带你读《2022技术人的百宝黑皮书》——合理使用线程池以及线程变量（10）https://developer.aliyun.com/article/1340059?groupCode=taobaotech
threadLocal.set()方法
/** *Sets the current thread's copy of this thread-local variable *to the specified value. Most subclasses will have no need to *override this method, relying solely on the {@link #initialValue} *method to set the values of thread-locals. * *@param value the value to be stored in the current thread's copy of * this thread-local. */ public void set(T value) { // 1. 获取当前线程 Thread t = Thread.currentThread(); // 2. 获取当前线程内部的ThreadLocalMap变量ThreadLocalMap map = getMap(t); if (map != null) // 3. 设 置 value map.set(this, value); else // 4. 若map为null则创建ThreadLocalMap createMap(t, value); }
ThreadLocalMap
从JDK源码可见，ThreadLocalMap中的Entry是弱引用类型的，这就意味着如果这个ThreadLocal只被这个 Entry引用，而没有被其他对象强引用时，就会在下一次GC的时候回收掉。
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.
threadLocal.set()方法
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*/ |
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static class Entry extends WeakReference<ThreadLocal<?>> { |
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/** The value associated with this ThreadLocal. */ |
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Object value; |
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Entry(ThreadLocal<?> k, Object v) { |
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super(k); |
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value = v; |
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} |
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} |
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// ... |
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} |
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带你读《2022技术人的百宝黑皮书》——合理使用线程池以及线程变量（12）https://developer.aliyun.com/article/1340057?groupCode=taobaotech
