java-ThreadLocal的实现

1.每个线程内部都维护一个ThreadLocalMap。

ThreadLocal.ThreadLocalMap threadLocals = null;

2.

ThreadLocal的set:   

 public void set(T value) {
        Thread t = Thread.currentThread();
        ThreadLocalMap map = getMap(t);
        if (map != null)
            map.set(this, value);
        else
            createMap(t, value);
    }

set的时候以ThreadLocal为key,放入在线程内部的ThreadLocalMap中。

3.

    <pre name="code" class="java">ThreadLocal的get:  

public T get() {
        Thread t = Thread.currentThread();
        ThreadLocalMap map = getMap(t);
        if (map != null) {
            ThreadLocalMap.Entry e = map.getEntry(this);
            if (e != null)
                return (T)e.value;
        }
        return setInitialValue();
    }

get的时候获取线程上的ThreadLocalMap，以 ThreadLocal为key取出value