return result;
}
}
return setInitialValue();
}
InheritableThreadLocal本身的ThreadLocalMap初始化在创建线程自己的时候，copy父线程的ThreadLocalMap，具体实现在Thread构造函数中，具体如下：
private void init(ThreadGroup g, Runnable target, String name,
long stackSize, AccessControlContext acc) {
//省略上面部分代码
if (parent.inheritableThreadLocals != null)
//这句话的意思大致不就是，copy父线程parent的map，
//创建一个新的map赋值给当前线程的inheritableThreadLocals。
this.inheritableThreadLocals =
ThreadLocal.createInheritedMap(parent.inheritableThreadLocals);
//ignore
}
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版权声明：本文为CSDN博主「凌霄~」的原创文章，遵循 CC 4.0 BY-SA 版权协议，转载请附上原文出处链接及本声明。
原文链接：https://blog.csdn.net/Pengjx2014/article/details/82635158
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