为什么ConcurrentHashMap不能被锁定为独占访问？ [英] Why ConcurrentHashMap cannot be locked for exclusive access?

问题描述

来自 #JCIP 的报价：

由于ConcurrentHashMap不能被锁定为独占访问，我们
不能使用客户端锁定创建新的原子操作，如
put-if-absent ，就像我们对Vector做的一样：

"Since a ConcurrentHashMap cannot be locked for exclusive access, we cannot use client-side locking to create new atomic operations such as put-if-absent, as we did for Vector"

为什么我们不能获取锁定 线程安全（例如 Collections.synchronizedxxx 工厂返回的同步集合）的原子方法：

Why we can't just acquire the lock in order to implement additional atomic methods and keep the collection thread-safe (like synchronized collections returned by Collections.synchronizedxxx factory) :

推荐答案

为什么？因为实现不支持它。 直接从 ConcurrentHashMap JavaDocs：

Why? Because the implementation does not support it. Straight from the ConcurrentHashMap JavaDocs:

有不支持锁定整个以阻止所有访问的方式

There is not any support for locking the entire table in a way that prevents all access

...根据定义，这是独占访问。

...which is, by definition, "exclusive access."

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