对threadlocal了解多少？

public class WorkerThread implements Runnable{
    public static ThreadLocal<Map> paramA = new ThreadLocal<>();
    private CountDownLatch latch;
    public WorkerThread(CountDownLatch latch) {
        this.latch = latch;
    }
    @Override
    public void run() {
        ThreadLocalTest tlt = new ThreadLocalTest();
        tlt.initParamA();
        tlt.useParamA();
        latch.countDown();
    }
}
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public class ThreadLocalTest {
    private static Logger logger = LoggerFactory.getLogger(ThreadLocalTest.class);
    private static int N = 100;
    public static void main(String[] args) {
        CountDownLatch latch = new CountDownLatch(N);
        for(int i=0; i<N; i++) {
            new Thread(new WorkerThread(latch)).start();
        }
        try {
            latch.await(); //等所有WorkerThread线程都执行完
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
    public void initParamA() {
        HashMap<String,String> map = new HashMap<>();
        map.put("name", Thread.currentThread().getName());
        WorkerThread.paramA.set(map);
    }
    public void useParamA() {
        String name = (String)WorkerThread.paramA.get().get("name");
        String threadName = Thread.currentThread().getName();
        logger.info("当前线程名{}，通过 ThreadLocal传递的线程名{}", threadName, name);
        if(!threadName.equals(name))
            logger.error("出现并发问题");
    }
}
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public static ThreadLocal<Map> paramA = new ThreadLocal<>();
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public void set(T value) {
        Thread t = Thread.currentThread();
        ThreadLocalMap map = getMap(t);
        if (map != null)
            map.set(this, value);
        else
            createMap(t, value);
    }
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();
    }
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ThreadLocal<Map> paramA = new ThreadLocal<>();
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/**
 * Set the value associated with key.
 *
 * @param key the thread local object
 * @param value the value to be set
 */
private void set(ThreadLocal<?> key, Object value) {
    // We don't use a fast path as with get() because it is at
    // least as common to use set() to create new entries as
    // it is to replace existing ones, in which case, a fast
    // path would fail more often than not.
    Entry[] tab = table;
    int len = tab.length;
    int i = key.threadLocalHashCode & (len-1);
    for (Entry e = tab[i];
         e != null;
         e = tab[i = nextIndex(i, len)]) {
        ThreadLocal<?> k = e.get();
        if (k == key) {
            e.value = value;
            return;
        }
        if (k == null) {
            replaceStaleEntry(key, value, i);
            return;
        }
    }
    tab[i] = new Entry(key, value);
    int sz = ++size;
    if (!cleanSomeSlots(i, sz) && sz >= threshold)
        rehash();
}
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