ThreadLocal

环境：jdk1.8

笔者代码：

public class Application {

    static class A {}

    public static void main(String[] args) {
        ThreadLocal tl = new ThreadLocal<>();
        tl.set(new A());
    }
}

源码：

public class Thread implements Runnable {

    ThreadLocal.ThreadLocalMap threadLocals = null;
}

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

    
    ThreadLocalMap getMap(Thread t) {
        return t.threadLocals;
    }

    
    void createMap(Thread t, T firstValue) {
        t.threadLocals = new ThreadLocalMap(this, firstValue);
    }


    static class ThreadLocalMap {
    //见下图
    }
}

    static class ThreadLocalMap {

        
        static class Entry extends WeakReference> {
            
            Object value;

            Entry(ThreadLocal k, Object v) {
                super(k);
                value = v;
            }
        }

        
        private static final int INITIAL_CAPACITY = 16;

        
        private Entry[] table;

        ThreadLocalMap(ThreadLocal firstKey, Object firstValue) {
            table = new Entry[INITIAL_CAPACITY];
            int i = firstKey.threadLocalHashCode & (INITIAL_CAPACITY - 1);
            table[i] = new Entry(firstKey, firstValue);
            size = 1;
            setThreshold(INITIAL_CAPACITY);
        }

        
        private Entry getEntry(ThreadLocal key) {
            int i = key.threadLocalHashCode & (table.length - 1);
            Entry e = table[i];
            if (e != null && e.get() == key)
                return e;
            else
                return getEntryAfterMiss(key, i, e);
        }
    }

综上所述：梳理上述逻辑可得如下图