ThreadLocal

时间:2025/8/22 20:53:03来源：https://blog.csdn.net/qq_55630615/article/details/141168336 浏览次数:0次

ThreadLocal

多线程中对于解决线程安全的一个操作类

为每个线程都分配一个独立的ThreadLocal对象副本

实现了线程间的数据隔离

//创建ThreadLocal对象,定义对象内资源的类型
ThreadLocal<String> tl = new ThreadLocal<>();set()//向对象中存入值,每个线程独立
get()//获取对象中的值,每个线程独立
remove()//清除

ThreadLocal实现原理

Thread类

thread类中维护了一个ThreadLocal的内部类ThreadLocalMap对象

ThreadLocalMap对象中维护了一个Entry数组

即每个线程中都维护了一个独立的Entry数组

我们将线程间独立的数据存储在这个Entry数组中

以ThreadLocal对象作为key,value作为值

这样就实现了同一个ThreadLocal对象的数据隔离

ThreadLocal.ThreadLocalMap threadLocals = null;

Set

public void set(T value) {//获取当前的线程对象Thread t = Thread.currentThread();//根据线程对象获取对应的mapThreadLocalMap map = getMap(t);if (map != null) {map.set(this, value);} else {createMap(t, value);}}

get

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();}

ThreadLocal的内存泄漏问题

因为ThreadLocalMap中的key是ThreadLocal的弱引用

 static class ThreadLocalMap {/*** The entries in this hash map extend WeakReference, using* its main ref field as the key (which is always a* ThreadLocal object).  Note that null keys (i.e. entry.get()* == null) mean that the key is no longer referenced, so the* entry can be expunged from table.  Such entries are referred to* as "stale entries" in the code that follows.*/static class Entry extends WeakReference<ThreadLocal<?>> {/** The value associated with this ThreadLocal. */Object value;Entry(ThreadLocal<?> k, Object v) {super(k);value = v;}}
}